PCB Tech - The meaning of PCB design substrate color

Many people like to judge the quality of the motherboard based on the color of the PCB substrate. In fact, the color of the motherboard is not directly related to performance. The color of the PCB board surface is actually the color of a solder resist (also called solder mask). Its function is to prevent the wrong soldering of the original electrical components during the soldering process. At the same time, it also has another function, which is to prevent the soldering components from being damaged. The circuit is oxidized and corroded during use, reducing the failure rate.
Under normal circumstances, observe that the PCB boards of large companies such as Huawei and ZTE are generally green, because the green process is the most mature and simple. But in extreme cases, there will be red, white, blue, yellow, and matte colors. In more extreme cases, there will be black, purple, chrysanthemum, bright green, etc. Under normal circumstances, white products must be used to make lights. When it comes to white PCB boards, most of the other colors are product grading systems, which vary from company to company. Some use red to indicate experiment boards, some use blue to indicate key boards, and some use black to indicate that they are used in computers. Internal panels. Each has its own rules and not detailed tables.
The most common color of PCB board is green, which is green board, also called green oil. The green solder mask is the oldest, cheapest and most popular. Generally speaking, the entire electronic board-level products have to go through the process of board making and post filming. In the process of making the board, there are several processes that have to go through the yellow light room. The visual effect of green in the yellow light room is better, but this is not Main. When SMT soldering, it is necessary to go through tinning, post filming and final AOI verification. These processes all need to be optically positioned and calibrated. The green background color is better for the recognition of the instrument.
Other common ones are red, yellow, green, blue and black. Due to process problems, many line inspections still rely on workers to see with their eyes (of course, most of them now use flying probe testing). It’s a tiring job to keep placards with bright eyes. Green is relatively the least harmful to the eyes. Therefore, green is mostly used.
Blue and black are because they are doped with cobalt and carbon, respectively, and have certain conductivity, so there is a risk of short circuit. Green PCB is more environmentally friendly and will not release toxic gases when used in a high-temperature environment.

In fact, if the color is too dark, it will often increase the difficulty of inspection and maintenance of the motherboard. Take the first black PCB substrate as an example. In the process of PCB washing, black is the most likely to cause chromatic aberration. If the raw materials used in the PCB factory and the self-made process are slightly different, the PCB defect rate will increase due to the chromatic aberration. Since the circuit traces of the black PCB are difficult to identify, it will increase the difficulty of later maintenance and debugging. Generally, motherboard manufacturers will not easily use black PCBs. Therefore, we see that even products with high quality requirements such as military and industrial products only use green PCB substrates.
So what is the effect of the solder mask ink color on the board? The ink has no influence on the finished product, but it has a great influence on the semi-finished product, mainly in the difficulty of making the semi-finished product. In addition, some people will say that the color still has an impact on the PCB board. Indeed, for example, there are matt green, sun green, dark green, light green, etc. in green. The color is a little different. The color is too light and it is easy to see the plug. After the hole process, the appearance of the board is not good, and the color is too dark. Then some manufacturers' inks are not good enough, the ratio of resin and dye is wrong, there will be problems such as bubbles, and the ink will drop in the final curing. In the problem of ink ratio, you can see a slight change in color, which you can't feel if you don't have many years of experience. (This problem is a bit complicated. Some inks are used in comparison with different machines. There are electrostatic spraying, spraying, and screen printing. The inks are different, the ratio is different, and the color is a little different. If you use it wrong, it will be a little bit small. Problems, but in fact, for the finished board, these are all appearance problems and have no effect on the product itself)
Although the color of the ink has no effect on the board, the thickness of the ink has a very large impact on the impedance, especially for the water-gold board. The thickness of the board is very strict. According to experience, use red ink, bubbles, and thickness. It is easier to control. The first is that the ink is more expensive and the quality is indeed desirable. The second is that this color can cover some blemishes on the circuit, and the green will be more obvious. The third is the imaging link. Red and yellow seem to have relatively stable exposure, green is not necessarily, white is the most difficult to control.
In summary, the color has no influence on the performance of the motherboard, and does not play a very important decisive role in PCB design. However, in PCB design and production, every detail in every link is strictly controlled. Whether the PCB board is a prerequisite for a good board. We know that PCB motherboards of different colors are more for product sales. Therefore, it is not recommended that users use PCB color as a reference factor for purchasing motherboards.