Heel Crack and Lead-Free Soldering Issues Affecting Power Electronics Packages

Heel crack is one of the most complicated reliability problems of wire bonding in the power electronic package. In this work, we investigate the effects of solder IR reflow to the heel crack both in experimental and FEA simulation study for the 2-5 mil (diameter) aluminum wire. The results show that the plastic strain at the heel region induced by the wire bonding process, influence of molding process and the coefficient of thermal expansion (CTE) mismatches between different components in package are the main causes of heel crack happened in IR reflow. With respect to the trend of lead free, the simulation is also processed under the three temperature hierarchies with different peak reflow temperature (220 D, 240 D, 260 D) and wetting time. From von mises stress and related plastic strain distributions, it can been seen that, during the reflow, the heel region of the wire is endured larger stress and plastic strain than other areas, and with the peak reflow temperature and wetting time increasing, the plastic strain also increases about 20%, which is very critical for material fatigue