quality Electronic Manufacture & SMT DIP factory

Different Solder mask colors for printed circuit board   Golden Triangle Group Ltd., can provide below solder mask colors to our customers: Green, blue, white, red, black, Yellow Orange, Purple, brown, gray Transparent

In the past 16 years, GT team cooperated with customers making their ideas to products, including flex board, rigid board, rigid-flex boars, Alum. Based boards successfully;   GT continuously provide the experienced researching and developing service to customers;   The software engineers used are Altum designer and PADS.   The main products focus on industrial control, automotive and medical field;   GT design and provide the Gerber file, BOM list and structure for customer’s approval before production;   GT also can provide the testing service before shipment based on the testing instruction from customer.

Circuit board with Pin assembled GT keeps on provide Printed circuit boards to one of our customers Located in Western Coast with hard gold plating 17’’ and depth routing control on boards’ center over 2 years; Occasionally, on one official video technological meeting with customer, GT showed customer with another different type of sample with Pin inserting on the PCB boards, which brought GT a new chance and serials orders---new designed with Pins assembled on the bottom side!  

  SMT feeder is a key part that ensures the accurate and efficient supply of electronic components. In the SMT production line, the feeder is like a "component transporter". Without the feeder delivering various electronic components to the designated positions in a timely and precise manner, the surface mount device (SMD) equipment would not be able to pick up the components smoothly and install them onto the circuit board, and the entire production line would come to a standstill.   For example, when manufacturing a PCB board, a large number of components such as capacitors and resistors of different specifications are required. The feeder can send these components to the positions accessible by the SMD heads in an orderly manner according to the program settings, ensuring that each component can be installed accurately, thus guaranteeing the normal production of the circuit board.   A feeder with high precision can reduce the position deviation of component placement and lower the defective product rate.

 

Good news from our team! The test fixture designed & researched by GT team is debugged successfully, and now it has been put into use. This test fixture is developed to test the high voltage of coil in PCBs, and it can test 2 panels PCB at the same time. If you have requirements on test fixture, please contact us. GT is not only specializing in PCB & PCBA, but also high-tech test fixture. We commit to offer one-stop service for our customers.      

Circuit Maker ---- EQ & WF Confirmation of PCB     After receive customer’s PCB purchasing order, our engineers start to inspect carefully customer’s design files (usually Gerber files), then prepare ENGINEERING QUESTION & WORK FILES to customer, which is an important guarantee to fabricate right product.     Since it is so, what is to be confirmed in ENGINEERING QUESTION? They can be divided into 4 main kinds of ENGINEERING QUESTION.   Firstly, if there is any inconsistency in the files or design customer offers, we need customer’s help to confirm use which one.   Secondly, if there is something wrong with the design itself, we need to point out the issue and give customer suggestion. If customer accept the suggestion or have other reasonable suggestion, then we arrange production.   Thirdly, if customer’s design is beyond process ability, we will offer customer our adjustment plan to confirm if they can accept, or whether they have other solutions.   Fourthly, if we want to add something that are no impact on functionality but useful during production process, we will provide customer suggestions for confirmation. Such as add fiducial mark, location holes, stamp holes etc.     As per WORK FILES, it is consistent with customer’s design files. Any modifications of WORK FILES are agreed by customer.

From the above picture, we can find that there is copper coated inner the hole which is named as via hole. Via holes are responsible for connecting conductor line on different layers.   GT can produce via holes in the minimum diameter of 1.0mm. How to let liquid copper flow into such small holes and plated equally on the via wall is a technological difficulty. GT follows the IPC class 2 standard to get cu in hole wall at least 18um. Meanwhile, GT uses the following 3 methods to guarantee the quality of via holes.   -- Ensure adequate plating time to get moderate thick cu in hole. -- With pure cooper ball to avoid copper blistering in holes. -- Using penetrating copper solution to prevent “dog bone phenomenon”   With above methods, via holes will perform well in signal transmission.

Circuit Maker ---- Golden Finger   Golden finger of printed circuit board refers to a row of golden-plated contacts on the edge of PCB. It is so named because it looks like fingers. Maybe you have seen a memory strip. It is a kind of common application of golden finger.   With wonderful electroconductivity, abrasive resistance and corrosion resistance, golden finger is mainly applied to establish reliable connection in electronic equipments, such as being Inserted slot,etc.   When making golden finger, some special technologies such as electrogilding, chemical gilding etc. are used to guarantee the quality & thickness of gold coating (standard thickness from 10"-60", over this thickness can be discussed case by case), which is to meet the requirements such as signal transmit, life cycle of insertion and removals etc.   GT is experienced in such kind of technic. If you have any inquiries about it, feel free to contact us！

Packaging of PCB & PCBA   When packaging for printed circuit board (PCB) & printed circuit board assembly (PCBA), what we consider is not only protection from physical damage, but also maintenance of stable performance.   The common 4 packaging methods of PCB & PCBA are as follow.   - Vacuum packaging PCBs are packed by vacuator, which protects PCBs from damp, oxidation and other pollution.     - Bubble wrap Packaging Such kind of bubble warp with anti-static and buffer function can give our PCB & PCBA good protection.   - Anti-static bag packing The bags with anti-static coating or material can protect PCBs from static electricity. And then PCBs are wrapped with foam to be pack in a box.   - Foam packing Such kinds of packaging method are usually custom for PCBA. It provide a certain of physical protection, preventing PCBAs from extrusion and collision, which will keep components save.   - Plastic seal tray packaging It is also a kind of bespoke packaging solution for PCBA. Place PCBAs on the plastic tray, then tie them up or cover a protective case, which provides cushioning effect.   In conclusion, anti-collision, anti-fouling, anti-static must be considered when we pack PCBs or PCBAs

Circuit Maker ---- PCB Cross-section Analysis   PCB cross-section analysis is an important analytical method used to detect and evaluate the quality & reliability of printed circuit boards (PCBs).   The main purposes of cross-section analysis are as follow.   To inspect the inner structure of PCBs, such as the copper thickness, uniformity and integrity of holes wall. To evaluate the lamination quality between multi-layer PCBs. To observe whether width, thickness and shape of circuits comply with the design requirements. To detect whether there are imperfects such as crack, voids, impurities etc.   In conclusion, cross-section analysis provides valuable information and basis to control, improve quality and analyze faults during PCBs production.

  The first one is material 1. Basic material: by price from low to high, SY, KB, GDM are often used for FR-4. 2. Thickness of PCB & copper thickness: the more thicker, the more expensive. 3. Solder mask: the photosensory is more expensive than plastislo ink. the more common the colour of solder mask, the cheaper. Green solder mask is the most cheapest one.   The second one is surface treatment. By price from low to high, it is OSP, HASL, HASL(LF), ENIG, other combined process.   The third one is thickness of copper foil. The thicker the copper foil, the more expensive By price from low to high, it is 18um(1/2OZ), 35um(1OZ), 70um(2OZ), 105um(3OZ), 140um(4OZ) etc.   The fourth one is quality acceptance standard. From low price to higher price, it is IPC 2, IPC 3, military standard.   The fifth one is model tooling cost and testing cost. 1. About model tooling cost, prototype or low-volume order, the outline will be gotten by drilling and milling. In large volume, it is necessary to open punching mould, which generates a cost. 2. About testing cost, flying probe is for prototype order. Batch order has been tested by E-test fixture. And the former is cheaper.   The sixth one: the bigger the order, the more cheaper. Because no matter how big or how small the order is, all of them has to make engineering data, film artwork etc. for production.   The seventh one: the shorter the lead time, the more expensive.   Of course, these are also other many factors, such as PCB type, size, layer quantity, half-hole, hole density, impedance, edge plating, fill in and plating over process etc. And it is not the more expensive the better, the design of PCB should be according to application scenarios.   The Are you curious how much your PCB costs? Do you want to purchase plan about PCB? Ok, share us design files such Gerber files, PcbDoc files for better quotations!   flying probe

At present, based on customers' design, normally we have four different methods to deall with the Via through holes:   First one: Via opening It can be understood as no solder mask on the through holes to expose welding ring for testing or installing plug-in components.   Second one: Via hole plugging with solder mask ink It means that the through holes are fully filled in with solder mask ink before solder mask process. Tin leaking that Tin exudes from through holes to component side during reflow soldering, which will results in short circuit. Via hole plugging with solder mask ink can solve this problem.   Third one: Via filled with resin After via filled with resin, the via will be plated over for via in pad. Such method will save the space for SMT component.   Forth one: Via copper paste plugging Thanks to its high thermal conductivity, via copper paste plugging is usually used in high-power board such as lighting PCB etc.  

Breakaway is usually on the both sides or all sides of PCB. When the distance between components and edge of the board is smaller than 5mm, breakaway is required. And the width of breakaway is about 3-10mm. 5mm breakaway is most common. Breakaway and PCB     There is no pad & via holes in breakaway. But location vias and mark points can be seen on breakaway.   Location is required during forming and testing processes, so we add 3 or 4 Dia 3mm location vias on breakaway to get standard forming. As for mark point, there are 2 or 4 dia 1mm ones in a diagonal on PCB for SMT process to calibration position.   Breakaway of PCB can be also named as transport edge, a blank edge for track transmission in SMT process.   PCBA are stably placed on the conveyor by its breakaway     So important role breakaway plays in PCB process, but it is not a part of PCB board. It even can be taken out after PCB assembly. To be more easily taken out, breakaway and board are connected by stamp holes or V-slot.   Stamp holes   V-slot     That breakaway is added on short sides or long sides and how wide the breakaway is are depended on actual production demand.  

Ball Grid Array (BGA for short) is one kind of package method for organic substrate.   Features of BGA as follow. -- High-density pins. In case of same size of package, BGA will adopt more pins, which more easily realizes connection of complicated circuit, and miniaturizes electronics. -- Better electrical performance. The short and thin pins make the signal transmission path shorten, and make parasitic inductance & capacitance less, which reduce signal delay & distortion. -- Better heat dispersion. The contact area of between the IC in BGA package and the board is bigger, which is beneficial to heat dispersion.   Therefore, BGA is widely applied in IC package, the used in electronics such as computer processor, image processor, memory chip.   To gain reliable adhesive force, the diameter of BGA pad is usually smaller than solder ball’s. and the diameter is reduced by 20% - 25%. The bigger pad, the smaller space to wire between two pads.    

Back Drill is one kind of special depth control drilling.   For exmaple, when making a 6L PCB, to conduct the electric signal from 1L to 6L, we usually drill through hole and then copper plating. But if we only need electric conduction from 1L to 3L, the STUB, a part of via copper doesn’t connect with electric signal from 4L to 6L, has to be removed.   Are you curious about the reason? The useless copper will functions like a antenna, generating signal radiation to interfere surrounding important signal, which will result in reflection, dispersion, delay etc. of signal transmission. It may even effect normal operation of electric line system. Therefore, the redundant part will be drilled out from the board back, which is usually named as back drill during PCB manufacture.   As a printed circuit maker over 16 years, GT is experienced in back drill process. If you have such requirement, fell free to contact us.

As we all know, there is through hole, blind via, buried via in printed circuit board as the above pic shows.   -- Through hole means the via running through top layer to bottom layer. -- Buried hole means the via hiding in middle layers. -- Blind hole means the via that can be seen only in top layer or bottom layer.   We use mechanically drilling to get through hole, and use laser drilling to get blind via and buried via.   Pic 1: To get first-order 6-layer PCB, firstly we use mechanically drilling to get through hole to get the through hole from L2 to L5. Secondly, we laminate L1 and L6 together, and then use laser drilling to get blind via between L1 and L2, L5 and L6.   Pic 2: To get second-order 6-layer PCB, firstly after laminating L2 and L5, we use laser drilling to get buried via between L2 and L3, L4 and L5, and use mechanically drilling to get through hole to get the through hole from L2 to L5. Secondly, we laminate L1 and L6 together, and then use laser drilling to get blind via between L1 and L2, L5 and L6.   We can find that first-order 6-layer PCB is laser drilled one time, second-order 6-layer PCB is laser drilled two times.   Therefore, the word, order here means the times of using laser drilling. So now what is third-order HDI? Do you know?

Have you seen a rigid-flexible printed circuit board with flexible layer at external layer? Do you know the fabrication difficulty of such kind of rigid-flexible PCB?   Let GT shows you a 6L rigid-flexible PCB.   Its flexible area is at external layer, which is a little test for a PCB manufactory, because the high temperature caused by laser drilling easily makes flexible layer black. Proudly, GT always does well in such test with over 15-years experience and receives great feedback from the customers. What's more, there is via on via in the board. To acheive that, first we drill out mechanical buried via between 2L & 3L, then fill the via with resin and plate it over, finally drill out laser blind via between 1L & 2L.   GT team always devotes to offer high quality electronic manufacturing services.  

As professional PCB&PCBA manufacturer, we are also experienced in provide below testing fixtures for customers; Our engineers can design the special usage fixture out according to customer’s needs.   Main types are as below: Pneumatic fixture High voltage testing fixture ICT testing fixture FT testing fixture Inductance testing fixture    

Rigid-flex printed circuit board   1, The rigid-flex PCB can meet the electronic trend for Lightness, Thinness, Shortness and Minimization on size, combining with rigid FR4 and flexible PI material.   2, The flexible part can replace the usage of plenty of connectors and save the cost.   3, During the usage period, the flex part can be bent over 100000 times with high durability.   4, It owns excellent heat dissipation performance with the structure and assure the long shelf life of products.   5, The rigid-flex PCB has requirements about the environment, avoid the high temperature and high humidity.   6.The rigid-flex PCB is much complicated than standard rigid board or flex board, so the production cost is higher than standard printed circuit board.  

Hole fillings during PCB manufacturing   Resin Filling, one of the PCB manufacturing technologies, is used to fill and seal the blind, buried and via-through holes, depending on customer’s design.   There are 4 main functions as follows: Firstly, the copper in holes is isolated by resin through filling holes to prevent copper oxidation and corrosion and avoiding the de-lamination among layers. Secondly, Plating over holes’ surface after resin filling can be better for assembling process, which prevents the solder paste from flowing into the hole, so that tin leakage is prevented; besides, it pre-long the shelf life the PCBA product, esp for via-in-pad design. Thirdly, it improves signal stability. Copper in holes is isolated from power cord by filling with resin, which can reduce crosstalk reaction and improve signal stability. Fourthly, it reduces impedance. Copper in holes is isolated from signal routes on outer layer by filling with resin, which can reduce capacitance effect and impedance.     Resin Filling Holes is widely used in high-frequency board and HDI board, it meets the requirements of high frequency, high speed, high density, high performance etc.

Via in Pad during PCB Design     What is via in pad?   Via in pad, means the via holes designed on the SMD PAD, specially designed on the BAG (Ball Grind Array) area which comes with extremely narrow trace width and space.   After resin filling hole, copper is plated over the hole as a metal cap/pad to guarantee the hole’s conduction action and smoothness, which is called Plating Over Filled Via. In short, we can understand via in pad as the hole below the pad.   Via in pad caters to the necessary of HDI. Owing to its conduction action, it can simplify routes and save horizontal space of printed circuit board, and improve board’s density and interactivity.                        Filled with Resin and Plated over to be Via in Pad        

Both ENIG and gold plating are surface treatment, are there any difference between them? Please see the table below:     ENIG Gold Plating Process Mode Make a metal layer on the surface of copper via the means of chemical deposit Make gold attach to the board by electroplating Advantage A soft gold, and it is easier to weld than gold plating A hard gold with stronger wear resistance, and it is usually used for gold fingers, key etc. Production Processes After soldermask Before soldermask

Via Hole in Printed Circuit Board (PCB)   To realize the electrical connection between different layers of the circuit board, via hole is born at the right moment. It functions as below:   -- Provide a conducting path: In the multi-layer circuit board, via holes can connect the circuits between each layer, to ensure that signals and power can be transmitted among different layers.   -- Fix components: With the help of via holes, components be fixed in the proper position, to achieve good electrical connection and mechanical stability.   -- Reduce the thickness of printed circuit board: Compared with the traditional wire connection, via holes can effectively reduce the overall thickness of printed circuit board.   -- Improve the flexibility of wiring: Enhances the flexibility of circuit board wiring, making the circuit design more compact and efficient.   Different types of via holes such as blind via holes, buried via holes, and through via holes, may have some slight differences in working principle, but overall, they are all to achieve the conduction and connection among various layers of printed circuit board. In practical applications. various factors are considered while choosing the appropriate type of via hole, such as the number of layers of printed circuit board, design requirements, cost, etc.

Layout standard for through-hole insertion (THT)   The distribution density of components on Printed Circuit Board (PCB) should be consistent. Whether it is a single-sided PCB or a double-sided PCB, all components should be installed on the same surface as far as possible. Only when the components on top layer are too dense, some components with limited height and small heat can be installed on the other side, such as SMD components, in order to facilitate the processing, installation and maintenance of the printed circuit board (PCB).             

There are two common welding processes, reflow welding and wave soldering, used in electronics manufacturing. Reflow soldering is a technique for welding SMD components by remelting the solder paste pre-allocated to the pad of a printed circuit board. Advantages: - Suitable for high precision, high density printed circuit board welding. - Can realize automatic production, and improve production efficiency. - High welding quality.     As per wave soldering, the welding surface of the plug-in plate is directly in contact with high temperature liquid tin for welding purposes. Advantages: - Large number of plug-in components can be welded quickly. - The cost is relatively low.     In actual production, according to the needs and characteristics of the product, choose the appropriate welding process. Sometimes a combination of these two welding methods is used.    

    Steel stiffener is sometimes used for reinforcement to increase the structural strength and stability of printed circuit board (PCB).   To prevent short circuits or signal interference, the electrical isolation between the steel plates and the circuit board must be guaranteed. To avoid stress-related issues caused by temperature variations, the matching coefficient of thermal expansion between the steel plates and the circuit board material should be considered.  

    SMT Processes   Processes Details Pics Step 1: Preparation 1. Generate SMT coordinate file according to Gerber file & BOM List   2. SMT programme   3. Prepare components   4. Arrange well inspection personnel for IPQC      Step 2: Laser Steel Mesh Laser steel mesh in line with pad layer. make hollow-out position of the steel mesh consistent with pads on the PCB, so that solder paste covers accurately the pads.          Step 3: Solder Paste Printing Cover the pads with solder paste             Step 4: 3D SPI Solder Paste Detection With the help of optical image technique to detect the condition of solder paste, such as offset, proportion, height, short circuit, etc.   It aims to screen poor printing PCB in time.          Step 5: SMT To place components on PCB with the help of Sm471 plus high-speed SMT machine  & Sm481 PLUS multifunctional SMT machine          Step 6: Reflow Soldering To fix components on PCB           Step 7: AOI Detection To inspect whether the appearance & welding spot of the components meet requirement.         

