Squeeze Flow and Thermal Resistance Characterization of Thermal Interface Materials

Thermal behavior of thermal interface materials (TIMs) has been widely studied and reported in the literature. The majority of these studies focus on the characterization of materials at pristine conditions. However, these materials undergo various thermo-mechanical stresses over the long duration of their application. Hence, there is a need to quantify the degradation of performance for optimizing the design and selection of such materials. In order to study degradation, it is critical to identify the mechanical property which ‘degrades'. In this work, the non-linear, rate dependent viscous behavior of TIMs such as thermal greases is modeled using the Herschel-Bulkley flow model. A custom-built parallel-plate rheometer is used to simultaneously characterize the thermal and flow behavior. The thermal conductivity measurement adheres to the ASTM-D5470 standard. A series of experiments at constant squeeze velocities are performed to extract the parameters describing the flow behavior. A three-parameter fit was performed using the numerical solution of Hershel-Bulkley model developed by Covey and Stanmore. Commercially available thermal greases were initially characterized at the pristine condition and also subjected to in-situ thermal baking. Velocity controlled squeeze experiments and thermal resistance characterization experiments are performed to characterize the mechanical and thermal behavior of TIMs.