Effect of local concavity of DBC substrate on junction-to-heatsink thermal resistance of power module designs

Abstract:
In this paper, we introduce a study focusing on the correlation between junction-to-heatsink thermal resistance and the local concavity of DBC substrates which highly depends on power module design parameters. A finite element simulation method is introduced which is capable to identify critical die area and DBC layer structure combinations resulting in large local concavities of the substrate and therefore negatively affecting the spreading of the thermal interface material and increasing the thermal resistance of the power module stack-up. The obtained simulation results show strong correlation with real-life measurements. Based on the results, it is concluded that a local concavity larger than 6micrometer can increase the thermal resistance of a die by more than 10% compared to an ideally flat power module stack-up. By using the presented simulation technique, the layer thicknesses of DBC substrates for future power module designs can be optimized for both achieving lower Rth by minimizing local concavity and maintaining mechanical robustness of the DBC.