【作者】 杨莺；

【导师】 周孑民；

【作者基本信息】 中南大学 ， 工程热物理， 2008， 博士

【摘要】 尺寸小型化与功率高密度化是当今电子封装器件两大主要发展趋势。高热流密度芯片发展要求封装器件具有更好的热耗散能力和更高的热可靠性;电子产品的小型化趋势及便携性要求则是空冷技术发展的助推剂。如何在承受高热流密度的同时保证电子封装器件的热性能是当今热工工程师所面临的重要课题。本研究以加速芯片耗散热的输出、降低工作温度、减少热失配与热应力、提高封装器件的热可靠性能和使用寿命为目标,对空气冲击射流换热特性、焊料的热机械性能进行基础性的实验研究;在此基础上,建立非线性热应力耦合数学模型,并以FC-CBGA封装器件为研究对象,以ANSYS为计算平台,对服役状态下器件温度和应力分布进行数值模拟研究,并对封装器件热可靠性进行评价与预测。主要工作如下:基于数值模拟辅助实验研究理念,针对换热实验系统与热机械性能测试系统,建立了相应数值模型。通过模拟动态测试过程,从数值角度定性与定量分析实验误差及其产生原因,并通过数值模拟辅助分析实验结果。研究表明,在合理选择数学模型和计算方法的前提下,实验数值结合法对发现实验方法与系统的缺陷,评价测试准确性,及定性及定量分析实验数据和解释现象具有裨益。该理念将贯穿于整个研究工作中。对毫米级孔径受限空气冲击射流换热特性进行了较系统的实验研究与理论分析。结果表明受限冲击射流换热性能与其流态与速度分布及空间受限程度密切相关,单孔直(无旋转)冲击射流在驻点区具有很强的局部换热特性;在相同Re下,单孔旋转冲击射流Nu存在明显的峰值外迁现象,因此提高旋转度可有效改善射流换热的均匀性;在相同流量下,由于射流之间的相互干涉和碰撞使驻点问的换热系数不再呈单调变化,多孔冲击射流换热较单孔更为均匀。为顺应焊料无铅化的趋势,对新型无铅焊料96.5Sn3.5Ag的热机械行为进行了探讨。研究表明,采用Anand粘塑性模型可对焊料96.5Sn3.5Ag热机械行为进行正确描述。并在焊料疲劳特性实验研究基础上,结合位错理论、断裂理论、蠕变损伤理论等对焊料疲劳行为进行理论分析,分析表明,软焊料疲劳失效机理与温度密切相关,蠕变损伤与疲劳损伤共同作用导致软焊料疲劳失效。本研究将为新型焊料热机械行为与失效机理研究提供有益思路。外部换热模式与器件内部参量的分布密切相关,故服役状态与均温状态热机械行为存在偏差,因此以服役状态为基准对器件的热机械行为与热可靠性能进行探讨更接近工程实际,其预测结果也更趋安全性。在服役状态下器件的热可靠性能研究涉及多场耦合研究;此外在室温条件下焊料已表现出蠕变等非弹性力学特性,故器件的热可靠性能研究还涉及非线性问题。本文在探讨了非定常温度场与应力场耦合机理的基础上,对耦合热弹塑性问题进行了简化与解耦,提出采用单向顺序耦合方法来求解固体材料内部非定常热应力场。并基于增量理论,对非线性热应力耦合问题及相应的有限元求解方法进行了探讨。基于非线性理论与有限单元法,在对服役状态倒装焊球阵列封装器件温度分布与应力分布进行瞬态数值模拟分析的基础上,对处于多轴应力条件下焊点高温低周疲劳寿命预测方法进行了探讨。在研究中,采用粘塑性模型对焊料热机械行为进行描述,并尽可能地再现了器件内部复杂的组成结构,以便更准确地描述服役条件下器件内部特别是凸焊点的热应力场;子模型方法的引入解决了器件内部组件尺寸级数差异带来的网格划分问题、计算效率问题与计算精度问题;“顺序耦合法”的使用则方便地解决了多场耦合、异相间耦合与同相内耦合等问题。本研究为开发基于倒装焊接的电子封装器件及提高电子封装器件热性能提供了数据与思路。更多还原

