Investigation of the Role of Void Formation at the Cu-to-Intermetallic Interface on Aged Drop Test Performance
Investigation of the Role of Void Formation at the Cu-to-Intermetallic Interface on Aged Drop Test Performance
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DOI：
10.1109/tepm.2006.890641
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发表时间：
2007-03
影响因子：
--
通讯作者：
Y. Liu;S. Gale;R. Wayne Johnson
中科院分区：
文献类型：
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作者：
Y. Liu;S. Gale;R. Wayne Johnson
芯片级封装（CSP）广泛应用于便携式电子产品中。机械跌落测试是这些产品的关键可靠性要求。随着向无铅焊料的转变，必须生成新的可靠性数据。CSP报告的大多数跌落试验可靠性数据是针对竣工条件的。然而，机械冲击在产品寿命期间的可靠性同样重要。本文系统地研究了CSP组件的表面光洁度（浸锡和浸银）和回流曲线（冷却速率）对跌落试验可靠性的影响。还对有机可焊性防腐剂（OSP）涂覆的板进行了有限的实验。Sn饰面提供初始Cu-Sn金属间化合物层，而Ag饰面和OSP涂层允许在回流循环期间形成初始Cu-Sn金属间化合物。组件的跌落测试结果与焊点的横截面分析相关，并作为125摄氏度下老化的函数。在125 ℃下老化480 h后，平均跌落失效次数减少约80%。在高温时效过程中，空洞在Cu-Sn金属间化合物与Cu的界面处发展，但裂纹路径是通过金属间化合物层并且不从空洞传播到空洞。因此，可以得出结论，空隙不会导致本研究中观察到的跌落试验存活率降低
Chip-scale packages (CSPs) are widely used in portable electronic products. Mechanical drop testing is a critical reliability requirement for these products. With the switch to lead-free solder, new reliability data must be generated. Most drop test reliability data reported for CSPs are for the as-built condition. However, the mechanical shock reliability over the life of the product is equally important. This paper provides a systematic study of surface finish (immersion Sn and immersion Ag) and reflow profile (cool down rate) on the drop test reliability of CSP assemblies. A limited experiment was also performed with organic solderability preservative (OSP)-coated boards. The Sn finish provides an initial Cu-Sn intermetallic layer, while the Ag finish and OSP coating allows the formation of the initial Cu-Sn intermetallic during the reflow cycle. Drop test results for assemblies as-built and as a function of aging at 125 degC are correlated with cross-sectional analysis of the solder joints. The mean number of drops to failure decreases by approximately 80% with aging at 125 degC through 480 h. Voids develop at the Cu-Sn intermetallic-to-Cu interface during high-temperature aging, but the crack path is through the intermetallic layer and does not propagate from void-to-void. Thus, it can be concluded that the voids do not contribute to the decrease in drop test survivability observed in this study