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

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 Ni3P, Ni12P5, and Ni2P 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 Ni2P phase was formed, Sri atoms diffused from the solder matrix into Ni2P. As a result, the original Ni2P transformed to Ni2SnP due to the in-diffusion of Sri. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.