Design considerations for a miniaturized TIM tester with extremely high measurement resolution

Abstract

This work describes relevant design considerations for the fabrication of a miniaturized thermal interface material characterization instrument that is capable of resolving interfacial thermal resistances (Rt) below 1 mm2.K/W. Leveraging previous work (Warzoha et al., 2017, Smith et al. 2016), the authors propose a reduction in the length scale of the primary heat meter bars to below 4 mm in order to sufficiently increase the temperature difference across the interface, thereby reducing the measurement uncertainty of Rt across high-performance materials. The analytical uncertainty analysis takes advantage of an increase in the number of temperature measurements that can be made across the length of each bar via infrared microscopy. In a preliminary numerical analysis, we find that extreme care must be taken to apply and remove heat uniformly from the end points of each bar, particularly as the length of the bar is reduced below 4 mm. To do this, longitudinal fins are directly integrated into the bottom heat meter bar assembly and are immersed in a heat transfer fluid that is advected within a custom cold plate assembly. We conduct a parametric study to determine the linearity of the thermal gradient along the length of each heat meter bar, which in turn provides us with an upper limit for the number of temperature measurements that can be made via infrared microscopy and therefore the minimum achievable measurement of Rt. Finally, we use this information to design a more suitable lower heat meter bar cooling technique for measuring the thermal resistance across a sintered silver-copper interface with an expected value of Rt = 0.1 mm2.K/W. To do this, we find it necessary to transition from a heat sink cooling mechanism to the use of jet impingement for heat dissipation at the bottom of the lower heat meter bar.