OSP (Organic Solderability Preservative) is a special chemical coating applied to the surface of copper on a PCB (Printed Circuit Board). This coating forms a thin protective film that keeps the bare copper from rusting or corroding when it’s stored. During PCB assembly, the coating can be easily removed by certain chemicals, exposing clean copper for soldering.
The OSP coating is like an invisible film, and you can’t see it easily with your eyes. Experts might use special techniques to check if it’s there. The challenge for PCB manufacturers is that OSP-finished PCBs look similar to regular bare copper boards, making it harder to inspect.