Electronics Cooling Using a Self-Contained, Sub-Cooled Pumped Liquid System

Abstract

Electronic thermal packaging design continues to look for novel solutions for enhancing the performance of microelectronic cooling solutions. Driven by increasing thermal performance requirements, particularly in densely packaged militarized electronic systems and other high density or extreme use products, thermal designers are showing that to achieve the necessary cooling, combinations of existing technologies may offer further enhancement than has already been demonstrated. This paper discusses the performance characteristics of a single phase, pumped liquid cooling system (LCS) employed in cooling microprocessors and considers the effects of including solid state cooling (a.k.a thermoelectric cooling) in conjunction with the pumped liquid system. The thermal performance of a baseline LCS without TEC is compared to the performance of a LCS with a TEC combined with two alternative "flux transformer" heat spreaders. The two alternative flux transformers included a solid copper plate and vapor chamber heat pipe. Each "flux transformer" was sandwiched between the concentrated thermal load of the microprocessor and the TEC. The paper discusses the predicted thermal performance for the various systems as well as presenting experimental results. In demonstration, the experimental results show that the addition of TEC's coupled with the vapor chamber heat pipe "flux transformer" provided the most favorable improvement in system performance over the power dissipation range tested. As the TEC electrical power was increased, the temperature gradient across the TEC's increased reducing their coefficient of performance. Eventually, the combined TEC and vapor chamber heat pipe flux transformer solution matched, and then exceeded the heat sink temperature achievable with a conventional single phase pumped liquid cooling system. For microprocessor and ASIC heat dissipations of up to 175 watts, this particular pumped liquid system incorporating TEC's coupled with a vapor chamber heat pipe flux transformer can significantly reduce processor temperatures.