Toughening Underfills by Stress-Absorbing Core-Shell Fillers

The application of electronic devices in harsh environments, such as automotive environment, necessitates that packaging material meet stringent reliability requirements. Underfills not only need to redistribute thermomechanical stress across solder joints, but also should be sufficiently toughened in order to resist crack propagations due to mechanical vibrations and thermomechanical stress expected of various driving conditions. Toughening additives in underfills often result in unfavorable changes in thermomechanical properties of the underfill. In this report, rigid nano-silica fillers are rubberized to form core-shell filler particles. The core-shell fillers are incorporated into epoxy, and thermomechanical properties, and curing and fracture behaviors of the nanocomposites are reported.