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

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(R)) 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 degrees 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 degrees 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). (C) 1999 Elsevier Science Ltd. All rights reserved.