Stress–strain characteristics of tin-based solder alloys at medium strain rate

• Published in: Materials letters 2008-06, Vol.62 (17), p.3031-3034
• Main Authors: Wong, E.H., Selvanayagam, C.S., Seah, S.K.W., van Driel, W.D., Caers, J.F.J.M., Zhao, X.J., Owens, N., Tan, L.C., Frear, D.R., Leoni, M., Lai, Y.-S., Yeh, C.-L.
• Format: Article
• Language: English
• Subjects: Characterization methods; Finite element modelling; Mechanical properties; Strain rate
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/j.matlet.2008.01.101

Drop impact reliability has become an important criterion when assessing the reliability of portable electronics. Finite element software such as ABAQUS is used to simulate solder joints during drop-impact tests and determine the drop-impact reliability of the product. This modelling requires the rate-dependent constitutive properties of the solder in the range of strain rates between 0.1 s − 1 to 300 s − 1 . Unfortunately, the constitutive properties of most solder materials in this range of strain rates have not been characterized. This paper presents the mechanical properties of four solder alloys — 63Sn37Pb, Sn1.0Ag0.1, Sn3.5Ag, and Sn3.0Ag0.5Cu at strain rates between 0.005 s − 1 and 300 s − 1 . The lead-free solder alloys tested exhibited greater strain rate sensitivity compared to 63Sn37Pb. In addition, both the lead-free solders with high Ag content (≥ 3%) exhibited much higher flow stresses compared to 63Sn37Pb. The higher flow stress could explain the lower reliability of these joints in drop tests as a result of shifting of the failure site from the ductile solder to the brittle intermetallic compound [Wong EH, Rajoo R, Mai Y-W, Seah SKW, Tsai KT, Yap LM. Proc. 55th Elec. Comp. & Tech. Conf. 2005;1202–9]. Based on the data obtained, Sn1.0Ag0.1 seems to be the most suitable lead-free alloy to replace eutectic tin-lead in products where drop-impact performance is required.