铜粉-石墨烯导热硅脂的制备及性能研究

研制高导热系数的导热硅脂是解决大功率电气、电子元器件散热问题的有效途径。本文以金属铜微米颗粒和改性石墨烯为导热填料制备导热硅脂。研究了不同粒径的金属铜颗粒级配比例以及改性石墨烯的填充量对导热硅脂的导热系数的影响规律,同时研究了所得导热硅脂的耐热稳定性。结果表明当小粒径铜粉占总铜粉体积的20%,并且改性石墨烯的质量分数为2%时,导热硅脂的导热系数为2.3 W/m K,是未添加石墨烯的导热硅脂的2.4倍,同时耐热稳定性完全符合国家标准的要求。研究结果显示了金属铜颗粒与改性石墨烯的协同作用,有利于高性能导热硅脂的设计和制造。     

大功率LED散热用高导热硅脂的研制

以二甲基硅油为基础油,通过添加不同粒径和含量的Al、Cu、Ag、AlN、SiC和石墨,制备了单一填料的单组分以及两种填料大小搭配的二元混合导热硅脂,研究了硬脂酸表面处理、填料种类、大小及比例对导热硅脂热导率的影响,得到了以下结果:硬脂酸处理能提高单组份Al、AlN硅脂的导热性能,但不适用于提高含石墨、SiC、Cu的硅脂的性能;填料填充的最佳比例在0.55~0.60之间;以Ag微粒作为第二填料增强Al和AlN为主填料的硅脂时,对导热率的增强效果高于AlN和Cu、Ag/AlN二元混合硅脂热导率5.5W·m-1·K-1。将制备的导热硅脂用于LED散热,结果表明自制导热硅脂实际散热效果优于市购热界面材料。     

非金属基导热材料对HPLED散热性能影响

由于光电转换效率较低,产生的多余熬已成为提升单位体积下大功率LED (HPLED)灯光输出量的主要瓶颈,使有效减少HPLED灯热流回路上各界面接触热阻成为重要课题.研究了不同的非金属基导热界面材料在不同环境温度条件下,应用于HPLED灯具模型中的第二界面处时对灯具散热情况的影响.结果表明,具有相变特征的非金属基导热界面材料.在其相变转化点位置之上的某一特定临界点后的热传导性能优于导热系数相对更高的非金属石墨基的界面材料.第二界面材料之间的接触热阻对发挥其导热能力有重要影响.     

基于红外测温的GaN HEMT器件结构函数法热阻测量

为了准确的测量GaN HEMT的热阻参数,在两种不同的管壳接触热阻条件下,利用经过改进的显微红外热像仪测量了GaN HEMT的降温曲线。采用结构函数算法对两种降温曲线进行分析,得到了反映器件各层材料热阻的积分结构函数曲线。当管壳接触层由空气变化为导热硅脂时,积分结构函数曲线发生了变化。通过结构函数曲线能够明确区分被测件不同层的热阻。可以将被测件的分成6层结构,与器件真实结构基本一致。     

LDMOS热阻的电学法测试与分析

基于结构函数理论,运用电学测试法,提取封装LDMOS导热路径上各层材料的热阻值,以及管壳与恒温平台之间的接触热阻值。对各层热阻进行分析,发现焊料层的热阻远大于理论值,提出了一种减小焊料层热阻的方法。改变管壳与恒温平台的接触情况,分别测出不同接触情况下的热阻值,对比发现接触情况会影响结到壳热阻的大小,提出了减小接触热阻的方法。     

高导热环氧模塑料的制备

介绍了导热系数大于3 W/(m·K)高导热环氧模塑料的制备。以低黏度多芳香环（MAR）环氧树脂和MAR酚醛树脂为基体,以偶联剂处理的球形氧化铝做导热填料,磷类做催化剂,经高速混合机混合、双螺杆挤出机挤出,合成高导热环氧模塑料。并研究了不同偶联剂类型对弯曲强度的影响。通过改变填充量至93%,导热系数最高可达5.6 W/(m·K),且有较好的弯曲性能和流动性能。     

