A High-Pressure Apparatus for the Characterization of Thermal Interface Materials

An apparatus has been designed and constructed to characterize thermal interface materials with unprecedented precision and accuracy. The design of the apparatus is based upon a popular implementation of ASTM D5470 where well-characterized meter bars are used to extrapolate surface temperatures and measure heat flux through the sample under test. Measurements of thermal resistance, effective thermal conductivity, and electrical resistance can be made simultaneously as functions of pressure or sample thickness. This apparatus is unique in that it takes advantage of small, well-calibrated thermistors for precise temperature measurements (±0.001 K) and incorporates simultaneous measurement of electrical resistance of the sample. Careful implementation of instrumentation to measure thickness and force also contribute to a low overall uncertainty. Finally, a robust error analysis provides uncertainties for all measured and calculated quantities. Baseline tests were performed to demonstrate the sensitivity and precision of the apparatus by measuring the contact resistance of the meter bars in contact with each other as representative low specific thermal resistance cases. A minimum specific thermal resistance of 4.68 × 10-6 m2•K/W was measured with an uncertainty of 2.7% using a heat transfer rate of 16.8 W. Additionally, example measurements were performed for a commercially available, graphite thermal interface material that demonstrate the relationship between thermal and electrical contact resistance.