高功率密度芯片微流道冷却的基础研究

With the rapid exponential growth of integrated level, the power dissipation per unit area of chip keeps increasing sharply. To reduce the Signal Noise Ratio (SNR) of electronics and protect them from performance degradation and package failure, it is necessary to implement a cooling process to efficiently lower the temperature of the integrated circuit. In all of cooling modes, the microchannel cooling method with a microchannel heat sink bonded on a silicon wafer, has greater potential because of the low thermal resistance, high cooling efficiency and easy integration with chip. This project focus on systematic and synthetical investigation on the characteristics of microchannels cooling to the high power density chips, which includes enhancing the heat transfer capability by using microchannels, reducing the flow resistance and decreasing the thermal stress. The main contents are as following: numerically and experimentally study the effects of microchannel geometry, cooling medium and microchannel material on the characteristics of fluid flow and heat transfer in microscale; experimentally measure the flow field transition and the fluid phase change by utilizing visualization techniques; numerically and experimentally study the flow resistance and heat transfer by using nanofluids with drag reducing agent (DRA) in microchannles; experimentally study of the characteristics of the drag reduction on super-hydrophobic surfaces; numerically study of the coupling problems between the thermal stress, fluid flow and heat transfer in microscale; finally, design and optimize a microchannel heat sink for high power density chips to achieve the target of chips cooling while maintain chips safe. By using both numerical analysis and experimental investigations, this work is expected to deeply understand the technical barrier existing in high power density chips cooling, and provides apprehensive references for practical producing in industries.

随着芯片集成度的指数式增长，单位面积上的功耗也急剧增加。为了降低器件的信噪比，防止性能退化和封装失效，必须要对集成电路进行有效地冷却。其中，硅片键合微流道冷却模式具有热阻低、冷却效率高、易于芯片集成等特点，具有较大的发展潜力。本项目针对硅片键合微流道冷却模式，从"微流道低压降强化换热"、"微流道流动减阻"及"降低微尺度热应力"三个方面对高功率密度芯片微流道冷却进行系统综合的数值及实验研究。研究包括：数值及实验研究流道几何特性、冷却介质以及热沉材料等对微流道内流动与换热特性的影响；对流动转捩点及相变流动特点进行可视化测量；数值及实验研究电场对纳米流体及减阻溶剂在微流道内流动减阻及换热的影响；实验研究超疏水表面对微流道流动减阻的影响；数值研究流动换热与芯片热应力的关系；最后以芯片冷却及安全为指标设计并优化适用于高功率密度芯片的微流道冷却方案。为解决高功率密度芯片冷却提供理论指导。

随着芯片集成度的指数式增长，单位面积上的功耗也急剧增加。为了降低器件的信噪比和封装失效，必须要对集成电路进行有效地冷却。微流道冷却模式因具有热阻低、冷却效率高、易于芯片集成等特点，具有较大的发展潜力。本项目针对流道冷却模式，从"微流道低压降强化换热"及"降低微尺度热应力"两个方面对高功率密度芯片微流道冷却问题进行系统的综合研究。研究包括：由波纹通道结构、钉泡通道表面构成的微流道几何特性对微流道流动换热特性的影响；建立了一种新的表面粗糙度的设置方案，并研究表面粗糙度对微流道流动换热特性的影响；从强化换热、流动减阻以及减小热应力三个方面优化设计了微流道热沉通道整体的布置方案；研究了金属泡沫微流道热沉的流动与换热特性及其在芯片冷却应用的可行性。研究表明：波纹微通道可以有效的强化微流道传热性能近60%，合理的钉泡结构不仅可以减小流阻同时可以强化换热；所建立的三维高斯表面粗糙度模型不仅便于实施，而且有效描述真实粗糙表面状况、准确预测了粗糙度对微流道换热能效的强化作用；通过与传统微流道热沉、微流道冲击射流热沉、双层微流道热沉等对比,发现矩形针肋热沉可以提升换热性能20%左右；通过对矩形针肋微流道热沉的结构优化发现增加矩形针肋孔隙率至0.75以及旋转针肋角度至30度热沉的换热性能可以有效的提高近15%；结合热应力分析发现，下阶梯型阵列布置的矩形针肋微流道热沉的顶盖热应变最小且换热性能最佳，是高热流密度芯片散热的较好选择。此外，在微流道内填充金属泡沫亦可以较传统微流道提高换热性能近1倍以上，但流阻较大；采用金属泡沫微肋布置不仅可以有效的强化换热，同时可以起到流动减阻的效果，整体换热性能较传统微流道提升约5%左右。