Enhanced Thermal Conductivity of the Underfill Materials Using Insulated Core/shell Filler Particles for High Performance Flip Chip Applications

In this study, we investigated the correlation between thermal conductivity and insulative shell thickness of SiO2 coated Ag (SCA) particles for the thermal filler material in the high performance underfill with focus on improved thermal conductivity. We synthesized the coating of various SiO2 insulation layer on the surface of spherical Ag powder and used them for underfill material formulation to achieve >2 W/mK grade high thermal conductivity capillary underfill. In order to achieve powder distribution with gaussian curve additional spherical alumina was mixed with SCA powder. This mixture blended with epoxy based multifunctional resin matrix. Trend profiling of thermal conductivity and electrical resistivity as a function of SiO2 shell thickness were performed. In addition, correlation of thermal conductivity and viscosity were investigated. Resulting capillary underfill with SCA powders showed 2.14 W/mK thermal conductivity and passed thermal cycling test corresponding to JEDEC LEVEL 3.