Effect of filler, toughening agent and coupling agent on the curing shrinkage of epoxy-based underfills

Epoxy-based underfills were commonly used in microelectronic packages to re-distribute stress in solder bumps induced by the thermal mismatch. In this case, the volume shrinkage caused by the epoxy has an important effect on the internal stress of encapsulation, which is often related to the reliability problems, such as deformation warpage and fracture. In our work, an improved real-time monitoring method was conducted to measure the curing shrinkage of different underfills. The influence of the filler content, particle size, types of toughening agent and coupling agent on the curing shrinkage of composites were systematically investigated. The crosslinking density of composites was determined by swelling degree, and the relationships between crosslinking density and shrinkage were also evaluated. Our experimental results explicates that the shrinkage of epoxy-based underfills has positive correlation with the cross-linking density of polymer matrix.