不同偶联剂表面处理氢氧化铝在覆铜板中的应用研究

通过研究不同类型偶联剂处理氢氧化铝填料对界面及其力学性能、耐碱性等方面的影响,为覆铜板产品配方设计提供借鉴。     

两种高温老化方式对功率白光LED光热参数的影响

测试和比较了大功率白光LED在高温耐电(HTCD)和高温存储(HTS)两种老化条件的光热性能变化。结果表明,在HTCD老化下,光通量衰减达到40～60%;而HTS下的衰减只有10～14%。这说明,电流应力对LED的寿命影响比较大。利用热阻瞬态响应法测试和结构函数理论分析两种高温老化条件下LED的热特性,结果表明,在HTCD老化下LED热阻的变化较HTS更为明显,并且热阻变化大多体现在导热Ag胶层。这主要是由于高温条件下电流应力引起Ag颗粒的空间分布不均,使粘结界面产生空隙导致热阻发生不同程度的改变。     

聚合物基热界面材料的研究现状北大核心CSCD

热界面材料可以有效地改善两个固体界面间的热传导,对于电子器件的性能、寿命和稳定性起着至关重要的作用。近年来,小型化、集成化已经成为电子器件的发展趋势,电子器件的功耗不断提升,所产生的热量越来越高,对热管理提出了更高的要求,所以,热界面材料的创新与优化也备受关注。因此,综述了热界面材料的研究进展,包括导热填料的种类、填充量和性质对于复合材料性能的影响,特别介绍了复合材料中导热填料链状及网状结构制备,包括模板法制备填料导热网络、静电纺丝构建链状填料、外加电磁场控制填料的取向。最后总结了现阶段热界面材料研究的问题,展望了未来热界面材料的研究方向。     

固态组件冷板热扩展体性能分析

固态技术和相控阵雷达是雷达领域研究的重要课题,固态末级功放组件、T／R组件内晶体管等大功耗、高热流密度器件在冷板上会形成局部热障,产生扩展热阻。文中对扩展热阻特性进行研究,探讨了影响扩展热阻的三个参数：厚度、对流换热系数和导热系数,并分析得出提高热扩展体的等效导热系数是减小扩展热阻、强化传热最有效的技术途径之一,最后在此基础上利用数值模拟方法对铜块、热管及蒸发室等三种热扩展体的散热性能进行了分析和比较。     

Analytical equations for predicting the thermal properties of isotropic conductive adhesives

This paper investigates a set of theoretical equations for analyzing the thermal properties of isotropic conductive adhesives (ICAs) containing several types of Cu filler particles. The thermal conductivity of ICAs containing randomly dispersed filler particles can be simulated well by Bruggeman’s equation for spherical particles and by Kanari’s equation for flake particles. The effect on the thermal conductivity of any residual voids can be taken into account in the analysis by the additional application of Bruggeman’s or Kanari’s equations with the appropriate shape factor. The linear thermal expansion coefficient of the ICAs was analyzed using Schapery’s scheme. The thermal expansion coefficients of ICAs with 40–50 vol.% of filler particles range between Schapery’s upper and lower limits. As the particle size of the filler decreases, the thermal expansion coefficient starts to approach the lower limit at a lowr volume fraction of the filler particles. The transition behavior of the thermal expansion coefficient is related to the characteristics of the network structure formed by percolating the filler particles.     

The Effect of Polydispersivity on the Thermal Conductivity of Particulate Thermal Interface Materials

A critical need in developing thermal interface materials (TIMs) is an understanding of the effect of particle/matrix conductivities, volume loading of the particles, the size distribution, and the random arrangement of the particles in the matrix on the homogenized thermal conductivity. Commonly, TIM systems contain random spatial distributions of particles of a polydisperse (usually bimodal) nature. A detailed analysis of the microstructural characteristics that influence the effective thermal conductivity of TIMs is the goal of this paper. Random microstructural arrangements consisting of lognormal size-distributions of alumina particles in silicone matrix were generated using a drop-fall-shake algorithm. The generated microstructures were statistically characterized using the matrix-exclusion probability function. The filler particle volume loading was varied over a range of 40%–55%. For a given filler volume loading, the effect of polydispersivity in the microstructures was captured by varying the standard deviation(s) of the filler particle size distribution function. For each particle arrangement, the effective thermal conductivity of the microstructures was evaluated through numerical simulations using a network model previously developed by the authors. Counter to expectation, increased polydispersivity was observed to increase the effective conductivity up to a volume loading of 50%. However, at a volume loading of 55%, beyond a limiting standard deviation of 0.9, the effective thermal conductivity decreased with increased standard deviation suggesting that the observed effects are a tradeoff between resistance to transport through the particles versus transport through the interparticle matrix gap in a percolation chain.      

