Improvement of Power Module System Solders by Directional Solidification

To improve the quality of large area solders in terms of void-rate and reliability, a novel directional solidification mechanism (DSM) for the soldering process was developed at PINK GmbH Thermosysteme. This mechanism controls the heat flow during cooling and thereby significantly reduces shrinkage-voids in system solder layers. In this study thermal simulations were performed to customize the mechanism to the test-vehicles. Afterwards, temperature measurements and soldering tests were performed to verify the simulations and the directional solidification mechanism. Lastly, the samples were analysed by x-ray and cross sectioning. To show the effect of DSM two groups of samples were assembled. Group A was cooled down with DSM and group B with a standard cooling plate. For this comparison, DBC-substrates were soldered to Cu-baseplates with a SAC305 solder. With DSM, the void-rate was 26 % and the standard deviation 50 % lower due to the reduction of shrinkage-voids.