(A) study on the thermal properties of underfill in flip-chip package

Abstract

Flip-chip technology has been a promising candidate for microelectronics in the next generation. In most of the microelectronic components including flip chip, there were many polymer composite materials having low thermal conductivities, such as 0.2 W/mK of epoxy. It is very important to improve the thermal properties of those polymer composites in the high integration electronic components. Underfill is an important part of the flip-chip package and is composed of epoxy polymer and the ceramic fillers. In this study, we investigated viscosity, coefficient of thermal expansion (CTE), density, thermal diffusivity, heat capacity and thermal conductivity of the underfills with various fillers. Selected filler materials were silica, alumina, BN, and diamond (thermal conductivity ; 1.5, 36, 300, and 2000 W/mK). Thermal conductivity of the underfill without filler was about 0.237 W/mK at 25℃, and increased to about 0.253 W/mK at 55℃. Underfill with diamond 60wt% filler showed the highest thermal conductivity of 1.19W/mK at 55℃. The effect of filler size was studied by using various size of spherical shape silica. For underfills having same filler content, CTE increased with increasing filler size due to reduce interphase area between the fillers and the resin compound. The underfill with larger filler size turned out to be filled in broader area because of increased surface tension and decreased viscosity of the underfill. Thermal conductivities of the underfills studied showed similar values, independent of filler size. A flip-chip package was fabricated to measure temperature distribution of the package. The package consisted of diode temperature sensor array (DTSA) chip on printed circuit board (PCB). The gap between the chip and the PCB was filled with the underfill materials. Underfill was loaded with various fillers such as silica, alumina, and diamond. The conotent of the fillers was 30wt% or 50wt%. To investigate temperature distributions of a DTSA, 0.8...