垂直定向散热石墨鳞片/铜复合材料的宏微观结构设计与制备

Graphite flake has excellent properties, such as high thermal conductivity low coefficient of thermal expansion and good machinability. When it is added into copper matrix, which has a high thermal conductivity, the composites are expected to become electronic packaging materials with excellent comprehensive properties. However, due to the high anisotropic property and poor interfacial bonding with copper, the composites can hardly reach the full potential thermal-physical properties. The macro orientation distribution and micro interface structure of graphite flake/Cu composites will be design in this project. Based on the a series of techniques, such as vacuum micro-evaporation plating and electroless plating on the surface of flakes, tap-casting method, copper-coated graphite sintering densification, the flakes will be highly oriented and interface of graphite-copper will be optimized to realize the mutually-perpendicular integration of high thermal conductivity plane and low coefficient of thermal expansion direction. The influence of slurry properties on orientation of flakes in tap-casting method will be studied. The influence of slurry component, viscosity and preform thickness on orientation of flakes as well as the effect mechanism of surface metal modification of graphite flakes on interface structure and interfacial thermal resistance of the composite will be revealed. The research is of great significance for promoting the application of graphite flake/copper matrix composites of vertical heat dissipation and meeting the modern semiconductor industry.

石墨鳞片具有高导热、低热膨胀和易加工等优良特性，与高热导的金属铜复合后，有望成为综合性能优异的电子封装散热材料。但由于石墨各向异性及与铜结合力差等问题，其优良的热物理性能难以充分发挥。本项目拟从鳞片宏观取向分布和微观界面结构角度出发，对石墨鳞片/铜复合材料进行设计。拟通过鳞片表面真空微蒸发镀改性加化学镀铜、刮浆取向成形及覆铜石墨烧结致密化等一系列技术手段，使鳞片在铜基体中呈高度定向排列并优化石墨-铜的界面结构，从而实现复合材料高热导方向与低热膨胀系数平面相互垂直的有机统一。重点研究刮浆成形中浆料特性对鳞片取向的影响，阐明浆料成分、粘度及浆膜厚度对鳞片取向的影响规律，揭示石墨鳞片表面改性方法对复合材料界面结构及界面热阻的影响机理。该项研究对于促进石墨鳞片/铜垂直散热材料的实际应用，满足现代半导体工业的发展具有重要的意义。

.随着电子元器件功率密度不断增加，其散热问题显得尤为突出，对电子封装材料的性能也要求越来越高。石墨鳞片具有高度各向异性的导热率和低热膨胀。鳞片在铜基体中的取向择优可实现复合材料高热导方向与低热膨胀系数平面相互垂直，从而实现复合材料的垂直定向散热。..本项目针对鳞片在铜基体中的分布取向不佳和铜碳界面结合差两个关键问题，对复合材料进行宏观取向构型和微观界面结构进行设计。研究了刮浆成形中鳞片取向、尺寸、体积分数的宏观构型要素，石墨鳞片铜界面微观结构对复合材料热物理性能的影响规律。..研究表明，通过真空微蒸发镀碳化钛对石墨鳞片进行表面改性，在石墨与铜的界面处引入200nm的碳化钛中间层，可达到优化铜碳界面结构的目的。采用PVB-乙醇-丙酮浆液的刮刀成形法制备了鳞片高度取向的预制坯体，配合真空压力烧结可实现鳞片在铜基体中呈高度定向排列。利用图像分析法和显微CT技术对复合材料中鳞片取向的表征，其中45%的鳞片倾角小于6°， 80%的鳞片小于12°。所制备的60vol.%镀碳化钛石墨鳞片复合材料在X-Y平面上热导率达到668 W/mK，Z方向的热膨胀系数为4.4ppm/K。..建立了各向异性石墨增强相界面热导的理论预测模型，掌握了各向异性石墨取向对复合材料热导率的影响规律。利用建立的理论模型计算了不同中间层的临界厚度，同时选择厚度敏感的Cr7C3镀层对模型的准确性进行验证，实验值和理论值偏差在4%以内，吻合度较高。该模型在与其他文献的石墨增强相铜基、铝基复合材料的实验值比较时展现出了良好的普适性。根据模型预测，从自身热导率、界面热阻及溶解度等综合考虑，在石墨铜界面中引入钨镀层是最佳选择。..本项目研究成果为指导石墨/金属基复合材料的开发设计提供了实验参考和理论依据，对于促进石墨鳞片系复合材料的应用、满足现代半导体工业的发展需求具有重要的意义。.