PCB (Printed circuit board) is component carrier for PCBA products.   SMT (Surface Mount Technology) is a technology to assemble components on PCB surface.   PCBA (Printed Circuit Board Assembly) is a finished product after SMT or DIP (Dual In-line Package) assembly technology.     The relationship among PCB, SMT, PCBA is carrier, assembly technology, finished product (or manufacturing process), which can be shown as below:        

Specification for Design of PCB Pad -- Pad Size (Three) Specification (or material number): Material specific parameters (mm): Pad design (mm): Printed tin stencil design: Notes: QFP (Pitch=0.4mm)         A=a+0.8,B=0.19mm P=p G1=e1-2*(0.4+a) G2=e2-2*(0.4+a)   The pin length is changed from a+0.70mm to a+0.80mm, which is good for repair and printed pull tip handling. For the height of 3.8mm LQFP pad design width is used 0.23mm (stencil opening width 0.19mm) QFP (Pitch=0.3mm)       A=a+0.7,B=0.17mm P=p G1=e1-2*(0.4+a) G2=e2-2*(0.4+a)   T=0.10mm. Pin opening width 0.15mm   PLCC (Pitch≧0.8mm)   A=1.8mm,B=d2+0.10mm G1=g1-1.0mm, G2=g2-1.0mm, P=p     BGA Pitch=1.27mm, Ball diameter: Φ=0.75±0.15mm     D=0.70mm P=1.27mm   Recommended stencil opening diameter is 0.75mm Does not represent the arrangement of the actual BGA bottom solder balls BGA Pitch=1.00mm, Ball diameter: Φ=0.50±0.05mm D=0.45mm P=1.00mm Recommended stencil opening diameter is 0.50mm Does not represent the arrangement of the actual BGA bottom solder balls BGA Pitch=0.80mm, Ball diameter: Φ=0.45±0.05mm D=0.35mm P=0.80mm   Recommended stencil opening diameter is 0.40mm Does not represent the arrangement of the actual BGA bottom solder balls BGA Pitch=0.80mm, Ball diameter: Φ=0.35±0.05mm D=0.40mm P=0.80mm Recommended stencil opening diameter is 0.40mm Does not represent the arrangement of the actual BGA bottom solder balls BGA Pitch=0.75mm, Ball diameter: Φ=0.45±0.05mm D=0.3mm P=0.75mm Recommended stencil opening diameter is 0.40mm Does not represent the arrangement of the actual BGA bottom solder balls BGA Pitch=0.75mm, Ball diameter: Φ=0.35±0.05mm D=0.3mm P=0.75mm Recommended stencil opening diameter is 0.35mm Does not represent the arrangement of the actual BGA bottom solder balls LGA (Ball-less BGA) Pitch=0.65mm, Pin diameter: Φ=0.3±0.05mm D=0.3mm, P=0.65mm Recommended stencil 1:1 opening Does not represent the arrangement of the actual BGA bottom solder balls QFN （Pitch≧0.65mm）       A=a+0.35,B=d+0.05 P=p,W1=w1,W2=w2 G1=b1-2*(0.05+a) G2=b2-2*(0.05+a)   Design independent pads for each pin. Note: If the ground pad to design the thermal over-hole, it should be 1.0mm-1.2mm gap evenly distributed in the central thermal pad, over-hole should be connected to the PCB inner metal ground layer, over-hole diameter recommended for 0.3mm-0.33mm It is recommended that the stencil pin opening length direction flare 0.30mm, ground pad opening bridge, bridge width 0.5mm, the number of bridges W1/2, W2/2, take the integer.   If the pad design has holes, stencil openings to avoid holes, grounding pad opening area of 50% to 80% of the grounding pad area can be, too much tin on the pin welding has a certain impact   QFN （Pitch

PCB Solder Pad Design Standard - Solder Pad Specification Size (Second) Specification (or material number): Material specific parameters (mm): Pad design (mm): Diode (SMA) 4500-234031-T0 4500-205100-T0 a=1.20±0.30 b=2.60±0.30,c=4.30±0.30 d=1.45±0.20,e=5.2±0.30 Diode (SOD-323) 4500-141482-T0   a=0.30±0.10 b=1.30±0.10,c=1.70±0.10 d=0.30±0.05,e=2.50±0.20 Diodes (3515)     a=0.30   b=1.50±0.1,c=3.50±0.20 Diodes (5025)   a=0.55 b=2.50±0.10, c=5.00±0.20 Triode (SOT-523) a=0.40±0.10,b=0.80±0.05 c=1.60±0.10,d=0.25±0.05 p=1.00         Triode (SOT-23)   a=0.55±0.15,b=1.30±0.10 c=2.90±0.10,d=0.40±0.10 p=1.90±0.10 SOT-25   a=0.60±0.20,b=2.90±0.20 c=1.60±0.20,d=0.45±0.10 p=1.90±0.10 SOT-26   a=0.60±0.20,b=2.90±0.20 c=1.60±0.20,d=0.45±0.10 p=0.95±0.05 SOT-223 a1=1.75±0.25,a2=1.5±0.25 b=6.50±0.20,c=3.50±0.20 d1=0.70±0.1,d2=3.00±0.1 p=2.30±0.05 SOT-89   a1=1.0±0.20,a2=0.6±0.20 b=2.50±0.20,c=4.50±0.20 d1=0.4±0.10,d2=0.5±0.10 d3=1.65±0.20,p=1.5±0.05 TO-252   a1=1.1±0.2,a2=0.9±0.1 b=6.6±0.20,c=6.1±0.20 d1=5.0±0.2,d2=Max1.0 e=9.70±0.70,p=2.30±0.10   TO-263-2 a1=1.30±0.1,a2=2.55±0.25 b=9.97±0.32,c=9.15±0.50 d1=1.3±0.10,d2=0.75±0.24 e=15.25±0.50,p=2.54±0.10   TO-263-3 a1=1.30±0.1,a2=2.55±0.25 b=9.97±0.32,c=9.15±0.50 d1=1.3±0.10,d2=0.75±0.24 e=15.25±0.50,p=2.54±0.10             TO-263-5   a1=1.66±0.1,a2=2.54±0.20 b=10.03±0.15,c=8.40±0.20 d=0.81±0.10,e=15.34±0.2 p=1.70±0.10 SOP (Pinout(Pitch>0.65mm)   A=a+1.0,B=d+0.1 G=e-2*(0.4+a) P=p   SOP (Pitch≦0.65mm)     A=a+0.7,B=d G=e-2*(0.4+a) P=p SOJ (Pitch≧0.8mm)       A=1.8mm,B=d2+0.10mm G=g-1.0mm,P=p QFP (Pitch≧0.65mm)     A=a+1.0,B=d+0.05 P=p G1=e1-2*(0.4+a) G2=e2-2*(0.4+a) QFP (Pitch=0.5mm)   A=a+0.9,B=0.25mm P=p G1=e1-2*(0.4+a) G2=e2-2*(0.4+a)          

  Note: The following design standards refer to the IPC-SM-782A standard and the design of some famous Japanese design manufacturers and some better design solutions accumulated in the manufacturing experience. For your reference and use (the general idea of pad design: CHIP pieces of standard size, according to the size specifications to give a pad design standards; size is not standard, according to its material number to give a pad design standards. IC, connector components in accordance with the material number or specifications grouped to give a design standard.) To reduce design problems to the actual production of many problems.     Specifications (or material number): 0201 (0603)   Material specific parameters (mm):     a=0.10±0.05，b=0.30±0.05,c=0.60±0.05     Pad design (mm):     Note: Applicable and common resistors, capacitors, inductors     Specifications (or material number): 0402 (1005)     Material specific parameters (mm):     a=0.20±0.10，b=0.50±0.10,c=1.00±0.10     Pad design (mm):     Printed tin stencil design: centered on the center of the pad, openings round D = 0.55mm   Stencil design: opening width 0.2mm (stencil thickness T recommended thickness of 0.15mm)   Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 0603 (1608)     Material specific parameters (mm):     a=0.30±0.20,b=0.80±0.15,c=1.60±0.15     Pad design (mm)     Note: Applicable and common resistors, capacitors, inductors   Specifications (or material number): 0805（2012）     Material specific parameters (mm)     a=0.40±0.20,b=1.25±0.15,c=2.00±0.20       Pad design (mm)       Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 1206 (3216)       Material specific parameters (mm)     a=0.50±0.20,b=1.60±0.15,c=3.20±0.20     Pad design (mm)     Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 1210（3225）     Material specific parameters (mm)     a=0.50±0.20,b=2.50±0.20,c=3.20±0.20         Pad design (mm)     Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 1812（4532）     Material specific parameters (mm)     a=0.50±0.20,b=3.20±0.20,c=4.50±0.20     Pad design (mm)       Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 2010（5025）     Material specific parameters (mm)     a=0.60±0.20,b=3.20±0.20,c=6.40±0.20     Pad design (mm)     Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 2512（6432）     Material specific parameters (mm)     a=0.60±0.20,b=3.20±0.20,c=6.40±0.20         Pad design (mm)     Note: Applicable and common resistors, capacitors, inductors   Specification (or material number): 5700-250AA2-0300       Material specific parameters (mm)       Pad design (mm)     Printed tin stencil design: 1:1 opening, not to avoid tin beads   Specification (or material number): Drain resistance 0404 (1010)   Material specific parameters (mm)     a=0.25±0.10,b=1.00±0.10,c=1.00±0.10,d=0.35±0.10,p=0.65±0.05     Pad design (mm)   Specification (or material number): Drain resistance 1206（3216）   Material specific parameters (mm)     a=0.30±0.15,b=3.2±0.15   c=1.60±0.15,d=0.50±0.15   p=0.80±0.10   Pad design (mm)     Specification (or material number): Drain resistance 1606（4016）   Material specific parameters (mm)     a=0.25±0.10,b=4.00±0.20   c=1.60±0.15,d=0.30±0.10   p=0.50±0.05       Pad design (mm)     Specification (or material number): 472X-R05240-10     Material specific parameters (mm)     a=0.38±0.05,b=2.50±0.10   c=1.00±0.10,d=0.20±0.05   d1=0.40±0.05,p=0.50   Pad design (mm)       Tantalum capacitors   Specification (or material number)   Material specific parameters (mm):       Pad design (mm):     2312 (6032)   a=1.30±0.30,b=3.20±0.30 c=6.00±0.30,d=2.20±0.10   A=2.00,B=2.20,G=3.20 2917 (7243)   a=1.30±0.30,b=4.30±0.30 c=7.20±0.30,d=2.40±0.10   A=2.00,B=2.40,G=4.50 1206（3216）   a=0.80±0.30,b=1.60±0.20 c=3.20±0.20,d=1.20±0.10   A=1.50,B=1.20,G=1.40 1411 (3528)   a=0.80±0.30,b=2.80±0.20 c=3.50±0.20,d=2.20±0.10   A=1.50,B=2.20,G=1.70     Aluminum electrolytic capacitors     Material specific parameters (mm):   Pad design (mm):         (Ø4×5.4) d=4.0±0.5 h=5.4±0.3 a=1.8±0.2,b=4.3±0.2 c=4.3±0.2,e=0.5~0.8 p=1.0 A=2.40,B=1.00 P=1.20,R=0.50 (Ø5×5.4) d=5.0±0.5 h=5.4±0.3 a=2.2±0.2,b=5.3±0.2 c=5.3±0.2,e=0.5~0.8 p=1.3 A=2.80,B=1.00 P=1.50,R=0.50 (Ø6.3×5.4) d=6.3±0.5 h=5.4±0.3 a=2.6±0.2,b=6.6±0.2 c=6.6±0.2,e=0.5~0.8 p=2.2 A=3.20,B=1.00 P=2.40,R=0.50 (Ø6.3×7.7) d=6.3±0.5 h=7.7±0.3 a=2.6±0.2,b=6.6±0.2 c=6.6±0.2,e=0.5~0.8 p=2.2 A=3.20,B=1.00 P=2.40,R=0.50 (Ø8.0×6.5) d=6.3±0.5 h=7.7±0.3 a=3.0±0.2,b=8.3±0.2 c=8.3±0.2,e=0.5~0.8 p=2.2 A=3.20,B=1.00 P=2.40,R=0.50 (Ø8×10.5) d=8.0±0.5 h=10.5±0.3 a=3.0±0.2,b=8.3±0.2 c=8.3±0.2,e=0.8~1.1 p=3.1 A=3.60,B=1.30 P=3.30,R=0.65 (Ø10×10.5) d=10.0±0.5 h=10.5±0.3 a=3.5±0.2,b=10.3±0.2 c=10.3±0.2,e=0.8~1.1 p=4.6 A=4.20,B=1.30 P=4.80,R=0.65    

  PCB Unpacking and Storage   If the PCB board is sealed and not unpacked, it can be used directly on the production line within 2 months of the manufacturing date.   If the PCB board is unpacked within 2 months of the manufacturing date, the unpacking date must be marked.   If the PCB board is unpacked within 2 months of the manufacturing date, it must be used up within 5 days after unpacking.     PCB Baking   If the PCB board is sealed and unpacked for more than 5 days within 2 months of the manufacturing date, please bake it at 120±5℃ for 1 hour   If the PCB board exceeds the manufacturing date by 2 months, please bake it at 120±5℃ for 1 hour before use.   If the PCB board exceeds the manufacturing date by 2 to 6 months, please bake it at 120±5℃ for 2 hours before use.   If the PCB board exceeds the manufacturing date by 6 months to 1 year, please bake it at 120±5℃ for 4 hours before use.   The baked PCB board must be used up within 5 days (put into IRREFLOW), or it needs to be baked for another hour before use.   If the PCB board exceeds the manufacturing date by 1 year, please bake it at 120±5℃ for 4 hours, and then spray tin again by the PCB factory before use.       PCB Baking Method   For large PCBs (including 16PORT or above), they should be placed flat, with a maximum of 30 pieces per stack. After baking, the oven should be opened within 10 minutes and the PCB should be placed flat for natural cooling (with a pressure prevention plate and a fixture for bowing prevention).   For small and medium-sized PCBs (including 8PORT or below), they should be placed flat, with a maximum of 40 pieces per stack in a flat position, while there is no limit on the number of pieces in an upright position. After baking, the oven should be opened within 10 minutes and the PCB should be placed flat for natural cooling (with a pressure prevention plate and a fixture for bowing prevention).   Storage and Baking of PCBs in Different Regions     The specific storage time and baking temperature of PCBs not only depend on the manufacturing ability and technology of the PCB manufacturers but also on the region.   PCBs produced by OSP process and pure gold sinking process generally have a shelf-life of 6 months after packaging, and it is generally not recommended to bake PCBs made by OSP process.     The storage and baking time of PCBs vary greatly depending on the region. In humid regions such as Guangdong and Guangxi in China, where there is a rainy season called "Hui Nan Tian", which is very humid during April and May, PCBs exposed in the air must be used within 24 hours, otherwise, they are prone to oxidation. After opening the package, it is best to use it within 8 hours. For some PCBs that need to be baked, the baking time will be longer. However, in inland regions, the weather is generally dry, and the storage time of PCBs can be longer, and the baking time can be shorter. The baking temperature is generally 120±5℃, and the baking time depends on the specific situation.    

  Flying Probe Test     The flying probe tester uses 4, 6, or 8 probes to perform high-voltage insulation and low-resistance continuity tests (open and short circuits of test lines) on PCB circuit boards without the need for test fixtures. Using "automatic optical focus positioning", it can monitor the testing process and fault points in real-time.     Advantages Of Flying Probe Test   1. High test density, the minimum pitch can reach 0.05mm or even smaller   2. Save the production time of the fixture, and the efficiency of proofing and shipping is higher   3. No fixture cost, low test cost     Shortcomings Of Flying Probe Test   1. The test pin breakage rate is high   2. Thin plate test is easy to jump pin   3. Only suitable for proofing   4. The pressure resistance cannot be tested, and the high-level high-density board test has a greater risk     Electric Test By Test Frame   The test frame test method relies on the test frame (that is, the fixture) to test whether there is a short circuit between the different network traces of the PCB, whether the PCB is open from the same network to each PAD, whether the visa is open, and can also perform insulation strength tests and impedance tests. Compared with the flying probe test, it is simply to make all the probes corresponding to the points on the circuit board that need to be tested at one time. When testing, the upper and lower ends can be pressed to test whether the whole board is good or bad.       Advantages Of Electric Test By Test Frame   1. High test accuracy   2. High test efficiency, shorten test man-hours   3. One-time fee, no additional charge for return order   4. Easy to maintain later   Shortcomings Of Electric Test By Test Frame   1. High initial production cost   2. Not suitable for proofing test      

  Electronic components can be seen everywhere in our life, and with the development of science and technology, the variety of electronic components has become more and more, but also began to be high-frequency, miniaturization of the direction of development. Today I bring you the five characteristics of electronic components, let's learn about them.     Five characteristics   1. Many product categories, a variety of complex. Only according to the former Ministry of Electronics, the preparation of electronic products classification and coding statistics, electronic components in addition to integrated circuits, there are 206 categories of products 2519 subcategories, including 13 categories of electrical vacuum devices 260 subcategories; semiconductor discrete devices (including laser, optoelectronic devices, etc.) 18 categories 379 subcategories; electronic components 17 professional, 161 categories 1284 subcategories. Electronic materials have 14 major categories and 596 subcategories.     2. It is a highly professional and multidisciplinary collection. There are great differences in production processes and production equipment, testing techniques and equipment. This is not only the difference between electric vacuum devices, semiconductor devices, and electronic components but also the difference between the main categories and even sub-categories of each industry. For example, different display devices, and different components, i.e. different capacitors, resistors, and sensitive components are also different. Of course, similar products at different stages require different production techniques and methods, therefore, electronic components have a production line, a generation of component products is a generation of production lines; some professional production of multilayer printed circuit board enterprises need to add new equipment every year.     3. Complete sets and into series. This is determined by the electronic circuit of the whole machine, band and frequency characteristics, precision, function, power, storage and use of the conditions and environment, and service life of the requirements.     4. The investment intensity varies widely, and varies greatly from period to period, especially in terms of production scale, product output, production conditions, and production environment requirements. Among them, high-tech, the need for large-scale production of products investment scale than the “eight five” period increased by an order of magnitude, often reaching 100 million U.S. dollars, the lowest is 50 million U.S. dollars; for other products, although the technical difficulty is also high, the output is limited, the degree of automation of equipment is low, the investment intensity is much smaller.     5. Each electronic component and its industry has its own different development pattern, but they are closely related to the development of electronic machinery and systems, including the development of electronic technology, the entire structure, and electrical assembly technology. However, in terms of industrial development, electronic equipment, and the entire machine system or a variety of electronic components between the existence of mutual promotion and mutual constraints.    

