Q. I have been working in electronics for about a year. I have noticed that some printed circuit boards have a kind of plastic coating on them, with holes for the solder joints. What is the coating for?
A. This is called a "solder mask". It helps keep solder off the copper foil traces when the board is made. Most manufacturers use "wave soldering". In this process, molten solder is pumped over a sort of dam which produces a stationary wave in the solder. The board is passed over this wave so that all the solder joints are formed at the same time. A solder mask is often placed on the board before the solder is applied.