Active coolant flow control for energy-efficient integrated package level micro-jet cooling

Liquid cooling is a promising technique for the cooling of high-performance and high-power applications. Typical liquid cooling solutions consists of a separate cooling unit with many parallel micro-scale channels, that is mounted on the chip using a thermal interface material as adhesive. For high performance liquid cooling solutions, this thermal interface material represents the thermal bottleneck and prevents boosting the power level for future applications. To limit the operating temperatures in electronic chip packages, the thermal resistance of these interface materials should be reduced or ideally, eliminated. In recent years, a package level integrated jet impingement based liquid cooling solution that delivers the liquid coolant cooling directly on the chip backside and avoids the use of the thermal interface material had been developed. The liquid coolant is ejected on the chip surface through an array of parallel vertical micro-jets. The cooling solution, fabricated using low-cost plastic fabrication techniques, demonstrates a high thermal performance, good temperature uniformity and a reduction in cooler size while it only requires a low pumping power for the coolant flow circulation. To increase the number of application options for this promising cooling method, we want to introduce active control of the flow rate in the individual liquid jets to match the temporal and spatial coolant flow rate distribution with the heat load of the chip and to improve the cooler design in order to reduce the cooler drop and improve the flow and temperature distribution. The objective of this PhD is to develop an active flow control actuation method and control strategy to control the flow rate in the jets depending on the local cooling need in order to maintain a constant chip temperature and to improve the energy efficiency of the cooler and the closed loop liquid cooling system. The design of the actuation mechanism should be compact to be integrated in the package level cooler. In this PhD work, the following activities are foreseen: 1) Modeling of the impact of the controllable flow rate. This task involves the conjugate heat transfer and flow CFD simulation of the flow distribution in the cooler, the pressure drop over the cooler and the resulting temperature distribution in the chip. 2) Development of an active flow control actuation method and control strategy to control the flow rate in the jets depending on the local cooling need in order to maintain a constant chip temperature and to improve the energy efficiency of the cooler and the closed loop liquid cooling system. The design of the actuation mechanism should be compact to be integrated in the package level cooler. 3) Demonstration of flow control on an advanced thermal test chip for the model validation and the experimental characterization of the cooler. 4) Application of topology optimization techniques for the complex internal geometry of the chip package level impingement cooler. The objective is to fabricate the improved cooler geometry using high-resolution 3D printing and to characterize the thermal performance of the cooler using imec’s high resolution thermal test chip.