Effect of aluminum concentration on the microstructure and mechanical properties of Sn-Cu-Al solder alloy

The effect of aluminum on the microstructure and mechanical properties of Sn-0.7Cu-xAl (x = 0-0.075) solder alloy is investigated. The results show that the microstructure of Sn-Cu solder alloy is refined by Al. The intermetallic compounds (IMC) in the Sn-Cu-Al solder alloy is varied from Cu6Sn5 in the Sn-Cu(0.01-0.025)A1 to Al2Cu in the Sn-0.7Cu-(0.05-0.075)Al. The volume fraction of the IMC and eutectic is raised with increasing aluminum concentration. The wettability of Sn-Cu-Al solder alloy is improved by aluminum. The spreading coefficient of Sn-0.7Cu-0.075Al is reached 70%. The tensile strength of Sn-Cu-Al alloy is decreased after aluminum adding to 0.025 wt.% and then is increased after aluminum adding to 0.075 wt.% due to the IMC variation and the volume fraction increasement of Al2Cu/Sn eutectic with high microhardness. The superior mechanical properties of Sn-0.7Cu-0.075Al are guaranteed by the refined microstructure, the dispersed IMC and the uniform stress distribution. The Sn-0.7Cu-0.075Al is an optimized lead-free solder alloy for the copper substrate. (C) 2015 Elsevier Ltd. All rights reserved.