Ag alloy wire bonding under electromigration test

Gold wire bonding has been widely utilized in semiconductor packaging industry for electrical connections. However, since the gold price is soaring in past ten years, the alternative materials, such as copper and silver, are the candidates to replace gold. The silver alloy wire has shown many advantages, including excellent electrical and thermal properties. However, not many studies have reported the electromigration (EM) induced failure of Ag alloy wire. This study employed silver alloy wires with 25.4μm diameter bonded on 4μm thick aluminum metallization of die pads to investigate their interfacial reaction and failure mechanism under current stressing of 8 × 10⁴A/cm² at ambient temperature of 175 °C. The resistance evolution of sample during current stressing and the microstructure of joint interface between silver alloy wire and Al bond pad were examined. The results show that the polarity effect of distinct surface morphology on ball bonds and of the different thickness of intermetallic compounds (IMCs) existed at the interface between the wires and Al pads. The corresponding mechanism and kinetic analysis for both void formation and IMCs growth will be proposed and discussed in the future. In addition, the ball pull test (BPT) was conducted before the electromigration test to understand the impact of various wire bonding parameters on mechanical properties.