Solder mask

Soldermask[2] is a printed circuit board (PCB) manufacturing process that uses a chemical or thermosetting resin to coat a thin film on a circuit board, which can effectively form a layer of reliable protection to avoid unwanted short-circuiting and leakage of the circuit board, and to improve the reliability and electrical performance of the circuit board.

[2] 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 onto the PCB.

The solder stop layer on a flexible board is also called coverlay or coverfilm.

[4] Typical names for these layers include tStop/bStop aka STC/STS[5][nb 1] or TSM/BSM (EAGLE), F.Mask/B.Mask (KiCad), StopTop/StopBot (TARGET), maskTop/maskBottom (Fritzing), SMT/SMB (OrCAD), MT.PHO/MB.PHO (PADS), LSMVS/LSMRS (WEdirekt)[6] or GTS/GBS (Gerber and many others[7]).