Tian Ye, Ren Ning, Zhao Zhihua, Wu Fengshun, Sitaraman Suresh K
School of Mechanical and Electrical Engineering, Henan University of Technology, Zhengzhou 450052, China.
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Materials (Basel). 2018 Dec 10;11(12):2509. doi: 10.3390/ma11122509.
As solder joints are being scaled down, intermetallic compounds (IMCs) are playing an increasingly critical role in the reliability of solder joints, and thereby an in-depth understanding of IMCs microstructure evolutions in micro-joints is of great significance. This study focused on coarsening behaviors of Ag₃Sn compounds in Sn-3.0Ag-0.5Cu (SAC305) micro-joints of flip chip assemblies using thermal shock (TS) tests. The results showed that the Ag₃Sn compounds grew and rapidly coarsened into larger ones as TS cycles increased. Compared with such coarsening behaviors during thermal aging, TS exhibited a significantly accelerating influence. This predominant contribution is quantitatively determined to be induced by strain-enhanced aging. Moreover, based on observations for Ag₃Sn microstructure evolutions during TS cycling, one particular finding showed that there are two types of coarsening modes (i.e., Ostwald ripening and Necking coalescence) co-existing in the Ag₃Sn coarsening process. The corresponding evolutions mechanism was elucidated in a combination of simulative analysis and experimental validation. Furthermore, a kinetic model of the Ag₃Sn coarsening was established incorporating static aging and strain-enhanced aging constant, the growth exponent () was calculated to be 1.70, and the predominant coarsening mode was confirmed to be the necking coalescence.
随着焊点尺寸不断缩小，金属间化合物（IMCs）在焊点可靠性方面发挥着越来越关键的作用，因此深入了解微焊点中IMCs的微观结构演变具有重要意义。本研究通过热冲击（TS）试验，聚焦于倒装芯片组件的Sn-3.0Ag-0.5Cu（SAC305）微焊点中Ag₃Sn化合物的粗化行为。结果表明，随着TS循环次数的增加，Ag₃Sn化合物不断生长并迅速粗化为更大的化合物。与热老化过程中的这种粗化行为相比，TS表现出显著的加速影响。经定量确定，这种主要影响是由应变强化老化引起的。此外，基于对TS循环过程中Ag₃Sn微观结构演变的观察，一个特别的发现是，在Ag₃Sn粗化过程中存在两种粗化模式（即奥斯特瓦尔德熟化和颈缩合并）同时存在。通过模拟分析和实验验证相结合的方式阐明了相应的演变机制。此外，建立了包含静态老化和应变强化老化常数的Ag₃Sn粗化动力学模型，计算得出生长指数（）为1.70，并确认主要的粗化模式为颈缩合并。
