THERMAL PERFORMANCE OF LIQUID SOLDER JOINT BETWEEN METAL FACES

摘要

Large-area metal-to-metal joints are found in the thermal management of power supply electronics. This study explores the use of a liquid phase solder layer (44.7Bi 22.6Pb 19.1In 8.3Sn 5.3Cd, 47℃ melting point) as an interface material for contact conductance enhancement, with the additional constraint that the solidified joint must be easily disassembled. An experimental test joint is constructed using two 76mm by 25mm oxidized 6061-T6 aluminum surfaces with significant overall flatness deviation (22 micron, wavelength comparable to the joint dimensions). Applied pressure is varied over a range of 7000-700000 Pa. The thermal resistance of the test joint is measured in the steady state using standard methods. The heat transfer through the solder layer is studied as a function of average solder thickness,, solder phase (solid to liquid), and applied pressure. An aluminum foil spacer is used as a containment seal. The measured thermal resistance of the test joint, composed of the liquid solder and the aluminum foil seal, is approximately 3-7% of the thermal resistance of dry contact between the aluminum test surfaces in air, at a given applied loading. The thermal resistance of the test joint is found to depend significantly on applied pressure for the solder in both solid and liquid state. Roughly 200 cycles of melting and freezing are found to have negligible effect on the liquid state thermal resistance.