Formation and morphology of the intermetallic compounds formed at the 91Sn-8.55Zn-0.45Al lead-free solder alloy/Cu interface

Formation and morphology of the intermetallic compounds (IMCs) formed at the 91Sn-8.55Zn-0.45Al lead-free solder alloy/Cu interface has been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED). The XRD analysis indicates that the γ-Cu5Zn8 IMC is found at the solder/Cu interface in the as-wetted sample. When heat treated at 423 K for 100 or 400 h, the IMC phases still remain as γ-Cu5Zn8 and Cu6Sn5. As the aging time increases from 400 to 1000 h, besides γ-Cu5Zn8 and Cu6Sn5, γ′-Cu9Al4 also appears. Planar-shaped γ-Cu5Zn8 and Cu6Sn5 are found near the solder and the Cu substrate, respectively. However, scallop-shaped γ-Cu5Zn8 is found at the eutectic 91Sn-8.55Zn-0.45Al solder alloy/Cu interface when aged at 423 K.