Oxidation and wetting characteristics of lead-free Sn-0.7Cu solder alloys with the addition of Fe and Bi

In this paper, the oxidation and wetting behaviour of Sn-0.7Cu and Sn-0.7Cu-0.05Fe-2Bi solder alloys has been investigated. The alloys were subjected to 200 °C in oxygen rich environment. Weight gain curves reveal that the oxidation behaviour obey the parabolic rate law. X-Ray photo electron spectroscopy (XPS) reveals the presence of SnO and SnO 2 oxide layer on the surface of Sn-0.7Cu solder alloys. SnO was formed as the basic oxide layer. However, at higher temperature SnO transforms into SnO 2 . Addition of Bi results in the formation of Bi 2 O 3 . The Pilling-Bedworth ratio of SnO, SnO 2 and Bi 2 O 3 oxides are 1.28, 1.35 and 1.23 respectively. These ratios confirm the passive nature of oxide layers. Wetting behaviour of Sn-0.7Cu and Sn-0.7Cu-0.05Fe-2Bi were investigated on Cu substrate. The addition of Bi and Fe improves the wetting properties of Sn-0.7Cu solder alloys. Alloying with Bi and Fe results in growth suppression of intermetallic compound at the interface. Increase in spreading rate, decrease in wetting angle and solder height reveals better performance of the Sn-0.7Cu-0.05Fe-2Bi solder alloy. • Addition of Bi decreases the oxidation resistance of Sn-0.7Cu solder alloy. • In Bi added alloy, the thickness of oxide layer increases due to formation of Bi 2 O 3 . • XPS analysis revealed Bi 2 O 3 as the outermost oxide layer, followed by SnO 2 and SnO. • Incorporation of Fe and Bi improves the wetting properties of Sn-0.7Cu alloy. • Growth suppression of IMC was observed with the addition of Bi and Fe.