Surface graft copolymerization enhanced adhesion of an epoxy-based printedcircuit board substrate (FR-4) to copper

The lamination of surface modified printed circuit board (PCB) substrate, F R-4(R), from argon plasma pretreatment and W-induced graft copolymerization with glycidyl methacrylate (GMA), to copper foil was carried out at elevat ed temperature and in the presence of an epoxy adhesive. The structure and chemical composition of the graft copolymerized surfaces and interfaces of the glass fiber-reinforced and epoxy-based FR-4 substrates were studied by X-ray photoelectron spectroscopy (XPS), The effects of the plasma pretreatm ent time, the UV illumination time, as well as the curing temperature, on t he adhesion strength between the FR-4 substrate and copper were investigate d. The assemblies involving GMA graft copolymerized FR-4, or the FR-4-GMA/e poxy resin/Cu assemblies, exhibited a significantly higher interfacial adhe sion strength and reliability, id comparison to those assemblies in which o nly epoxy adhesive alone was used. The enhanced adhesion in the assemblies involving GMA graft copolymerized substrate arises from the fact that the c ovalently tethered GMA graft chains on the FR-4 surface can become covalent ly incorporated into the epoxy resin, resulting in the toughening of the ep oxy matrix and increased interaction with copper.