Surface characteristics and adhesive strengths of metal on O2 ion beam treated polyimide substrate

A polyimide surface was modified by oxygen ion beam bombardment to improve its adhesion to a subsequently deposited NiCr (nickel-chromium alloy) overlayer. The changes in the chemical composition, morphology and adhesion property of the modified polyimide surface were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and the 90° peel test. The results show that the oxygen ion beam treatment of the polyimide induces the formation of oxygen functional groups and the rearrangement of the imide groups in the polyimide substrate film. An increase in its surface roughness resulted in a substantial improvement in the adhesion strength between the polyimide and NiCr overlayer. The improved adhesion strength, however, was found to be reduced after thermal aging at 150 °C for 168 hrs, which was attributed to the thermal oxidative degradation of the polyimide at the interface. We also observed that the ion beam treatment was effective in retarding the adhesion loss caused by the thermal aging.