STUDY ON LEAD-FREE SOLDER JOINT RELIABILITY BASED ON GRAIN ORIENTATION
XU Jiayu, CHEN Hongtao, LI Mingyu
1) Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055
2) State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001
Cite this article:
XU Jiayu CHEN Hongtao LI Mingyu. STUDY ON LEAD-FREE SOLDER JOINT RELIABILITY BASED ON GRAIN ORIENTATION. Acta Metall Sin, 2012, 48(9): 1042-1048.
Abstract During service, coefficient of thermal expansion (CTE) mismatch between different materials in electronic devices can lead to stress and strain concentration, and the creep and fatigue damage will accumulate, leading to final failure of solder joints. The main constituent of Pb-free solder joint is β-Sn, which is body-centered tetragonal metal. There is big difference in CTE and elastic modulus along different directions of β-Sn, showing strong anisotropy. Therefore, solder joints with different orientations show quite different thermo-mechanical responses. In this study, ball grid array (BGA) assemblies were subjected to thermal cycling, and the orientation of the solder joints was characterized by EBSD to track the orientation evolution in different solder joints. Surface Evolver was adopted to simulate the three-dimensional shape of the solder joint. Based on the shape and grain structure of real lead-free solder joints, the thermal stress and strain distribution in BGA assemblies under thermal loading were computed. Sub-model based on grain numbers and orientation distribution is solved to get the strain distribution of the three typical solder joints. The experimental and simulated results show that grain orientation significantly influences the solder joint reliability and failure mode. For single-grained solder joints, stress and strain concentration is located in the solder bulk near the interface, where recrystallization accompanied with initiation and propagation of cracks. However, for multi-grained solder joints, the distribution of stress and strain depends on grain orientation. Recrystallization and cracking tend to divert from the interfacial region into the solder bulk along the pre-existing grain boundary. Some special solder joints with grain boundary perpendicular to the interface are not favorable for deformation, exhibiting higher reliability. When the grain boundary inclined at 45o to the pad, the original grain boundaries produce large stress and strain concentration under combined action of shear stress and anisotropy of Sn grains, accelerating the crack initiation and propagation, and fracture occurred along the original grain boundaries, increasing the probability of early failure.
Supported by National Natural Science Foundation of China (No.50905042) and State Key Laboratory of Advanced Welding and Joining Foundation,
Harbin Institute of Technology (No.AWPT-M12-02)
[1] Telang A U, Bieler T R, Choi S, Subramanian K N. J Mater Res, 2002; 17: 2294
[2] Zeng K, Tu K N. Mater Sci Eng, 2002; R38: 55
[3] Bieler T R, Jiang H R, Lehman L, Kirkpatrick T, Cotts E, Nandagopal B. IEEE Trans Components Packag Technol, 2008; 31: 370
[4] Wang YW, Lu K H, Guta V, Stiborek L, Shirley D, Chae S H, Im J, Ho P S. J Mater Res, 2012; 27: 1131
[5] Son P V, Fujitsuka A, Ohshima K I. J Electron Mater, 2012; 41: 1893
[6] Henderson DW,Woods J J, Gosselin T A, Bartelo J, King D E, Korhonen T M, Korhonen M A, Lehman L P, Cotts E J, Kang S K, Lauro P, Shih D Y, Goldsmith C, Puttlitz K J. J Mater Res, 2004; 19: 1608
[7] Mattila T T, Vuorinen V, Kivilahti J K. J Mater Res, 2004; 19: 3214
[8] Telang A U, Bieler T R, Zamiri A, Pourboghrat F. Acta Mater, 2007; 55: 2265
[9] Zhou B, Bieler T R, Lee T K, Liu K C. J Electron Mater, 2010; 39: 2669
[10] Chen H T, Mueller M, Mattila T T, Li J, Liu X W, Wolter K J, Paulasto M. J Mater Res, 2011; 26: 2103
[11] Chen H T, Wang L, Han J, Li M Y,Wu Q B, Kim J M. J Electron Mater, 2011; 40: 2445
[12] Chen H T, Han J, Li J, Li M Y. Microelectron Reliab, 2012; 52: 1112
[13] Chen H T, Han J, Li M Y. J Electron Mater, 2011; 40: 2470
[14] Lee T K, Zhou B, Bieler T, Liu K C. J Electron Mater, 2012; 41: 273
[15] Lee T K, Xie W, Zhou B, Bieler T, Liu K C. J Electron Mater, 2011; 40: 1967
[16] Vandevelde B, Gonzalez M, Limaye P, Ratchev P, Beyne E. Microelectron Reliab, 2007; 47: 259
[17] Gong S G, Xie G L, Huang Y Q. ANSYS APDL and Command Manual. Beijing: China Mechine Press, 2009: 235