PCB Solder Pad Design Standard - SMT Solder Pad Naming Rule Suggestions (Inch: IN; metric millimeter with MM, the decimal point in the middle of the data with d, the following data are some of the size parameters of the components, these parameters can determine the size and shape of the pad. (Separated by "X" between different parameters)   Ordinary resistance (R), capacitance (C), inductance (L), magnetic beads (FB) class components (component shape rectangular)   Component type + size system + appearance size specifications named. Such as: FBIN1206, LIN0805, CIN0603, RIN0402, CIN0201;   Row resistance (RN), row capacity (CN): component type + size system + size specifications + P + number of pins named   Such as: RNIN1206P8. on behalf of the resistance, external specifications size 1206, a total of 8 pins;   Tantalum capacitor (TAN): component type + size system + external size specifications named   Such as: TANIN1206, representing tantalum capacitor, its external size is 1206;   Aluminum electrolytic capacitor (AL): component type + size system + external size (diameter of upper part X height of component) specification   For example: ALMM5X5d4, representing aluminum electrolytic capacitor, the diameter of the upper part is 5mm and the height of the element is 5.4mm;   Diode (DI): Here mainly refers to the diode with two electrodes   Divided into two categories: Planar diode (DIF): component type + size system + and PCB contact part of the pin size specifications (length X width) + X + pin span size named. Such as: DIFMM1d2X1d4X2d8. indicates that the plane type diode, the pin length 1.2mm, width 1.4mm, the span between the pins is 2.8mm; Cylindrical diode (DIR): component type + size system + external size specifications named. DIRMM3d5X1d5. said cylindrical diode, external dimensions of 3.5mm long, 1.5mm wide   Transistor type components (SOT type and TO type): directly named with standard specification name   Such as SOT-23, SOT-223, TO-252, TO263-2 (two-pin type), TO263-3 (three-pin type).   SOP type components: as shown in the figure     Naming rules: SOP + size system + size e + X + size a + X + size d + X + pin center distance p + X + number of pins j Such as: SOPMM6X0d8X0d42X1d27X8. represents SOP components, e=6mm,a=0.8mm,d=0.42mm,p=1.27mm,j=8 SOJ type components: as shown in the figure     Naming rules: SOJ + size system + size g + X + size d2 + X + pin center distance p + X + number of pins j Such as SOJMM6d85X0d43X1d27X24. represents SOJ components, g=6.85mm,d2=0.43mm,p=1.27mm,j=24 PLCC type components: as shown in the figure     Naming rules: PLCC + size system + size g1 +X+ size g2 +X+ size d2 +X+ pin center distance p+X+ number of pins j For example: PLCCMM15d5X15d5X0d46X1d27X44. represents PLCC components, g1=15.5mm,g2=15.5mm,d2=0.46mm,p=1.27mm,j=44 QFP type components: as shown in the figure     Naming rules: QFP + size system + size e1 +X+ size e2 +X+ size a +X+ size d +X+ pin center distance p+X+ number of pins j For example: QFPMM30X30X0d6X0d16X0d4X32. represents QFP components, e1=30mm,e2=30mm,a=0.6mm,d=0.16mm,p=0.4mm,j=32 QFN type components: as shown in the figure     Naming rules: QFN + size system + size b1 + X + size b2 ( + X + size w1 + X + size w2 ) + X + size a + X + size d + X + pin center distance p + X + number of pins j Such as: QFNMM5X5X3d1X3d1X0d4X0d3X0d8X32. represents QFN components, b1=5mm,b2=5mm,w1=3.1mm,w2=3.1mm,a=0.4mm,d=0.3mm,p=0.8mm,j=32 If there is no grounding pad, the red part is removed. Other types of components: use the material number to name the pad size Such as 5400-997100-10, 6100-150002-00, 6100-151910-01, 5700-ESD002-00, 5400-997000-50 and other irregular, complex components.        

  1. PCB Board Surface Treatment   Hard gold plating, full plate gold plating, gold finger, nickel palladium gold OSP: Lower cost, good weldability, harsh storage conditions, short time, environmental protection process, good welding, smooth.   Tin spray: The tin plate is generally a multi-layer (4-46 layers) high-precision PCB template, has been a number of large communications, computer, medical equipment and aerospace enterprises and research units can be used (gold finger) as the connection between the memory and the memory slot, all signals are transmitted through the gold finger.   Goldfinger is made up of a number of electrically conductive contacts that are gold in color and are arranged like fingers, so it is called "Goldfinger". Goldfinger is actually coated with copper by a special process because gold is highly resistant to oxidation and conduction. However, because of the expensive price of gold, more memory is used to replace tin, from the 1990s began to popularize tin material, the current motherboard, memory and graphics card and other equipment "Gold finger" Almost all use tin material, only part of the high-performance server/workstation accessories contact point will continue to use gold plating, the price is naturally expensive.     2. The Reason For Choosing The Gilt Plating   As the integration of IC becomes higher and higher, the IC feet are denser and denser. The vertical tin-spraying process is difficult to flatten the thin pad, which brings difficulties to SMT mounting. In addition, the shelf life of the tin spray plate is very short. And the gold-plated plate solves these problems:   (1) For the surface mounting process, especially for 0603 and 0402 ultra-small table paste, because the flatness of the welding pad is directly related to the quality of the solder paste printing process, and plays a decisive influence on the quality of the reflow welding behind, so the whole plate gold plating in high density and ultra-small table paste process often see.   (2) In the trial production stage, affected by components procurement and other factors are often not the board to immediately weld, but often have to wait for a few weeks or even months to use, the shelf life of the gold plate is many times longer than the lead-tin alloy, so we are willing to use. Moreover, the cost of gold-plated PCB at the sampling stage is almost the same as that of a lead-tin alloy plate. But with more and more dense wiring, line width, and spacing has reached 3-4mil.   Therefore, it brings about the problem of the short circuit of gold wire: As the frequency of the signal becomes higher and higher, the signal transmission in the multi-coating caused by the skin effect has a more obvious influence on the quality of the signal.   Skin effect refers to high-frequency alternating current, current will tend to concentrate on the surface of the wire flow. According to calculations, skin depth is related to frequency.   3. The Reason For Choosing The Gold Plating   In order to solve the above problems of the gold-plated plate, the use of gold-plated PCB has the following characteristics:   (1) Because of the different crystal structures formed by sinking gold and gold plating, sinking gold will be more yellow than gold plating, and customers are more satisfied.   (2) Because the crystal structure formed by gold plating and gold plating is different, gold plating is easier to weld, will not cause poor welding, or cause customer complaints.   (3) Because the gold plate only has nickel gold on the pad, the signal transmission in the skin effect is in the copper layer will not affect the signal.   (4) Because of the denser crystal structure of gold plating, it is not easy to produce oxidation.   (5) Because the gold plate only has nickel gold on the pad, so it will not be produced into gold wire caused by short.   (6) Because the gold plate only has nickel gold on the welding plate, so the welding on the line and the combination of copper layer is more firm.   (7) The project will not affect the spacing when making compensation.   (8) Because the gold and gold plating formed by the crystal structure is not the same, the stress of the gold plate is easier to control, for the products of the state, more conducive to the processing of the state. At the same time, because the gold is softer than the gold, so the gold plate is not the wear-resistant gold finger.   (9) The flatness and service life of the gold plate is as good as that of the gold plate.     4. Gilt Plating Vs Gold Plating   In fact, the plating process is divided into two kinds: One is electric plating, and one is sinking gold.   For the gilding process, the effect of tin is greatly reduced, and the effect of sinking gold is better; unless the manufacturer requires binding, most manufacturers will choose the gold sinking process now! In general, under common circumstances PCB surface treatment for the following: Gold plating (electric gold plating, gold plating), silver plating, OSP, spray tin (lead and lead-free), these are mainly for fr-4 or cem-3 plate, paper base material and coating rosin surface treatment; poor tin (poor tin eating) if the exclusion of solder paste and other patch manufacturers production and material process reasons.   Here only for PCB problem, there are the following reasons:   (1) During PCB printing, whether there is an oil permeating film surface on the pan position, which can block the effect of tin coating; can be verified by a tin bleaching test.   (2) Whether the pan position meets the design requirements, that is, whether the welding pad design can ensure the supporting role of parts.   (3) Whether the welding pad is contaminated, the results can be obtained by an ion contamination test; the above three points are basically the key aspects that PCB manufacturers consider.   The advantages and disadvantages of several ways of surface treatment are that each has its own advantages and disadvantages!   Gilding, it can make the PCB storage time longer, and by the outside environment temperature and humidity changes less (compared with other surface treatments), generally can be stored for about a year; spray tin surface treatment second, OSP again, these two surface treatment in the environment temperature and humidity storage time should pay attention to many.   Under normal circumstances, the surface treatment of sunken silver is a little different, the price is high, the preservation conditions are harsher, need to use non-sulfur paper packaging treatment! And the storage time is about three months! In terms of the tin effect, sinking gold, OSP, spray tin, and so on are actually similar, the manufacturer is mainly considering the cost performance!  

PCB Solder Pad Design Guidelines - Some Requirements for PCB Design MARK point: This type of point is used to automatically locate the position of the PCB board in SMT production equipment, and must be designed when designing PCB boards. Otherwise, SMT production will be difficult or even impossible.   The MARK point is recommended to be designed as a circular or square shape parallel to the edge of the board, with circular being the best option. The diameter of the circular MARK point is generally 1.0mm, 1.5mm, or 2.0mm. It is recommended to use a diameter of 1.0mm for the MARK point design (if the diameter is too small, the PCB manufacturer's tin spraying on the MARK point will be uneven, making it difficult for the machine to recognize or affecting the accuracy of printing and component installation; if it is too large, it will exceed the window size recognized by the machine, especially the DEK screen printing machine).   The MARK point is generally designed at the diagonal of the PCB board, and the distance between the MARK point and the edge of the board should be at least 5mm to prevent the machine from clamping the MARK point partially and causing the machine camera to fail to capture the MARK point.   The position of the MARK point should not be designed symmetrically to prevent the operator from placing the PCB board in the wrong direction during the production process, causing the machine to mount components incorrectly and causing losses.   There should not be any similar test points or solder pads within 5mm around the MARK point, otherwise the machine may incorrectly recognize the MARK point and cause losses in production.   The position of through holes: Improper design of the through hole can lead to insufficient or even no solder during SMT production welding, seriously affecting the reliability of the product. Designers are advised not to design the through hole on top of the solder pad. When designing the through hole around the solder pad of ordinary resistors, capacitors, inductors, and beads, the edge of the through hole and the edge of the solder pad should be kept at least 0.15mm. For other ICs, SOTs, large inductors, electrolytic capacitors, diodes, connectors, etc., the through hole and solder pad should be kept at least 0.5mm away from the edge (because the size of these components will expand when designing the steel mesh) to prevent the solder paste from flowing out of the through hole during the component reflow process;   When designing the circuit, pay attention that the width of the line connecting the solder pad should not exceed the width of the solder pad, otherwise, some components with small spacing are prone to solder bridging or insufficient solder. When adjacent pins of IC components are used as ground, designers are advised not to design them on a large solder pad, which makes it difficult to control SMT welding.   Due to the wide variety of electronic components, the solder pad sizes of most standard components and some non-standard components have been standardized. In future work, we will continue to do this work well to serve design and manufacturing and achieve satisfactory results for everyone.      

  1. Preface Of PCB Design   With the increasing market competition of communication and electronic products, the life cycle of products is shortening. The upgrading of original products and the release speed of new products play an increasingly critical role in the survival and development of the enterprise. In the manufacturing link, how to obtain new products with higher manufacturability and manufacturing quality with less lead-in time in production has become more and more the competitiveness pursued by people of vision.   In the manufacture of electronic products, with the miniaturization and complexity of products, the assembly density of circuit boards is becoming higher and higher. Accordingly, the new generation of SMT assembling process which has been widely used requires designers to consider the manufacturability at the very beginning. Once the poor manufacturability is caused by poor consideration in the design, it is bound to modify the design, which will inevitably prolong the time of product introduction and increase the cost of introduction. Even if the PCB layout is slightly changed, the cost of re-making the printed board and SMT solder paste printing screen board is up to thousands or even tens of thousands of yuan, and the analog circuit even needs to be re-debugging. The delay of the import time may cause the enterprise to miss the opportunity in the market and be in a very disadvantageous position strategically. However, if the product is manufactured without modification, it will inevitably have manufacturing defects or increase manufacturing costs, which will be more costly. Therefore, when enterprises design new products, the earlier the manufacturability of the design is considered, the more conducive to the effective introduction of new products.   2. Contents to be considered in PCB design   The manufacturability of PCB design is divided into two categories, one is the processing technology of producing printed circuit boards; The second refers to the circuit and structure of the components and printed circuit boards of the mounting process. For the processing technology of producing printed circuit boards, the general PCB manufacturers, due to the influence of their manufacturing capacity, will provide designers with very detailed requirements, which is relatively good in practice. But according to the author's understanding, the real in practice that has not received enough attention, is the second type, namely manufacturability design for electronic assembly. The focus of this paper is also to describe the manufacturability issues that designers must consider in the stage of PCB design.   Manufacturability design for electronic assembly requires PCB designers to consider the following at the beginning of PCB design:   2.1 Appropriate selection of assembly mode and component layout in PCB design   The selection of assembly mode and the component layout is a very important aspect of PCB manufacturability, which has a great impact on assembly efficiency, cost and product quality. In fact, the author has come into contact with quite a lot of PCB, and there is still a lack of consideration in some very basic principles.   (1) Select the appropriate assembly method   Generally, according to different assembly densities of PCB, the following assembly methods are recommended:   Assembly method Schematic General assembly process 1 Single-sided full SMD Single panel printed solder paste, reflow soldering after placement 2 Double-sided full SMD A. B-side printed solder paste, SMD reflow soldering or B-side spot (printed) glue solid words after being peak soldering 3 Single-sided original assembly Printed solder paste, post placement reflow soldering of SMD poor future wave soldering of perforated components 4 Mixed components on side A Simple SMD only on side B Printed solder paste on side A, SMD reflow soldering; after dotting (printing) glue fixing SMD on side B, mounting perforated components, wave soldering THD and SMD on side B 5 Insert on side A Simple SMD on side B only After curing the SMD with spot (printed) adhesive on the B-side, the perforated components are mounted and wave soldered to the THD and B-side SMD     As a circuit design engineer, I should have a correct understanding of the PCB assembling process, so that I can avoid making some mistakes in principle. When selecting the assembly mode, in addition to considering the assembly density of PCB and the difficulty of wiring, it is necessary to consider the typical process flow of this assembly mode and the level of process equipment of the enterprise itself. If the enterprise does not have a good wave welding process, then choose the fifth assembly method in the table above may bring you a lot of trouble. It is also worth noting that if the wave soldering process is planned for the welding surface, it should be avoided to complicate the process by placing a few SMDS on the welding surface.   (2) Component layout   The layout of PCB components has a very important impact on production efficiency and cost and is an important index to measure the PCB design of the connectability. Generally speaking, the components are arranged as evenly, regularly, and neatly as possible, and arranged in the same direction and polarity distribution. The regular arrangement is convenient for inspection and conducive to improving the patch/plug-in speed, uniform distribution is conducive to heat dissipation and optimization of the welding process. On the other hand, in order to simplify the process, PCB designers should always be aware that only one group welding process of reflow welding and wave welding can be used on either side of the PCB. This is especially noteworthy in the assembly density, PCB welding surface must be distributed with more patch components. The designer should consider which group welding process to use for the mounted components on the weld surface. Preferably, a wave soldering process after patch curing can be used to weld the pins of the perforated devices on the component surface at the same time. However, wave welding patch components have relatively strict constraints, only 0603 and above size chip resistance, SOT, SOIC (pin spacing ≥1mm and height less than 2.0mm) welding. For components distributed on the welding surface, the direction of the pins should be perpendicular to the transmission direction of PCB during wave crest welding, so as to ensure that the welding ends or leads on both sides of the components are immersed in welding at the same time. The arrangement order and spacing between adjacent components should also meet the requirements of wave crest welding to avoid the "shielding effect", as shown in FIG. 1. When using wave soldering SOIC and other multi-pin components, should be set in the direction of tin flow at two (each side 1) solder feet, to prevent continuous welding.     Components of similar type should be arranged in the same direction on the board, making it easier to mount, inspect, and weld the components. For example, having the negative terminals of all radial capacitors facing the right side of the plate, having all the DIP notches facing the same direction, etc., can speed up instrumentation and make it easier to find errors. As shown in Figure 2, since board A adopts this method, it is easy to find the reverse capacitor, while Board B takes more time to find it. In fact, a company can standardize the orientation of all the circuit board components it makes. Some board layouts may not necessarily allow this, but it should be an effort.   What manufacturability issues should be considered in PCB design   Also, similar component types should be grounded together as much as possible, with all component feet in the same direction, as shown in Figure 3.     However, the author has indeed encountered quite a number of PCBS, where the assembly density is too high, and the welding surface of the PCB must also be distributed with high components such as tantalum capacitor and patch inductance, as well as thin-spaced SOIC and TSOP. In this case, it is only possible to use double-sided printed solder paste patch for backflow welding, and plug-in components should be concentrated as far as possible in the distribution of components to adapt to manual welding. Another possibility is that the perforated elements on the component face should be distributed as far as possible in a few main straight lines to accommodate the selective wave soldering process, which can avoid manual welding and improve efficiency, and ensure the quality of welding. Discrete solder joint distribution is a major taboo in selective wave soldering, which will multiply the processing time.   When adjusting the position of components in the printed board file, it is necessary to pay attention to the one-to-one correspondence between components and silkscreen symbols. If the components are moved without corresponding moving the silkscreen symbols next to the components, it will become a major quality hazard in manufacturing, because in actual production, silkscreen symbols are the industry language that can guide production.   2.2 The PCB must be equipped with clamping edges, positioning marks and process positioning holes necessary for automatic production.   At present, electronic mounting is one of the industries with a degree of automation, the automation equipment used in the production requires automatic transmission of PCB, so that the transmission direction of PCB (generally for the long side direction), the upper and lower each have a not less than 3-5mm wide clamping edge, in order to facilitate automatic transmission, avoid near the edge of the board due to the clamping can not automatically mounting.   The role of positioning markers is that PCB needs to provide at least two or three positioning markers for the optical identification system to accurately locate PCB and correct PCB machining errors for the assembly equipment which is widely used in optical positioning. Of the positioning markers commonly used, two must be distributed on the diagonal of the PCB. The selection of positioning marks generally uses standard graphics such as a solid round pad. In order to facilitate identification, there should be an empty area around the marks without other circuit features or marks, the size of which should not be less than the diameter of the marks (as shown in Figure 4), and the distance between the marks and the edge of the board should be more than 5mm.       In the manufacturing of PCB itself, as well as in the assembling process of semi-automatic plug-in, ICT testing and other processes, PCB needs to provide two to three positioning holes in the corners.   2.3 Rational use of panels to improve production efficiency and flexibility   When assembling PCB with small sizes or irregular shapes, it will be subject to many restrictions, so it is generally adopted to assemble several small PCB into PCB of appropriate size, as shown in Figure 5. Generally, PCB with a single side size of less than 150mm can be considered to adopt the splicing method. By two, three, four, etc., the size of large PCB can be spliced to the appropriate processing range. Generally, PCB with a width of 150mm~250mm and length of 250mm~350mm is the more appropriate size in automatic assembling.   Another way of the board is to arrange the PCB with SMD on both sides of a positive and negative spelling into a large board, such a board is commonly known as Yin and Yang, generally for the consideration of saving the cost of the screen board, that is, through such a board, originally need two sides of the screen board, now only need to open a screen board. In addition, when the technicians prepare the running program of the SMT machine, the PCB programming efficiency of Yin and Yang is also higher.   When the board is divided, the connection between the sub-boards can be made of double face V-shaped grooves, long slot holes and round holes, etc., but the design must be considered as far as possible to make the separation line in a straight line, in order to facilitate the board, but also consider that the separation side can not be too close to the PCB line so that the PCB is easy to damage when the board.   There is also a very economical board and does not refer to the PCB board, but to the mesh of the grid graphic board. With the application of an automatic solder paste printing press, the current more advanced printing press (such as DEK265) has allowed the size of 790×790mm steel mesh, set up a multi-sided PCB mesh pattern, can achieve a piece of steel mesh for the printing of multiple products, is a very cost saving practice, especially suitable for the product characteristics of small batch and variety of manufacturers.     2.4 Considerations of testability design   The testability design of SMT is mainly for the current ICT equipment situation. Testing issues for post-production manufacturing are taken into account in circuit and surface-mounted PCB SMB designs. To improve testability design, two requirements of process design and electrical design should be considered.   2.4.1 Requirements of process design   The accuracy of positioning, substrate manufacturing procedure, substrate size and probe type are all factors that affect the reliability of the probe.   (1) positioning hole. The error of positioning holes on the substrate should be within ±0.05mm. Set at least two positioning holes as far apart as possible. The use of nonmetallic positioning holes to reduce the thickness of the solder coating can not meet the tolerance requirements. If the substrate is manufactured as a whole and then tested separately, the positioning holes must be located on the motherboard and each individual substrate.   (2) The diameter of the test point is not less than 0.4mm, and the spacing between adjacent test points is more than 2.54mm, not less than 1.27mm.   (3) Components whose height is higher than *mm should not be placed on the test surface, which will cause poor contact between the probe of the online test fixture and the test point.   (4) Place the test point 1.0mm away from the component to avoid impact damage between the probe and the component. There should be no components or test points within 3.2mm of the ring of the positioning hole.   (5) The test point shall not be set within 5mm of the PCB edge, which is used to ensure the clamping fixture. The same process edge is usually required in conveyor belt production equipment and SMT equipment.   (6) All detection points shall be tinned or metal conductive materials with soft texture, easy penetration, and non-oxidation shall be selected to ensure reliable contact and prolong the service life of the probe.   (7) the test point can not be covered by solder resistance or text ink, otherwise, it will reduce the contact area of the test point, and reduce the reliability of the test.   2.4.2 Requirements for electrical design   (1) The SMC/SMD test point of the component surface should be led to the welding surface through the hole as far as possible, and the hole diameter should be greater than 1mm. In this way, single-sided needle beds can be used for online testing, thus reducing the cost of online testing.   (2) Each electrical node must have a test point, and each IC must have a test point of POWER and GROUND, and as close as possible to this component, within the range of 2.54mm from the IC.   (3) The width of the test point can be enlarged to 40mil wide when it is set on the circuit routing.   (4) Evenly distribute the test points on the printed board. If the probe is concentrated in a certain area, the higher pressure will deform the plate or needle bed under test, further preventing part of the probe from reaching the test point.   (5) The power supply line on the circuit board should be divided into regions to set the test breakpoint so that when the power decoupling capacitor or other components on the circuit board appear short circuit to the power supply, find the fault point more quickly and accurately. When designing breakpoints, the power-carrying capacity after resuming the test breakpoint should be considered.   Figure 6 shows an example of a test point design. The test pad is set near the lead of the component by the extension wire or the test node is used by the perforated pad. The test node is strictly forbidden to be selected on the solder joint of the component. This test may make the virtual welding joint extrude to the ideal position under the pressure of the probe, so that the virtual welding fault is covered up and the so-called "fault-masking effect" occurs. The probe may directly act on the endpoint or pin of the component due to the bias of the probe caused by the positioning error, which may cause damage to the component. What manufacturability issues should be considered in PCB design?   3. Closing remarks on PCB Design   The above are some of the main principles that should be considered in PCB design. In the manufacturing design of PCB oriented to electronic assembly, there are quite a lot of details, such as the reasonable arrangement of the matching space with the structural parts, reasonable distribution of silkscreen graphics and text, appropriate distribution of heavy or large heating device location, In the design stage of PCB, it is necessary to set up the test point and test space in the appropriate position, and consider the interference between the die and the nearby distributed components when the couplings are installed by the pull and press riveting process. A PCB designer, not only considers how to obtain good electrical performance and a beautiful layout but also an equally important point which is manufacturability in PCB design, in order to achieve high quality, high efficiency, low cost.    

