A New Method for Evaluating Fatigue Life of Micro-Solder Joints in Semiconductor Structures
A New Method for Evaluating Fatigue Life of Micro-Solder Joints in Semiconductor Structures
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评估半导体结构微焊点疲劳寿命的新方法
DOI：
10.1115/ipack2005-73331
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
Y. Naka
中科院分区：
文献类型：
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作者：
H. Tanie;T. Terasaki;Y. Naka
传统上，半导体结构中焊点的疲劳寿命是使用科芬-曼森定律来估计的。然而，随着结构变得小型化或更薄，使用传统方法准确估计疲劳寿命变得困难。这是因为在小型或更薄的接头中，疲劳寿命受到裂纹扩展的强烈影响，而传统的方法无法很好地评估这种现象。因此，我们开发了一种评估疲劳寿命的新方法，该方法考虑了微焊点中裂纹扩展的影响。在微焊点中，焊料裂纹路径不仅可能在焊料和焊盘界面本身处扩展，而且可能在界面附近扩展。人们已经提出了许多裂纹扩展方法，但尚未提出可以重现裂纹路径的模型。我们的裂纹扩展模型中焊料的疲劳寿命是根据裂纹扩展过程中累积的损伤来评估的，并自动计算裂纹路径。使用该模型，我们分析了球栅阵列 (BGA) 结构的裂纹路径，并确定该模型可以重现上述特征裂纹路径。当使用有限元方法计算疲劳寿命时，最困难的问题之一是修正单元尺寸的影响。我们确定了计算出的寿命对元件尺寸的依赖性，并开发了一个公式来近似所提出的模型中的这种依赖性。然后，我们使用该公式计算了经过机械疲劳测试的三种不同尺寸 BGA 焊点的疲劳寿命。发现计算的寿命与测量的寿命相对应。此外，我们应用这种方法来评估阻焊层定义（SMD）结构和非阻焊层定义（NSMD）结构的疲劳寿命差异。两者都是BGA焊点的典型结构。我们确定NSMD结构的疲劳寿命比SMD结构长。造成这种差异的主要原因是 NSMD 结构的裂纹扩展寿命比 SMD 结构长，尽管两种结构的裂纹萌生寿命相同。版权所有 © 2005 by ASME
Conventionally, the fatigue life of solder joints in semiconductor structures is estimated using Coffin-Manson’s law. However, as the structures have become miniaturized or thinner, accurately estimate fatigue life has become difficult using conventional methods. This is because the fatigue life is strongly affected by crack propagation in miniaturized or thinner joints, and the conventional methods cannot evaluate this phenomenon well. We have therefore developed a new method for evaluating fatigue life that takes into account the influence of crack propagation in micro-solder joints. In micro-solder joints, a solder crack path might propagate not only at the solder and land interface itself, but also near the interface. Many crack-propagation have been proposed, but a model that can reproduce a crack path has yet to be proposed. The fatigue life of a solder in our crack-propagation model is evaluated based on the damage that accumulates during crack propagation, and the crack paths are automatically calculated. Using this model, we analyzed the crack path of a ball grid array (BGA) structure, and we determined that the model could reproduce the above-mentioned characteristic crack paths. When the fatigue life is calculated using a finite element method, one of the most difficult issues is correcting for the effect of element size. We determined the calculated life dependency on element size, and we developed a formula for approximating this dependency in the proposed model. We then used this formula to calculate the fatigue life of three different size BGA solder joints that were subjected to mechanical fatigue testing. The calculated lives were found to correspond with the measured lives. Furthermore, we applied this method to evaluate the differences in the fatigue life of a solder-mask-defined (SMD) structure and a non-solder-mask-defined (NSMD) structure. Both are typical structures of BGA solder joints. We determined that the fatigue life of the NSMD structure was longer than that of the SMD structure. The main cause for this difference is that the crack-propagation life of the NSMD structure was longer than that of the SMD structure, even though the crack-initiation lives of both structures were the same.Copyright © 2005 by ASME