Friends who study circuits will have this question: Why are most of the boards green? In fact, the PCB is not necessarily green. It depends on what color the designer wants to make, and what color it is. Generally, green is used because green is less irritating to the eyes, and production and maintenance personnel are not prone to fatigue when they are staring at the PCB for a long time. Common colors are blue, yellow, black, and red. All colors are paints that are sprayed on the surface after they are manufactured. There is another reason, because the color commonly used by everyone is green, so the green paint used by the factory is the most, so the cost of using oil is relatively low. And because when repairing the PCB, different wirings are easier to distinguish the difference from the background color, while black and white are relatively unsightly. In summary, I believe that everyone knows more or less about this. In fact, the small details in learning are everywhere. As long as you discover and explore, the fun can make your learning less monotonous. tedious.