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

Seven encapsulants with operating temperature up to 250 °C 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 (T_g) 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 °C. 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.