基于同步辐射成像的锡铋/石墨烯(Sn-Bi/Graphene)热界面材料研究

针对电子元器件散热对高热导率和低热阻及使用可靠的热界面材料（TIM）迫切需求，基于量子力学金属导热自由电子气理论，项目提出将高导热长电子自由程石墨烯（GNS）复合到低熔点锡铋（Sn-Bi）合金，获得新型高导热锡铋/石墨烯（Sn-Bi/GNS）TIM理论。开发高导热Sn-Bi/GNS复合材料电化学沉积工艺，可控制备不同成分、GNS体积比和微观结构的Sn-Bi/GNS复合材料，结合导热率测试深入研究其导热机理。基于同步辐射成像研究压力下Sn-Bi/GNS复合材料重熔微观结构演变，设计有效重熔工艺，实现与基底界面纳米尺度紧密接触，进一步减小界面接触热阻。最后测试Sn-Bi/GNS复合材料剪切和拉伸强度，基于同步辐射成像微拉伸转动装置，观测拉伸破坏过程微观结构演变，深入研究GNS机械强韧机理。项目最终成果高强高导热Sn-Bi/GNS复合材料，有望应用于高性能电子和高能激光系统散热。

Thermal management systems including heat spreader and heat sink are necessary to dissipate heat away from electronics to keep them from overheating or burning. Thermal interface material (TIM) is used to bond electronic devices to heat spreaders for thermal management purposes. Desirable attributes of TIM include a low melting temperature, necessary for device protection during bonding, high thermal conductivity, good bonding and tensile strength, and low thermal interface resistance. According to the free electron gas theory of the thermal conductivity(inverse of the thermal resistivity) of metal in quantum mechanics, this project propose the high-thermal conductivity Sn-Bi/Graphene nanosheets (Sn-Bi/GNS) composites by combining the graphene of high thermal conductivity with long free electron path and low melt Sn-Bi alloy with high density electrons. Then this project aims to develop novel Sn-Bi/GNS composites that Sn-Bi alloy filled continuously with uniform GNS realize good interfacial bonding ensuring electron redistribution between GNS and Sn-Bi. The good interfacial bonded Sn-Bi/GNS is the key to achieving high thermal conductivities. An electrochemical deposition process will be developed for which uniformly distributed GNS and good interfacial bonding can be achieved. The Sn-Bi/GNS composite will be blended to meet the design requirements and to tailor the coefficient of thermal expansion so as to promote durability of the bond. The Sn-Bi/GNS composite film with different ratio of GNS, Sn-Bi content and micro-structure will be fabricated by electro-chemical deposition and micro-nano fabrication process. Experimental approaches will be taken to measure the resultant properties including shear and tensile strength and thermal conductivity of Sn-Bi/GNS composite material application to the TIM materials. Also re-melt under pressure and micro test system will be developed to detect the structure change under pressure and tensile test. Using synchrotron fast X-ray micro-tomography, an experimental set-up was developed to study in situ and in real-time the microstructural evolution of Sn-Bi/GNS composites during melt. The enhance mechanism of GNS in Sn-Bi/GNS composites as investigated by micro-mechanical test with real imaging with synchrotron X-ray imaging. In situ X-radiographic investigations of solidification fundamentals and phenomena of Sn-Bi/GNS composites will be investigated at resolutions approaching true video microscopy. Effective processes to realize nanoscale intimate contacts between Bi-Sn/GNS composite TIMs and contact substrates will be also proposed and performed for reducing the thermal interface resistance further. The proposed innovative Sn-Bi/GNS bonding material and method can improve the thermal management of advanced electronics including but not limited to integrated circuit, power electronics, and various laser systems.