Coverlay

Flex PCB specifications are among the most frequently underspecified documents in electronics procurement. Buyers write “flex PCB, polyimide base” and assume the supplier will fill in the rest correctly. Sometimes they do. Often they do not — and the failure mode is a board that cracks, delaminates, or develops intermittent opens after a few thousand flex cycles. Understanding why polyimide behaves the way it does, and why the protective layer choices matter as much as the base material, is the foundation of a correct flex PCB specification.