Investigation and Evaluation of High-Temperature Encapsulation Materials for Power Module Applications

Abstract

With the advent of ultra-wide bandgap semiconductor materials, such as gallium oxide (Ga2O3) and aluminum nitride (AlN), higher temperature and higher voltage operation of power devices are becoming realizable. However, conventional polymeric and organic encapsulant materials are typically limited to operating temperatures of 200 degrees C and below. In this work, six materials were identified and evaluated as candidates for use as encapsulants for operation and high-voltage insulation at and above 250 degrees C. High-temperature silicone gel was used as a reference material and was compared with five novel encapsulants including an epoxy resin, a hydro-set cement, two low-melting point glass compounds, and a ceramic potting compound. Gas pycnometry was utilized to evaluate the voiding concentration to avoid partial discharge. Each material was then processed onto a direct-bonded-aluminum substrate test coupon to evaluate compatibility with a commonly used metal-ceramic substrate and processability for use in a power module. The insulation capability of each material was evaluated by testing the partial discharge inception voltage (PDIV) across a 1-mm gap etched in the substrate. The dielectric stability was then tested by soaking the materials in air at 250 degrees C for various intervals and observing the degradation of their PDIVs and appearances. The results of each test were compared, and conclusions were drawn about each material’s feasibility for use as a dielectric encapsulation material for a power module operating at temperatures exceeding 200 degrees C.