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Application of Conduction-Cooled PCBs and Composite Housing Materials in an Aerospace Electronic System
Keywords: Composite, CTE-matched, Conduction-cooled PCB
This presentation will describe development and thermal modeling data for an electronics enclosure, with application to airborne, ground-fixed, ground-mobile, shipboard, and even spaceborne systems, which has been designed with: A. Direct package or die attach of semiconductor devices to mounting locations on a CTE-controlled PCB that incorporates one or more thermal layers manufactured from copper-graphite composite material.(1) Thermal management for these high heat flux devices is obtained by providing a low impedance thermal path to the copper-graphite composite layer within the PCB, which in turn conducts the heat load to the electronic system housing. B. Use of a similar copper-graphite composite to manufacture the housing, providing heat transfer from the PCBs to an ultimate heat sink. The housings also are designed to incorporate copper-diamond composite inserts, cast at specific locations, to which the highest dissipating packaged semiconductor devices are directly attached; these composite inserts isotropically spread and aid in dissipating the high heat load from these discrete devices. Thermal modeling data will be shown which describe the devices in generic form and demonstrate improvements of as much as 10°C in device operating temperature, through the use of CTE-matched thermally conductive composite materials of these types. Comparative data will be shown for the same housing manufactured from Al-6061, as is typically used in electronics systems. Comparative test data for materials is incorporated. The manufacturing process for both composite materials will be described. This presentation follows two previous presentations which outlined the goals and the development processes employed for the graphite composite layers inserted into high-reliability PCBs, designed for industry-standard printed circuit manufacturing equipment. The value of this presentation is to demonstrate practical results achieved following these multiyear thermal materials development programs, as steps towards the elimination of material layers within what have previously been industry-standard types of semiconductor packaging practices. Goals for these development programs include weight reduction, reduced component operating temperatures for improved performance and enhanced reliability, improved CTE matching to the semiconductor die to allow elimination of intermediate package materials to achieve lowered thermal resistances through the final design stack, PCB warpage control, and ultimately lower system Life Cycle Costs by incorporation of commercially available components, materials, and manufacturing processes. Note 1: Presentations in 2011 and 2012 described the materials process development for copper-graphite composites embedded as PCB thermal cores per IPC standards. This presentation introduces the use of PCBs containing such thermal cores and the use of diamond composite inserts within an innovative system and enclosure design supporting high heat flux GaN RF semiconductors, to improve heat transfer, provide CTE matching, and reduce weight for a proposed aerospace system design. Materials described in this presentation are suitable to meet current EU legislative requirements.
David L Saums, Principal
Amesbury, MA

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