Abstract
In flexible printed circuits (FPCs), polyimide (PI) resin, which has low dielectric constant, is used for the substrate, and copper, which has low resistance, is used for the wiring. In general, a surface modification technique is applied to the PI resins because the adhesion between PI and copper is poor. Oxygen plasma treatment is a modification technique that should improve adhesion. The treatment increases fine surface roughness and activates the PI surface by introducing functional groups. In this study, the effects of plasma treatment on the surface properties of PI film and on the adhesion of copper plating film to PI film were investigated for high-quality FPCs. In the RF-reactive ion etching (RF-RIE) plasma treatment, oxygen was used as the processing gas. It was at a flow rate of 30 sccm for 3∼20 minutes. The adhesive strength of the copper plating film to PI film was measured using a 90° peel tester. The oxygen plasma treatment improved the adhesion, and the adhesive strength of around 400 N/m is close to a practical level.
