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Fabrication and Qualification of Aluminum-Silicon Carrier Plates for Space Applications

Alloys of Aluminum and Silicon [AlSi aka Controlled Expansion (CE) alloys] are engineered to suit co-efficient of thermal expansion (CTE) of advanced materials used in various industries. CTE of CE alloys can be tuned between 7.5 and 20 ppm/°C by varying proportions of major constituents viz. Aluminum and Silicon. One such composition is CE9F with CTE of 9 ppm/°C, making it suitable as carrier plate in Microwave Integrated Circuits (MIC) for Space applications. Compared to Kovar alloys being used at present as MIC carrier plates, CE alloys offer advantages of lower weight and higher thermal conductivity. However, their machining and plating is relatively difficult. In this paper, we report machining of CE9F alloy plates by using Electrostatic Discharge machining (EDM) method, gold plating on the machined plates of CE9F alloys, and attachment of alumina substrates on the alloys. As certain difficulties were faced during these phases, machined carrier plates were procured and qualification samples were realized. The samples are subjected to various tests to evaluate its performance. After successful completion of all these tests, the material (CE9F alloy) is qualified for its applications in ISRO's Space programmes.