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 imidaz ole (VIDZ) on pristine and argon plasma-pretreated polyimide (PI or Ka pton HN(R)) films with simultaneous lamination to copper foils was dem onstrated. The simultaneous thermal grafting and lamination process wa s carried out in the temperature range of 80-160 degrees C under atmos pheric conditions and in the complete absence of a polymerization init iator. The adhesion strength was found to be strongly dependent on the rate of cooling after the thermal grafting and lamination, with the a dhesion substantially improved by annealing. An ultimate T-peel streng th greater than 14 N/cm and a lap shear adhesion strength approaching 2000 N/cm(2) were achieved for the polyimide-copper interface for graf ting and lamination carried out at 120 degrees C before cohesive failu re occurred in the polyimide film. The T-peel and lap shear adhesion s trengths are reported as a function of the cooling rate after thermal grafting and lamination, the argon plasma pretreatment time of the pol yimide films, the thermal lamination temperature, and the thermal lami nation time. The effect of moisture on the lamination strength was als o investigated. The surface compositions of the polyimide films and co pper foils after delamination were studied by X-ray photoelectron spec troscopy (XPS). The thickness of the graft interfacial layer was of th e order of 200 nm, as derived from the cross-sectional view of the sca nning electron micrograph.