Effect of solder diffusion barriers on the joint reliability of SiC power devices operated above 300°C

Abstract

The SiC power devices can operate at high junction temperatures (Tj) as high as beyond 300°C and at high switching frequencies. The application of SiC devices in power electronics can improve the efficiency and can increase the power density of the converters. To realize the outstanding ability of the SiC devices, the high temperature packaging technology is crucial. The ceramic/Cu/Ni(P) is the standard substrate for power module packaging. The AuGe eutectic solder is the commonly used high temperature solder. However, this solder is prone to react with the Ni(P) layer, resulting in degradation of the joint. In order to solve this problem, we prepared two types of diffusion barrier on the surface of the package substrate: one is a thin TiN layer and the other is a thin W layer. The thickness of each diffusion barrier was 250 nm. The SiC Schottky Barrier Diode (SBD) power chips (2.0mm×2.0mm) were die-bonded on the modified package substrates with a vacuum reflow process. The bonded samples were aged at 330°C in air. The mechanical and electrical properties of the bonded samples were evaluated before and after the high temperature aging. The die shear strength of the SiC-SBD bonded on a non-modified package substrate dramatically decreased in the initial aging test stage, and decreased to less than one third of the initial value after 400 hrs. In contrast, the die shear strength of the SiC device bonded on the W-modified package substrate almost did not decrease after aging for 400 hrs. After 1000 hrs, the die shear strength was 2 times higher than that on the non-modified substrate. No change was observed in the electrical resistance after 1000 hrs. For the SiC devices bonded on the TiN-modified substrate, the electrical resistivity increased from 74 to 82.5 mΩ after aging for 1000 hrs. Decomposition of the TiN diffusion barrier was observed. The W diffusion barrier exhibits better result than the TiN diffusion barrier in improving the reliability of SiC power devices operated above 300°C.