  Nowadays, circuit board manufacturers are flooding the market with various prices and quality issues that we are completely unaware of. So the obvious question we face is, how to choose the materials for PCB multilayer board processing? The materials commonly used in processing are copper-clad laminates, dry film, and ink. Below is a brief introduction to these materials.     Copper-clad laminates     Also known as double-sided copper clad board. Whether the copper foil can firmly adhere to the substrate depends on the adhesive, and the peel strength of copper-clad laminates mainly depends on the performance of the adhesive. The commonly used thicknesses of copper-clad laminates are 1.0 mm, 1.5 mm, and 2.0 mm.   Types of copper-clad PCB/laminates     There are many classification methods for copper-clad laminates. Generally, according to different reinforcement materials of the board, they can be divided into five categories: paper-based, glass fiber cloth-based, composite-based (CEM series), multi-layer board-based, and special materials-based (ceramic, metalcore, etc.). If the classification is based on the resin adhesive used for the board, the commonly used paper-based CCLs include phenolic resin (XPC, XXXPC, FR-l, FR-2, etc.), epoxy resin (FE-3), polyester resin, and various types. The commonly used glass fiber cloth-based CCLs include epoxy resin (FR-4, FR-5), which is currently the most widely used glass fiber cloth-based type.     Copper Clad PCB Board Materials     There are also other special resin-based materials (with glass fiber cloth, polyimide fiber, non-woven fabric, etc. as reinforcing materials): bismaleimide-modified triazine resin (BT), polyamide-imide resin (PI), biphenyl acyl resin (PPO), maleic anhydride-styrene resin (MS), polyoxoacid resin, polyolefin resin, etc. Classified by the flame retardancy of CCLs, there are two types of flame retardant and non-flame retardant boards. In recent years, with increasing concern for environmental issues, a new type of flame retardant CCL that does not contain halogens has been developed, called "green flame retardant CCL." With the rapid development of electronic product technology, CCLs are required to have higher performance. Therefore, from the performance classification of CCLs, they can be further divided into general performance CCLs, low dielectric constant CCLs, high-heat-resistant CCLs, low thermal expansion coefficient CCLs (generally used for package substrates), and other types.     In addition to the performance indicators of copper-clad laminates, the main materials to be considered in PCB multilayer board processing are the glass transition temperature of copper-clad PCB laminates. When the temperature rises to a certain region, the substrate changes from the "glass state" to the "rubber state." The temperature at this time is called the glass transition temperature (TG) of the board. In other words, TG is the highest temperature (％) at which the base material maintains its rigidity. That is to say, under high temperatures, ordinary substrate materials not only exhibit phenomena such as softening, deformation, and melting but also manifest in the sharp decline of mechanical and electrical properties.       Copper Clad PCB Board Process   The general TG of PCB multilayer board processing plate is above 130T, high TG is generally greater than 170°, and medium TG is approximately greater than 150°. Usually, printed boards with a TG value of 170 are called high TG printed boards. When the TG of the substrate is increased, the heat resistance, moisture resistance, chemical resistance, and stability of the printed board are improved. The higher the TG value, the better the temperature resistance performance of the board material, especially in lead-free processes where high TG is more widely used.     With the rapid development of electronic technology and the increase in information processing and transmission speed, in order to expand communication channels and transfer frequencies to high-frequency areas, it is necessary for PCB multilayer board processing substrate materials to have lower dielectric constant (e) and low dielectric loss TG. Only by reducing e can high signal propagation speed be obtained, and only by reducing TG can signal propagation loss be reduced.     With the precision and multilayering of printed boards and the development of BGA, CSP, and other technologies, PCB multilayer board processing factories have put forward higher requirements for the dimensional stability of copper-clad laminates. Although the dimensional stability of copper-clad laminates is related to the production process, it mainly depends on the three raw materials that make up the copper-clad laminates: resin, reinforcing material, and copper foil. The commonly adopted method is to modify the resin, such as modified epoxy resin; reduce the proportion of the resin, but this will reduce the electrical insulation and chemical properties of the substrate; the influence of copper foil on the dimensional stability of copper-clad laminates is relatively small.     In the process of PCB multilayer board processing, with the popularization and use of photosensitive solder resist, in order to avoid mutual interference and produce ghosting between the two sides, all substrates must have the function of shielding UV. There are many methods for blocking ultraviolet rays, and generally, one or two of the glass fiber cloth and epoxy resin can be modified, such as using epoxy resin with UV-BLOCK and automatic optical detection function.  

PCB Manufacturing Balanced Copper Design Specifications 1. During stackup design, it is recommended to set the center layer to the maximum copper thickness and further balance the remaining layers to match their mirrored opposite layers. This advice is important to avoid the potato chip effect discussed earlier.   2. Where there are wide copper areas on the PCB, it is wise to design them as grids rather than solid planes to avoid copper density mismatches in that layer. This largely avoids bow and twist issues.   3. In the stack, the power planes should be placed symmetrically, and the weight of copper used in each power plane should be the same.   4. Copper balance is required not only in the signal or power layer, but also in the core layer and prepreg layer of the PCB. Ensuring an even proportion of copper in these layers is a good way to maintain the overall copper balance of the PCB.   5. If there is excess copper area in a particular layer, the symmetrical opposite layer should be filled with tiny copper grids to balance. These tiny copper grids are not connected to any network and do not interfere with functionality. But it is necessary to ensure that this copper balancing technique does not affect signal integrity or board impedance.   6. Technology to balance copper distribution   1) Fill Pattern Cross-hatching is a process in which some copper layers are latticed. It actually involves regular periodic openings that almost look like a large sieve. This process creates small openings in the copper plane. The resin will bond firmly to the laminate through the copper. This results in stronger adhesion and better copper distribution, reducing the risk of warping. Here are some benefits of shadowed copper planes over solid pours: Controlled impedance routing in high-speed circuit boards. Allows for wider dimensions without compromising circuit assembly flexibility. Increasing the amount of copper under the transmission line increases the impedance. Provides mechanical support for dynamic or static flex panels.   2) Large copper areas in grid form   Area copper areas should always be gridded. This can usually be set in the layout program. For example, the Eagle program refers to areas of the grid as "hatches". Of course, this is only possible if no sensitive high-frequency conductor traces are present. The "grid" helps avoid "twist" and "bow" effects, especially for boards with only one layer. 3) Fill copper-free areas with (grid) copper Copper-free areas should be filled with (grid) copper.   Advantage: Better uniformity of the plated through hole walls is achieved. Prevents twisting and bending of circuit boards.   4) Copper area design example Generally Good Perfect No fill/grid Filled area Filled area + Grid   5) Ensure copper symmetry     Large copper areas should be balanced with "copper fill" on the opposite side. Also try to spread the conductor traces as evenly as possible across the board. For multi-layer boards, match symmetrical opposing layers with "copper fill". 6) Symmetrical copper distribution in layer build-up The copper foil thickness in a circuit board build-up layer should always be distributed symmetrically. It is possible to create an asymmetrical layer buildup, but we strongly advise against it due to possible distortion. 7. Use thick copper plates If the design allows, choose thicker copper plates instead of thinner copper plates. The chance factor of bowing and twisting gets higher when you're using thin plates. This is because there is not enough material to keep the board rigid. Some standard thicknesses are lmm, 1.6mm, 1.8mm. At thicknesses below 1 mm, the risk of warping is twice as high as with thicker plates. 8. Uniform trace Conductor traces should be evenly distributed on the circuit board. Avoid copper sockets as much as possible. Traces should be distributed symmetrically on each layer. 9. Copper Stealing You can see that the current builds up more in areas where isolated traces exist. Due to this fact, you cannot get smooth square edges. Copper stealing is the process of adding small circles, squares, or even planes of solid copper to large empty spaces on a circuit board. Stealing copper distributes copper evenly across the board.   Other advantages are: Uniform plating current, all traces etch the same amount. Adjust the thickness of the dielectric layer. Reduces the need for over-etching, thereby reducing costs. Steal copper   10. Copper filling If a large copper area is required, the open area is filled with copper, which is done to maintain balance with the symmetrical opposite layer.   11. The power plane is symmetrical It is very important to maintain copper thickness in each signal or power plane. Power planes should be symmetrical. The simplest form is to put the power and ground planes in the middle. If you could get power and ground closer together, the loop inductance would be much smaller and therefore the propagation inductance would be less. " 12. Prepreg and core symmetry Just keeping the power plane symmetrical is not enough to achieve a uniform copper cladding. Matching prepreg and core material is also important in terms of layering and thickness issues.   Prepreg and core symmetry   13. Copper weight Fundamentally speaking, copper weight is a measure of the thickness of copper on the board. A specific weight of copper is rolled over a one square foot area on one layer of the board. The standard copper weight we use is 1 ounce or 1.37 mils. For example, if you use 1 ounce of copper over a 1 square foot area, the copper will be 1 ounce thick.   copper weight Copper weight is a determining factor in the current carrying capability of the board. If your design has high voltage, current, resistance or impedance requirements, you can modify the copper thickness. 14. Heavy copper Heavy copper has no universal definition. We do use 1 oz as a standard copper weight. However, if the design calls for more than 3 oz, it is defined as heavy copper. The higher the copper weight, the higher the current carrying capacity of the trace. The thermal and mechanical stability of the circuit board is also improved. It is now more resistant to high current exposure, excessive temperatures, and frequent thermal cycling. All of these can weaken conventional board designs.     Other advantages are: High power density Greater ability to accommodate multiple copper weights on the same layer Increase heat dissipation   15. Light copper Sometimes, you need to reduce the copper weight to achieve a specific impedance, and it is not always possible to adjust the trace length and width, so achieving a lower copper thickness is one of the possible methods. You can use the trace width calculator to design the correct traces for your board.   Distance to Copper Weight When you use thick copper cladding, you need to adjust the spacing between traces. Different designers have different specifications for this. Here is an example of the minimum space requirements for copper weights: Copper Weight Space Between Copper Features and Minimum Trace Width 1 oz 350,000 (0.089 mm) 2 oz 8 million (0.203mm) 3 oz 10 mil (0.235mm) 4 oz 14 million (0.355mm)        

  The copper substrate to do thermoelectric separation refers to a production process of copper substrate is a thermoelectric separation process, its substrate circuit part and thermal layer part in different line layers, the thermal layer part directly contact with the lamp bead heat dissipation part, to achieve the best heat dissipation thermal conductivity (zero thermal resistance).     Metal core PCB materials are mainly three, aluminum-based PCB, copper-based PCB, iron-based PCB. with the development of high-power electronics and high-frequency PCB, heat dissipation, volume requirements are increasingly high, the ordinary aluminum substrate can not meet, more and more high-power products in the use of copper substrate, many products on the copper substrate processing process requirements are also increasingly high, so what is the copper substrate, copper substrate has What are the advantages and disadvantages.     We first look at the above chart, on behalf of the ordinary aluminum substrate or copper substrate, heat dissipation needs to be insulated thermal conductive material (purple part of the chart), processing is more convenient, but after the insulating thermal conductive material, the thermal conductivity is not so good, this is suitable for small power LED lights, enough to use. That if the LED beads in the car or high-frequency PCB, heat dissipation needs are very large, aluminum substrate and ordinary copper substrate will not meet the common is to use thermoelectric separation copper substrate. The line part of copper substrate and the thermal layer part are on different line layers, and the thermal layer part directly touches the heat dissipation part of the lamp bead (such as the right part of the picture above) to achieve the best heat dissipation (zero thermal resistance) effect.     Advantages of copper substrate for thermal separation.   1. The choice of copper substrate, high density, the substrate itself has a strong thermal carrying capacity, good thermal conductivity and heat dissipation.   2. The use of thermoelectric separation structure, and lamp bead contact zero thermal resistance. Maximum reduction of lamp bead light decay to extend the life of the lamp beads.   3. Copper substrate with high density and strong thermal carrying capacity, smaller volume under the same power.   4. Suitable for matching single high-power lamp beads, especially COB package, so that the lamps achieve better results.   5. According to different needs, various surface treatment can be carried out (sunken gold, OSP, tin spray, silver plating, sunken silver + silver plating), with excellent reliability of surface treatment layer.   6. Different structures can be made according to different design needs of the luminaire (copper convex block, copper concave block, thermal layer and line layer parallel).   Disadvantages of thermoelectric separation copper substrate.   Not applicable with single electrode chip bare crystal package.      

