Current induced rapid phase transformation in Au/Sn reaction couple

Abstract The phase evolution as well as microstructural change of thin film Au/Sn reaction couple was investigated at room temperature with respect to 1.0 × 10 4  A/cm 2 of current stressing. Transmission electron microscopy (TEM) equipped with nano beam electron diffraction (NBED) and energy dispersive X-ray spectrometer (EDS) revealed the fully conversion of Sn layer into AuSn and Au 5 Sn IMCs after deposition. The rapid phase transformation of Au 5 Sn to Au and AuSn, regardless of direction of electron flow, was evidenced by TEM during short time of current stressing. The electron impingement induced lattice strain of Au 5 Sn higher than the offset yield limit was anticipated through in-situ XRD investigation. The lattice adjustment of Au 5 Sn to AuSn due to escape of Au from Au 5 Sn crystal was responsible for the phase transformation. The polarity migration of produced Au atoms from Au 5 Sn crystal to the anode gave rise to the numerous nano voids formation at the original Au 5 Sn/Au interface with forward electric current and dilution of Sn in Au layer with reverse current stressing.