Experimental Method to Measure High-Temperature Hygroscopic Swelling in Epoxy Mold Compounds and Dielectric Build-Up Films

In this study, high-temperature hygroscopic swelling characterization of different epoxy mold compounds (EMCs) and dielectric build-up films (DBFs) were analyzed using an experimental technique. The approach maintains specimens in a saturated state using a high-pressure enclosure, while digital image correlation (DIC) was used to measure in situ strain change in the specimen due to hygrothermal expansion. Hygroscopic swelling strain is obtained by removing the thermal strain component. This enables swelling characterization measurements above the temperature and humidity capability of typical commercial instruments. The results showed that moisture induced swelling is significant compared with thermal expansion and increases significantly with temperature above the glass transition temperature (T_g). EMCs were found to absorb more moisture and swell more compared to DBFs with comparable properties. The coefficient of hygroscopic swelling (CHS) for DBFs and EMCs was quite similarly low at low temperatures, but for EMCs, the CHS increased more at high temperatures. Results are compared against analytical solutions, other measurement methods, and published data.