Temperature and Flux Effect on Contact Angles and Intermetallic between Sn-8Zn-3Bi Lead-free Solder and Cu Substrate

The influences of temperatures and fluxes on contact angles, intermetallic (IMC) phase and thickness of Sn-40Pb and Sn-8Zn-3Bi solders on copper substrate were investigated. As expected, the contact angle decreases and the intermetallic thickness increases as the temperature increases. The Sn-40Pb solder exhibits a lower contact angles compared to Sn-8Zn-3Bi solder for all the fluxes tested. The Sn-40Pb/Cu system exhibits a single Cu6Sn5 intermetallic. The Sn-8Zn-3Bi/Cu interface exhibits ε(Cu-Zn) and γ-Cu5Zn8 phases and soldering at 280oC exhibits a single γ-Cu5Zn8 phase. Sn-40Pb/Cu gives higher intermetallic thickness compare to Sn-8Zn-3Bi/Cu system when soldering was done at 220oC. On the other hand, the IMC thickness formed by Sn-8Zn-3Bi/Cu system is higher than Sn-40Pb/Cu system for all other temperatures. Although, the fluxes have no significant influence on the thickness of IMC formed, ZnCl2 generally gives lower IMC thickness