Development of a Thermal Metrology Standard for Evaluation of Cold Plate Thermal Resistance as a Performance Metric

Abstract

A significant number of investigations have been performed to develop and optimize cold plates for direct-to-chip cooling of processor packages. Many investigations have reported computational simulations using commercially available computational fluid dynamic tools that are compared to experimental data. Generally, the simulations and experimental data are in qualitative agreement but often not in quantitative agreement. Frequently, the experimental characterizations have high experimental uncertainty. In this study, extensive experimental evaluations are used to demonstrate the errors in experimental thermal measurements and the experimental artifacts during testing that lead to unacceptable inconsistency and uncertainty in the reported thermal resistance. By comparing experimental thermal data, such as the temperature at multiple positions on the processor lid, and using that data to extract a meaningful measure of thermal resistance, it is shown that the data uncertainty and inconsistency are primarily due to three factors: (1) inconsistency in the thermal boundary condition supplied by the thermal test vehicle (TTV) to the cold plate, (2) errors in the measurement and interpretation of the surface temperature of a solid surface, such as the heated lid surface, and (3) errors introduced by improper contact between cold plate and TTV. A standard thermal test vehicle (STTV) was engineered and used to provide reproducible thermal boundary conditions to the cold plate. An uncertainty analysis was performed in order to discriminate between the sources of inconsistencies in the reporting of thermal resistance, including parameters such as mechanical load distribution, methods for measuring the cold plate base, and TTV surface temperatures. A critical analysis of the classical thermal resistance definition was performed to emphasize its shortcomings for evaluating the performance of a cold plate. It is shown that the thermal resistance of cold plates based on heat exchanger theory better captures the physics of the heat transfer process when cold plates operate at high thermodynamic effectiveness.