Reliability Improvement of a Double-Sided IGBT Module by Lowering Stress Gradient Using Molybdenum Buffers

A double-sided 1200-V/600-A multichip half-bridge insulated gate bipolar transistor (IGBT) module was fabricated utilizing molybdenum as stress-relief buffer and sintered nanosilver as die-attachment. By using the double-sided packaging, the volume, parasitic inductance, and junction temperature were decreased significantly, and thus the higher power density could be achieved. However, the thermomechanical stress was also increased. In this paper, molybdenum instead of the most common copper was used as a stress-relief buffer between chips and substrate, and thus the thermomechanical stress decreased greatly without significantly increasing the junction temperature. Specifically, by using molybdenum instead of copper as the buffer material, the simulation results showed that the IGBT junction temperature at total power loss of 200 W only increased by 5.2% (2.22 degrees C), but the corresponding thermomechanical stress decreased by 9.8% (5.58 MPa), and the sintering residual stress decreased by 20.1% (48.88 MPa). Thermal performance, static and dynamic electrical performance, and reliability via power cycling test of the double-sided module were also characterized experimentally. No degradation of the power devices proved that the way to double-sided packaging power devices could be used for future manufacturing of high-power density power module.