Electroless Pure Ni Plating Having Higher Reliability of Joint Strength with Sn-Ag-Cu Solder

Abstract

We studied the interfacial reaction layer and joint strength reliability using Sn-Ag-Cu solder on electroless pure Ni/Au plating and Ni-P/Au plating with various P contents. Solder ball pull strength was measured by a hot-ball pull method. In the measured results, decreased P contents resulted in increased average pull strength and smaller scatter. In the Ni-P plating samples, a P-rich layer and dendritic heterogeneous intermetallic compounds (Cu, Ni) ₆Sn₅ formed at the joint interface. The thickness of the P-rich layer increased as the P contents of the Ni-P film increased. On the other hand, in pure Ni plating samples, no P-rich layer and only homogeneous (Cu, Ni) ₆Sn₅ formed at the joint interface. Cross-sectional SIM images of the fracture surface showed that the Ni-P plating samples were ruptured at the upper P-rich layer and the layer between the P-rich layer and the intermetallic compounds (Cu, Ni) ₆Sn₅, whereas the pure Ni plating sample was ruptured at the intermetallic compounds (Cu, Ni) ₆Sn₅. It is suggested that the P-rich layer affects the loss of pull strength. The pure Ni plating samples showed the highest average pull strength, and the smallest scatter, and it is evident that pure Ni plating without P obtained higher reliability.