Mechanical Reliability Evaluation of Chip Scale Power Package

ThinPak™ is a highly volumetrically efficient technology for packaging high power semiconductor devices for a wide range of applications. Its elimination of wirebonds lowers thermal and electrical resistivity and impedance, while its two sided solder attach enhances cooling, thus promising improved performance and reliability. In this study, the thermomechanical durability of the ThinPak™ module was investigated using physics-of-failure modeling and accelerated thermal cycle testing. Post-test analysis of samples indicated that failure occurred first in the eutectic solder used to attach the ThinPak™ to the DBC substrate. The high lead solder in the ThinPak™ itself was very robust against failure. Viscoplastic stress analysis combined with Coffin-Manson damage modeling was used to quantify creep-fatigue accumulation. The failure criterion of a 20% increase in forward voltage drop was used in conjunction with stress analysis to assess the time to failure at the DBC/ThinPak™ interface. The calibrated constants for the fatigue ductility and exponent were then used to assess the life of the assembly for different temperature loading conditions.