Phase transformation of the phosphorus-rich layer in SnAgCu/Ni–P solder joints

Abstract

Abstract The interfacial morphologies for the Sn–3Ag–0.5Cu/Ni–P joint were investigated using a field emission electron probe microanalyzer (FE-EPMA). As the Ni–Sn–P formed, several layers of P-rich layers including Ni 3 P, Ni 12 P 5 , and Ni 2 P were observed. The relationship between Ni–Sn–P formation and the evolution of P-rich layers was quantitatively analysed by FE-EPMA and by using the phase diagram of binary Ni–P. It was also proposed that once the Ni 2 P phase was formed, Sn atoms diffused from the solder matrix into Ni 2 P. As a result, the original Ni 2 P transformed to Ni 2 SnP due to the in-diffusion of Sn.