Enhancement of creep resistance and thermal behavior of eutectic Sn-Cu lead-free solder alloy by Ag and In-additions

The eutectic Sn-0.7Cu solder alloy is widely used in electronic packaging in which the creep property of the solder joint is essential to meet the global demand for longer operating lifetime in their applications. In this study, the influence of Ag and In additions on tensile creep behavior and thermal properties of bulk eutectic Sn-Cu solder alloy is reported. Results show that addition of Ag and In resulted not only in the formation of new Ag3Sn and gamma-SnIn4 intermetallic compounds (IMCs), but also in the refinement of grain size of Sn-0.7Cu solder from similar to 0.50 to similar to 0.15 mu m. Accordingly, the creep properties of the Ag or In-containing solder alloys are notably improved. The creep strain rate increases and creep lifetime decreases as the applied stress level and temperature increase. Room and elevated-temperature creep rate of bulk Sn-Cu solder was reduced by 521.0\% after Ag addition, but for In addition the reduction was about 200.7\%. These differences are attributed to the presence of new Ag3Sn and gamma-SnIn4 precipitates and their rules in classical dispersion strengthening as a separate phases. Moreover, the eutectic temperature of Sn-0.7Cu is decreased from 227.4 to 217.8 and 224.0 degrees C with the addition of Ag and In, respectively. (C) 2012 Elsevier Ltd. All rights reserved.