LPI Soldermask

Liquid Photo Imagable Solder Mask is the outermost coating on a printed circuit board that sits between the copper and the components -- it's what gives PCBs their color.

Colored SolderMask

LPI is applied as a liquid coat that covers an entire PCB. Then patterns of light are projected on the liquid and the high energy photons cause the material to harden and adhere to the PCB.

LPI protects copper traces and prevents liquid solder from migrating during the reflow process.

» PCB Design Glossary