Enhancing thermal performance in embedded computing for ruggedized military and avionics applications

Embedded computing systems used in many military and avionics applications are trending toward higher heat fluxes, and as a result performance is being hindered by thermal limitations. This is intensified by the high ambient conditions experience by today's modern warfighter. In many applications liquid cooling is replacing air flow through chassis for both thermal and environmental benefits. Although liquid cooled solutions prevent contaminates from being introduced into the electronics cage, it does introduce leak risks, particularl y with line replaceable units that are consistently swapped in and out of the card cage. For this reason it's preferred to attach the liquid cooling loop externally to the card cage and often at the base. As a result, there are several components in the thermal path that contribute to the overall thermal resistance including the thermal interface material, conduction card, wedge lock interface, and card cage wall. This paper outlines a series of passive thermal improvements which are easily integrated into legacy, or existing, systems and can provide a 3–4x increase in dissipated power. The first area for improvement is the conduction card. Heat pipes may be incorporated into conventional conduction cards to significantly reduce thermal gradients as heat is transferred from the electronics to the wedge lock connection at the card cage wall. Likewise, heat pipes may also be used to enhance the thermal performance of the card cage wall by embedding them directly into the chassis itself, or by bolting on heat pipe embedded heat spreaders. Both solutions are particularly amenable to retrofitting and new designs. Embedding heat pipes within the conduction cards and cage provides significantly higher effective thermal conductivity with minimal size, weight, and cost consequences, especially when compared to copper and annealed pyrolytic graphite alternatives.