Effect of soldering condition on formation of intermetallic phases developed between Sn–0.3Ag–0.7Cu low-silver lead-free solder and Cu substrate

In this paper, effect of soldering time and temperature on formation of intermetallic compounds developed between Sn–0.3Ag–0.7Cu lead-free solder and copper substrate was investigated. Dip soldering was performed at 250, 270, and 290 °C with soldering time of 5, 10, 15, and 20 s. Either ɛ-Cu3Sn or η-Cu6Sn5 intermetallic phase was found at the interface between the solder and the substrate depending on the soldering condition, i.e., soldering time and soldering temperature. ɛ-Cu3Sn was found only when the substrate was soldered at 250 °C for 5 and 10 s. At other soldering conditions, only η-Cu6Sn5 was found at the interfacial zone. Crystal structure of ɛ-Cu3Sn intermetallic phase was orthorhombic, and it was hexagonal structure for η-Cu6Sn5. Transformation of the intermetallic phases was also discussed.

► Intermetallic phases found at soldered joint of Sn-0.7Cu-0.3Ag solder and Cu substrate depending on the soldering condition.
► Either η-Cu6Sn5 or ɛ-Cu3Sn phase has been found at the as-soldered interfacial zone.
► ɛ-Cu3Sn phase has not been reported in literature as the initial intermetallic phase at the as-soldered interfacial zone.
► ɛ-Cu3Sn is able to transform to η-Cu6Sn5 as the soldering time increases.