Study on mono-dispersed nano-size silica by surface modification for underfill applications

In order to improve the rheological behavior of the nanosilica composite no-flow underfill, filler surface treatment using silane coupling agents was investigated to reduce the filler–filler interaction and to achieve the mono-dispersity of the nanosilica in the underfill resin. The experimental conditions of the surface treatment were investigated in a design of experiment (DOE) in terms of the pre-treatment methods, coupling agent types, concentrations, and treatment durations. The particle dispersion after treatment was evaluated by the laser particle analyzer and the transmission electron microscopy (TEM). A mono-dispersed nanosilica solution in the polar medium was achieved using optimal experimental condition. The surface chemistry of the nanosilica was studied using Fourier transformed infrared spectroscopy (FTIR). The wettability of underfill resin and water on the silane treated glass slides was studied using a goniometer. Based on the investigations, the silane-treated nanosilica fillers were incorporated into an underfill resin to formulate a nanocomposite no-flow underfill. It was found that the proper filler treatment could significantly reduce the viscosity of the nanocomposite. The viscosity of nanosilica/epoxy underfill is significantly influenced by the surface chemistry of filler. The nanosilica modified by amine-type coupling agent is even worse than the unmodified nanosilica in terms of compatibility with epoxy underfill and viscosity.