Microstructure, interfacial IMC and mechanical properties of Sn-0.7Cu-xAl (x = 0-0.075) lead-free solder alloy

The effect of aluminum concentration on the microstructure, wettability, interfacial IMC and mechanical properties of Sn-0.7Cu lead-free solder alloy is investigated. The results show that the microstructure of Sn-Cu-Al solder alloy consists of β-Sn, eutectic and IMC, and the microstructure of Sn-0.7Cu alloy is refined by adding aluminum. The interfacial IMC at the boundary of β-Sn in the Sn-0.7Cu-(0.01-0.025)Al is Cu6Sn5, and it is varied to Al2Cu in the Sn-0.7Cu-(0.05-0.075)Al. The wettability of Sn-Cu-Al solder alloy is improved by aluminum, the spreading coefficient of Sn-0.7Cu-0.075Al reaches about 70%. The thickness of the scalloped interfacial IMC is dominated by the IMC variation, and the chemical reaction between Cu and segregated Al. The mechanical properties of Sn-Cu-Al solder alloy are decreased slightly by adding aluminum. The tensile strength and the creep resistance of Sn-0.7Cu-(0.05-0.075)Al are superior to Sn-0.7Cu-(0.01-0.025)Al due to the hindering dislocation slipping by the disperse Al2Cu. Sn-0.7Cu-(0.05-0.075)Al is an applicable lead-free solder alloy for the Cu substrate.