Comparative analysis of the process window of aluminum and copper wire bonding for power electronics applications

Today's state-of-the-art top level interconnect technology in power modules is an aluminum wire wedge/wedge bond process. Being the bottleneck for realizing even higher switching frequencies and thus higher junction temperatures made possible by upcoming wide bandgap semiconductors, innovative packaging technologies such as copper wire wedge/wedge bonding are a key issue in pushing the technological frontier of power electronics even further. With its higher electrical and thermal conductivity as well as its lower coefficient of thermal expansion copper wire bonding bears the chance of a significant improvement in one of the most sensitive lifetime limiting areas of power modules. In contrast copper's higher young's modulus as well as a higher strain hardening require increased bond parameters resulting in new challenges for the bonding process. A smaller and more sensitive process window is expected to be the other side of the coin. This study aims to display the advantages and challenges of the aluminum and copper wire bonding process for power modules with special focus on a comparative analysis of their process windows. To obtain statistically significant conclusions all tests are performed in randomized rotatable central composite response surface design of experiment studies. A comparison of attainable shear forces as well as observed failure modes will be the bases to define criteria for acceptance that are applicable for the used wire bond material. This deep understanding of all process and process influencing parameters will be needed in order to set up and evaluate a reliable and optimized production process for power modules.