Optimization of Ag-alloy ribbon bonding - An approach to reliable interconnection for high power IC packaging

Ultrasonic ribbon bonding has drawn much attention in power electronic packaging as compared to conventional heavy wire bonding. This study evaluated the bondability of 100 × 1500 μm Ad-4Pd ribbon bonded on direct bonded copper (DBC) substrates metallized with Ni/Pd/Au layers through adjustment of the bonding parameters. The bonding patterns on the wedge bonds along with cross-sectional images of the polished interface were investigated, and the pull force and joint properties were examined by pull and shear tests. Failure codes indicated heel damage resulting from excessive ultrasonic energy, which was explained from the deformation point of view. Furthermore, footprint studies of the sheared surfaces indicated that increasing the bonding power could promote the bonding surface, as evidenced by the transition of the surface morphology from fretting to microwelds and finally fractured pieces of ribbons. This study may be of great importance in explaining the special features of ultrasonic ribbon bonding, as well as in providing a feasible solution for power electronic packaging with a better understanding of the importance of optimizing the bonding parameters.