【作者】 周洪彪；

【导师】 张化宇； 严格；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 硕士

【摘要】 当焊点处于温度循环负载时,容易产生热疲劳,因此焊点的热疲劳问题被提到了研究的前沿。本文通过热循环实验对无铅焊点的可靠性进行研究,分析了焊点在热循环条件下的失效模式和失效机理、介绍了无铅焊料焊点寿命预测的路径并建立了焊点寿命预测模型、通过有限元模拟了焊点在热循环过程应力应变的变化,模拟计算了焊点寿命并与加速寿命实验结果对比。本文研究内容主要包括以下几个方面:(1)焊点界面金属间化合物对焊点可靠性有很大影响。研究发现钎料的拉伸强度随着界面AuSn4金属化合物的逐渐生成产生较大降幅,当(Cu,Au)Sn金属化合物生成时拉伸强度降幅更为明显,研究表明富铜IMC层和AuSn4层间的结合性能是整个界面最脆弱的地方。(2)分析了焊点热循环条件下焊点失效现象及机理。研究发现焊点在热循环中存在两类主要的失效模式:一类是焊点在IMC附近产生裂纹;另一类是焊点出现整体剥离。其中,焊点裂纹常常出现在AuSn4层与该层下的富Cu金属化合物层间,并在其界面扩展传播,最终导致失效。另外,焊点剥离失效由于Au和FeNi原子与钎料结合成金属化合物相继耗尽,而Ta原子的晶格结构难于与其余金属原子结合成金属化合物,在不断的热冲击导致的剪应力,最终导致焊点从该界面处剥离。(3)并运用威布尔分布的数学统计方法计算出了确定的SAC无铅焊点热循环寿命预测数学模型,得出了微焊点在工作条件下的寿命为14年。(4)焊点在热循环条件下应力应变过程有限元分析结果表明:在热循环条件下,焊点钎料内的应力应变响应呈周期性变化,与热循环过程相匹配,焊点内高的等效应力发生在热循环的低温阶段;非弹性应变在总应变中占主导地位,在热循环的高温阶段,几乎等于总应变;非弹性应变在热循环的升降温阶段累积明显,在高低温的恒温阶段累积不明显。(5)通过有限元模拟SAC焊点的热疲劳寿命结果与加速寿命实验所得的焊点热疲劳寿命结果较吻合,表明实验所得寿命预测数学模型能较可靠的运用于对SAC焊点在热循环环境中的寿命预测。更多还原

【Abstract】 Solder joint is easy to be thermal fatigue when it is loaded with cyclic temperature, so the problem of solder joint thermal fatigue has been brought up as a research advancing front. In this paper, the reliability of lead-free solder was study by thermal cycling test. The failure modes and mechanism of solder joint under thermal cycling condition were researched. The method and path of lead-free solder lifetime prediction were introduced, and model of lifetime prediction was established by accelerating life test. The stress and strain of solder joint during thermal cycling were simulated by ANSYS software. Lifetime was calculated by ANSYS and compared with results of accelerated thermal cycling test. The main contents of this thesis include:(1) IMCs (intermetallic compounds) have an important effect on the reliability of solder joint under thermal cycling condition. The push strengthen has obvious decrease with AuSn4 IMC formation, and more decreases with (Cu,Au)Sn IMC formation. Finally, research indicates that the interface between Cu-rich IMC layer and AuSn4 IMC layer is the weakest among the whole interface.(2) The failure phenomenon and mechanism of lead-free solder joint in thermal cycling condition were analyzed. Researches show there are two kinds of solder joint failure modes during thermal cycling. One mode is that cracks often form at the IMCs interface, and another is that solder joints wholly peel off. Cracks often form and grow along the interface between AuSn4 layer and lower Cu-rich IMC layer, and lead to be failure finally. When the seed-layers of Au and FeNi quickly diffuse and grow into IMC in high temperature, the peeling off is apt to happen at the interface between Ta seed-layer and Fe/Ni seed-layer. The reasons are that Ta poor adhesion with brittle IMC and high cyclic shear loading on there.(3) Lifetime prediction model of SnAgCu solder is established by using Weibull Stat. distributing method, and the lifetime of solder in normal working condition is calculated to be 14 years.(4) The stress and strain of solder joint in thermal cycling condition are analyzed by finite element software. The stress and strain of solder respond with periodicity change, which matches with thermal cycling process. The high equivalent stress occurs at the low temperature stage in thermal cycling. Non-elastic strain is dominant in total strain, and the non-elastic strain at the high temperature stage almost amounts to the total strain. The cumulation of non-elastic strain is very obvious at the rise and drop temperature stage during thermal cycling, whereas is not obvious at the high and low temperature dwell stage.(5) The results of finit element simulation and accelerated life test are basically match and validate that lifetime prediction model is reliable to predict the lifetime of SnAgCu solder in thermal cycling condition.更多还原