Reactive infiltration in fabricating silicon carbide composites for electronic packaging

The silicon carbide (SiC) composite is a promising material to improve thermal dissipation and thermal expansion matching for electronic packaging, but its wide application has been greatly hindered by the high fabrication cost. To address this cost issue, two new reactive infiltration methods have been proposed and developed to fabricate SiC composite in a net-shape manner. They are Method 1--locally magnesium-enhanced infiltration and Method 2--globally carbon-enhanced infiltration.; In Method 1, a magnesium wetting agent was strategically inserted at the interface between SiC powder and Al-Si alloy. The molten Al-Si alloy was assisted by chemical reaction to infiltrate into the porous SiC powder in an inert atmosphere sealed in a quartz tube or a steel cup. The infiltration kinetics was characterized by measuring the infiltration weight gain with respect to time. It was found that the infiltration kinetics could be divided into three stages: infiltration initiation, rapid infiltration, and slow infiltration, and most of the weight gain occurred in the rapid infiltration stage. The rapid infiltration was due to the magnesium-silicon oxide reaction and the magnesium accumulation at the infiltration front. Modeling of the infiltration kinetics showed the magnesium dilution increased the dynamic contact angle, which in turn decreased the infiltration rate. The SiC oxidation, Mg content and temperature were shown to be important factors affecting the infiltration.; In Method 2, a carbon wetting agent is coated globally on every SiC particle. To accomplish this coating, a slip casting, drying, curing and carbonization process was developed. A crucibleless infiltration method was designed to fabricate SiC composites in an open atmosphere protected by nitrogen. The temperature change of SiC preform during infiltration was monitored to determine the infiltration kinetics. The silicon-carbon reaction was found to create a spontaneous infiltration of molten Si or molten Al-Si into SiC preforms. The key infiltration parameters were investigated, and the dimensional and surface finish retentions of SiC preforms during infiltration were also evaluated.; Based on the experiments with the two methods, three key steps for reactive infiltration have been identified. They are the direct contact of liquid Al or liquid Si with solid SiC, the initiation of chemical reaction at the liquid-solid interface (the infiltration front) and the maintenance of a complete wetting during infiltration. Oxidation of liquid metal is the major barrier to the direct liquid-solid contact. The application of a wetting agent was found very effective not only to kill the oxygen but also to initiate the chemical reaction and induce a complete wetting.; Finally the microstructure of the as-fabricated composites was analyzed, and their mechanical and thermal properties were characterized by testing and modeling.