Novel surface modification of nanosilica for low stress underfill

We report a novel surface modification method to improve the interfacial bonding and compatibility of nanosilica with epoxy matrix. This approach utilized a two-layer modification strategy that not only provides a layer of functional groups at the surface to match the surface energy of nanosilica with epoxy resin, but also generates a large filler-matrix interphase transition region by covalent bonding that enables more efficient CTE reduction. It is found that dispersion of nanosilica is dramatically improved compared to untreated particles. The CTE of nanocomposites containing two-layer modified nanosilica is a 5-15 ppm/K lower than those filled with conventionally modified nanosilica at the similar loadings. Additionally, the nanocomposites developed in this study do not show significant Tg reduction. These results show that our surface modification method is very promising in developing novel nanosilica-based underfills.