PCB Factory Impedance Control Guidelines Impedance control purpose To determine the requirements of impedance control, to standardize the impedance calculation method, to formulate the guidelines of impedance test COUPON design, and to ensure that the products can meet the needs of production and customer requirements.   Definition of impedance control Definition of impedance At a certain frequency, the electronic device transmission signal line, relative to a reference layer, its high-frequency signal or electromagnetic wave in the propagation process of resistance is called characteristic impedance, it is a vector sum of electrical impedance, inductive resistance, capacitive resistance .......   Classification of impedance At present, our common impedance is divided into: single-ended (line) impedance, differential (dynamic) impedance, common   Impedance of these three cases Single-ended (line) impedance: English single ended impedance, refers to the impedance measured by a single signal line. Differential (dynamic) impedance: English differential impedance, refers to the differential drive in the two equal-width, equal-spaced transmission lines tested to the impedance. Coplanar impedance: English coplanar impedance, refers to the signal line in its surrounding GND / VCC (signal line to its two sides of GND / VCC The impedance tested when the transmission between the GND/VCC (equal distance between the signal line to its two sides GND/VCC).   Impedance control requirements are determined by the following conditions When the signal is transmitted in the PCB conductor, if the length of the wire is close to 1/7 of the signal wavelength, then the wire becomes a signal PCB production, according to customer requirements to decide whether to control the impedance If the customer requires a line width to do impedance control, the production needs to control the impedance of the line width. Three elements of impedance matching: Output impedance (original active part), characteristic impedance (signal line), and input impedance (passive part) (PCB board) impedance matching When the signal is transmitted on the PCB, the characteristic impedance of the PCB board must match the electronic impedance of the head and tail components. Once the impedance value is out of tolerance, the transmitted signal energy will be reflected, scattered, attenuated or delayed, resulting in an incomplete signal and signal distortion. Impedance influencing factors: Er: dielectric permittivity, inversely proportional to the impedance value , dielectric constant according to the newly provided "sheet dielectric constant table" calculation . H1, H2, H3, etc.: line layer and grounding layer between the media thickness, and impedance value is proportional. W1: impedance line line width; W2: impedance line width, and impedance is inversely proportional. A: when the inner bottom copper for HOZ, W1 = W2 + 0.3mil; inner bottom copper for 1OZ, W1 = W2 + 0.5mil; when the inner bottom copper for 2OZ W1 = W2 + 1.2mil. B: When the outer base copper is HOZ, W1=W2+0.8mil; when the outer base copper is 1OZ, W1=W2+1.2mil; when the outer base copper is 2OZ, W1=W2+1.6mil. C: W1 is the original impedance line width. T: copper thickness, inversely proportional to the impedance value.   A: The inner layer is the substrate copper thickness, HOZ is calculated by 15μm; 1OZ is calculated by 30μm; 2OZ is calculated by 65μm. B: The outer layer is copper foil thickness + copper plating thickness, depending on the hole copper specifications, when the bottom copper is HOZ, hole copper (average 20μm, minimum 18μm ), the table copper calculated by 45μm; hole copper (average 25μm, minimum 20μm), the table copper calculated by 50μm; hole copper single point minimum 25μm, the table copper calculated by 55μm. C: When the bottom copper is 1OZ, hole copper (average 20μm, minimum 18μm), the table copper is calculated by 55μm; hole copper (average 25μm, minimum 20μm), the table copper is calculated by 60μm; hole copper single point minimum 25μm, the table copper is calculated by 65μm. S: the spacing between adjacent lines and lines, proportional to the impedance value (differential impedance). C1: substrate solder resistance thickness, inversely proportional to the impedance value; C2: line surface solder resistance thickness, inversely proportional to the impedance value; C3: interline thickness, inversely proportional to the impedance value; CEr: solder resist dielectric constant, and the impedance value is inversely proportional to . A: Printed once solder resist ink, C1 value of 30μm, C2 value of 12μm, C3 value of 30μm. B: Printed twice solder resist ink, C1 value of 60μm, C2 value of 25μm, C3 value of 60μm. C: CEr: calculated according to 3.4.     Scope of application:Differential impedance calculation before outer resistance welding Parameter Description. H1:Dielectric thickness between outer layer and VCC/GND W2:Impedance line surface width W1:Bottom width of impedance line S1:Differential impedance line gap Er1:dielectric layer dielectric constant T1:Line copper thickness, including substrate copper thickness + plating copper thickness     Scope of application:Differential impedance calculation after outer resistance welding Parameter Description. H1:Thickness of dielectric between outer layer and VCC/GND W2:Impedance line surface width W1:Bottom width of impedance line S1:Differential impedance line gap Er1:dielectric layer dielectric constant T1:Line copper thickness, including substrate copper thickness + plating copper thickness CEr:Impedance dielectric constant C1:Substrate resist thickness C2:Line surface resist thickness C3:Differential impedance interline resist thickness   Design of impedance test COUPON COUPON add location Impedance test COUPON is generally placed in the middle of the PNL, not allowed to be placed on the edge of the PNL board, except in special cases (such as 1PNL = 1PCS). COUPON design considerations To ensure the accuracy of impedance test data, COUPON design must completely simulate the form of the line inside the board, if the impedance line around the board is protected by copper, the COUPON should be designed to replace the protection line; if the board resistance line is "snake" alignment, the COUPON also needs to be designed as a "snake" alignment. If the resistance line in the board is "snake" alignment, then the COUPON should also be designed as "snake" alignment. Impedance test COUPON design specifications Single-ended (line) impedance: Test COUPON main parameters: A: test hole diameter ∮ 1.20MM (2X/COUPON), this is the size of the tester probe B: test positioning hole: unified by ∮2.0MM production (3X/COUPON), gong board positioning with; C: two test hole spacing of 3.58MM Differential (dynamic) impedance   Test COUPON main parameters: A: test hole diameter ∮ 1.20MM (4X/COUPON), two of them for the signal hole, the other two for the grounding hole, are the size of the tester probe; B: test positioning hole: unified according to the production of ∮ 2.0MM (3X/COUPON), gong board positioning with; C: two signal hole spacing: 5.08MM, two grounding hole spacing for: 10.16MM.   Design COUPON notes The distance between the protection line and the impedance line needs to be greater than the width of the impedance line . Impedance line length is generally designed in the range of 6-12INCH. The nearest GND or POWER layer of the adjacent signal layer is the ground reference layer for impedance measurement. The protection line of the signal line added between the two GND and POWER should not obscure the signal line of any layer between GND and POWER layers. The two signal holes lead to the differential impedance line, and the two ground holes must be grounded at the same time in the reference layer. In order to ensure the uniformity of copper plating, it is necessary to add a power grabbing PAD or copper skin in the outer empty board position.   Differential coplanar impedance Test COUPON main parameters: the same differential impedance Differential coplanar impedance type: Reference layer and impedance line in the same level, that is, the impedance line is surrounded by the surrounding GND / VCC, the surrounding GND / VCC is the reference level. POLAR software calculation mode, see 4.5.3.8; 4.5.3.9; 4.5.3.12. The reference layer is the GND/VCC on the same level and the GND/VCC layer adjacent to the signal layer. (The impedance line is surrounded by the surrounding GND/VCC, and the surrounding GND/VCC is the reference layer).  

PCB Copper Plating Inspection The purpose of copper plating   Deposit a thin layer of copper on the entire printed circuit board (especially on the hole wall) for subsequent hole plating, to make the hole metalized (with copper inside for conductivity), and achieve interlayer conductance.   As for the sub-processes of copper plating, there are usually three Pre-plating treatment (grinding the board) Before copper plating, the China PCB board is ground to remove burrs, scratches, and dust from the surface and inside the holes.     Copper plating   Using the board material itself to catalyze the oxidation-reduction reaction, a thin layer of copper is deposited on the holes and surface of the printed circuit board, acting as a conducting lead for subsequent plating to achieve hole metallization.   Backlight level testing   By making hole wall sections and observing them with a metallographic microscope, the coverage of deposited copper on the hole walls is confirmed. (Note: Backlight level is generally divided into 10 levels. The higher the level, the better the coverage of deposited copper on the hole walls. The industry standard is usually ≥8.5 levels.)     The purpose of this PCB copper plate process is mainly for inspection, which will not affect the quality of the product. However, since this inspection is very important, it is often separated from the production line and listed as one of the daily tasks in the laboratory. Therefore, if you find that some PCB manufacturers do not have corresponding inspection stations around their copper plating lines, don't be surprised. It is probably done in the laboratory.   In addition, copper plating is not the only process that can be used as a preparation for plating. Black hole and black mask can also be used. As for the specific differences among the three.      

LDI Technology Is The Solution To The High-density PCB With the advancement of high integration and assembly (especially chip-scale/µ-BGA packaging) technology of electronic components (groups). Greatly it promotes the development of "light, thin, short, and small" electronic products, high-frequency/high-speed digitalization of signals, and large-capacity and multi-functionalization of electronic products. Development and progress, which requires PCB to quickly develop in the direction of very high density, high precision and multi-layer. In the current and future periods of time, in addition to continuing to use (laser) micro-hole development, it is important to solve the "very high density" problem in PCBs. The control of fineness, position, and inter-layer alignment of wires. The traditional "photographic image transfer" technology, it is close to the "manufacturing limit" and it is difficult to meet the requirements of very high-density PCBs, and the use of laser direct imaging (LDI) is the goal to solve the problem of "very high density (referring to occasions where L/S ≤ 30 µm)" fine wires and interlayer alignment in PCBs before and in the future the main method of the problem.   1. The Challenge Of Very High-Density Graphics The requirement of high density PCB is in essence mainly from IC and other components (components) integration and PCB manufacturing technology war. (1) Challenge Of Integration Degree Of IC And Other Components. We must clearly see that the fineness, position and micro-porosity of PCB wire are far behind the IC integration development requirements are shown in Table 1. Table 1 Year Integrated Circuit Width /µm PCB Line Width /µm Ratio 1970 3 300 1:100 2000 0.18 100~30 1:560 ~ 1:170 2010 0.05 10~25 1:200 ~ 1:500 2011 0.02 4~10 1:200 ~ 1:500 Note: The size of the through hole is also reduced with the fine wire, which is generally 2~3 times the width of the wire. Current and future wire width/spacing (L/S, unit -µm) Direction: 100/100→75/75→50/50→30/3→20/20→10/10, or less. The corresponding micropore (φ, unit µm):300→200→100→80→50→30, or smaller. As can be seen from the above, PCB high density is far behind IC integration. The biggest challenge for PCB enterprises now and in the future is how to produce "very high-density" refined guides the problems of line, position and microporosity. (2) Challenges Of PCB Manufacturing Technology. We should see more; Traditional PCB manufacturing technology and process can not adapt to the development of PCB "very high density". ①The graphic transfer process of traditional photographic negatives is lengthy, as shown in Table 2. Table 2 Processes required by the two graphics conversion methods Graphic Transfer Of Traditional Negatives Graphics Transfer For LDI Technology CAD/CAM： PCB design CAD/CAM： PCB design Vector/raster conversion, light painting machine Vector/raster conversion, laser machine Negative film for light painting imaging, light painting machine / Negative development, developer / Negative stabilization, temperature and humidity control / Negative inspection, defects and dimensional checks / Negative punching (positioning holes) / Negative preservation, inspection (defects and dimensions) / Photoresist (laminator or coating) Photoresist (laminator or coating) UV bright exposure (exposure machine) Laser scanning imaging Development (developer) Development (developer)   ② The graphic transfer of traditional photographic negatives has a large deviation. Due to the positioning deviation of the graphic transfer of the traditional photo negative, the temperature and humidity of the photo negative (storage and use) and the thickness of the photo. The size deviation caused by the "refraction" of light due to the high degree is above ± 25 µm, which determines the pattern transfer of traditional photo negatives. It is difficult to produce PCB wholesale products with L/S ≤30 µm fine wires and position, and interlayer alignment with the transfer process technology.   2 Role Of Laser Direct Imaging (LDI) 2.1 The Main Disadvantages Of Traditional PCB Manufacturing Technology   (1) The Position Deviation And Control Cannot Meet The Requirements Of Very High Density. In the pattern transfer method using photographic film exposure, the positional deviation of the formed pattern is mainly from the photographic film. The temperature and humidity changes and alignment errors of the film. When the production, preservation and application of photographic negatives are under strict temperature and humidity control, The main size error is determined by the mechanical positioning deviation. We know that the highest precision of mechanical positioning is ±25 µm with repeatability of ±12.5 µm. If we want to produce PCB multilayer diagram with L/S=50 µm wire and φ100 µm. Obviously, it is difficult to produce products with a high pass rate only due to the dimensional deviation of mechanical positioning, let alone the existence of many other factors (photographic film thickness and temperature and humidity, substrate, lamination, resist thickness and light source characteristics and illuminance etc.) due to size deviation! More importantly, the dimensional deviation of this mechanical positioning is "uncompensable" because it is irregular. The above shows that when the L/S of the PCB is ≤50 µm, continue to use the pattern transfer method of photographic film exposure to produce. It is unrealistic to manufacture "very high density" PCB boards because it encounters dimensional deviations such as mechanical positioning and other factors the "manufacturing limit"! (2) The Product Processing Cycle Is Long. Due to the pattern transfer method of photo negative exposure to manufacturing "even high density" PCB boards, the process name is long. If compared with laser direct imaging (LDI), the process is more than 60% (see Table 2). (3) High Manufacturing Costs. Due to the pattern transfer method of photo negative exposure, not only many processing steps and long production cycle are required, so more multi-person management and operation, but also a large number of photo negatives (silver salt film and heavy oxidation film) for collection and other auxiliary materials and chemical materials products, etc., data statistics, for medium-sized PCB companies. The photo negatives and re-exposure films consumed within one year are enough to buy LDI equipment for production or put into LDI technology production could recover the investment cost of LDI equipment within one year, and this has not been calculated by using LDI technology to provide high product quality (qualified rate) benefits! 2.2 Main advantages of Laser Direct Imaging (LDI) Since LDI technology is a group of laser beams directly imaged on the resist, it is then developed and etched. Therefore, it has a series of advantages. (1) The Position Degree Is Extremely High. After the workpiece (board in the process) is fixed, laser positioning and vertical laser beam Scanning can ensure that the graphic position (deviation) is within ±5 µm, which greatly improves the positional accuracy of the line graph, which is a traditional (photographic film) pattern transfer method can not be achieved, for high-density manufacturing (especially L/S ≤ 50µmmφ≤100 µm) PCB (especially the interlayer alignment of "very high density" multi-layer boards, etc.) It is undoubtedly important to ensure product quality and improve product qualification rates. (2) The Processing Is Reduced And The Cycle Is Short. The use of LDI technology can not only improve the quality of "very high density" multi-layer boards' quantity and production qualification rate, and significantly shorten the product processing process. Such as pattern transfer in manufacturing (forming inner layer wires). When on the layer that forms the resist (in-progress board), only four steps are required (CAD/CAM data transfer, laser scanning, development, and etching), while the traditional photographic film method. At least eight steps. Apparently, the machining process is at least halved!     (3) Save Manufacturing Costs. The use of LDI technology can not only avoid the use of laser photoplotters, automatic development of photographic negatives, Fixing the machine, diazo film developing machine, punching and positioning hole machine, size and defect measuring/inspecting instrument, and storage and maintenance of a large number of photographic negatives equipment and facilities, and more importantly, avoid the use of a large number of photographic negatives, diazo films, strict temperature and humidity control the cost of materials, energy, and related management and maintenance personnel is significantly reduced.      

Introduction to PCB Substrate Materials Copper-clad PCB mainly plays three roles in the entire printed circuit board: conduction, insulation, and support.   Classification method of copper-clad PCB According to the rigidity of the board, it is divided into rigid copper-clad PCB and flexible copper-clad PCB. According to the different reinforcing materials, it is divided into four categories: paper-based, glass cloth-based, composite-based (CEM series, etc.) and special material-based (ceramic, metal-based, etc.). According to the resin adhesive used in the board, it is divided into: (1) Paper-based board: Phenolic resin XPC, XXXPC, FR-1, FR-2, epoxy resin FR-3 board, polyester resin, etc.   (2) Glass cloth-based board: Epoxy resin (FR-4, FR-5 board), polyimide resin PI, polytetrafluoroethylene resin (PTFE) type, bismaleimide-triazine resin (BT), polyphenylene oxide resin (PPO), polydiphenyl ether resin (PPE), maleimide-styrene fatty resin (MS), polycarbonate resin, polyolefin resin, etc. According to the flame-retardant performance of copper-clad PCB, it can be divided into two types: flame-retardant type (UL94-VO, V1) and non-flame-retardant type (UL94-HB).   Introduction of main raw materials of copper-clad PCB According to the method of copper foil production, it can be divided into rolled copper foil (W class) and electrolytic copper foil (E class) Rolled copper foil is made by repeatedly rolling the copper plate, and its resilience and elastic modulus are greater than those of electrolytic copper foil. The copper purity (99.9%) is higher than that of electrolytic copper foil (99.8%). It is smoother than electrolytic copper foil on the surface, which is conducive to the rapid transmission of electrical signals. Therefore, rolled copper foil is used in the substrate of high-frequency and high-speed transmission, fine-line PCBs, and even in the PCB substrate of audio equipment, which can improve the sound quality effect. It is also used to reduce the coefficient of thermal expansion (TCE) of fine-line and high-layer multi-layer circuit boards made of "metal sandwich board". Electrolytic copper foil is continuously produced on the copper cylindrical cathode by a special electrolytic machine (also called a plating machine). The primary product is called raw foil. After surface treatment, including roughening layer treatment, heat-resistant layer treatment (copper foil used in paper-based copper-clad PCB does not require this treatment), and passivation treatment. Copper foil with a thickness of 17.5㎜ (0.5OZ) or less is called ultra-thin copper foil (UTF). For production below 12㎜ in thickness, a "carrier" must be used. Aluminum foil (0.05～0.08mm) or copper foil (about 0.05㎜) is mainly used as a carrier for 9㎜ and 5㎜ thick UTE produced at present.   The glass fiber cloth is made of aluminum borosilicate glass fiber (E), D or Q type (low dielectric constant), S type (high mechanical strength), H type (high dielectric constant), and a vast majority of copper-clad PCB uses E type Plain weave is used for glass cloth, which has the advantages of high tensile strength, good dimensional stability, and uniform weight and thickness. The basic performance items characterize glass cloth, including the types of warp yarn and weft yarn, fabric density (number of warp and weft yarns), thickness, weight per unit area, width, and tensile strength (tensile strength). The primary reinforcing material of paper-based copper-clad PCB is impregnated fiber paper, which is divided into cotton fiber pulp (made of cotton short fiber) and wood fiber pulp (divided into broadleaf pulp and coniferous pulp). Its main performance indexes include uniformity of paper weight (generally selected as 125g/㎡ or 135g/㎡), density, water absorption, tensile strength, ash content, moisture, etc.   The main characteristics and uses of flexible copper-clad PCB Required features Example of main use Thinness and high bendability FDD, HDD, CD sensors, DVDs Multi-layer Personal computers, computers, cameras, communication equipment Fine-line circuits Printers, LCDs High heat resistance Automotive electronic products High density installation and miniaturization Camera Electrical characteristics (impedance control) Personal computers, communication devices   According to the classification of insulating film layer (also known as dielectric substrate), flexible copper clad laminates can be divided into flexible copper clad laminates of polyester film, flexible copper clad laminates of polyimide film and flexible copper clad laminates of fluorocarbon ethylene film or aromatic polyamide paper. CCL. Classified by performance, there are flame-retardant and non-flame-retardant flexible copper clad laminates. According to the classification of manufacturing process method, there are two-layer method and three-layer method. The three-layer board is composed of an insulating film layer, a bonding layer (adhesive layer), and a copper foil layer. The two-layer method board only has an insulating film layer and a copper foil layer. There are three production processes: The insulating film layer is composed of thermosetting polyimide resin layer and thermoplastic polyimide resin layer. A layer of barrier metal (barriermetal) is first coated on the insulating film layer, and then copper is electroplated to form a conductive layer. Vacuum sputtering technology or evaporation deposition technology is adopted, that is, the copper is evaporated in a vacuum, and then the evaporated copper is deposited on the insulating film layer. The two-layer method has higher moisture resistance and dimensional stability in the Z direction than the three-layer method.   Problems that should be paid attention to when storing copper clad laminates Copper-clad laminates should be stored in low-temperature, low-humidity places: the temperature is below 25°C, and the relative temperature is below 65%. Avoid direct sunlight on the board. When the board is stored, it should not be stored in an oblique state, and its packaging material should not be removed prematurely to expose it. When handling and handling copper clad laminates, soft and clean gloves should be worn. When taking and handling boards, it is necessary to prevent the corners of the board from scratching the copper foil surface of other boards, causing bumps and scratches.    

