Effects of strain rate and temperature on mechanical behavior of SACB solder alloy

Abstract

With the deep research of the reliability of electronic package, more and more investigator realizes that the study on the high strain rate behavior of materials is necessary. Drop impact reliability has become an important criterion when assessing the reliability of portable electronics. The quality of solder joints directly determines the drop-impact reliability of the product. Therefore, to study the dynamic stress-strain constitutive relationship and the fracture/failure behavior of the solder material due to an external impact rate loading become important. Solder balls, as a structural member of the electronic product, are used to connect the microchip and the associated printed circuit board by a proper joining technique such as the surface mount technology (SMT). The static compressive properties of Sn3.0Ag0.7Cu3.0Bi lead-free solder are studied through quasi-static compression testing. In addition, The mechanical behavior of the two lead-free alloy, at strain rates ranging from 3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 1.2times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and temperatures between 25degC and 140degC, was investigated with the compressive split-Hopkinson pressure bar (SHPB). The dynamic property of Sn-3.0Ag-0.7Cu-3.0Bi alloy was assessed by means of split Hopkinson pressure bar test technique. The strain rate sensitivity of the lead-free solder is characterized using a modified split Hopkinson pressure bar system. The experimental results indicate that, the strain rate sensitivity parameter increases along with increasing strain and strain rate, but decreases with increasing temperature. The addition of Bi delays the sensitivity of strain rate of the lead-free solder. The influence of the addition of Bi on the dynamic stress - strain constitutive relationship and the fracture/failure behavior of the solder material is investigated. The activation energy varies inversely with the flow stress, and has a low value at high deformation strain rates or low temperatures. In this paper, Quasi-static and high strain rate properties of the lead-free solder with temperature are given. Basing on these experimental data, the constitutive relation of Johnson-cook model for this kind of material was built up.