Electroless plating of copper on polyimide films modified by plasma graft copolymerization with 4-vinylpyridine

Surface modification of argon plasma-pretreated polyimide (PI, Kapton® HN) films by plasma graft copolymerization with 4-vinylpyridine (4VP) was carried out. The effects of glow discharge conditions on the chemical composition and structure of the plasma-polymerized 4VP (pp-4VP) films were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy, respectively. The XPS and FTIR results revealed that the pyridine groups in the pp-4VP layer could be preserved to a large extent under proper glow discharge condition. The topography of the modified PI surface was investigated by atomic force microscopy (AFM). The pp-4VP film with well-preserved pyridine groups was used not only as the chemisorption sites for the palladium complexes (without the need for prior sensitization by SnCl2) during the electroless plating of copper, but also as an adhesion promotion layer to enhance the adhesion of the electrolessly deposited copper with the PI film. The T-peel adhesion strength of the electrolessly deposited copper to the pp-4VP grafted PI (pp-4VP-PI) film could reach about 7 N/cm. This adhesion strength was much higher than that of the electrolessly deposited copper to the pristine or the Ar plasma-treated PI film.