Mechanical properties of intermetallics formed during thermal aging of Cu-Al ball bonds

In high power automotive electronics copper wire bonding is regarded as most promising alternative for gold wire bonding in 1st level interconnects and therefore subjected to severe functional requirements. In the Cu-Al ball bond interface the growth of intermetallic compounds may deteriorate the wire bond. The thermo-mechanical properties of these intermetallic compounds are crucial in the prediction of the long term behavior. To determine the mechanical properties diffusion couples were aged and 5 separate intermetallic compounds were melted using the pure elements Cu and Al. These samples were annealed in vacuum at high temperature and chemically analyzed in order to identify the intermetallic compounds. The measured hardness, indentation Young's moduli and densities of these intermetallic compounds are presented. Consequences of the thermo-mechanical properties of the intermetallic compounds are crucial for the prediction of the long term mechanical behavior of Cu-Al ball bonds.