【Abstract】 The two trends in the electronics packaging component field nowadays are the miniaturization in the size and high intensity in power. Development of high heat flux chips requires better heat dissipation performance and higher thermal reliability of the electronics packaging, meanwhile, the miniaturization tendency and portability demand of the electronics packaging accelerate the research on the air-cooling technology. So the crucial issue which the thermodynamic engineering is facing is how to ensure the thermal performance while the components burden heavier thermal load.The main purposes of the research are to accelerate the interior heat diffusion, reduce the mean operating temperature, relieve the inner thermal mismatch and thermal stress, and then improve thermal reliability and lengthen service life of the packaging component. In the thesis, experimental investigation on heat-transfer characteristics of air impingement jet and thermo-mechanical performance of solders was accomplished. After that, the numerical model about non-linear thermal-stress coupling was built, the interior distribution of temperature and stress of FC-CBGA electronic packaging component under the operating condition was simulated via ANSYS software, and then thermal capability of the component was evaluated and predicted. The details were expatiated as follows.Firstly, based on the concept of experimental investigation combined with accessorial numerical calculation, the corresponding numerical models were built according to the experimental systems. Then the experimental error and its causation were analyzed qualitatively and quantitively by simulating the dynamic testing process. Meanwhile the numerical simulation was applied to analyze the experimental results accessorially. Investigation indicated that it was feasible and beneficial for the experimental-simulation combination method to detect the limitation of experimental method and system, evaluate the testing precision, analyze experimental results and interpret phenomena qualitatively and quantitively. The concept was embodied through the thesis. Secondly, the heat-transfer characteristics of confined air impinging jet with millimeter-level aperture nozzles were investigated experimentally and analyzed theoretically. It could be demonstrated that the heat transfer performance has the direct relationship with the flow state, velocity distribution and confined degree of impinging jet. Comparison of the experimental results, the non-swirl impinging jet has an excellent local heat transfer performance at the stagnation zone, while the peak value of Nu for the swirl impinging jet exists outward transition phenomena along the radius of impact surface. Furthermore, multi-jets could improve the uniformity of heat transfer in the condition of same flux because that the phenomena of coherence and collision between the jets result in the heat trensfer coefficient not present monotone distribution anymore between stagnation zones.Thirdly, to develop, investigate and use replacer of lead solders is the international trend. So experiments on 96.5Sn3.5Ag-a new lead-free solder were accomplished to discuss the thermo-mechanical behaviors. The conclusion could be drawn that Anand visco-plastic model can be applied to describe the thermo-mechanical behaviors of solder 96.5Sn3.5Ag correctly. Meanwhile, based on the fatigue-characteristic experments and relevant theories involved in dislocation theroy, fracture mechanics, creep-damage theory, et al, the fatigue behaviors of solder were analyzed theoretically. It can be enunciated that absolute temperature has an important effect on failure mechanism of solders and the synergism of creep-damage and fatigue damage brings on fatigue failure of solders. The investigation provides the useful data for thermo-mechanical behaviors and failure mechanism of new-style solders.Exterior heat exchange modes influence parameters distribution inside packaging components, then distinction in thermo-mechanical behaviors exists between operating states and uniform temperature states. So the discussion about the thermo-mechanical behaviors and thermal capability of the component in the operating states could approach the engineering practice more closely. In the operating states, the research of thermal capability on packaging components is involved in multi-field coupling problems. Furthermore, the solders present obvious nonlinear mechanical characteristics such as creep, so the research of thermal capability is also involved in non-linear problems. In this thesis, the coupling mechanism of unsteady temperature and stress fields was discussed. After that, coupling thermal-elastoplastic problems were simplified and decoupled, and the one-way sequential coupling technique was adopted to analyze the unsteady thermal stress inside the solid materials. Besides, based on increment theory, the nonlinear thermo-stress coupling issue and corresponding numerical solution based on Finite Element Method were discussed.According to the theories mentioned above, the transient temperature and stress fields of FC-CBGA electronics packaging component in the operating states were simulated. After that, the method of high-temperature low-cycle fatigue life prediction about pumps in multiaxial stress condition was discussed. In the numerical simulation research, in order to describe the temperature and stress distribution inside the component especially inside the solder bumps more precisely, model of visco-plasticity was applied to describe the thermo-mechanical behaviors of solders and a full size model was built which reconstruct the interior configuration as detailed as possible. Furthermore, some techniques were applied to solve specific problems in simulating. Sub-model method based on local influence theorem was introduced to solve the issues such as grid division, computational precision and efficiency caused by scale level discrepancy among subassemblies inside electronics packaging components and it was proved availably. And sequential coupling technique was adapted to solve coupling problems such as multi-fields coupling, heterophase coupling, inphase coupling, et al.The research provides experimental and theoretical foundation for development of electronics packaging components based on flip bonding and for improvement of thermal performance about electronics packaging components.更多还原