LAUSR

Abstract The grain morphology and mechanical strength of the high-melting-temperature intermetallic joints formed in the asymmetrical Ni/Sn/Cu system using a transient liquid phase (TLP) soldering process were investigated. The grain morphology of the (Cu, Ni)6Sn5 compounds subsequently exhibited fine rounded, needlelike and coarse rounded shapes from the Ni side to the Cu side, which was highly in accordance with the Ni concentration gradient across the intermetallic joints. The thermodynamic analysis indicates that the critical Ni concentration which determined the grain morphology between the needlelike shape and the coarse rounded shape is approximately 11 at% at the soldering temperature of 260 °C. The growth of the Cu3Sn compounds was suppressed and exhibited the grain morphology of fine rounded shape. The melting temperature and the shear strength of the intermetallic joints are 418.4 ± 0.1 °C and 49.8 ± 0.3 MPa, respectively. The shear fracture was inclined to occur in the area of (Cu, Ni)6Sn5 grains with the coarse rounded shape.