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

Abstract 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.