Drainage-Induced Dry-Out of Thermal Greases

In this study, the mechanism of grease dry-out, a long-term failure mode of thermal greases, is investigated using optical microscopy and infrared (IR) thermography. Results show that the dry-out phenomenon is accelerated in aged greases and we suggest that this is due to inhomogenieties in the filler packing structure that develop over time due to segregation of the grease components, though they may also occur at time zero due to insufficient mixing during grease formulation. Theories describing fluid flow through porous media are used as a preliminary framework for understanding the grease dry-out process and its dependence on local variations in the grease microstructure and on matrix-filler compatibility.      

Oxidation Prevention and Electrical Property Enhancement of Copper-Filled Isotropically Conductive Adhesives

This paper describes the development and characterization of isotropically conductive adhesives (ICAs) incorporating copper (Cu) powders as electrically conductive fillers, along with a silane coupling agent for oxidation protection of copper powders, for environmentally friendly, low cost and high thermal reliability applications in microelectronics packaging. The effect of silane coupling agent materials and concentration on the electrical conductivity, thermal stability and reliability of Cu-filled ICAs was investigated for potential alternatives of conventional silver-filled ICAs. The surface characteristics of silane thin films on copper surfaces, such as their hydrophobicity and thermal stability, were also evaluated to compare the performance of antioxidant behaviors of different silane coupling agents for Cu-filled ICAs. The low contact resistance and high thermal stability of the contact resistance of Cu-filled ICAs were achieved by addition of an optimized silane coupling agent. Greater thermal stability and improved reliability of Cu-filled ICAs under high temperature and humidity conditions were achieved with a silane coupling agent of high molecular weight and hydrophobicity. The bulk resistivity of ∼10⁻⁴ Ωcm of Cu-filled ICAs was achieved with bimodal filler loading.     

封装用环氧模塑料制备及其线膨胀性能研究

文章主要对集成电路封装用环氧树脂模塑料的配方进行研究,以高纯度酚醛环氧树脂为基体树脂,二甲基咪唑为催化剂,分别以结晶硅微粉、熔融硅微粉、球形硅微粉为填充料,通过改变催化剂、偶联剂、固化剂和填充料的类型或用量,并通过添加纳米二氧化硅改性剂,从而获得各配方环氧树脂模塑料扫描电子显微镜表征的微观结构、线膨胀系数等性能。进而对封装用塑料进行配方优化,获得较优配方,使环氧塑封料达到线膨胀系数小、应力低的目的,使之合乎大规模集成电路封装用模塑料的性能要求。     

一类新型高导热环氧模塑料的制备

采用Si3N4陶瓷作填料,制备了一类新型高导热的环氧模塑料,研究了Si3N4的含量、分布及其形态对复合材料的导热性能及介电性能的影响。结果表明:随着Si3N4粉末体积填充量的增加,复合材料的热导率显著提高,当填充量体积分数为60%时,复合材料的热导率达到2.3W/(m·K),其介电常数随体积填充量的增加亦有所增加,但仍然维持在低水平。采用Agari模型进行理论计算的结果表明,该体系导热性能的提高与Si3N4填料之间热传导网络的形成有关。     

Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

The thermal properties of epoxy‐based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the “synergistic” filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size‐dissimilar fillers, has a well‐defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of f_g = 15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches f_Cu ≈ 40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, f_g = 40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. A thermal conductivity of 13.5 ± 1.6 Wm^?1K^?1 is achieved in composites with binary fillers of f_g = 40 wt% and f_Cu = 35 wt%. It has also been demonstrated that the thermal percolation can occur prior to electrical percolation even in composites with electrically conductive fillers. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.     

封装结构与材料导热系数对FC-BGA热性能的影响

应用计算流体动力学仿真技术对一种带金属散热盖的FC-BGA封装热性能作参数化研究,分析相关结构参数与材料导热系数对封装热性能的影响。研究中考虑的因子包括基板层数、导热树脂与金属散热盖粘合剂的导热系数、金属散热盖结构参数及基板导热系数。探讨了封装体中主要的热量传递途径及各途径上的热流量分配。     

螺纹型激光晶体热透镜效应研究

分析了激光晶体热效应的影响因素,利用热传导方程推导出激光晶体由于内部温度分布不均匀造成的端面热形变与晶体表面积的关系.针对普通圆棒晶体和螺纹棒晶体,分别计算了它们的热形变和热焦距,结果表明螺纹棒晶体可有效地改善激光晶体的热效应.