Assessment of Au-Ge Die Attachment for an Extended Junction Temperature Range in Power Applications

Abstract

A eutectic Au-Ge (12 wt%) die attach system has traditionally been used in electrical characterization of SiC devices in a temperature range up to 300°C. However, only fragmentary results have been reported concerning the applicability of the system. In this paper, a eutectic Au-Ge die attach system composed of 0.3-mm-thick, 2×2 mm2 SiC dies soldered on ceramic (SiN) substrates with Ni/Au-plated Cu foil is systematically discussed on the basis of the results of storage tests at 300°C and thermal cycle tests ranging from −40°C to 300°C. Die attachments were performed at ~400°C by using a vacuum reflow soldering system. Shear testing of the samples indicated that the initial dies had very strong shear strength of more than 100 MPa. After 300°C storage for 3000 hours in air, it was found that their shear strength markedly dropped, but still maintained an average value two times larger than the JAITA standard of 6.2 MPa specified in IEC 749 for die shear strength. The test results for a thermal cycle from −40°C to 300°C showed that although the shear strength of the samples gradually declined with an increasing number of cycles, it was still 10 MPa on average even after 2000 cycles.