Polyurethane-modified epoxy resin: cure and mechanical properties

While the more common method of inorganic filler incorporation to reduce coefficient of thermal expansion (CTE) of underfill (UF) materials has reached its threshold, this paper describes an alternative route of chemically incorporating polyurethane precursor (PU-precursor) as a pre-cross-linker to a conventional UF epoxy system. Resultant system was characterized to understand the effect of incorporated PU on its cure temperature, glass transition temperature (Tg), modulus, and surface wetting. The results demonstrate that the less than 5% of incorporated PU is capable of affecting the system CTE and modulus, while surface wetting is improved and cure onset occurs below 100degC.