Die Attach for High Temperature Electronics Packaging

AuSi, patterned Au and off-eutectic Sn-Au-Sn die attach materials and processes have been investigated for SiC die attach for high temperature applications. AuSi shear test results after 3000 hours of aging at 325C in air showed only a slight decrease in shear strength when assembled on Mo:Mn/Pd/Au metallized AlN. However, when assembled on Mo:Mn/Ni/Au metallized AlN, the die shear strength decreased dramatically after only 500 hours at 325C in flowing nitrogen. The patterned Au die attach showed a decrease in shear strength and a change in failure mode after storage at 500C in air. The initial failure mode was in the Au bump, but after 500 hours at 500C, the failure mode shifted to failure near the SiC die interface. A similar change in failure mode was observed with offeutectic Sn-Au-Sn die attach stored at 500C. In both cases there was evidence of Ti diffusion from the Ti/Ti:W/Au thin film metallization stack on the backside of the SiC die.