【作者】 元鑫；

【导师】 韩国明；

【作者基本信息】 天津大学 ， 材料加工工程， 2006， 硕士

【摘要】 为适应集成电路的发展,以满足电子产品在大功率、高速度、高密度、高精度和高可靠性等方面的需要,电子封装在保证可靠性的前提下,提高速度、提高功率、提高散热能力、增加I/O数、减少尺寸和降低成本,也向着高密度方向发展。多芯片组件(MCM)作为电子封装技术中的一种新型封装形式,倍受电子工业界的关注,而焊点可靠性问题是发展MCM技术的关键影响因素之一。焊点的可靠性问题是电子封装技术领域亟待解决的重要课题,是决定电子产品质量与发展的基本问题。实践证明,热作用是封装组件失效破坏的主导因素,因此对热循环条件下的焊点可靠性进行研究有着非常重要的意义。本课题选择无铅钎料Sn3.5Ag0.75Cu作为MCM焊点材料,利用ANSYS有限元软件建立MCM的三维条形模型;基于统一型粘塑性Anand本构方程,进行-55℃～125℃热循环模拟。确定了MCM中最危险的焊点部位以及该焊点中最危险区域,分析了无铅钎料Sn3.5Ag0.75Cu焊点在热循环过程中的应力应变分布和变化规律,使用Darveaux方程预测了焊点的热疲劳寿命,并与63Sn37Pb钎料的焊点热疲劳寿命作了对比,对无铅钎料Sn3.5Ag0.75Cu焊点可靠性做了评定。研究发现:在MCM组件经热循环后,最危险的组件为小芯片;在小芯片上,最危险的部位为小芯片的边缘。在同一芯片下,焊点的等效变形、等效应力、等效应变,从所在芯片中心向边缘逐渐增大。最危险的焊点是小芯片下离小芯片中心最远的焊点。焊点的应力应变的最大区域是与上下焊盘连接的区域,最危险的部位位于焊点与芯片上边焊盘连接的拐角处,裂纹就是从这里开始产生,并逐渐向里扩展,延伸到整个焊点。非弹性应变在升降温阶段积累明显,在保温阶段积累不明显,这是温度和应力综合作用的结果。在高温保温阶段,应力水平相对较低,应变的积累不明显;而在低温保温阶段,应力虽然较高,但温度较低,非弹性应变也不明显。因此,升降温对焊点的寿命影响至关重要。本文选用以能量为基础的Darveaux寿命预测模型,预测了无铅钎料Sn3.5Ag0.75Cu焊点初始产生裂纹的循环次数和焊点的热疲劳寿命,并和63Sn37Pb钎料的焊点热疲劳寿命作了对比,结果表明无铅钎料Sn3.5Ag0.75Cu焊点的热疲劳寿命大于63Sn37Pb钎料焊点的热疲劳寿命。更多还原

【Abstract】 In order to adapt the development of the integrated circuit, electronic productions must satisfy the requests of big power, high speed, high density, high precision, high reliability etc. Electronic packages develop in the direction of high density with ensuring the high reliability. Packaging technologies are changing at an ever more rapid pace. IC packages are becoming smaller in size, faster in speed, higher in power, stronger in elimination of the heat and lower cost. In addition to these, the numbers of electrical interconnection (I/O) in IC packages have been maximized. The multi-chip module (MCM) is one of new electronic packages and gets attention from the people in electronic industries. However, the reliability of the solder joint is one of the key factors during the development of MCM.The problems about the reliability of the solder joint are important and urging to solve in the electronic package. The reliability of the solder joint decides the quality and development of electronic production. In fact, heat is the main reason for the failure of electronic package. So the reliability study of the solder joint is very important under the condition of thermal recycle.In this paper, the lead-free solder Sn3.5Ag0.75Cu was chose in the simulation of MCM. A 3-D slice model of MCM was built using the soft ANSYS. Based on the Amand’s constitutive model, the process of thermal cycle was simulated on the temperature condition from -55℃to 125℃. The position of the most danger solder joint and the region of the danger solder joint were decided. The variety rule of the stress and strain was acquired. The thermal fatigue life of the solder joint was predicted using the Darveaux’s equation. The thermal fatigue life of the lead-free solder joint Sn3.5Ag0.75Cu contrasted with the Sn37Pb solder’s thermal fatigue life.The reliability of the lead-free solder joint was assessed. The research finds: During the thermal cycle, the little chips around the big chip are the most danger; the edges of the chip are most danger in the same little chip. The equivalent deformation, equivalent stress and equivalent strain of solder joints under the same chip increase from centre to edges. The dangerous solder joint is in the edge far from the centre of the little chip. Stress and strain are biggest is in the region where the danger solder ball joints with pad. The most dangerous spot is in the edge of the top surface of the dangerous solder joint and the crack comes into being on this spot and expends from there. The accumulation of inelastic strain is obvious during the fluctuation of temperature, but not obvious under constant temperature. The reason is that both temperature and stress combine to affect the accumulation of inelastic strain. So the fluctuation of temperature is the main factor that affects the life of the solder joint. The Darveaux’s equation was used to predict the thermal fatigue life of the Sn3.5Ag0.75Cu solder joint. The Sn3.5Ag0.75Cu solder joint’s life is longer than the 63Sn37Pb solder joint’s by contrasting with each other.更多还原