Comparative study of thermally conductive fillers in underfill for the electronic components

General underfill for the flip-chip package had a low thermal conductivity of about 0.2 W/mK. Thermal properties of underfill were measured with various fillers, such as silica, alumina, boron nitride, (BN) and diamond. Coefficient of thermal expansion (CTE) was changed by filler content and CTE of silica 60 wt.% was 28 ppm; BN 30 wt.%, 25 ppm; alumina 60 wt.%, 39 ppm; and diamond 60 wt.%, 24 ppm. The viscosity of underfill was measured with the cone and plate rheometer. Thermal diffusivity was measured with the laser flash method. Diamond filler loaded underfill showed the highest thermal conductivity 60 wt.%; 1.17 W/mK at 55 °C. Thermal conductivity of underfill was changed with a transition of heat capacity by the temperature increment in same filler content. In case of different filler content, thermal conductivity was changed with a transition of the thermal diffusivity.