Investigation to Improve Reliability of Substrates Having Low Thermal Resistance Using Thicker Cu Circuit Layer

Abstract:
Due to the spread of BEVs, there is a strong trend of using SiC devices. To make full use of the advantages of the SiC devices, higher operation temperature is desired. These conditions require the substrates to have lower thermal resistance and reliability under higher temperature. Generally speaking, lower thermal resistance is achieved by using thicker Cu layer. However, it is also known that it deteriorates the reliability of the substrate. We have been working on solving this trade-off with unique materials, structures, and processes. A structure was proposed where pure Al layer was inserted between the Cu layer and the ceramic layer, and it was experimentally proven to increase the reliability of the substrate due to the stress relaxation capability of pure Al. The stress relaxation effect of the Al layer was confirmed with simulations. Two methods were tested to create such a structure. One is to attach Cu plates directly onto a DBA substrate, and the other is to attach Cu plates via a special bonding material, that eases the bonding with lower temperature and pressure. Both methods were proven to work properly with experimental results where the substrates were exposed to TCT between -40 and 175deg C for 1,000 cycles and showed no delamination/cracks.