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) (PTFE) film via UV-induced graft copolymerization were carried out to improve the adhesion and adhesion reliability with evaporated copper. The PTFE film surface was modified by graft copolymerization with a monomer, such as 2-hydroxylethyl methacrylate (HEMA), acrylic acid (AAc), methacrylic anhydride (MAAn), and glycidyl methacrylate (GMA). A double graft copolymerization process, involving initially the graft copolymerization with HEMA, AAc or MAAn, which contained the functional moities for curing the epoxide groups, and subsequently by graft copolymerization with GMA, which contained the epoxide group, was also employed. The adhesion strength of the evaporated Cu on the singly and doubly graft-copolymerized PTFE film was affected by the type of monomer used during graft copolymerization, the concentration of the graft, the extent of O2 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 conditions was about 19 N/cm. The adhesion strengths of the Cu/PTFE laminates remained practically unchanged after the Level I test (85°C and 85% relative humidity for 168 h). The good adhesion strength and adhesion reliability must have resulted from the strong affinity of the graft chains for Cu, the extensive crosslinking of the graft chains at the metal/polymer interface, and the fact that the graft chains where covalently tethered on the PTFE surface. The cohesive failure of the metal/polymer laminates was also investigated