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.