【作者】 张平；

【导师】 宣益民；

【作者基本信息】 南京理工大学 ， 工程热物理， 2013， 博士

【摘要】 随着电子芯片的集成度、封装密度和工作频率的迅速提高,芯片热流密度迅速增加,给芯片散热带来了极大挑战,而界面结构是电子器件本身以及器件互连和封装中普遍存在的现象,有效的界面接触热阻控制是电子产品性能和可靠性方面关心的重要问题。因此,在研究高功率密度电子设备的热控新方法中,研究散热通路上不同固体之间的界面接触传热问题,解决高功率密度电子设备的热控技术首要界面接触强化传热问题,对保证电子设备的工作性能和可靠性有着重要意义。本文围绕电子设备接触界面传热性能的测试方法、影响因素以及强化传热方法开展了研究工作,探索了固体材料导热系数和接触热阻的高精度测试方法、固-固接触界面传热特性的影响因素以及新型热界面材料的强化传热特性,为电子设备的热控设计提供了实践指导。本文的主要工作包括以下几个方面：1.固体材料导热系数和接触热阻的高精度测试方法的建立通过采用传统的标准导热系数和接触热阻测试系统的单方向加载热流方式对标准材料进行了不同方向的热流加载测试,观测到通过单方向的热流加载方式测得的导热系数与标准参考值有一定的偏差,且在不同热流加载方向时测得的接触热阻值也都会存在一定的偏差。从实验不确定度分析入手,综合考虑了各种误差因素,分析了此类附加误差可能产生的原因,建立了一种通过采用分别交替从上下方向加载热流进行导热系数和接触热阻测试并对此双向测试的导热系数和接触热阻值进行调和平均计算来基本消除此类附加误差的方法,以此达到更高精度的测试固体材料导热系数和接触热阻的目的,并搭建了一套改进的可分别从上下方向加载热流进行测试的稳态导热系数和接触热阻测试系统。对纯度为99.999%的纯铜材料和Elkonite公司的30W3铜-钨合金这两种参考材料的导热系数进行了测试验证,并与相关参考值进行了对比分析,结果表明该方法可以高精度地测试固体材料的导热系数。也对几种材料试样对的接触热阻进行了测试验证和详细讨论,结果表明该方法也可以高精度地测试固体材料的接触热阻。2.固-固接触界面传热特性的影响因素分析通过对5A05H112、3A21H112、3A21、6061H112和6063这5种电子设备散热领域常用的铝合金材料的接触界面传热情况进行了较为系统的试验研究,并根据实验数据分析了表面均方根粗糙度、表面微观硬度和材料导热系数的差异对固-固界面接触传热特性的影响。发现材料的表面均方根粗糙度(车削,小于工业常用粗糙度4.5μm以下)会和平面度一起耦合作用于材料的界面传热特性,单纯的追求较高的材料表面光洁度并不能很好地改善材料的界面接触传热特性。所做的一些探索性工作对于搞清楚固-固界面接触热阻的影响因素以及对电子设备的热控设计都具有很重要的指导意义。3.新型热界面材料的组份对强化传热性能的影响特性研究通过实验研究把MWCNTs、纳米铜颗粒以及它们的混合物添加到环氧树脂基体材料中,制备了纳米铜／环氧树脂、MWCNTs/环氧树脂以及MWCNTs/纳米铜／环氧树脂复合材料,并测量了制备的环氧树脂基复合材料的热导率,研究了纳米铜和MWCNTs此两种热导率相近填料及其不同的掺杂比例对环氧树脂基复合材料的界面传热性能的影响,并对其微观形貌采用SEM电镜进行观察,研究了材料的微观结构特征对界面传热性能的影响。证明了环氧树脂基复合材料的界面传热性能不仅与材料的导热系数相关,还与填料的性质、热界面材料的浸润性、流动性、微尺度结构特征及其纳米复合物的结构特征都有关。制备得到的70wt%掺杂比例的纳米铜/环氧树脂复合材料测得的最小接触热阻为11.5mm2K/W(未添加任何热界面材料时为660mm2K/W),优于文献报道的碳纳米管阵列作为单独热界面材料的接触热阻值(19.8～100mm2K/W)。更多还原

