Interfacial fracture strength and toughness of copper/epoxy-resin interfaces

We present results examining the interfacial fracture toughness of Cu₂O/epoxy-resin interfaces, which is an important parameter in microelectronic packaging design. Tensiometer measurements of the epoxy-resin surface energy together with contact angle measurements of epoxy-resin/Cu₂O wetting yield an estimate of the thermodynamic work of adhesion of 0.074 Jm^-2. Double cleavage drilled compression (DCDC) and pull test samples were used to evaluate the critical stress intensity and strain energy release rate for interface fracture and found to be 0.05 MPa-m^1/2 and 1.4 Jm^-2. These sample geometries yielded only interface failure with no trace of fracture occurring in either the copper or the epoxy-resin component. The difference between the values of the thermodynamic work of adhesion and the critical strain energy release rate is attributed to plastic processes most likely occurring in the copper layer of the sandwich sample configuration of the DCDC sample.