Low Temperature Pb-Free Solder Preform Technology for Molded Power Module Package Attach Designed for Improved Thermomechanical Performance

In this paper, a low-temperature Pb-free soldering solution for high power density power electronics is discussed. To this point, a critical trade-off between cost, complexity, and performance has been required when designing in a thermal management/mechanical attach solution for power modules. Here, a SAC-In alloy solution is presented in a solder preform configuration that can be used with reflow temperatures below that of industry standard lead-free and/or high temp. solders. This alloy is a drop-in replacement relative to existing soldering processes and offers improved thermal performance beyond organic-based thermal management solutions (e.g., thermal grease, silicones, PCM's) [1]. Further, with a peak reflow temperature below similar to 215 degrees in molded package-to-cooler attach soldering applications, this SAC-In solution prevents delamination within the module assembly. In addition, the reduced processing temperature removes the risk of damage to components and materials in molded package power modules, mitigates warpage and material stress issues during the soldering process, reduces energy consumption, and provides a consistent, repeatable process for high volume manufacturing (HVM). This Bifree alloy offers mechanical properties and ductility that contribute to robust lifecycle performance comparable to standard Pb-free alloys as shown by thermal shock testing -40 degrees/+125 degrees C.