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Design, Manufacturing and Reliability Tests of a Wide AlSi Fully Hermetic Package for Space Applications
Keywords: Aluminium Silicon, Hermetic packaging, Space applications
Microwave products for space applications like receivers and converters need more and more functionalities. But, this is synonym to very large package which can lead, for a standard Kovar® based solution, weight increase and thermal management problem. Choosing another package material is not an easy puzzle regarding space specifications required : lightweight, high thermal conductivity for the management of heat dissipation by conduction, easy to machine and to plate, thermal expansion coefficient close to components for the reliability of the assembly, embed RF and DC connectors, hermeticity. Unlike fully metallic packages (Aluminium, Titanium, …), solutions based on a composite approach are attractive. Among the aluminium alloys, AlSi alloy is a very interesting material : it can be machined from the block, presents no plating issue and has been tested internally fully hermetic. A 93mm x 43mm package has been designed and manufactured, based on : a fully machined AlSi body, Nickel/Gold plated, four K connectors designed for applications up to 30GHz with alumina substrates directly connected to the microwave pin, one DC connector with 8 pins, six mechanical fasteners for assembly to the next level, thick metal ring is brazed on top of the peripheral AlSi wall to be compatible with the seam welding process. Thermal analysis show remarkable results : only 3.2°C thermal gradient within the package and 10°C margin on junction temperature for most critical active components (more than 20°C and no margin respectively for a Kovar® based version). Last very smart result is the total weight : only 32g ! To evaluate the reliability towards space requirements, four test files have been defined : mechanical tests, thermal cycles, RGA tests and isotherm storage.
Philippe Monfraix, Engineer
Alcatel Alenia Space
Toulouse BP 33787,
France


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