Characterization of Encapsulants for High-Voltage High-Temperature Power Electronic Packaging

Abstract

Seven encapsulants with operating temperature up to 250 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> are surveyed for possible use in high-temperature high-power planar packages. Processability is assessed by studying the flow fronts and the cured properties of the surveyed materials between paralleled plates. Material B failed in the flow test because it dried out in seconds. Materials A, C, and D failed the curability test because A and C showed volume shrinkage during curing, while D cracked after curing owing to its brittle nature. It is found that elastic materials that usually correspond to low glass transition temperatures <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(T_{g})$</tex> </formula> tend to perform better with regard to large-area planar-structure packages. Materials E–G are confirmed to be comparatively stable with respect to temperature, and both dielectric strength and dielectric permittivity decrease by about 40 and 30%, respectively, as the temperature is increased from 25 to 250 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> . The thermal aging test show that the materials harden during the aging process. Meanwhile, cracking starts in the material matrix. The dielectric strength of the sample drops by 60–70% to only around 10 kV/mm once cracking occurs.