Surface modification of poly(tetrafluoroethylene) films by graft copolymerization for adhesion improvement with evaporated copper

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film via UV light-induced graft copolymerization with 1-vinylimidazole (VIDz) and glycidyl methacrylate (GMA) were carried out to improve the adhesion with evaporated copper. The surface compositions of the graft-copolymerized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The graft yield increases with the monomer concentration. The adhesion strength of the graft-copolymerized PTFE film and the evaporated copper is affected by the type of monomer used for graft copolymerization, the graft concentration! the plasma posttreatment time after graft copolymerization, and the extent of heat posttreatment after evaporation of copper. A double graft copolymerization process, which involved first the graft copolymerization with VIDz, followed by graft copolymerization with GMA, was also employed to enhance the adhesion of evaporated Cu to PTFE. The T-type peel strength of the PTFE/Cu interface so obtained is about 15 N/cm, which represents a 10-fold increase over that obtained when the PTFE film was treated by plasma only. The mechanism of the peel strength enhancement. and the cohesive failure of the polymer-metal interface were also investigated.