Studies of adhesion of metal films to polyimide

Bonding of Cu/Cr films to several polyimides has been studied as a function of polymer surface modification by ion beam and chemical pretreatment. The effects of the metal deposition method and parameters have also been examined. The materials of interest include a low thermal expansion polyimide derived from 3,3′,4,4′-biphenyl tetracarboxylic acid dianhydride-p-phenylene diamine (BPDA-PDA) polyamic acid, and pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) polyimide, formed from polyamic acid or polyamide ethyl ester precursors. The metal/polyimide adhesive strength was determined by the 90° peel test, while the interfacial regions were examined using x-ray photoelectron spectroscopy and ellipsometry. It is found that for PMDA-ODA systems, exposure to low energy Ar+ and/or O+2 ions improves adhesion of the metal overlayer, while for BPDA-PDA polyimide, the role of O+2 is more significant. The fracture location is found to lie 20–300 Å within the polymer, depending upon the ion beam dose and the specific polyimide employed.