Copper-Wire Stress Buffers for Extending Lifetime of Double-Sided Bidirectional SiC Modules

The mismatch of coefficients of thermal expansion (CTE) causes tremendous thermomechanical stress in die attachment of double-sided bidirectional modules (BMs), thus reducing the reliability of the module. The thermomechanical reliability of a double-sided power module is the most critical issue, which needs to be addressed. People have proposed a number of ways to improve the reliability by reducing the CTE mismatches using such as Moly spacer instead of copper or junction temperature rise using high conductive spacer. This work first proposed a composite buffer, namely copper-wire-spacer (CWS), with low elastic modulus, capable of reducing thermomechanical stress by >50%. The lifetime of the double-sided BM with the CWS buffer is 40.0% and 42.9% longer than that with the conventional solid copper buffer, and is only 6.67% and 6.25% shorter than that with the moly buffer under the thermal shocking tests and the power cycling tests, respectively. The novel method of reducing the elastic modulus of the spacer could be a novel and good concept to reduce the thermomechanical stresses as well as improving the reliability of double-sided power modules. It can provide new guidance to design and packaging reliable double-sided power modules.