Polysiloxane-Based Surface Modification of Silica Fillers for Low Stress Underfill

We report a surface modification method to improve the filler-matrix interface in silica-epoxy composites. A double-layer modification scheme was used to coat silica with polysiloxane-based surface modifier molecules. The polysiloxane coating reaction was confirmed by SEM, DSC, and TGA analyses, and the coated silica exhibit good chemical compatibility with the epoxy matrix. The CTE of epoxy composite containing the polysiloxane-modified silica showed an ultra-low value of 29 ppm/K, which was more than 20 ppm/K lower than composites filled with conventionally modified silica. The composites show an increase in Tg, suggesting good polysiloxane-epoxy interfacial properties.