Mechanical characterization of doped SAC solder materials at high temperature

Reliable lead free solders are needed for products exposed to extreme environments such as those used in the automotive, avionics, and oil-exploration industries, as well as in military applications. In this study, stress-strain curves have been measured for several doped Sn-Ag-Cu (SAC) solder materials at high temperatures up to 200 °C, and their performances have been compared to those for standard SAC alloys. The doped lead free solder materials are referred to as SAC_R (Ecolloy), SAC_Q (CYCLOMAX), and Innolot by their vendors. SAC_R and SAC_Q are formulated with Sn, Ag, Cu, and Bi (SAC+Bi), while Innolot includes an engineered combination of six elements. Tensile specimens were formed in rectangular cross-section glass tubes using a vacuum suction process, and a water quenched (WQ) solidification profile was utilized. This profile resulted in extremely fine microstructures, and mechanical properties near the upper limit possible for each alloy. Uniaxial tensile testing was performed on the three doped alloys at temperatures of 25, 50, 75, 100, 125, 150, 175, and 200 °C, and a strain rate of 0.001 sec-1. For the SAC_Q alloy, testing was also performed at strain rates of 0.0001 and 0.00001 sec−1, and the Anand constitutive parameters were calculated. The results for the doped solders were compared to standard SAC105 and SAC405 lead free alloys. The mechanical properties of SAC_R were found to exceed those for SAC105 at all temperatures, even though SAC_R does not contain any silver. In addition, the mechanical properties of SAC_Q and Innolot were found to match or exceed those of SAC405 at all temperatures. The new alloys show great promise for use in extremely harsh environments.