The color of PCB surface is actually the color of solder resist, which can prevent the wrong soldering of components, prolong the service life of devices, and prevent the oxidation and corrosion of devices. If you know something about electronic products, you will find that the color of PCB is green in most cases.
This is mainly because the green solder mask process is the most mature and simple, and the green board is also more environmentally friendly. In addition to green, PCB boards have other colors, such as white, yellow, red, blue, matte colors, and even chrysanthemum, purple, black, bright green, etc. White is the necessary color that is used to make lamps and lanterns, and other colors are used to distinguish product samples. From R&D to product landing, the experimental board may be purple, the key board will be red, and the computer internal board will be black depending on the different uses of the PCB, which will be distinguished and marked by different colors. As for the green oil, its solder resist ink has the longest history, lowest price and most popularity.
There are many advantages:
1. Several processes of board making and laminating need to be carried in the yellow light room, where the green PCB board has the best visual effect;
2. In SMT patch processing, green is more easily for the bottom plate to be recognized by the instrument as optical positioning and calibration are required in the steps of tinning, patching and AOI calibration;
3. Some inspections rely on workers' observation (but now flying probe tester has replaced observation in most cases), which needs workers keep staring at the board under strong light, and green is friendly to eyes;
4. Green PCBs are relatively environmentally friendly, and no toxic gas will be released when the waste boards are recycled at high temperature. Other colors, such as blue and black, have weak electrical conductivity, which may lead to short circuit as these colors are doped with cobalt and carbon. In addition, colors like black, purple, and blue lights are too dark, which will increase the difficulty of the inspection and maintenance of the motherboard, and the process is not easy to control.
Taking the black board as an example, the black board is most likely to cause obvious color difference and high PCB defect rate due to problems in the production process and the ratio of raw materials. What's more, the traces of black circuit board is hard to identify, which will increase the difficulty of maintenance and debugging. Therefore, PCB factories hardly use black PCB. Even the fields of military industry and industrial control all use green PCBs in their products with extremely high quality requirements. To sum up, it is not difficult for us to understand why the color of PCB is mostly green.