[en] The morphology and phase transformation of the intermetallic compounds (IMCs) formed at the Sn-9Zn-3.5Ag/Cu interface in a solid-state reaction have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The monoclinic η'-Cu₆Sn₅ transforms to the hexagonal η-Cu₆Sn₅ and the orthorhombic Cu₅Zn₈ transforms to the body-centered cubic (bcc) γ-Cu₅Zn₈ as aged at 180 deg. C. The scallop-shaped Cu₆Sn₅ layer is retained after aging at 180 deg. C for 1000 h. In the solid-state reaction, Ag is repelled from η'-Cu₆Sn₅ and reacts with Sn to form Ag₃Sn, and the Cu₅Zn₈ layer decomposes. Kirkendall voids are not observed at the Sn-9Zn-3.5Ag/Cu interface even after aging at 180 deg. C for 1000 h