Study on the effects of surface hydroxyl of silica fillers on the mechanical properties of underfills

As the flip-chip bump becomes smaller, the filler in underfill becomes nano-sized silica particles. However, there are few studies on the influence of the surface chemical state of silica on the mechanical properties of underfills. To explore this point, we prepared calcined and uncalcined SiO 2 nanoparticles, respectively, and then used them to fabricate two types of epoxy-based composites. And we compared the mechanical and thermal properties of two different composite materials. We found that the -OH-free SiO 2 filled composite materials have better properties. The SEM image of the cross-section shows that the compatibility of -OH-free SiO 2 with epoxy resin matrix is better. Therefore, the surface hydroxyl groups of SiO 2 have a deteriorated effect on the reliability of the underfills. Finally, the reasons were explored through section analysis and thermodynamic analysis.