Electroless deposition of copper on polyimide films modified by surface graft copolymerization with nitrogen-containing vinyl monomers

Surface modification of Ar-plasma-pretreated polyimide (PI) films (Kaptong (R) HN films) via UV-induced graft copolymerization with 1-vinylimidazole (VIDz), 4-vinylpyridine (4VP), and 2-vinylpyridine (2VP) under atmospheric conditions was carried out to improve their adhesion with the electrolessly deposited Cu. The surface compositions of the graft-copolymerized PI films were characterized by X-ray photoelectron spectroscopy. The adhesion strength of the electrolessly deposited Cu on the surface-graft-copolymerized PI film was affected by the type of monomers used for graft copolymerization and the graft concentration. T-peel adhesion strengths of about 15, 10, and 6 N/cm were obtained for the Cu/graft-modified PI assemblies involving, respectively, the VIDz, 4VP, and 2VP graft-copolymerized PI films. These adhesion strengths are much higher than those obtained for assemblies involving electrolessly deposited Cu on pristine or on Ar-plasma-treated PI films. The adhesion strengths involving the VIDz and 4VP surface-graft-copolymerized PI films are also higher than those involving PI films modified by chemical etching. The cohesive failure inside the PI substrate of the Cu/graft-modified PI assemblies during delamination suggested that not only were the grafted polymer chains covalently tethered on the PI film, they were also incorporated into the metal matrix during the electroless plating process.