Influencing Factors of PCB Plating and Filling Process Physical impact parameters of printed circuit fabrication   The physical parameters that need to be studied include anode type, anode-cathode spacing, current density, agitation, temperature, rectifier, and waveform.   Anode type   Speaking of anode type, it is nothing but a soluble anode and an insoluble anode. Soluble anodes are usually made of phosphorous-containing copper spheres, which easily produce anode mud, pollute the plating solution, and affect its performance. Insoluble anodes, also known as inert anodes, are generally made of titanium mesh coated with a mixture of tantalum and zirconium oxides. Insoluble anodes have good stability, do not require anode maintenance, do not produce anode mud, and are suitable for both pulse and DC plating. However, the consumption of additives is relatively high.   Anode-cathode spacing   The spacing between the cathode and the anode in the electroplating filling process of PCB manufacturing service is very important and differs in design for different types of equipment. However, it should be noted that no matter how it is designed, it should not violate Faraday's law.   Agitation of custom-made circuit boards   There are many types of agitation, including mechanical oscillation, electric vibration, air vibration, air agitation, and jet flow (Educator).   For electroplating filling, jet flow design is generally preferred based on the configuration of traditional copper tanks. However, factors such as whether to use bottom spray or side spray, how to arrange spray pipes and air agitation pipes in the tank, the hourly flow rate of spray, the spacing between the spray pipe and the cathode, and whether the spray is in front of or behind the anode (for side spray) all need to be considered in designing the copper tank. In addition, the ideal way is to connect each spray tube to a flow meter in order to monitor the flow rate. Due to the large amount of jet flow, the solution is prone to heating up, so temperature control is also very important.   Current density and temperature   Low current density and low temperature can reduce the deposition rate of surface copper while providing enough Cu2+ and a brightener to the hole. Under these conditions, the filling capacity can be enhanced, but the plating efficiency is also reduced.   Rectifier in custom printed circuit board process   The rectifier is an important part of the electroplating process. Currently, research on electroplating filling is mostly limited to full-panel electroplating. If graphic electroplating filling is considered, the cathode area will become very small. At this time, the output accuracy of the rectifier is highly required.   The choice of rectifier output accuracy should be determined according to the product's lines and hole sizes. The thinner the lines and the smaller the holes, the higher the accuracy required for the rectifier. Generally, a rectifier with an output accuracy of within 5% is suitable. Choosing a rectifier with too high accuracy will increase equipment investment. The selection of output cable wiring for the rectifier should first be placed as close as possible to the plating tank to reduce the length of the output cable and the rise time of the pulse current. The selection of the cable cross-sectional area should be based on a current-carrying capacity of 2.5A/mm². If the cable cross-sectional area is too small, the cable length is too long, or the voltage drop of the circuit is too high, the current transmission may not reach the required production current value.   For tanks with a width greater than 1.6m, a double-sided power supply should be considered, and the lengths of the double-sided cables should be equal. This can ensure that the current error on both sides is controlled within a certain range. Each flyback pin of the plating tank should be connected to a rectifier on both sides, so that the current on both sides of the part can be adjusted separately.       Waveform   Currently, there are two types of electroplating filling from the waveform point of view, pulse electroplating and direct current (DC) electroplating. Both of these electroplating filling methods have been studied by researchers. DC electroplating filling uses traditional rectifiers, which are easy to operate, but are helpless for thicker boards. Pulse electroplating filling uses PPR rectifiers, which are more complicated to operate but have stronger processing capabilities for thicker boards.   Impact of the Substrate   The impact of the substrate on electroplating filling cannot be ignored. Generally, there are factors such as dielectric layer material, hole shape, thick-to-diameter ratio, and chemical copper plating layer.   Dielectric layer material   The dielectric layer material has an impact on filling. Non-glass-reinforced materials are easier to fill than glass-reinforced materials. It is worth noting that glass fiber protrusions in the hole have a negative effect on chemical copper plating. In this case, the difficulty in electroplating filling lies in improving the adhesion of the seed layer rather than the filling process itself.   In fact, electroplating filling on glass fiber-reinforced substrates has been applied in practical production.     Thick-to-diameter ratio   Currently, both manufacturers and developers attach great importance to fill technology for holes of different shapes and sizes. The filling capacity is greatly influenced by the ratio of the thickness to the diameter of the hole. Relatively speaking, the DC system is more commonly used in commerce. In production, the size range of the holes will be narrower, generally with a diameter of 80µm~120µm and a depth of 40µm~80µm, and the thick-to-diameter ratio does not exceed 1:1.   Chemical copper plating layer   The thickness, uniformity, and placement time of the chemical PCB copper plate layer all affect the filling performance. The filling effect is poor if the chemical copper plating layer is too thin or uneven. Generally, it is recommended to perform filling when the thickness of the chemical copper is >0.3µm. In addition, the oxidation of chemical copper also has a negative impact on the filling effect.      

Via holes, also known as through holes, play a role in connecting different parts of a circuit board. With the development of the electronics industry, PCBs also face higher requirements for production processes and surface-mounting technology. The use of via hole filling technology is necessary to meet these requirements.     Does the via hole of the PCB need a plug hole?   Via holes play the role of interconnection and conduction of lines. The development of the electronics industry also promotes the development of PCB, and also puts forward higher requirements for printed board manufacturing technology and surface mount technology. The Via hole plugging process came into being, and the following requirements should be met at the same time:   There is only enough copper in the via hole, and the solder mask can be plugged or not; There must be tin-lead in the via hole, with a certain thickness requirement (4 microns), and there must be no solder resist ink entering the hole, causing tin beads to be hidden in the hole; The via holes must have solder resist ink plug holes, are opaque, and must not have tin rings, tin beads, and flatness.   With the development of electronic products in the direction of "light, thin, short and small", PCBs are also developing towards high density and high difficulty, so there are a large number of SMT and BGA PCBs, and customers require plug holes when mounting components. Five functions:   Prevent short circuit caused by tin penetrating through the component surface through the via hole when the PCB is over wave soldering; especially when we put the via hole on the BGA pad, we must first make the plug hole and then gold-plate it to facilitate BGA soldering. Avoid flux residues in the via holes; After the surface mount and component assembly of the electronics factory are completed, the PCB must be vacuumed to form a negative pressure on the testing machine; Prevent the solder paste on the surface from flowing into the hole to cause false soldering and affect the placement; Prevent tin beads from popping out during wave soldering, causing short circuits.   Realization of Conductive Hole Plug Technology   For surface mount boards, especially BGA and IC mounting, the via hole plug hole must be flat, with a bump of plus or minus 1mil, and there must be no red tin on the edge of the via hole; tin beads are hidden in the via hole, in order to achieve customer satisfaction According to the requirements of the requirements, the via hole plug hole technology can be described as varied, the process flow is extremely long, and the process control is difficult. There are often problems such as oil loss during hot air leveling and green oil solder resistance tests; oil explosion after curing.   Now, according to the actual production conditions, we will summarize the various plugging processes of PCB, and make some comparisons and elaborations on the process and advantages and disadvantages: Note: The working principle of hot air leveling is to use hot air to remove excess solder on the surface of the printed circuit board and in the holes. It is one of the surface treatment methods of printed circuit boards.   Plug Hole Process After Hot Air Leveling   The process flow is: board surface solder mask → HAL → plug hole → curing. The non-plug hole process is used for production, and the aluminum sheet screen or ink blocking screen is used to complete the through hole plug holes of all the fortresses required by the customer after hot air leveling. The plugging ink can be photosensitive ink or thermosetting ink. In the case of ensuring the same color of the wet film, the plugging ink uses the same ink as the board surface. This process can ensure that the via hole does not drop oil after hot air leveling, but it is easy to cause plugging ink to contaminate the board surface and make it uneven. It is easy for customers to cause virtual soldering (especially in BGA) during placement. So many customers do not accept this method.   Hot Air Leveling Front Plug Hole Process   Use aluminum sheets to plug holes, solidify, and grind the board to transfer graphics   This process uses a CNC drilling machine to drill out the aluminum sheet that needs to be plugged to make a screen, and then plug the hole to ensure that the via hole is full. Plugging ink can also be thermosetting ink, which must have high hardness. , The shrinkage of the resin changes little, and the binding force with the hole wall is good. The process flow is: pretreatment → plug hole → grinding plate → graphic transfer → etching → solder mask on the board surface. This method can ensure that the through-hole plug hole is flat, and hot air leveling will not cause quality problems such as oil explosion and oil drop at the edge of the hole. However, this process requires thicker copper to make the copper thickness of the hole wall meet the customer's standard, so The requirements for copper plating on the whole board are very high, and the performance of the grinding machine is also very high, to ensure that the resin on the copper surface is completely removed, and the copper surface is clean and free from pollution. Many PCB factories do not have permanent copper thickening process, and the performance of the equipment cannot meet the requirements, resulting in that this process is not used much in PCB factories.   After plugging the hole with aluminum sheet, directly screen the solder mask on the surface of the board   This process uses a CNC drilling machine to drill out the aluminum sheet that needs to be plugged to make a screen, install it on the screen printing machine for plugging, and stop it for no more than 30 minutes after completing the plugging. Use a 36T screen to directly screen the solder on the board. The process flow is: pre-treatment - plugging - silk screen printing - pre-baking - exposure - development - curing This process can ensure that the oil on the via hole cover is good, the plug hole is smooth, the color of the wet film is consistent, and after hot air leveling It can ensure that the via hole is not filled with tin, and no tin beads are hidden in the hole, but it is easy to cause the ink in the hole to be on the pad after curing, resulting in poor solderability; after hot air leveling, the edge of the via hole is foamed and oil is removed. This process is adopted The production control of the method is relatively difficult, and process engineers must adopt special processes and parameters to ensure the quality of plug holes.   Aluminum plate plug hole, developing, pre-curing, and grinding the plate, then carry out solder masking on the plate surface   Use a CNC drilling machine to drill out the aluminum sheet that requires the plug hole to make a screen, install it on the shift screen printing machine for the plug hole, the plug hole must be full, and it is better to protrude on both sides, and then after curing, the plate is ground for surface treatment. The process flow is: pre-treatment - plug hole - pre-baking - development - pre-curing - board surface solder mask Since this process uses plug hole curing to ensure that the via hole does not drop oil or explode after HAL, but after HAL, Tin beads hidden in via holes and tin on via holes are difficult to completely solve, so many customers do not accept them.   Soldering and plugging of the board surface are completed at the same time   This method uses a 36T (43T) screen, installed on the screen printing machine, using a backing plate or a nail bed, and plugging all the via holes while completing the board surface. The process flow is: pre-processing -- silk screen --Pre-baking -- exposure -- development-- curing This process takes a short time and has a high utilization rate of the equipment, which can ensure that the via hole does not drop oil and the via hole is not tinned after the hot air is leveled. However, due to the use of silk screen for plugging , There is a large amount of air in the via hole. When curing, the air expands and breaks through the solder mask, causing voids and unevenness. There will be a small amount of via hole hidden tin in the hot air leveling. At present, after a lot of experiments, our company has selected different types of inks and viscosities, adjusted the pressure of silk screen, etc., basically solved the hole and unevenness of the via, and has adopted this process for mass production.

How To Avoid Pits And Leaks On The Design Side Of PCB Boards! The design of electronic products is from drawing schematic diagrams to PCB layout and wiring. Due to a lack of knowledge in this area of work experience, various mistakes often occur, hindering our follow-up work, and in severe cases, the circuit boards made cannot be used at all. Therefore, we should try our best to improve our knowledge in this area and avoid all kinds of mistakes.   This article introduces the common drilling problems when PCB drawing boards are used, so as to avoid stepping on the same pits in the future. Drilling is divided into three categories, through the hole, blind hole, and buried hole. Through holes include plug-in holes (PTH), screw positioning holes (NPTH), blind, buried holes, and via holes (VIA) through holes, all of which play the role of multi-layer electrical conduction. Regardless of the type of hole, the consequence of the problem of missing holes is that the entire batch of products cannot be used directly. Therefore, the correctness of the drilling design is particularly important. Case Explanation of Pits And Leaks On The Design Side Of PCB Boards Problem 1: The Altium-designed file slots are misplaced; Description of the problem: The slot is missing, and the product cannot be used. Reason analysis: The design engineer missed the slot for the USB device when making the package. When he found this problem when drawing the board, he did not modify the package, but directly drew the slot on the hole symbol layer. In theory, there is no big problem with this operation, but in the manufacturing process, only the drilling layer is used for drilling, so it is easy to ignore the existence of slots in other layers, resulting in the missed drilling of this slot, and the product cannot be used. Please see the picture below; How to avoid pits: Each layer of the OEM PCB design file has the function of each layer. Drill holes and slot holes must be placed in the drill layer, and it cannot be considered that the design can be manufactured.         Question 2: Altium-designed file via hole 0 D code; Description of the problem: The leakage is open and non-conductive. Cause analysis: Please see Figure 1, there is a leak in the design file, and the leak is indicated during the DFM manufacturability check. After checking the cause of the leak, the diameter of the hole in the Altium software is 0, resulting in no holes in the design file, see Figure 2. The reason for this leakage hole is that the design engineer made a mistake when drilling the hole. If the problem of this leakage hole is not checked, it is difficult to find the leakage hole in the design file. The leakage hole directly affects the electrical failure and the designed product cannot be used. How to avoid pits: DFM manufacturability testing must be carried out after the circuit diagram design is completed. The leaked vias cannot be found in manufacturing and production during design. DFM manufacturability testing before manufacturing can avoid this problem.     Figure 1: Design file leak     Figure 2: Altium aperture is 0     Question 3: The file vias designed by PADS cannot be output; Description of the problem: The leakage is open and non-conductive. Cause Analysis: Please see Figure 1, when using DFM manufacturability testing, it indicates many leaks. After checking the cause of the leakage problem, one of the vias in PADS was designed as a semi-conducting hole, resulting in the design file not outputting the semi-conducting hole, resulting in a leak, see Figure 2. Double-sided panels do not have semi-conducting holes. Engineers mistakenly set via holes as semi-conducting holes during design, and output semi-conducting holes are leaked during output drilling, resulting in leaky holes. How to avoid pits: This kind of misoperation is not easy to find. After the design is completed, it is necessary to conduct DFM manufacturability analysis and inspection and find problems before manufacturing to avoid leakage problems.     Figure 1: Design file leak     Figure 2: PADS software double-panel vias are semi-conducting vias      

  PCB circuit board impedance refers to the parameters of resistance and reactance, which hinders AC power. In pcb circuit board production, impedance processing is essential.     The reasons for PCB circuit boards have impedance   The PCB circuit (bottom) should consider the plug-in installation of electronic components, and consider the issues of electrical conductivity and signal transmission after plug-in. Therefore, it is required that the lower the impedance, the better, and the resistivity should be lower than 1 & TImes; 10 per square centimeter. Below-6.   During the production process of the PCB circuit board including SMT printed circuit board, it needs to go through the process of sinking copper, electroplating tin (or chemical plating, or thermal spraying), connector soldering and other process manufacturing processes, and the materials used in these links must ensure the resistivity bottom to ensure The overall impedance of the circuit board is low enough to meet product quality requirements and can operate normally.   The tinning of PCB circuit boards is the most prone to problems in the production of the entire circuit board, and it is the key link that affects impedance. The biggest drawbacks of the electroless tin plating layer are easy discoloration (both easy to oxidize or deliquesce), poor solderability, which will make the circuit board difficult to solder, too high impedance, resulting in poor conductivity or instability of the entire board performance.   There will be various signal transmissions in the conductors of the PCB circuit board. When the frequency must be increased in order to increase its transmission rate, if the line itself is different due to factors such as etching, stack thickness, and wire width, it will cause the impedance to change. To make its signal distorted, leading to the degradation of the performance of the circuit board, it is necessary to control the impedance value within a certain range.     The meaning of impedance for PCB circuit boards   For the electronics industry, according to industry surveys, the most lethal weaknesses of electroless tin plating are easy discoloration (both easy to oxidize or deliquesce), poor solderability leading to difficult soldering, high impedance leading to poor conductivity or instability of the entire board 2. Easy-to-chang tin must cause short circuit of PCB circuit and even burn or fire.     It is reported that the first study of chemical tin plating in China was Kunming University of Science and Technology in the early 1990s, and then Guangzhou Tongqian Chemical (Enterprise) in the late 1990s. Until now, the two institutions have recognized the two institutions as Get the best. Among them, according to our contact screening surveys, experimental observations, and long-term endurance tests on many enterprises, it was confirmed that the tin plating layer of Tongqian Chemical is a low-resistivity pure tin layer. The quality of conductivity and soldering can be guaranteed to a high level. No wonder they dare to guarantee to the outside that their coatings will not change color, no blistering, no peeling, and no long tin whisker for one year without any sealing and anti-discoloration agent protection.     Later, when the entire social production industry developed to a certain extent, many later participants often belonged to plagiarism. In fact, quite a few companies themselves did not have the R & D or pioneering capabilities. Therefore, many products and their users’ electronic products (circuit boards) The bottom of the board or the overall electronic product) performance is poor, and the main reason for the poor performance is due to the impedance problem, because when the unqualified electroless tin plating technology is used, it is actually the tin plated on the PCB circuit board. Not really pure tin (or pure metal elementary substance), but tin compounds (that is, not metal elementary substances at all, but metal compounds, oxides or halides, and more directly non-metallic substances) or tin A mixture of a compound and a tin metal element, but it is difficult to find with the naked eye …     Because the main circuit of the PCB circuit board is copper foil, the soldering point of the copper foil is a tin plating layer, and the electronic components are soldered on the tin plating layer by a solder paste (or solder wire). In fact, the solder paste is melting. The state soldered between the electronic component and the tin plating layer is metal tin (ie, a conductive metal element), so it can be simply pointed out that the electronic component is connected to the copper foil on the bottom of the PCB through the tin plating layer, so the tin plating layer The purity and impedance are the key; but before we plug in the electronic components, we use the instrument to test the impedance directly. In fact, the two ends of the instrument probe (or test lead) also pass through the copper foil on the bottom of the PCB first. The tin plating on the surface communicates with the copper foil on the bottom of the PCB. So tin plating is the key, the key to the impedance, the key to the performance of the PCB, and the key to be easily overlooked.     As we all know, except metal simple compounds, their compounds are all poor conductors of electricity or even non-conductive (also, this is also the key to the distribution capacity or transmission capacity in the circuit), so this tin-like coating exists in this kind of conductive rather than conductive For tin compounds or mixtures, their ready-made resistivity or future oxidation and resistivity after the electrolytic reaction due to moisture and its corresponding impedance are quite high (which has affected the level or signal transmission in digital circuits), and The characteristic impedances are also inconsistent. So it will affect the performance of the circuit board and its entire machine.     Therefore, in terms of the current social production phenomenon, the coating material and performance on the bottom of the PCB are the most and most direct reasons affecting the characteristic impedance of the entire PCB, but because it has the ability to electrolyze with the aging of the coating and moisture. Because of its variability, the anxiety effect of its impedance becomes more recessive and changeable. The main reason for its concealment is that the first cannot be seen by the naked eye (including its changes), and the second cannot be measured constantly because it has Variability over time and ambient humidity, so it is always easy to ignore.    

