Microstructure and shear strength of a Au–In microjoint

Two types of Au–In microjoints, i.e. Au/In/Au in which In foil was used and Au/In, were prepared by either solid state interdiffusion (SSID) or solid–liquid interdiffusion (SLID) bonding for single lap tensile test. Deposition of the Au and In thin films was carried out by thermal evaporation on a polyethylene terephthalate (PET) substrate. It is found that the shear strength of the Au/In microjoints is higher than that of Au/In/Au using In foil. It is also observed that the fracture mode of Au–In microjoints depends on the types of In used. Failure of the Au/In microjoints appeared to be along the joint–substrate interface, whereas it occurred within the In foil for the other type of specimens. Examination of the Au/In microjoints by glancing angle X-ray diffraction reveals the presence of the two major constituent phases, Au7In3 and Au, as well as other intermetallics AuIn2, Au10In3, and Au9In4 in small amount. On the other hand, only the intermetallic AuIn2 and pure In were observed in the Au/In/Au microjoints, where the total thickness of In is much higher than that of Au.