Deformation behavior and constitutive equation of Sn-37Pb solder alloy at cryogenic temperature

Abstract

In this work, the tensile property, ductile-to-brittle transition (DBT) mechanism and constitutive relations of 63Sn-37Pb (Sn-37Pb) solder alloy at cryogenic temperature were studied by uniaxial tensile experiments for different temperatures. The tensile strength of Sn-37Pb solder alloy increases from 38.2MPa (293K) to 178.9MPa (123K) and then declines to 145.2MPa (77K) with decreases of temperature, and its fracture elongation changes from 42.8% (293K) to 10.2% (77K). Mechanical behavior of Pb second phase in Sn-37Pb alloy at low temperatures is illustrated: when the temperature drops to 123K and below, the fracture failure of β-Sn matrix occurs in an open mode. As a result, Sn-37Pb solder alloy fails by brittle fracture mode. Anand model is adopted as a unified viscoplastic intrinsic law to describe the intrinsic relationship of Sn-37Pb solder alloys. Above 123K, Anand model can effectively fit the stress-strain curves of Sn-37Pb solder alloys. When the temperature lower than 123K, the deformation characters of Sn-37Pb solder alloys change from elasto-viscoplastic to elasto-plastic, and Anand model is unable to continue to fit the intrinsic relationship of Sn-37Pb solder alloys. Sn-37Pb solder alloy exhibits more obvious strain hardening at low temperature, and its low-temperature intrinsic response is successfully described by Hollomon’s equation. The research method of the solder alloy is of great significance to solve the reliability problem of low temperature electronic devices.