Surface modification of nano-size SiO2 filler for flip chip underfill applications

Nano-sized spherical SiO
₂
-filled polymer-based underfill play an important role in improving the reliability of high-density flip-chip packaging. However, how to allow extremely high filler loading while maintaining a low viscosity and meanwhile how to achieve desired coefficient of thermal expansion (CTE) with lower filler loading are two major challenges due to the serious agglomeration of nanofillers in the polymer matrix. Currently, the study on rheological and thermal expansion behavior of composites mainly focuses on the effect of morphology, content, size and distribution of fillers, while is relatively few from the aspects of filler surface design and interface tailoring of nanocomposite. Therefore, in our work, we attempt to conduct surface modification of SiO
₂
nanofiller with Bis-F epoxy resin and systematically investigate the effect of surface chemistry of filler on the rheological and thermal expansion properties. The results showed that using Bis-F modified SiO
₂
as fillers, the viscosity of amine system was decreased, while the anhydride system increased, which was probably due to the competition ability between two factors associated with the improved compatibility and increased reactivity. However, there was no obvious contribution to the CTE reduction from filler surface modification, which probably due to the low grafting density of epoxy on the filler. Therefore, how to rationally design surface of nanofiller and further optimization of a comprehensive performance of polymer based packaging materials should be carefully considered in future work.