Effect of Co content on the microstructure, spreadability, conductivity and corrosion resistance of Sn-0.7Cu alloy

Abstract

The effect of Co content on the microstructure, spreadability, conductivity and corrosion resistance of Sn-0.7Cu (mass%, mass fraction except specified) based lead-free solder was studied in this paper. With the addition of Co, the microstructure of Sn-0.7Cu-xCo (x = 0.5, 1.0, 1.5, 2.0) alloy consists of Cu6Sn5, CoSn2 intermetallics, and β-Sn matrix. The morphology of CoSn2 phase changes from small blocks to flake like, short rod-like, and then to massive bulk shape with the increase of Co content. A small amount of CoSn phase formed in Sn-0.7Cu-2.0Co solder alloy. Adding Co reduce the spreading area of Sn-0.7Cu solder alloy slightly. The spread area decreases with the increase of Co content from 0.5% to 1.5%, and then increases again with the addition of 2.0% Co. Sn-0.7Cu-0.5Co solder obtains the largest spreading area among the Sn-0.7Cu-xCo solders. The thickness of reaction layer between Sn-0.7Cu-xCo solder alloys and copper plate is increased with the increase of Co content. The conductivity of the Sn-0.7Cu alloy decreases with the increase of Co content, but the leave of decrease is acceptable. Meanwhile, corrosion resistance of Sn-0.7Cu solder alloy is improved with the addition of Co under salt spray atmosphere. The mass loss rate of Sn-0.7Cu-xCo solder alloy decreases with the increase of Co content.