Thermal graft copolymerization-induced adhesion improvement of a FR-4®/PETG® laminate

The lamination of a glass fibre-reinforced and epoxy-based printed circuit board (PCB) substrate, FR-4®, to an amorphous thermoplastic copolyester of dimethyl terephthalate with ethylene glycol and 1,4-cyclohexanedimethanol, PETG®, was studied. The lamination was achieved by the simultaneous surface graft copolymerization of glycidyl methacrylate (GMA) on the argon plasma-pretreated FR-4® substrate and PETG® film at an elevated temperature. The plasma-treated surfaces and the delaminated surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The adhesion strength between the FR-4® substrate and the PETG® film was assessed by the T-peel test method. The adhesion strength was affected by the plasma pretreatment time of the substrates, the lamination time, and the lamination temperature. The FR-4®/GMA/PETG® assembly from the simultaneous graft copolymerization with GMA and lamination exhibited a significantly more rapid lamination rate and a higher adhesion strength than those of the FR-4®/epoxy/PETG® assembly from the epoxy adhesive-induced lamination of the plasma-pretreated FR-4® and PETG® films. The phenomena are consistent with the presence of covalently bonded GMA graft chains on the surfaces of plasma-pretreated PETG® and FR-4® films in the former assembly. The FR-4 ®/GMA/PETG® assembly failed by a combined cohesive and adhesional mechanism.