Underfill materials have been widely used to improve the reliability of IC packages. Recently there is an increasingly demand for low stress underfill with low CTE, low modulus and good flowablity. In this report, surface modified nanosilica and polyhedral oligomeric silsesquioxanes (POSS) are used as potential CTE reducing fillers. The dispersion of these fillers in epoxy resin was studied by analyzing the optical properties, curing behaviors and glass transition temperature. It is found that compared with modified nanosilica, POSS is more compatible with the epoxy polymer matrix possibly due to molecular level mixing and chemical bonding.
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