Solder mask

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Solder mask or solder resist is a lacquer like layer of polymer that provides a permanent protective coating for the copper traces of a printed circuit board (PCB) and prevents solder from bridging between conductors, thereby creating short circuits. Solder mask was created primarily to facilitate wave soldering used in mass assembly. The solder mask is most often applied with a green tint but is available in a wide variety of colors and finishes. It also provides some protection from the environment.

Solder mask comes in different media depending upon the demands of the application. The lowest cost solder mask is epoxy liquid that is silkscreened through the pattern on to the PCB. Other types are the liquid photoimageable solder mask (LPSM) inks and dry film photoimageable solder mask (DFSM). LPSM can be silkscreened or sprayed on the PCB, exposed to the pattern and developed to provide openings in the pattern for parts to be soldered to the copper pads. DFSM is vacuum laminated on the PCB then exposed and developed. All three processes go through a thermal cure of some type after the pattern is defined.