Effects of strain rate and temperature on the stress-strain response of solder alloys

To ensure reliable design of soldered interconnections as electronic devices become smaller, requires greater knowledge and understanding of the relevant mechanical behavior of solder alloys than are presently available. The present paper reports the findings of an investigation into the monotonic tensile properties of bulk samples of three solder alloys; a lead-tin eutectic and two lead-free solders (tin-3.5 copper and a tin-3.5 silver alloy). Temperatures between-10 and 75 degrees C and strain rates between 10(-1) and 10(-3) s(-1) have been studied. Both temperature and strain rate may have a substantial effect on strength, producing changes well in excess of 100%. Strength is reduced by lowering strain rate and increasing temperature, and Sn-37 Pb is usually most sensitive to the latter. Expressions for strain and strain rate hardening have been developed. The Sn-0.5 Cu alloy is usually the weakest and most ductile. Sn-37 Pb is strongest at room temperature but with increasing temperature and lower strain rates it becomes inferior to Sn-3.5 Ag. Ductility changes with temperature and strain rate for all three alloys are generally small with inconsistent trends. The role of such data in stress analysis and modeling is considered and the paramount importance of employing data for conditions appropriate to service, is emphasized.