Novel Low Temperature Alloy for Molded Power Module Soldering to Customized Heatsinks

Inhalt:
Transfer-molded Silicon Carbide (SiC) power modules are becoming more and more popular for automotive applications. One way to ensure good thermal performance over the required lifetime is to solder the modules directly to a custommade heatsink designed for a particular application, such as electric vehicles. However, most mold epoxies have a glass transition temperature (Tg) around 200°-220°C which poses an issue in compatibility with the current Pb-free solders available. The reason being these solders require minimum peak processing temperatures of 235 - 250 °C which is highly likely, if not certain, to cause delamination of the molded epoxy from the die and substrate surface. For this purpose, a novel Pb-free alloy is introduced which can be reflowed with peak temperatures <220°C. Critically, this alloy shows thermomechanical reliability equal to that of current higher-temp industry bench-marks and improved reliability relative to existing alloy with a similar or lower processing temperatures.