Adhesion improvement of Cu-based substrate and epoxy molding compound interface by hierarchical structure preparation

Abstract

For microelectronic industry, Cu-based substrate and epoxy molding compound (EMC) interface is inherently weak and most likely to delaminate, well-known as a major threat for integrated circuits (ICs) reliability. In this paper, hierarchical whisker-like oxide/Cu cone structure was for the first time to be fabricated by combining electroless plating with heat treatment methods to enhance the interface adhesion between Cu-based substrate and EMC. The surface morphology was characterized by scanning electron microscope (SEM). Result shows that the hierarchical whisker-like oxide/Cu cone film is fine, dense and uniform; Single Cu cone structure is about 3–5μm in height and 1μm in root diameter; a layer of whisker-like oxide grows perpendicularly to circular surface of Cu cone, with length ranging from tens to hundreds of nanometers. Adhesion strength between the as-prepared substrates and EMC were measured by button shear test. With consideration of oxidation caused by practical processes (e.g. wire bonding), the interface of EMC and porous oxide formed at 260°C for 5min was taken as standard sample, representative of practical interface. To further study the effect of whisker-like oxide and Cu cone solely on adhesion performance, whisker-like oxide, porous oxide/Cu cone were investigated as well. Button shear test results reveal that interfacial adhesion strength of EMC and whisker-like oxide, porous oxide/Cu cone, hierarchical whisker-like oxide/Cu cone are 85%, 110% and 162% higher than that of standard interface. Moreover, the mechanism for adhesion improvement was discussed by facture surface observation, failure path assumption and force–displacement curve analysis. Results show that interface of EMC and hierarchical whisker-like oxide/Cu cone exhibits brittle/ductile property with about 3–5μm thick EMC left on the fracture surface, indicating cohesive failure caused by remarkable mechanical interlocking effect.