Low-temperature thermal graft copolymerization of 1-vinyl imidazole on polyimide films with simultaneous lamination to copper foils

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) on pristine and argon plasma-pretreated polyimide (PI or Kapton HN(R)) films with simultaneous lamination to copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80-160 degrees C under atmospheric conditions and in the complete absence of a polymerization initiator. The adhesion strength was found to be strongly dependent on the rate of cooling after the thermal grafting and lamination, with the adhesion substantially improved by annealing. An ultimate T-peel strength greater than 14 N/cm and a lap shear adhesion strength approaching 2000 N/cm(2) were achieved for the polyimide-copper interface for grafting and lamination carried out at 120 degrees C before cohesive failure occurred in the polyimide film. The T-peel and lap shear adhesion strengths are reported as a function of the cooling rate after thermal grafting and lamination, the argon plasma pretreatment time of the polyimide films, the thermal lamination temperature, and the thermal lamination time. The effect of moisture on the lamination strength was also investigated. The surface compositions of the polyimide films and copper foils after delamination were studied by X-ray photoelectron spectroscopy (XPS). The thickness of the graft interfacial layer was of the order of 200 nm, as derived from the cross-sectional view of the scanning electron micrograph.