Definition

Flexible PCBs (FPCs or flex circuits) use thin, flexible polyimide substrate (typically 12.5-50 µm) with copper traces and polyimide coverlay instead of rigid laminate and solder mask. Flex circuits can be single-sided, double-sided, or multilayer. They're classified as static flex (bent once during assembly) or dynamic flex (repeatedly bent in operation). Dynamic flex requires careful trace routing (perpendicular to bend), radiused corners, and no plated through-holes in the bend zone. Flex enables compact packaging and moving connections.