Comparative thermal and thermomechanical analyses of solder-bump and direct-solder bonded power device packages having double-sided cooling capability

Solder-bump (SB) and direct-solder (DS) interconnections offer the possibility of double-sided cooling for packaging power devices. Packages with SB and DS bonded power devices were fabricated to investigate their reliability and the effectiveness of double-sided cooling. Thermal and thermomechanical characteristics of both packages were analyzed via temperature cycling experiment and computer simulation by finite element modeling (FEM). Thermal analysis results show that double-sided cooling is more effective in the DS package and it has a significantly lower device operating temperature; however, if the same temperature range of cycling is imposed on both packages, the mismatched coefficients of thermal expansion (CTE) lead to larger thermally induced stresses at the silicon-solder interface in the DS package. From a combined thermal and thermomechanical point of view, the DS package is superior over the SB package because the former is expected to experience less temperature changes during operation than the latter one. Locations of maximum stresses in the FEM analysis are also consistent with the crack initiation positions observed in the temperature-cycled packages.