Solder resist application
Areas that should not be soldered may be covered with solder resist (solder mask). The solder mask is what gives PCBs [Printed Circuit Boards] their characteristic green color, although it is also available in several other colors, such as red, blue, purple, yellow, black and white. One of the most common solder resists used today is called “LPI” (liquid photoimageable solder mask). A photo-sensitive coating is applied to the surface of the PWB [When a PCB has no components installed, it is less ambiguously called a printed wiring board (PWB) or etched wiring board.], then exposed to light through the solder mask image film, and finally developed where the unexposed areas are washed away.