Interfacial reactions between In-Sn solder and Ni-Fe platings

Interfacial interactions in a Ni-xFe-Sn-In eutectic solder (x = 30 at.%, 55 at.%) have been examined. Transmission and scanning electron microscopy (TEM/SEM) were utilized to investigate the structure, composition, and morphology of the intermetallic compounds (IMCs). Upon reflow, Ni ₃Sn ₄ and FeSn ₂ phases appeared at the interface along with Cu ₆Sn ₅ in the solder. Annealing experiments revealed the formation of a bilayer IMC that was Fe-rich adjacent to the Ni-Fe metallization and Ni-rich on the solder side. Kinetic studies established the apparent activation energies for both systems to be 51.8 kJ/mol and 85.1 kJ/mol, for 30 at.% and 55 at.% Fe contents, respectively. In the Fe-rich system, globular Ni ₃Sn ₄ crystals were formed upon reflow, but were changed into a cubic/faceted structure after annealing.