【Abstract】 With the development of the microchips, the thermal management for the electronics is facing the rigorous challenges. As the electronics become extremely fast and small, it unavoidably leads to high heat flux. If the high heat flux can’t be removed immediately, electronics will be heated up to very high temperature, which will adversely depress the performance and reliability of the electronic components. However, the interfaces of different materials are the base structure of electronic components. Therefore, enhanced heat transfer across interfaces is an imminent key point in a wide of scientific and engineering applications. The research work of this paper focuses on the heat transfer characters of the solid-solid interfaces of electronic materials. The high-precision measurement method of thermal conductivity and thermal contact resistance, the study of influencing factors on TCR in quantity and the thermal interface material incorporated with nano-copper particles and the mutil-walled carbon nanotubes are all investigated to provide guidance for the thermal management. The main research work of this paper includes the following aspects.1A high-precision method to measure thermal conductivity and thermal contact resistance using reversible heat fluxIn the thermal conductivity and thermal contact resistance (TCR) measurement of solids using traditional steady-state test methods, it is observed that the test thermal conductivity results differ from their standard values when only one directional heat flux is introduced and the measured TCR results are unavoidable to be impacted also by the direction of exerting heat flux. In order to improve the measurement precision, we proposed a method by using harmonic mean value of thermal conductivity and TCR in two directions of exerting heat flux to diminish this effect. Meanwhile, a modified experimental apparatus has been designed and established to high-precisely measure thermal conductivity and TCR of solids. To verify the accuracy of the method, the thermal conductivities and TCRs of samples of99.999%standard pure copper and Elkonite copper-tungsten alloy30W3are measured and discussed in detail.The results indicate that the processing thermal conductivity data well match the reference values, and the present method also has high precision and can be used in a relatively wide range of TCR measurement for solids.2. Research on the influencing factors on TCR of solid-solidThe heat transfer characters between conventional aluminum alloy materials (type:5A05H112,3A21H112,3A21,6061H112and6063) are been investigated through the experimental measurement in detail. The influence on TCR of RMS roughness, micro-hardness value and thermal conductivity of materials are all been discussed. The results indicate that the heat transfer characters is not relate to the RMS roughness in range of commonly manufacture level (<4.5μn), but relate to the flatness, micro-hardness value and thermal conductivity of materials. This exploring work will have merits to study the influencing factors on TCR and to provide guidance for the thermal management.3. Research on the influencing heat transfer characters on fraction of new type thermal interface materialTo enhance heat transfer performance of epoxy resin as a thermal interface material (TIM), multi-walled carbon nanotubes (MWCNTs) and nano-copper particles are incorporated into an epoxy resin to form hybrid composites. The total TCR between the heated and cooled surfaces as well as its components such as the bulk resistance (RBLT) of the TIM, and the boundary resistance (RB) between the TIM and the joint surfaces above and below the TIM of the composite are measured. The influence of the compound in different proportions of MWCNTs and nano-copper particles on the RBLT and the RB is discussed in detail. The results indicate that the total TCR is related not only to the thermal conductivity of the TIM, but also to the other factors such as the property of the filler, the viscosity and the surface morphology of the TIM. Being compared with nano-copper/epoxy composite, for example, the total TCR of the MWCNTs composite can not be reduced in quantity due to the higher RB for the high elasticity modulus of carbon nanotubes and the agglomeration of MWCNTs with nano-particles, although the thermal conductivities of the composites increase with the MWCNTs content. Compared with the total TCR value of19.8-100mm2K/W with the CNT array TIMs, the minimum total TCR can be obtained as11.5mm2K/W (dry self-contact:660mm2K/W) with the composite filled with70wt%nano-copper.更多还原