Application of Low Melt Alloys as Compliant Thermal Interface Materials: A Study of Performance and Degradation under Thermal Duress

Abstract

Thermal interface materials (TIMs) are a crucial part of thermal management in micro-electronics and often can account for a significant portion of the overall thermal budget. Generally, materials with high thermal conductivities and low thermal resistances are ideal candidates for the application as a TIM. Low melt alloys (LMAs) are promising TIM candidate materials due their inherent high thermal conductivities, good wetting properties, and their mechanical compliance addressing the coefficient of thermal expansion mismatch concerns. In this work, the interstitial thermal performance of three different alloys, alloy 1 (75.5 Ga, 24.5 In, melting point (MP): 16oC), alloy 2 (100 Ga, MP: 30oC), and alloy 3 (51 In, 32.5 Bi, 16.5 Sn, MP: 60oC) has been tested using widely accepted ASTM D-5470 standard methodology. The thermal performance of LMAs was measured in terms of thermal resistance (temperature drop across the LMA joint per unit heat flux). The effect of interfacial pressure on the thermal resistance was also investigated within the range of 34.5 to 345 kPa. The reliability of LMA interfaces was investigated in terms of high temperature aging (130oC), thermal cycling (-40oC to +80oC and -40oC to +125 oC), and highly accelerated stress testing (85oC and 85% relative humidity). The interactions of alloys with various substrate materials (copper, nickel, and tungsten) were studied by coating a thin layer of nickel (about 5 µm) and a thin layer of tungsten (about 2 µm) onto the bare copper surfaces comprising the interfacial joint. Finally, to compare the performance of LMAs, some commercial TIMs (greases, phase change materials, and thermal pads) were also tested using the same methodology and apparatus.