【作者】 祝渊；

【导师】 康飞宇； 陈克新；

【作者基本信息】 清华大学 ， 材料科学与工程， 2011， 博士

【摘要】 本文根据微电子领域最新涌现的散热需求，提出柔性散热材料这一全新概念，用以提升和整合相关散热材料的制备、设计、测量和应用技术，作为热管理技术领域新的研究方向。使用发泡法自蔓延燃烧合成法制备了长径比可控的高导热长柱状β-Si3N4粉体，结合其他粉体，与不同的有机基体相进行复合，制成了导热胶、导热泥、导热膏和导热垫片四类柔性散热材料。其中重点研究了导热胶和导热泥的设计、制备与应用技术，因为它们的应用背景为平面散热和整板均温，是热管理技术的重要发展趋势之一。导热胶采用环氧树脂或者硅灌封胶为基体材料，β-Si3N4粉体作为主要填料，分析了复合材料热导率和流动性随填料本征性能、颗粒长径比、粉体表面改性等因素的变化规律。重点论述了各因素对复合热导率的作用机理，引入了MG方程和渗流理论来分别描述填料弥散和连通状态的热导率规律，辅以界面热阻模型、伪晶界模型、排除体积等概念和二步法等数学手段，修正了MG方程和渗流标度率，并且首次给出了渗流标度率中斜率的物理意义。导热泥的制备以高分子量、硬度适中的生胶和乙烯基硅油配合作为基体胶，球形Al2O3粉体作为主要填料，实现了材料的无限压缩特性。同时系统研究了填料性能及其填充方式对导热泥的热导率和使用性能的影响，讨论了偶联剂、分散剂、触变剂和硫化剂的用法、用量及使用效果。基于Angstrom法，开发了测量平面散热材料面内热扩散率的仪器，作为下一步各向异性高导热柔性散热材料的研究的硬件支持。研究了样品夹持方式、热电偶加载方式、输入波形和电路放大方式、测试温度、样品长度等对测量结果的影响。最终实现了对高热扩散率的材料的测量，如柔性石墨片和铜片等，测量误差可以控制在10%以内。更多还原

【Abstract】 A new concept of flexible heat dissipating materials was proposed accordingto the emerging application scenarios in the microelectronics industry. Flexibleheat dissipating materials point a new research direction in thermal managementby integrating and enhancing the preparation, design, measurement andapplication technology of related materials.Elongated β-Si3N4powders of controllable aspect ratio were prepared byfoaming combustion synthesis method. Together with other powders, the β-Si3N4powders were applied into various organic matrices to form flexible compositesof different physical states. The resulting composites included thermal adhesive,thermal mud, thermal grease and thermal pad. Thermal adhesive and thermal mudwere chosen as focuses, on which the design, preparation and applicationtechnology were studied. The main applications of thermal adhesives and thermalmud were as in-plane heat dissipating and temperature uniforming materials,which were an important trend in thermal management.Thermal adhesive was prepared with silicon rubber encapsulants as thematrix material and β-Si3N4powders as the main fillers. The thermal conductivityand fluidity of the resulting composites varied with the intrinsic properties, aspectratio and surface modification of the fillers. To reveal the thermal conductingmechanisms, MG equation and percolation theory were introduced to describe thevariation rules of discontinuous filler phase and continuous filler phase,respectively. With the consideration of interface thermal resistance,pseudo-grain-boundary model and exclusive volume assumption, using two-stepmethod and other mathematical means, we revised the MG equation and the scalelaw of percolation theory. For the first time, we give the physical meaning of theslope of the scale law.Thermal mud was prepared with silicone rubber of high molecular weight,moderate hardness and the spherical Al2O3powders. The resulting compositescould be compressed with no limit. The influences of filler properties and fillingmethods on thermal conductivities and application effects were systematically examined. The use of the coupling agent, dispersing agent, thixotropic agent andcuring agent were also discussed.An in-plane thermal diffusivity measuring equipment was developed basedon Angstrom method. This equipment is a necessary supportive hardware forresearching anisotropic flexible heat dissipating materials. The way ofsample-holding and thermocouple loading, the choices of input waveform, circuitamplification method, testing temperature and the sample length were determined.The as-developed equipment can effectively measure the materials with highthermal diffusivity such as flexible graphite sheet and copper. The error can becontrolled within10%.更多还原