FPC covering film, also known as CVL in the industry, can generally be called protective film to protect the circuit from oxidation and damage. The components of FPC covering film include curing agent, butanone, diluent, rubber, etc. Covering film is a film that covers and presses onto the surface of a substrate. It is generally polyimide resin, also known as PI, used for welding resistance and has little effect on signal shielding.

1. Protect the copper foil from exposure to air and prevent oxidation of the copper foil.

2. Cover for subsequent surface treatment. Cover areas that do not require gold plating with CVL.

3. In the subsequent SMT, solder mask plays a role.