A coverlay is a flexible insulating film used in flex PCBs to protect exposed copper traces from mechanical damage and contamination. It also provides electrical insulation between conductive features. The material is designed to withstand repeated bending in dynamic applications.
In rigid circuit boards, a solder mask layer provides circuit protection and insulation. In FPCs, the coverlay serves the same purpose while maintaining flexibility.
PCB designers should clearly specify all coverlay requirements in their fabrication notes to avoid manufacturing errors.
Make sure the following details are included:
-
Material type and thickness: Specify the polyimide film and adhesive thickness used in the coverlay stack.
-
Color: Define the required coverlay color (for example, amber, black, or clear).
-
Openings and clearances: Indicate the dimensions and required clearance around vias and component pads.
-
Adhesive type: Mention whether acrylic or epoxy adhesive should be used based on the thermal requirements.
-
Layer reference: Clearly call out the coverlay layers to avoid confusion during CAM processing.