A Method to Minimize Junction Temperature Difference of Dies in Multichip Power Modules

The multichip power modules are widely applied in high-capacity industrial converters. And the junction temperature difference among dies is inevitable due to thermal coupling between adjacent chips. This can further result in current imbalance among paralleled dies. In this paper, the mechanism of junction temperature difference resulting from thermal coupling between adjacent dies is analyzed. And a method is proposed to mitigate the junction temperature difference. Specifically, the bottom copper layer of the direct bonding copper substrate (DBC) is modified to balance the equivalent thermal resistances from each die to the heatsink. The method can effectively suppress the junction temperature difference and promote current sharing. And it is cost-efficient compared to the methods, which adopt advanced heat spreader technologies, such as indirect microchannel coolers, heat pipes and jet impingement cooling. Also the method is well compatible with the conventional packaging technologies. The procedure to determine the layout of the bottom copper layer on the substrate is discussed in detail. And the effectiveness of the proposed method is verified by simulations from electro-thermal coupling perspective.