Fining Technology of Al-50% Si Powder - A Material for Hermetically-Sealed Casing of Multichip Subsystem

Abstract

A material for hermetically-sealed casing of multichip subsystem needs the characteristics such as high thermal conductivity, low density, low thermal expansion coefficient, automatic sealing, simplicity and convenience of subsequent application workmanship .The material that is mostly suitable to be used is Al-50% Si compound material prepared by the spray deposition method. The powder metallurgy process (PM) was studied for preparing the Al-Si compound material in this paper.The median particle size of the Al-Si powder must be less than 5μm. The ball-milling technique was adopted to reduce the particle size of Al-Si powder. The result shows: the change in ball-milling speed affects the particle size of Al-50 Si powder greatly and the increase of rotating speed can facilitate powder fining and homogenization. By determining other process parameters, it is found the ball-milling time is the major factor affecting the particle size. As the ball-milling time extends, the particle size reduces. Compared to the dry milling process, the alcohol wet milling process can improve the fine powder output, reduce particle size distribution range, avoid powder agglomeration and get good homogenization. Less particle size also result in higher density and less Si phase particle size in Al-50 Si compound. In the following condition, namely the ratio of grinding media to material is 5:1, the rotating speed 350 rpm and ball-milling time 20 hrs, the median particle size of Al-50 Si powder is 4.64μm.