Reliability characterization of heavy wire bonding materials

Ultrasonic heavy wire bonding is one of the most relevant interconnection technologies in automotive and power electric devices. The reliability of electronic components in these fields is mainly determined by the interconnection lifetime during application and, thus by the strength and fatigue characteristics of the mechanically and thermo-mechanically loaded bonding wire materials. In the current paper, mechanical and micro structure properties of different heavy bonding wire materials including Al-, Cu- and Al-clad Cu wires are analyzed in their initial state prior to bonding. Fatigue properties were estimated in the form of the Coffin-Manson equation for the wires loaded in uniaxial cyclic testing. In addition, corresponding microstructure properties were investigated using Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD). The applied approach aims at an improved understanding of basic material properties governing the general reliability behavior of the wires independently from any specific application. The results obtained, enable a more detailed understanding of the material aspects governing the low cycle fatigue behavior of different heavy bonding wires. In particular, they provide an explanation for the superior life time behavior of Cu- and Al clad Cu wires compared to Al wires. In addition, the data derived support establishing improved and consistent quantitative life time models based on finite element analysis for different electronic devices.