Effect of sample perimeter and temperature on Sn–Zn based lead-free solders

This paper presents studies conducted on Sn–40Pb, Sn–9Zn and Sn–8Zn–3Bi lead-free solders for electronic applications. Differential Scanning Calorimeter (DSC) profile and the microstructure of the solders were discussed. The wettability between different copper perimeter and molten solders with the presence of flux at 250 °C was investigated. The withdrawal force divided by the sample perimeter was used to calculate the surface tension of the molten solders. The wetting properties of the solders were tested at different temperatures using two types of fluxes. The surface tension of Sn–40Pb, Sn–9Zn and Sn–8Zn–3Bi solders was 0.357, 0.481 and 0.4523 N/m, respectively, and these values showed good agreement with reported data. The Cu6Sn5 IMC phase was formed between Sn–40Pb solder and Cu substrate. The Sn–9Zn solder exhibits Cu6Sn5 and γ-Cu5Zn8 phases with Cu substrate while Sn–8Zn–3Bi solder forms a mixture of Cu–Sn + Cu–Zn phase as a first layer from the solder and γ-Cu5Zn8 phase as a second layer next to the Cu substrate. For Sn–8Zn–3Bi solder the MHS flux improves the wetting force and contact angle at higher temperatures. Increase in sample perimeter has no effect on contact angle but the addition of Bi to the Sn–Zn system reduces the surface tension and contact angle.