Difference Between PCB and PCBA What is PCB? PCB stands for Printed Circuit Board. It is a thin board made of insulating material, usually fiberglass or plastic, with conductive pathways or tracks printed onto it. The conductive pathways or tracks connect different components of the electronic device, allowing the flow of electricity to complete the circuit. The circuit design of the PCB is created using a computer-aided design (CAD) software program. The PCB is then fabricated using a process that involves the deposition of copper onto the board, followed by etching to remove the unwanted copper, leaving behind the desired circuit pattern. PCBs have revolutionized the electronics industry by making the manufacture of electronic devices more efficient, cost-effective, and reliable. They are used in a wide range of electronic products, from simple devices like calculators to complex systems like aerospace and military applications. What is PCBA? PCBA stands for Printed Circuit Board Assembly. It refers to the process of assembling electronic components onto a PCB to create a functional electronic device. The components may include resistors, capacitors, diodes, transistors, integrated circuits, and other electronic components. The assembly process involves placing the components onto the PCB, followed by soldering to create a strong mechanical and electrical connection. PCBAs are used in a wide range of electronic products, including computers, smartphones, televisions, medical devices, and automotive electronics. They are essential in creating functional electronic devices and are critical to the success of the electronics industry.   Difference between PCB and PCBA The main difference between PCB and PCBA is that a PCB is a board with conductive pathways, while a PCBA is a completely functional electronic device with components assembled onto the PCB. Here are some other differences between PCB and PCBA: Complexity: A PCB is less complex than a PCBA. A PCB only contains conductive pathways or tracks, while a PCBA contains components, conductive pathways, and other elements such as connectors, switches, and batteries. Functionality: A PCB is not functional by itself. It needs to be populated with components and assembled to create a functional electronic device, which is a PCBA. Manufacturing process: The manufacturing process for PCBs is different from the process for PCBAs. PCBs are fabricated using a process that involves the deposition of copper onto the board, followed by etching to remove unwanted copper. PCBA, on the other hand, involves the assembly of electronic components onto the PCB using pick-and-place machines, followed by soldering. Design: PCB and PCBA have different design requirements. The design of the PCB focuses on creating a conductive pathway to connect different components of the electronic device. The design of the PCBA, on the other hand, focuses on optimizing the placement of components on the PCB to ensure optimal performance.   Advantages of PCB and PCBA PCB and PCBA offer several advantages that have made them essential in the electronics industry. Here are some of the benefits of PCB and PCBA: Cost-effective: PCBs and PCBAs are cost-effective compared to traditional wiring methods. They can be mass-produced, reducing the cost of production per unit. High reliability: PCBs and PCBAs are highly reliable because they are manufactured using automated processes, ensuring consistency in quality and reliability. Compact size: PCBs and PCBAs allow electronic devices to be designed in smaller sizes, making them more portable and convenient. Efficient performance: PCBs and PCBAs are designed to optimize the performance of electronic devices. The design of the PCB and PCBA allows for optimal placement of components and pathways, reducing signal interference and improving the overall efficiency of the electronic device.   Faster production time: The manufacturing process for PCBs and PCBAs is highly automated, allowing for faster production times and reducing the time it takes to bring electronic devices to market. Ease of repair: PCBs and PCBAs are designed for easy repair and replacement of components, reducing the downtime of electronic devices and ensuring that they remain operational for longer periods. In conclusion, PCB and PCBA are two essential components in the electronics industry, and they differ significantly in terms of their functionality, complexity, and manufacturing process. PCB is a board with conductive pathways, while PCBA is a completely functional electronic device with components assembled onto the PCB. The advantages of PCB and PCBA include cost-effectiveness, high reliability, compact size, efficient performance, faster production time, and ease of repair. Understanding the difference between PCB and PCBA is essential for anyone involved in the electronics industry, from designers and engineers to manufacturers and end-users.        

Design Requirements for the Manufacturability of PCB Solder Pads and Steel Mesh PCB manufacturing design Mark position: Diagonal corners of the board Quantity: minimum of 2, suggested 3, with additional Local Mark for boards over 250mm or with Fine Pitch components (non-chip components with pin or solder spacing less than 0.5mm). In FPC production, bad board identification is also necessary considering panel count and yield rate. BGA components require identification marks at the diagonal and the periphery. Size: a diameter of 1.0mm is ideal for the reference point. A diameter of 2.0mm is ideal for identifying bad boards. For BGA reference points, a size of 0.35mm*3.0mm is recommended.   PCB size and splicing board According to different designs, such as cell phones, CDs, digital cameras and other products in the PCB board size to not more than 250 * 250mm is better, FPC shrinkage exists, so the size of not more than 150 * 180mm is better.   Reference point size and diagram   1.0mm diameter reference point on PCB   Diameter 2.0mm bad plate reference point BGA reference point (can be made by silkscreen or sunken gold process) Fine pitch components after the MARK   Minimum component spacing No cover lay resulting in the displacement of components after welding   Minimum component spacing to 0.25mm as the limit (the current SMT process to achieve 0.20 but the quality is not ideal) and between the pads to have solder resist oil or cover film for solder resistance.   Stencil design for manufacturability In order to make the stencil better formed after solder paste printing, the following requirements should be taken into account when selecting the thickness and opening design. Aspect Ratio greater than 3/2: For Fine-Pitch QFP, IC and other pin type devices. For example, 0.4pitch QFP (Quad Flat Package) pad width is 0.22mm and length is 1.5mm. If the stencil opening is 0.20mm, the width-thickness ratio should be less than 1.5, which means the net thickness should be less than 0.13. Area Ratio (area ratio) greater than 2/3: for 0402, 0201, BGA, CSP and other small pin class device area ratio greater than 2/3, such as 0402 class component pads for 0.6 * 0.4 if the stencil according to 1:1 open hole according to the area ratio greater than 2/3 know network thickness T should be less than 0.18, the same 0201 class component pads for 0.35 * 0.3 derived from the network thickness should be Less than 0.12. From the above two points to derive the stencil thickness and pad (component) control table, when the stencil thickness is limited after how to ensure the amount of tin under, how to ensure the amount of tin on the solder joint, which will be discussed later in the stencil design classification. Stencil opening section  

Design of Steel Mesh Openings for Surface Mount Technology (SMT) Component and its Solder Pads Chip component size: including resistors (row resistance), capacitors (row capacity), inductors, etc     Side view of the component     Front view of the component     Inverted view of the component   Dimensional drawing of the component   Dimension table of the component   Component type/resistance Length (L) Width (W) Thickness (H) Weld end length (T) Inside distance of weld end (S) 0201 （1005） 0.60 0.30 0.20 0.15 0.30 0402 （1005） 1.00 0.50 0.35 0.20 0.60 0603 （1608） 1.60 0.80 0.45 0.35 0.90 0805 （2012） 2.00 1.20 0.60 0.40 1.20 1206 （3216） 3.20 1.60 0.70 0.50 2.20 1210 （3225） 3.20 2.50 0.70 0.50 2.20   Solder requirements for chip component solder joints: including resistance (row resistance), capacitance (row capacity), inductance, etc   Lateral offset   Side offset (A) is less than or equal to 50% of the component's solderable end width (W) or 50% of the pad, whichever is smaller (determining factor: placement coordinate pad width)   End offset   End offset must not exceed the pad, (determining factor: placement coordinate pad length and inner distance)   Solder end and pad   The solder end must contact with the pad, the proper value is the solder end completely on the pad. (Determining factor: the length of the pad and the inner distance)   Positive solder end solder joint on the minimum height of tin   Minimum solder joint height (F) is the smaller of 25% of the solder thickness (G) plus the height of the solderable end (H) or 0.5 mm. (Determining factors: stencil thickness, component solder end size, pad size)   Solder height on the front solder end   The maximum solder joint height is the solder thickness plus the height of the solderable end of the component. (Determining factors: stencil thickness, component solder end size, pad size)   The maximum height of the frontal solder end   Maximum height can exceed the pad or climb to the top of the solderable end, but can not touch the component body. (Such phenomena occur more in 0201, 0402 class components)   Side solder end length   The best value side solder joint length is equal to the length of the solderable end of the component, the normal wetting of the solder joint is also acceptable. (Determining factors: stencil thickness, component solder end size, pad size)   Side solder end height   Normal wetting.   Chip component pad design: including resistance (resistance), capacitance (capacitance), inductance, etc   According to the component size and solder joint requirements to derive the following pad size:   Schematic diagram of chip component pads   Chip component pad size table   Component type/ resistance Length (L) Width (W) Inside distance of weld end (S) 0201（1005） 0.35 0.30 0.25 0402（1005） 0.60 0.60 0.40 0603（1005） 0.90 0.60 0.70 0805（2012） 1.40 1.00 0.90 1206（3216） 1.90 1.00 1.90 1210（3225） 2.80 1.15 2.00   Chip component stencil opening design: including resistance (row resistance), capacitance (row capacity), inductance, etc.   0201 class component stencil design   Design points: components can not float high, tombstone   Design method: net thickness 0.08-0.12mm, open horseshoe shape, the inner distance to maintain 0.30 total under the tin area of 95% of the pad.     Left: Stencil under the tin and pad anastomosis diagram, right: component paste and pad anastomosis diagram   0402 class components stencil design   Design points: components can not float high, tin beads, tombstone   Design mode:   Net thickness 0.10-0.15mm, the best 0.12mm, the middle open 0.2 concave to avoid tin beads, the inner distance to maintain 0.45, resistors outside the three ends plus 0.05, capacitors outside the three ends plus 0.10, the total under the tin area for the pad of 100%-105%.   Note: The thickness of the resistor and capacitor are different (0.3mm for the resistor and 0.5mm for the capacitor), so the amount of tin is different, which is a good help to the height of the tin and the detection of AOI (automatic optical inspection).   Left: Stencil under the tin and pad anastomosis diagram, right: component paste and pad anastomosis diagram   0603 class components stencil design   Design points: components to avoid tin beads, tombstone, the amount of tin on   Design method:   Net thickness 0.12-0.15mm, the best 0.15mm, the middle open 0.25 concave avoid tin beads, the inner distance to maintain 0.80, resistors outside the three ends plus 0.1, capacitors outside the three ends plus 0.15, the total under the tin area for the pad of 100%-110%.   Note: 0603 class components and 0402, 0201 components together when the stencil thickness is limited, in order to increase the amount of tin must take the additional way to complete.   Left: Stencil under the tin and pad anastomosis diagram, right: component solder paste and pad anastomosis diagram   Stencil design for chip components with size larger than 0603 (1.6*0.8mm)   Design points: components to avoid tin beads, the amount of tin on   Design method:   Stencil thickness 0.12-0.15mm, best 0.15mm. 1/3 notch in the middle for avoiding tin beads, 90% of the lower tin volume.   Left: Stencil under the tin and pad anastomosis diagram, right: 0805 above components stencil opening schematic      

Compression of Multilayer PCBs   Advantages of PCB Multilayer Boards High assembly density, small size, and light weight; Reduced interconnection between components (including electronic components), which improves reliability; Increased flexibility in design by adding wiring layers; Ability to create circuits with certain impedances; Formation of high-speed transmission circuits; Simple installation and high reliability; Ability to set up circuits, magnetic shielding layers, and metal core heat-dissipating layers to meet special functional needs such as shielding and heat dissipation. Exclusive Materials for PCB Multilayer Boards Thin copper-clad laminates Thin copper-clad laminates refer to the types of polyimide/glass, BT resin/glass, cyanate ester/glass, epoxy/glass, and other materials used to make multilayer printed circuit boards. Compared with general double-sided boards, they have the following features: More stringent thickness tolerance; More stringent and higher requirements for size stability, and attention should be paid to the consistency of cutting direction; Thin copper-clad laminates have low strength and are easily damaged and broken, so they need to be handled with care during operation and transportation; The total surface area of thin-line circuit boards in multilayer boards is large, and their moisture absorption capacity is much larger than that of double-sided boards. Therefore, materials should be strengthened for dehumidification and moisture-proof in storage, lamination, welding, and storage. Prepreg materials for multilayer boards (commonly known as semi-cured sheets or bonding sheets) Prepreg materials are sheet materials composed of resin and substrates, and the resin is in the B-phase. Semi-cured sheets for multilayer boards must have: Uniform resin content; Very low content of volatile substances; Controlled dynamic viscosity of resin; Uniform and suitable resin flowability; Gelation time that meets regulations. Appearance quality: should be flat, free of oil stains, foreign impurities, or other defects, with no excessive resin powder or cracks. PCB Board Positioning System The positioning system of the circuit diagram runs through the process steps of multilayer photo film production, pattern transfer, lamination, and drilling, with two types of pin-and-hole positioning and non-pin-and-hole positioning. The positioning accuracy of the entire positioning system should strive to be higher than ±0.05mm, and the positioning principle is: two points determine a line, and three points determine a plane.   The main factors affecting the positioning accuracy between multilayer boards The size stability of the photo film; The size stability of the substrate; The accuracy of the positioning system, the accuracy of the processing equipment, operating conditions (temperature, pressure), and the production environment (temperature and humidity); The circuit design structure, the rationality of the layout, such as buried holes, blind holes, through holes, solder mask size, uniformity of wire layout, and setting of the internal layer frame; The thermal performance matching of the lamination template and the substrate. Pin-and-hole positioning method for multilayer boards Two-hole positioning-often causes size drift in the Y direction due to restrictions in the X direction; One hole and one slot positioning-With a gap left at one end in the X direction to avoid disordered size drift in the Y direction; Three-hole (arranged in a triangle) or four-hole (arranged in a cross shape) positioning-to prevent changes in size in the X and Y directions during production, but the tight fit between the pins and holes locks the chip base material in a "locked" state, causing internal stress that can cause warping and curling of the multilayer board; Four-slot hole positioning-based on the centerline of the slot hole, the positioning error caused by various factors can be evenly distributed on both sides of the centerline rather than accumulated in one direction.    

Common PCB Board Materials and Dielectric Constants Introduction of PCB Materials   They are generally divided into five categories according to the different reinforcement materials used for the boards: paper-based, glass fiber cloth-based, composite-based (CEM series), laminated multi-layer board-based, and special material-based (ceramic, metal core-based, etc.). If categorized by the resin adhesive used for the boards, for common paper-based CCI, there are various types such as phenolic resin (XPC, XXXPC, FR-1, FR-2, etc.), epoxy resin (FE-3), polyester resin, etc. For common glass fiber cloth-based CCL, there is epoxy resin (FR-4, FR-5), which is the most commonly used type. There are also other special resins (using glass fiber cloth, polyimide fiber, non-woven fabrics, etc., as reinforcing materials) such as bismaleimide-triazine modified resin (BT), polyimide resin (PI), p-phenylene ether resin (PPO), maleimide-styrene resin (MS), polycyanurate resin, polyolefin resin, etc. According to the flame retardancy performance of CCL, they can be divided into flame-retardant type (UL94-V0, UL94-V1) and non-flame-retardant type (UL94-HB) boards. In recent years, with increasing awareness of environmental protection issues, a new type of CCL variety without brominated compounds has been introduced in flame-retardant CCLs, called "green flame-retardant CCL". As electronic product technology develops rapidly, higher performance requirements are placed on CCL. Therefore, from the performance classification of CCL, they can be further divided into general performance CCL, low dielectric constant CCL, high heat-resistant CCL (L for general boards is above 150℃), low coefficient of thermal expansion CCL (generally used on packaging boards), and other types.   Details of parameters and applications are as follows: 94-HB: Ordinary paper board, not fireproof (the lowest-grade material, used for punching perforations, cannot be used as a power supply board) 94-V0: Flame-retardant paper board (used for punching perforations) 22F: Single-sided semi-fiberglass board (used for punching perforations) CEM-1: Single-sided fiberglass board (must be drilled with a computer, cannot be punched) CEM-3: Double-sided semi-fiberglass board (except for double-sided paper board, it is the lowest-end material for double-sided boards. Simple double-sided boards can be made with this material, and it is cheaper than FR-4) FR-4: Double-sided fiberglass board. The flame-retardant properties are divided into 94VO-V-1-V-2-94HB. The semi-cured sheet is 1080=0.0712mm, 2116=0.1143mm, 7628=0.1778mm. FR4 and CEM-3 are both used to indicate the board material, with FR4 being a fiberglass board and CEM-3 being a composite-based board.   Dielectric Constant of PCB Materials Research on the dielectric constant of PCB materials is because the speed and signal integrity of the signal transmission on PCB are affected by the dielectric constant. Therefore, this constant is extremely important. The reason why hardware personnel overlook this parameter is that the dielectric constant is determined when the manufacturer chooses different materials to make the PCB board. Dielectric constant: When a medium is subjected to an external electric field, it will produce an induced charge that weakens the electric field. The ratio of the original applied electric field (in vacuum) to the final electric field in the medium is the relative dielectric constant (or dielectric constant), also known as the dielectric constant, which is related to the frequency. The dielectric constant is the product of the relative dielectric constant and the absolute dielectric constant of vacuum. If a material with a high dielectric constant is placed in an electric field, the strength of the electric field will experience a significant decrease within the dielectric. The relative dielectric constant of an ideal conductor is infinite. The polarity of polymer materials can be determined by the material's dielectric constant. Generally, substances with a relative dielectric constant greater than 3.6 are polar substances; substances with a relative dielectric constant in the range of 2.8 to 3.6 are weak polar substances; and substances with a relative dielectric constant less than 2.8 are non-polar substances.     Dielectric Constant of FR4 Materials The dielectric constant (Dk, ε, Er) determines the speed at which the electrical signal propagates in the medium. The speed of electrical signal propagation is inversely proportional to the square root of the dielectric constant. The lower the dielectric constant, the faster the signal transmission. Let's take an analogy. When you are running on the beach, the depth of the water that covers your ankles represents the viscosity of the water, which is the dielectric constant. The more viscous the water, the higher the dielectric constant, and the slower you run. The dielectric constant is not easy to measure or define. It is not only related to the characteristics of the medium, but also to the testing method, testing frequency, material state before and during testing. The dielectric constant also changes with temperature, and some special materials take temperature into consideration during development. Humidity is also a significant factor affecting the dielectric constant; as the dielectric constant of water is 70, a small amount of water can cause significant changes. FR4 Material Dielectric Loss: It is energy loss caused by the dielectric polarization and dielectric conductivity lag effect of the insulation material under the action of electric field. Also known as dielectric loss or simply loss. Under the action of an alternating electric field, the deficiency angle of the cosine of the vector combination between the current passing through the dielectric and the voltage across the dielectric (power factor angle Φ) is called the dielectric loss angle. The dielectric loss of FR4 is generally around 0.02, and the dielectric loss increases as the frequency increases. FR4 Material TG Value: It is also called the glass transition temperature, which is generally 130℃, 140℃, 150℃, and 170℃.   FR4 Material Standard Thickness The commonly used thicknesses are 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.6mm, 1.8mm, and 2.0mm. The thickness deviation of the board varies with the production capacity of the board factory. The common copper thickness for FR4 copper-clad boards is 0.5oz, 1oz, and 2oz. Other copper thicknesses are also available, and they need to be consulted with the PCB manufacturer to determine.    

