The growth mechanism of an interfacial (Cu,Ni)(6)Sn(5) compound at the Sn(Cu) solder/Ni(P) interface under thermal aging has been studied in this work. The activation energy for the formation of the (Cu,Ni)(6)Sn(5) compound for cases of Sn-3Cu/Ni(P), Sn-1.8Cu/Ni(P), and Sn-0.7Cu/Ni(P) was calculated to be 28.02 kJ/mol, 28.64 kJ/mol, and 29.97 kJ/mol, respectively. The obtained activation energy for the growth of the (Cu,Ni)(6)Sn(5) compound layer was found to be close to the activation energy for Cu diffusion in Sn (33.02 kJ/mol). Therefore, the controlling step for formation of the ternary (Cu,Ni)(6)Sn(5) layer could be Cu diffusion in the Sn(Cu) solder matrix.
