Effect of Bonded Ball Shape on Gold Wire Bonding Quality Based on ANSYS/LS-DYNA Simulation

Gold wire bonding processes on Cu/low-K dies are simulated with two sequential bonding processes: capillary lowering down and USG power bonding. The major purpose of this modeling is to verify one engineering fact in wire bonding: bonded ball shape has significant impact on the IMC performance, i.e., the bond quality. In this study BBR is defined as the ratio of the bond ball height (BBH) to bond ball diameter (BBD) and regarded as the basic feature of bonded ball shape. The simulation results indicate that BBR at 25% has the highest appearance frequency of tensile strain in bond interface, and the appearance frequency of tensile strain decreases with BBR increasing from 25% to 45%. Since high appearance frequency of tensile strain in bond interface may cause good IMC, the BBR at 25% could be the best for IMC performance and bond quality. This conclusion from simulation is almost coincident with all gold wire bonding practices where the BBR needs to be kept around 25% for the best bonding performance.