Thermal Characterization of Al-Si Materials Prepared by Die Casting Method

Abstract

Recently heat spreader becomes more important for the heat diffusion of a micro processor unit (MPU). Physically, it needs a material with both low thermal expansion a and high thermal conductivity K. Although Cu-W, AIN and Al-SiC have hitherto been studied exhaustively as materials suitable for application in various heat spreaders, these materials have been limited to special uses because of a high price resulting from the complicated fabrication processes. Until now the study of heat spreader has hardly been made on Al-Si system, because this material tends to become more brittle and to make the fabrication more difficult as Si content increases, particularly in the composition range available for heat spreaders. Although there are such troublesome problems in Al-Si, we investigated both thermal conductivity K and thermal expansion a of Al-Si materials prepared by the conventional casting method. As a result, the Al-50Si material was found to have values of K = 150 W/m ⋅K and a =10 x10^-6/K, respectively, which satisfy the thermal characterization required for heat spreaders. However the brittle Si phase in Al-50Si was needled to a length of about 0.5 mm, resulting in a marked lowering of tenacity. For this reason, the die casting method was employed to control the grain size, so that so precipitated Si phases became smaller needles of a length of approximately 30μm, leading to the effective improvement of tenacity.