Common Components and Steel Mesh Aperture Design in SMT Process Design of pads and stencil openings for SOT23 (triode small crystal type) components   Left: SOT23 component front view size, Right: SOT23 component side view size   SOT23 solder joint minimum requirement: minimum side length equal to pin width. SOT23 solder joint best requirement: Solder joint wets normally in the pin length direction (determining factors: amount of tin under the stencil, component pin length, pin width, pin thickness and pad size). SOT23 solder joint maximum requirement: Solder can rise to, but must not touch the component body or tail package. SOT23 pad stencil design Key point: the amount of tin under. Method: Stencil thickness 0.12 according to 1:1 hole opening Similar design is SOD123, SOD123 pads and stencil openings (according to 1:1 openings), note that the body can not take the pads, otherwise it is easy to cause the displacement of components and floating high.   Wing-shaped components (SOP, QFP, etc.) of the pad and stencil design Wing-shaped components are divided into straight wing and gull wing, straight wing-shaped components in the pad and stencil hole design should pay attention to the internal cut to prevent solder on the component body. Wing-shaped components solder joint minimum requirements: the minimum side length equal to the width of the pin. Wing-shaped components solder joints best requirements: solder joints in the direction of the length of the pin normal wetting (determining factors pad size stencil under the amount of tin). Winged component solder joints maximum requirement: solder can rise to, but must not touch the component body or tail end package.   Typical wing component SQFP208 dimensional analysis   Number of pins: 208 Pin spacing: 0.5 mm Leg length: 1.0 Effective solder length: 0.6 Leg width: 0.2 Inside distance: 28   Typical wing component SQFP208 pad design: 0.4mm in front and 0.60mm behind the effective tin end of the component 0.25mm in width. Stencil design for wing component SQFP208: 0.5mm pitch QFP wing component, stencil thickness 0.12mm, length open 1.75 (plus 0.15), width open 0.22mm, internal pitch remain 27.8 unchanged. Note: In order not to short circuit between the component pins, and the front end of good wetting, stencil openings in the design should pay attention to the internal shrinkage and additional, additional should not exceed 0.25, otherwise easy to produce tin beads, net thickness of 0.12mm.   Wing-shaped components pads and stencil design applications Solder pad design: pad width 0.23 (component foot width 0.18mm), length 1.2 (component foot length 0.8mm). Stencil opening: length 1.4, width 0.2, mesh thickness 0.12.   Pad and stencil design of QFN class components QFN (Quad Flat No Lead) class components are a kind of pinless components, widely used in the field of high frequency, but because of its welding structure for the castle shape, and for the pinless type welding, so there is a certain degree of difficulty in the SMT welding process.   Solder joint width: The width of the solder joint shall not be less than 50% of the solderable end (determining factors: width of the solderable end of the component, width of the stencil opening).   Solder joint height: Blanching point height is 25% of the sum of the solder thickness and component height. Combined with the QFN class components themselves and the size of the solder joint requirements pad and stencil design corresponds to the following: Point: not to produce tin beads, floating high, short circuit on this basis to increase the weldable end and the amount of tin under. Method: The pad design according to the size of the component on the solderable end plus at least 0.15-0.30mm, (up to 0.30, otherwise the component is prone to produce on the tin height is insufficient). Stencil: on the basis of the pad plus 0.20mm, and the middle of the heat sink pad bridge openings, to prevent components floating high.   BGA ( Ball Grid Array ) class component size BGA ( Ball Grid Array ) class components in the design of the pad is mainly based on the diameter of the solder ball and spacing:: After welding solder ball melting and solder paste and copper foil to form intermetallic compounds, at this time the diameter of the ball becomes smaller, while the melting of the solder paste in the intermolecular forces and liquid tension between the role of retraction. From there, the design of pads and stencils are as follows: The design of the pad is generally smaller than the diameter of the ball 10%-20%. The stencil opening is 10%-20% larger than the pad. Note: fine pitch, except when the 0.4 pitch at this time by 100% open hole, 0.4 within the general 90% open hole. To prevent short circuit.   BGA ( Ball Grid Array ) class component size Ball Diameter Pitch Land Diameter Aperture Thickness 0.75 1.5, 1.27 0.55 0.70 0.15 0.60 1.0 0.45 0.55 0.15 0.50 1.0, 0.8 0.40 0.45 0.13 0.45 1.0, 0.8, 0.75 0.35 0.40 0.12 0.40 0.8, 0.75, 0.65 0.30 0.35 0.12 0.30 0.8, 0.75, 0.65, 0.5 0.25 0.28 0.12 0.25 0.4 0.20 0.23 0.10 0.20 0.3 0.15 0.18 0.07 0.15 0.25 0.10 0.13 0.05   BGA class components pad and stencil design comparison table BGA class components in the soldering in the solder joint mainly appear in the hole, short circuit and other problems. Such problems have a variety of factors, such as BGA baking, PCB secondary reflow, etc., the length of reflow time, but only for the solder pad and stencil design should pay attention to the following points: Solder pad design should pay attention to avoid as much as possible through-hole, buried blind holes and other holes that may appear to steal tin class appear on the pad. For larger pitch BGA (more than 0.5mm) should be the right amount of tin, can be achieved by thickening the stencil or expand the hole, for fine pitch BGA (less than 0.4mm) should reduce the diameter of the hole and stencil thickness.  

Advantages And Disadvantages Of PCB Smt Stencil Processing Methods   The original SMT stencil manufacturing process was mainly made of photographic plates, and then by chemical etching. Of course, there are laser cutting processing methods or electroforming processing methods for processing SMT steel mesh plates. In the process of continuous production and processing of SMT stencils, it was found that the three processing methods outlined above have their own advantages and disadvantages.   The advantages and disadvantages of the three SMT stencil processing methods are compared below:   First, the chemical etching method is the earliest processing method used in SMT stencil processing.   Advantages of the chemical corrosion method: Leak processing of the SMT stencil is performed by chemical corrosion without the need for expensive equipment investment, and the processing cost is relatively low.   Disadvantages of the chemical corrosion method: the corrosion time is too short, the hole wall of the SMT stencil may have sharp corners, and the time may be enlarged, and the side wall corrosion may not make the hole wall smooth. Accuracy cannot be grasped very accurately.   Second, the laser processing method is currently the most commonly used SMT steel mesh processing method, it relies on laser energy to melt the metal, and then cut out the opening in the stainless steel plate.   Advantages of the laser processing method: the processing speed is much faster than the chemical etching method, and the opening size of the stencil is well controlled, especially the added hole wall has a certain taper (tapered about 2 degrees), which is easier to remove mold.   Disadvantages of the laser processing method: When the openings of the SMT stencil are dense, the local high temperature generated by the laser sometimes deforms the adjacent hole wall, and the roughness of the metal hole wall formed by melting is not high, so it is necessary if necessary. Hole wall trimming is required. In addition, the laser processing method increases processing costs by requiring specialized equipment.   The current SMT stencil processing methods are completed by laser cutting. Laser cutting is made using file data, with high accuracy and small tolerances.   Third, electroforming is a process that relies on metal materials (mainly nickel) to continuously accumulate and accumulate to form metal SMT stencils.   Advantages of the electroforming method: The SMT stencil made by the method not only has high opening size accuracy and smooth hole walls, which is conducive to the quantitative distribution of printed solder paste, but also the openings are not easily blocked by the solder paste, thereby reducing the number of times to clean the SMT stencil.   Disadvantages of electroforming: The cost of manufacturing SMT stencils by electroforming is high and the production cycle is long.   Through continuous research and practice, it has been found that whether it is a chemical etching method or a laser cutting method of SMT stencils, there will be opening blockages of varying degrees during printing. SMT stencils need to be cleaned frequently, so the electroforming method has become a thin pin. The main processing method of SMT stencil printing for pitch components is solder paste.        

Aluminum Substrate Production Process Specifications And Production Difficulties   Aluminum substrate is a metal-based copper-clad board with good heat dissipation, mostly used in the production of LED lights. Here, let Shenzhen PCB manufacturers for you to explain the aluminum substrate production process specifications and difficulties.   Aluminum substrate production process specifications.   (1) the aluminum substrate is often applied to power devices, so the copper foil is thicker. (2) aluminum substrate prior to the protective film to give protection, otherwise, chemicals will leach, resulting in a damaged appearance. (3) the production of the aluminum substrate using a milling cutter hardness, milling speed is at least two-thirds slower. (4) processing aluminum substrate must be for the gong head plus alcohol heat dissipation.   The aluminum substrate production process is difficult. (1) the use of mechanical processing of aluminum substrates, drilling holes in the hole edge does not allow burrs, otherwise it will affect the pressure resistance test. (2) in the entire aluminum substrate production process is not allowed to rub the aluminum base surface, by hand touch, or by a certain chemical will produce surface discoloration, blackening. (3) in the aluminum substrate over high voltage test, communication power aluminum substrate requires 100% high voltage test, the board surface on the dirty, holes and aluminum base edge burrs, line serrations or touch any insulation layer will lead to high voltage test fire, leakage, breakdown.      

Why do PCBs need plugged holes? Plugging holes can prevent solder from penetrating through the drilled hole during wave soldering, causing short circuit and the ball of solder to pop out, resulting in a short circuit in the PCB. When there are blind vias on BGA pads, plugging the holes is necessary before the gold plating process in order to facilitate BGA soldering. Plugged holes can prevent flux residue from remaining inside the through holes and maintain surface smoothness. It prevents surface solder paste from flowing into the hole, causing false soldering and affecting assembly. What are the plugged hole techniques for PCB?   Plugged hole processes are varied and lengthy, and difficult to control. Currently, common plugged hole processes include resin plugging and electroplating filling. Resin plugging involves copper plating the holes first, then filling them with epoxy resin, and finally, copper plating the surface. The effect is that the holes can be opened and the surface is smooth without affecting soldering. Electroplating filling involves filling the holes directly with electroplating without any gaps, which is beneficial for the soldering process, but the process requires high technical ability. Currently, the blind hole electroplating filling for HDI printed circuit boards is usually accomplished through horizontal electroplating and continuous vertical electroplating filling, and then subtractive copper plating. This method is complex, time-consuming, and wastes electroplating liquid.   The global electroplated PCB industry has rapidly grown to become the largest segment of the electronic component industry, accounting for a unique position and a production value of $60 billion per year. The demands for slim and compact electronic devices have continuously compressed the board size and have led to the development of multi-layer, fine-line, and micro-hole printed circuit board designs.   In order to not affect the strength and electrical performance of printed circuit boards, blind holes have become a trend in PCB processing. Direct stacking on blind holes is a design method for obtaining high-density interconnections. To produce stacked holes, the first step is ensuring flatness of the hole bottom. Electroplating filling is a representative method for producing flat hole surfaces.   Electroplating filling not only reduces the need for additional process development but is also compatible with current process equipment, and promotes good reliability.   Advantages of electroplating filling: Favorable for designing stacked holes and Via on Pad, which increases the board's density and enables more I/O foot packages to be applied. Improves electrical performance, facilitates high-frequency design, improves connection reliability, increases operating frequency, and avoids electromagnetic interference. Facilitates heat dissipation. Plugging holes and electrical interconnection are completed in one step, avoiding defects caused by resin or conductive adhesive filling, and also avoiding CTE differences caused by other material filling. Blind holes are filled with electroplated copper, avoiding surface depression, and conducive to the design and production of finer lines. The copper column inside the hole after electroplating filling has better conductivity than conductive resin/adhesive and can improve heat dissipation of the board.      

"Balanced Copper" in PCB Manufacturing PCB manufacturing is the process of building a physical PCB from a PCB design according to a certain set of specifications. Understanding the design specification is very important as it affects the manufacturability, performance and production yield of the PCB. One of the important design specifications to follow is "Balanced Copper" in PCB manufacturing. Consistent copper coverage must be achieved in each layer of the PCB stackup to avoid electrical and mechanical issues that can hinder circuit performance.   What does PCB balance copper mean? Balanced copper is a method of symmetrical copper traces in each layer of the PCB stackup, which is necessary to avoid twisting, bending or warping of the board. Some layout engineers and manufacturers insist that the mirrored stack-up of the top half of the layer be completely symmetrical to the bottom half of the PCB.   PCB balance copper function Routing The copper layer is etched to form the traces, and the copper used as the traces carries the heat along with the signals throughout the board. This reduces damage from irregular heating of the board that could cause internal rails to break. Radiator Copper is used as the heat dissipation layer of the power generation circuit, which avoids the use of additional heat dissipation components and greatly reduces the manufacturing cost. Increase the thickness of conductors and surface pads Copper used as a plating on a PCB increases the thickness of conductors and surface pads. In addition, robust interlayer copper connections are achieved through plated through-holes. Reduced ground impedance and voltage drop PCB balanced copper reduces ground impedance and voltage drop, thereby reducing noise, and at the same time, it can improve the efficiency of the power supply. PCB balance copper effect In PCB manufacturing, if the distribution of copper between stacks is not uniform, the following problems may occur: Improper stack balance Balancing a stack means having symmetrical layers in your design, and the idea in doing so is to forego areas of risk that could deform during the stack assembly and lamination stages. The best way to do this is to start the stack house design in the center of the board and place the thick layers there. Often, the PCB designer's strategy is to mirror the top half of the stackup with the bottom half. Symmetrical Superposition PCB layering The problem mainly comes from using thicker copper (50um or more) on cores where the copper surface is unbalanced, and worse, there is almost no copper fill in the pattern. In this case, the copper surface needs to be supplemented with "false" areas or planes to prevent spillage of prepreg into the pattern and subsequent delamination or interlayer shorting. No PCB delamination: 85% of the copper is filled in the inner layer, so filling with prepreg is enough, there is no risk of delamination. No Risk of PCB Delamination   There is a risk of PCB delamination: copper is only filled by 45%, and the interlayer prepreg is insufficiently filled, and there is a risk of delamination.     3. The thickness of the dielectric layer is uneven Board layer stack management is a key element in designing high-speed boards. In order to maintain the symmetry of the layout, the safest way is to balance the dielectric layer, and the thickness of the dielectric layer should be arranged symmetrically like the roof layers. But it is sometimes difficult to achieve uniformity in dielectric thickness. This is due to some manufacturing constraints. In this case, the designer will have to relax the tolerance and allow for uneven thickness and some degree of warpage. The cross section of the circuit board is uneven One of the common unbalanced design problems is improper board cross-section. Copper deposits are larger in some layers than others. This problem stems from the fact that the consistency of the copper is not maintained across the different layers. As a result, when assembled, some layers get thicker, while other layers with low copper deposition stay thinner. When pressure is applied laterally to the plate, it deforms. To avoid this, the copper coverage must be symmetrical with respect to the center layer. Hybrid (mixed material) lamination Sometimes designs use mixed materials in the roof layers. Different materials have different thermal coefficients (CTC). This type of hybrid structure increases the risk of warpage during reflow assembly.   The influence of unbalanced copper distribution Variations in copper deposition can cause PCB warpage. Some warpages and defects are mentioned below: Warpage Warpage is nothing but a deformation of the shape of the board. During the baking and handling of the board, the copper foil and the substrate will undergo different mechanical expansion and compression. This leads to deviations in their coefficient of expansion. Subsequently, internal stresses developed on the board lead to warping. Depending on the application, the PCB material can be fiberglass or any other composite material. During the manufacturing process, circuit boards undergo multiple heat treatments. If the heat is not evenly distributed and the temperature exceeds the coefficient of thermal expansion (Tg), the board will warp.   Poor electroplating of conductive pattern   To properly set up the plating process, the balance of copper on the conductive layer is very important. If the copper is not balanced on the top and bottom, or even in each individual layer, overplating can occur and lead to trace or underetching of connections. In particular, this concerns differential pairs with measured impedance values. Setting up the correct plating process is complex and sometimes impossible. Therefore, it is important to supplement the copper balance with "fake" patches or full copper.   Supplemented with Balanced Copper   No Supplemental Balance Copper If the bow is unbalanced, the PCB layer will have cylindrical or spherical curvature In simple language, you can say that the four corners of a table are fixed and the top of the table rises above it. It was called the bow and was the result of a technical glitch The bow creates tension on the surface in the same direction as the curve. Also, it causes random currents to flow through the board. Bow Bow effect Twisting twist is affected by factors such as circuit board material and thickness. Twist occurs when any one corner of the board is not aligned symmetrically with the other corners. One particular surface goes up diagonally, and then the other corners twist. Very similar to when a cushion is pulled from one corner of a table while the other corner is twisted. Please refer to the figure below. Distortion Effect Resin voids are simply the result of improper copper plating. During assembly stress, stress is applied to the plate in an asymmetric manner. Since pressure is a lateral force, surfaces with thin copper deposits will bleed resin. This creates a void at that location. Measurement of Bow and Twist According to IPC-6012, the maximum allowable value for bow and twist is 0.75% on boards with SMT components, and 1.5% for other boards. Based on this standard, we can also calculate the bend and twist for a specific PCB size. Bow allowance = plate length or width × percentage of bow allowance / 100 The twist measurement involves the diagonal length of the board. Considering that the plate is constrained by one of the corners and the twist acts in both directions, factor 2 is included. Maximum permissible twist = 2 x board diagonal length x twist allowance percentage / 100 Here you can see examples of boards that are 4" long and 3" wide, with a 5" diagonal.   Bending allowance over the entire length = 4 x 0.75/100 = 0.03 inches Bending allowance in width = 3 x 0.75/100 = 0.0225 inches Maximum permissible distortion = 2 x 5 x 0.75/100 = 0.075 inches