Interfacial reaction between eutectic Sn-58Bi lead-free solder and electroless Ni-P plating

Interfacial reactions between eutectic Sn-58Bi lead-free solder and Cu or electroless Ni-P plating were studied. The joining temperature was 180°C , the aging temperature was 60°C -120°C , and the aging time was 5 to 30 d. The interfacial reaction products determined by SEM, EDAX and XRD are Cu₆Sn₅ on the solder/Cu interface, and Ni₃Sn₄ on the solder/Ni-P interface. In addition, there is a P-rich layer between Ni₃Sn₄ and Ni layer. The growth rate of Cu6Sns is much faster than that of Ni₃Sn₄. The growth rate of Ni₃Sn₄ was found to decrease with increasing P content in the electroless Ni-P plating. The kinetics of the intermetallic compound growth follows a parabolic law of time, as controlled by the diffusion mechanism. The apparent activation energies are 90.87 kJ/mol for the growth of Cu₆Sn₅, 101.43 kJ/mol for Ni₃Sn₄ on Ni-9%P plating and 117.31 kJ/mol for Ni₃Sn₄ on Ni-16%P plate, respectively.