Assessment of encapsulants for high-voltage, high-temperature power electronic packaging

Eight encapsulants with operating temperatures up to 250°C were surveyed for use in planar packages for wide-bandgap dice. Two of the encapsulants failed processability test because they were not able to flow, and another two failed because they induced voids or cracks after curing. The dielectric results of the remaining four encapsulants showed that both dielectric strength and permittivity decreased almost 40% when the temperature was increased to 250°C. As the three encapsulants were used to encapsulate a power module, it was proven that all of them could protect the package from early breakdown caused by the poor dielectric strength of air. The thermal aging test showed that materials were hardened during the aging process, and cracking started in the material matrix. The dielectric strength of the sample would drop 60%-70% to only around 10 kV/mm once cracking occurred.