Microstructural and Hardness Change at Aluminum-Scandium Wire Bond Interface during High Temperature Operation in Active Power Cycle Test

Abstract

Aluminum bonding wire alloyed with a small amount of scandium (Al-Sc wire) has a potential to improve the reliability of power device. In this study, the failure mechanism of Al-Sc wire bond in active power cycle (APC) test at high temperature was investigated in comparison with conventional pure Al wire. EBSD and nanoindentation analyses were carried out to analyze the grain size and hardness evolution at bond interface during APC test. In addition to SEM microstructural analysis, TEM analysis was also conducted to reveal the detailed microstructure of Al-Sc wire bond. Our analysis demonstrated that the Al-Sc wire is able to retain its hardness very well by suppressing the grain coarsening by the presence of Al₃Sc nanoparticles even under high temperature, however the softening on the metallization side by grain coarsening coupled with the void formation just below the bond interface leads to a rapid growth of fatigue crack on the metallization side of bond interface.

Fig. 19 Schematic of thermal stress and crack path in Al-Sc wire bond. (online color)