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

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.

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。

开发电化学沉积工艺，将高导热长电子自由程石墨烯（GNS）复合到低熔点高电子密度的锡铋（Sn-Bi）合金，获得新型高导热锡铋/石墨烯（Sn-Bi/GNS）TIM；电化学沉积工艺可以将GNS较均匀的分散到Si-Bi合金中，GNS的加入有效提高了Si-Bi合金的导热率，增强TIM与基底的结合，这不仅降低了界面热阻，还提高了TIM和基片之间连接的可靠性。研究电沉积制备Sn-Bi/GNS复合材料，表面活性剂种类、碳链长短、表面活性剂含量对电沉积速率与材料性能的影响，测量了不同石墨烯浓度下Sn-Bi/GNS复合材料的热导率，加入阳离子表面活性剂十四烷基三甲基溴化铵（MTAB）后得到的镀层加工性好，电阻率低。增大镀液中MTAB浓度，优化石墨烯和MTAB的配比，通过电沉积法获得的复合材料最高热导率为41.39 W/(m•K)，较纯锡铋电沉积样品提升了63%。对比了球磨法制备Sn-Bi/GNS复合材料，同时研究了球磨转速、球磨时间对粉末结构与材料性能的影响。球磨法获得的复合材料的最高热导率为26.63 W/(m•K)。研究了不同制样的峰值温度熔融后Cu-SnBi/GNS-Cu三层结构试样界面热阻的变化规律，当峰值温度为260℃，接触压力为3g（237Pa）时，Cu-SnBi/GNS-Cu试样的界面热阻降低了50.7%，且界面传热性能最佳，传热性能非常稳定，在高温传热环境下的可靠性较高。不同热源功率下对比了SnBi/GNS复合材料和目前市场上性能较好的导热硅脂、导热硅胶垫的传热性能，SnBi/GNS传热性能始终最佳，且随着功率的增大，其传热性能优势更为明显。研究了不同峰值温度和保温时间对Cu-SnBi/GNS试样界面熔融工艺对结合强度的影响，Cu-SnBi/GNS结合强度当峰值温度为260℃，保温时间为5min熔融后Cu-SnBi/GNS结合强度最大提高了39.2%。研究了不同热老化温度下SnBi/GNS和SnBi试样拉伸强度的变化规律。GNS的存在有效地抑制了试样的热老化进程。在100℃热老化处理下，SnBi/GNS的抗老化性能提高了27.7%，有效地阻碍了颗粒的生长以及裂纹孔洞的产生，提升了TIM的抗热老化性能。项目基于AFM研究石墨烯表面特性研究，为石墨烯和金属等界面结合提供基础。

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