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

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: