Have you ever wondered why PCB circuit boards always wear a green coat? This is actually closely related to a special coating called the solder mask. This green protective film mainly functions to prevent the copper traces from oxidizing when exposed to air.
 
It's important to note that the solder mask itself is semi-transparent and can take on a variety of colors by adding different pigments. However, the reason why green has become the mainstream can mainly be attributed to the following reasons. Firstly, green has less irritation to the eyes, effectively reducing visual fatigue and making the inspection and soldering of the circuit board more effortless and efficient. Secondly, the production cost of green PCBs is relatively low. Considering these factors, it's easy to understand why green has become the preferred color for PCB circuit boards.
 
I believe now you have a clearer understanding of this phenomenon.