Key factor analysis of nano silica on the dispersion in underfill

The miniaturization of the electronic devices requires smaller packaged chips, and the distance between the chip and the substrate becomes smaller, which make it necessary to introduce the nano-silica in the filler for advanced packaging. However, the nano-silica is easy to settle in the underfill and block the packing, because it tends to agglomerate due to its large specific area. Unfortunately, the addition of nano-silica in the underfill could also largely improve the viscosity, giving rise to the unacceptable low flowability. Therefore, it is necessary to investigate the key factors that could influence the dispersion of nano-silica in the epoxy resin. In this paper, the time domain nuclear magnetic resonance spectrometer (NMR) technique was used to study the dispersion of silica fillers. This research studied the nano-silica particle size impact and the surface modification impact on the dispersion of nano-silica in epoxy resin. The shape and size distribution of three types of particles were characterized before studying the relaxation property. The three types of particles were then modified with silane coupling agents. The results of time domain NMR relaxation rate showed that the surface modified nano-silica particles have lower relaxation time, meaning the better dispersity in the epoxy. Meanwhile, after surface modification, larger fillers obtained better dispersity compared with smaller fillers, which result in the uniform dispersion in the resin.