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 c onditions 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 streng th of the electrolessly deposited Cu on the surface-graft-copolymerized PI film was affected by the type of monomers used for graft copolymerization a nd 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, res pectively, the VIDz, 4VP, and 2VP graft-copolymerized PI films. These adhes ion strengths are much higher than those obtained for assemblies involving electrolessly deposited Cu on pristine or on Ar-plasma-treated PI films. Th e adhesion strengths involving the VIDz and 4VP surface-graft-copolymerized PI films are also higher than those involving PI films modified by chemica l etching. The cohesive failure inside the PI substrate of the Cu/graft-mod ified PI assemblies during delamination suggested that not only were the gr afted polymer chains covalently tethered on the PI film, they were also inc orporated into the metal matrix during the electroless plating process.