Effect of homogenization heat treatment on microstructure and bond strength of high strength Au bonding wire

Abstract

Wire Bonding is the dominant IC interc-onnection process presently used in the semiconductor assembly industry. The flexibility, adaptability and effective cost of wire bonding will continue to keep it as the key process for the interconnection of integrated circuits to substrates. However, wire bonding still has certain technological difficulties to overcome for following of semiconductor roadmap. Increasing miniaturization of electronic circuits calls for smaller wire diameter. This requires the development of Au bonding wires with increased mechanical strength and good bondability to their functionality. Generally, there are two methods to increase mechanical strength of Au wire. The first is change of chemistry of Au wire and the other is control of manufacturing process. But various chemistry of a material already has been proprietary knowledge for various types of commercial bonding wires: ‘hard’, ‘medium-hard’ or ‘soft wires’. And manufacturing process based on detailed working mechanism and thermal property of gold wire was not fully understood. The production of fine Au bonding wire is basically a cold drawing process. In conventional production, properly refined and doped gold is cast into cylindrical bars and rolled or swaged into millimeters in diameter. And then, cold drawn wire through various dies to final sizes around 25um diameter. When the wire is drawn, energy is stored in the wire as a result of cold-working and the wire becomes harder and more brittle as the deformation proceeds. At that time, bonding wire is needed to release from excessive accumulation of stress through recovery and annealing. Role of this heat-treatment is important to archive good drawability of the wire, desired mechanical properties and homogeneity of the wire. In this study, the effect of homogenization heat treatment on microstructure, texture and mechanical property of doped 25um diameter Au bonding wire were characterized. Homogenization heat treatment was...