Microstructure and thermal performance of lotus-type porous Cu/solder composite joints

With the miniaturization and improved efficiency of power modules, the increase in heat generation density has become a critical issue. Therefore, it is essential to develop bonding layers with high heat dissipation performance. In this study, the relationship between the structure, equivalent thermal conductivity, and thermal resistance of a previously proposed lotus Cu/solder composite (LSC) joint was investigated to further reduce thermal resistance. Estimations based on the rule of mixtures indicated that reducing the solder thickness, void fraction, and intermetallic compound (IMC) thickness was effective in lowering the thermal resistance. The factors critical in achieving a thinner solder layer and lower void fraction include the use of a vacuum process, an appropriate solder amount, and low bonding pressure. Steady-state thermal measurements revealed that thinner solder layers and lower void fractions significantly improved heat dissipation, which was consistent with the estimation results. Furthermore, thermal resistance measurements of a simulated module demonstrated that the module using the LSC joint achieved a 13% reduction in thermal resistance compared with that using a conventional solder joint. The findings of this study provide clear design guidelines for LSC joints and demonstrate their strong potential for advancing the thermal management of next-generation, high-power-density electronic devices.