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

Abstract

A simple technique of thermal graft copolymerization of 1-vinyl imidazole (VIDZ) in the presence of a small amount of a crosslinking agent (XLA) on plasma-pretreated polyimide (PI or Kapton HN®) films with simultaneous lamination of copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80-150°C under atmospheric conditions and in the complete absence of a polymerization initiator. Significant improvement in adhesion was achieved by the presence of a XLA, such as 2,4,6-triallyloxy-1,3,5-triazine (TATZ), or 1,3,5-triallyl benzene tricarboxylate (TBTC), in VIDZ during the thermal graft copolymerization and lamination process. T-peel adhesion strength exceeding 17 N/cm can be readily achieved for the polyimide-copper interface for grafting and lamination carried out at the reduced temperature of 100°C. The T-peel adhesion strengths are reported as a function of the cooling rate, the argon plasma pre-treatment time of the polyimide films, the thermal lamination temperature, and the thermal lamination time. The polyimide-copper interface graft copolymerized and laminated in the presence of a XLA also exhibited substantially improved resistance to moisture. The surface compositions of the polyimide films and copper foils from the delaminated interfaces were studied by X-ray photoelectron spectroscopy (XPS). The enhanced interfacial adhesion has resulted in cohesive failure deep inside the PI film as is also revealed by the scanning electron micrograph (SEM).