Consolidation of Nano-Composites for Thermal Management

Abstract

This paper describes the consolidation of ultra fine (“nano”) grained W-Cu and Mo-Cu composite materials used as thermal management substrates in microelectronics applications. Both W/Cu and Mo/Cu composites having W and Mo dispersed phases in the size range of 300-700 nm and excellent microstructural homogeneity were synthesized by chemical precursor techniques. Consolidation to high densities (96 - 99% of theoretical) was accomplished by the standard commercial practice of cold pressing followed by pressureless sintering and also by rapid consolidation at high pressures. The high pressure short duration consolidation techniques allowed the benefits of nano-powders to be preserved by minimizing grain growth during consolidation. The use of these methods provides alternatives to the costly and tedious techniques of infiltration of a refractory metal skeleton or powder mixing. Both of the latter approaches are subject to local inhomogeneities and variations in thermal properties. Thermal conductivity and thermal expansion values of 220 W/mK (extrapolated from 86% to 100% density) and 10.5 ppm/°C for90W/10Cu (by weight) and 141 W7 mK and 10.4 ppmTC respectively for 90Mo/10Cu (by weight) compositions, were obtained at room temperature. Characterization was accomplished by X-ray diffraction and scanning electron microscopy (SEM) supplemented by energy dispersive spectroscopy (EDAX/ EDS)