High Temperature Lead Free Solder Alloy for High Power Semiconductor Device Packaging Applications

Power semiconductor modules typically undergo extreme temperature swings and are subjected to fast switching applications. SAC and SnSb alloys are popular material choices of Pb-free type for die attach applications. The melting temperature of SAC and SnSb alloys are typically around 220 deg C and 240 deg C respectively. These solder materials have the disadvantages of a poor reliability against thermomechanical stress at elevated temperature. In this paper, Pb free solder alloy which has a melting temperature more than 3000C has considered for die attach. This solder alloy exhibits significantly higher shear strength and more reliable than base line solders. The solder material after isothermal aging at high temperature (200 deg C) and thermal shock test for 1000 cycles (with a DeltaT=225 deg C) maintains their superior shear strength. The substrate level power cycling with deltaT=120 deg C confirmed the solder material performs 135k cycles without die solder degradation. The SEM/EDS microstructural analysis confirmed the various intermetallic phases of the soldered material improved the bond strength.