Thermo-mechanical properties of epoxy formulations with low glass transition temperatures

In microelectronics industry, epoxy is widely used as molding compounds, underfill encapsulants, and coatings for the protection of integrated circuits. It is possible to formulate epoxy materials with properties ranging from extreme flexibility to high strength and hardness. This paper presents the characterization of thermo-mechanical properties of epoxy formulations with low glass transition temperatures. Nine different formulations were prepared with different epoxy resins 1,4-butanediol diglycidyl ether (BDE), neopentyl glycol diglycidyl ether (NGDE), and diglycidyl 1,2-cyclohexanedicarboxylate (DCHC), cured with methylhexahydrophthalic anhydride (MHHPA) as hardener and different catalysts tertiary amine dimethylbenzylamine (DMBA), imidazole derivative 1-cyanoethyl-2-ethyl-4-methylimidazole (2E4MZ-CN), and metal chelate cobalt(II) acetylacetonate (CAA). Differential scanning calorimeter (DSC) was used to investigate the curing properties. The thermomechanical properties were characterized before and after moisture absorption. The glass transition temperature increases in the following order: NGDE<BDE<DCHC. These formulations showed higher moisture pickup than epoxy formulation based on bisphenol-A type epoxy resin. Significant decrease in glass transition temperature was observed after moisture absorption. The higher moisture pickup, the greater reduction in glass transition temperature. Loss factor versus temperature of moisture absorbed samples showed new peaks, indicating the interaction between the absorbed moisture and the polymer matrix.