Numerical Study of Wire Bonding—Analysis of Interfacial Deformation Between Wire and Pad

Abstract

The purpose of the present study is to understand the interfacial deformation between pad and wire and the effect of the pad thickness, the pad hardness, and the tool shape on the interfacial deformation. The relationship between the bondability and the interfacial deformation (surface exposure to produce the clean surface) is summarized, because the bondability is largely affected by the interfacial deformation. A simple model of wire bonding is proposed for the numerical analysis. The model is based on the finite element method for rate sensitive materials and applicable to very large deformation processes. The numerical simulation made it possible to visualize the interfacial contacting process which occurs for several milli-seconds. It was suggested that the periphery bond is produced easily as the pad thickness decreases and the pad hardness increases. On the other hand, it was found that the thick pad and the groove tool can help the center bond formation. These results is explained by the distributions of the interfacial extension and the equivalent stress on the bonding interface. Also, the damage to the substrate (Si chip) is discussed, based on the numerical results.