METALLIC COATINGS FOR ENHANCEMENT OF THERMAL CONTACT CONDUCTANCE

The reliability of standard electronic modules may be improved by decreasing overall module temperature. This May be accomplished by enhancing the thermal contact conductance at the interface between the module frame guide rib and the card rail to which the module is clamped. Some metallic coatings, when applied to the card rail, would deform under load, increasing the contact area and associated conductance. This investigation evaluates the enhancements in thermal conductance afforded by vapor deposited silver and gold coatings. Experimental thermal conductance measurements were made for anodized aluminum 6101-T6 and electroless nickel-plated copper C11000-H03 card materials to the aluminum A356-T61 rail material. Conductance values for the electroless nickel-plated copper junction ranged from 600 to 2800 W/m2K (105.7-493.1 Btu/h ft2-degrees-F), and those for the anodized aluminum junction ranged from 25 to 91 W/M2K (4.4-16 Btu/h ft2-degrees-F) for contact pressures of 0.172-0.862 MPa (25-125 psi) and mean junction temperatures of 20-100-degrees-C (68-212-degrees-F). Experimental thermal conductance values of vapor deposited silver- and gold-coated aluminum A356-T61 rail surfaces indicate thermal enhancements of 1.25-2.19 for the electroless nickel-plated copper junctions and 1.79-3.41 for the anodized aluminum junctions. The silver and gold coatings provide significant thermal enhancement; however, these coating-substrate combinations are susceptible to galvanic corrosion under some conditions.