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, Ni3Sn4 and FeSn2 phases appeared at the interface along with Cu6Sn5 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 Ni3Sn4 crystals were formed upon reflow, but were changed into a cubic/faceted structure after annealing.