Adhesion and adhesion reliability enhancement of evaporated copper on surface modified poly(tetrafluoroethylene) films from graft copolymerization

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PT FE) him via UV-induced graft copolymerization were carried out to improve t he adhesion and adhesion reliability with evaporated copper. The PTFE film surface was modified by graft copolymerization with a monomer, such as 2-hy droxylethyl mathacrylate (HEMA), acrylic acid (AAc), methacrylic anhydride (MAAn), and glycidyl methacrylate (GMA), A double graft copolymerization pr ocess, involving initially the graft copolymerization with HEMA, AAc or MAA n, which contained the functional moities for curing the epoxide groups, an d subsequently by graft copolymerization with GMA, which contained the epox ide group, was also employed. The adhesion strength of the evaporated Cu on the singly and doubly graft-copolymerized PTFE film was affected by the ty pe of monomer used during graft copolymerization, the concentration of the graft, the extent of O-2 plasma post-treatment after graft copolymerization , and the extent of thermal treatment after metallization, The T-type peel adhesion strength of the Cu/PTFE laminate obtained under the optimum condit ions was about 19 N/cm, The adhesion strengths of the Cu/PTFE laminates rem ained practically unchanged after the Level I test (85 degrees C and 85% re lative humidity for 168 h), The good adhesion strength and adhesion reliabi lity must have resulted from the strong affinity of the graft chains for Cu , the extensive crosslinking of the graft chains at the metal/polymer inter face, and the fact that the graft chains where covalently tethered on the P TFE surface. The cohesive failure of the metal/polymer laminates was also i nvestigated.