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42 SMT Magazine • March 2014 based on their performance in early circuit-board reliability testing programs. The mechanical be- havior of these alloys shows that the addition of Bi to SnAg or SAC leads to a different response to isothermal aging than is seen in SAC305. These results do not necessarily explain the per- formance of Bi-containing alloys in reliability testing, but they do show the extent to which the mechanical behavior of different alloys can vary. The results of this research demonstrates the need for microstructure-based material prop- erties for modeling of solder joint behavior in long-lifetime high-reliability systems but they also suggest that the additions of small amounts of Bi could decrease changes in solder alloy prop- erties over time and result in more readily pre- dictable solder joint deformation. acknowledgements The research described here was supported by The Aerospace Corporation's Independent Re- search and Development program, and was un- dertaken with the enthusiastic support of Dr. L. Parker Temple III. I thank numerous colleagues for their contributions: Dhruv Patel, Ben Nelson, Byron Zeigler, Jay Yamasaki, Robert Castaneda, and Brian Gable, as well as student interns Kareem Hammoud, Jonathan Salfity and Swati Bhanderi. All trademarks, service marks and trade names are the property of their respective owners. SmT references 1. NCMS, Lead-Free Solder Project: Final Report, National Center for Manufacturing Sci- ences, Ann Arbor, Mich., 1997. 2. NCMS, Lead-free, High-temperature, Fa- tigue-resistant solder: Final Report, National Center for Manufacturing Sciences, Ann Arbor, Mich., 2001. 3. JCAA-JGPP, JCAA-JGPP Lead Free Solder Project Joint Test Report, Executive Summary, International Trade Bridge, Dayton, Ohio, 2006. 4. NASA TEERM, NASA-DoD Lead-Free Elec- tronics Project Joint Test Report, December 2011. 5. F.W. Gayle, G. Becka, J. Badgett, G. Whit- ten, T.Y. Pan, A. Grusd, B. Bauer, R. Lathrop, J. Slattery, I. Andersen, J. Foley, A. Gickler, D. Napp, J. Mather, C. Olson, JOM, 53 (2001) 17- 21. 6. P.T. Vianco, J.A. Rejent, J. Elec. Mat., 28 (1999) 1127-1137. 7. D. Fritz, B. Russell, G. Latta, in: 7th IPC International Conference on Reliability, Re- work and Repair of Lead-Free Electronics, IPC, Raleigh, NC, 2008. 8. F.A. Mohamed, K.L. Murty, J.W. Morris, Met. Trans. A, 4 (1973) 935-940. 9. D.B. Witkin, Mat. Sci. Eng. A, 532 (2012) 212-220. 10. D.B. Witkin, J. Elec. Mat., 41 (2012) 190- 203. 11. A.U. Telang, T.R. Bieler, A. Zamiri, F. Pourboghrat, Acta Mat., 55 (2007) 2265-2277. 12. T.K. Lee, B. Zhou, L. Blair, K.C. Liu, T.R. Bieler, J. Elec. Mat., 39 (2010) 2588-2597. 13. H. Ma, J.C. Suhling, Y. Zhang, P. Lall, M.P. Bozack, 57th IEEE ECTC (2007), 653-668. 14. Y. Zhang, Z. Cai, J.C. Suhling, P. Lall, M.P. Bozack, 58th IEEE ECTC (2008), 99-112. 15. J.-P. Clech, SMTAI04, Proceedings, SMTA (2004). 16. H. Ma, J. Mat. Sci., 44 (2009) 3841-3851. 17. D. Mittlin, C.H. Raeder, R.W. Messler, Met. Mat. Trans. A, 30 (1999) 115-122. 18. P.T. Vianco, J.A. Rejent, A.C. Kilgo, J. Elec. Mat., 33 (2004) 1389-1400. 19. P.T. Vianco, J.A. Rejent, A.C. Kilgo, J. Elec. Mat., 33 (2004) 1473-1484. 20. R.S. Lakes, Rev. Sci. Inst., 75 (2004) 797- 810. 21. L. Yang, L. Yin, B. Roggeman, P. Borge- sen, 60th IEEE ECTC (2010) 1518-1523. 22. A.S. Nowick, B.S. Berry, Anelastic Relax- ation in Crystalline Solids, Academic Press, New York, 1972. 23. L.S. Cook, R.S. Lakes, Scripta Met. Mat., 32 (1995) 773-777. 24. V. Venkatadri, L. Yin, Y. Xing, E. Cotts, K. Srihari, P. Borgesen, 59th IEEE ECTC (2009) 398-405. 25. T.K. Lee, W. Xie, B. Zhou, T.R. Bieler, K.C. Liu, J. Elec. Mat., 40 (2011) 1967-1976. NOTE: This article was presented at the IPC APEX EXPO Technical Proceedings. David b. Witkin is an engineer with The aerospace corporation. mEchaNIcaL BEhavIOr OF BISmUTh PB-FrEE SOLDErS continues feaTure