Adhesion improvement of a poly(tetrafluoroethylene)-copper laminate by thermal graft copolymerization

Abstract

Poly(tetrafluoroethylene) (PTFE)-copper laminates were achieved by surface graft copolymerization of glycidyl methacrylate (GMA) on an argon plasma-pretreated PTFE film at elevated temperature with simultaneous lamination of a copper foil in the presence of an epoxy resin adhesive. The plasma pretreatment introduces peroxides which are thermally degraded into radicals to initiate the graft copolymerization of GMA on the PTFE surface. The graft copolymerization with concurrent lamination of copper was carried out in the complete absence of a polymerization initiator or system degassing. The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The adhesion strength between the PTFE film and copper was assessed by the T-peel test method. The adhesion strength was affected by the plasma pretreatment time, as well as by the grafting and curing temperatures. The PTFE/GMA-epoxy resin/Cu assembly exhibits a significantly higher measured adhesion strength, compared with those of the PTFE/epoxy resin/Cu and PTFE/GMA/Cu assemblies. The PTFE/GMA-epoxy resin/Cu joint delaminated by cohesive failure inside the bulk of the PTFE film. This suggests that the enhanced adhesion between the graft-modified PTFE film and the copper surface is attributable to the formation of covalent bonds between the tethered GMA graft chains on PTFE and the epoxy resin network.