The role of a ternary Ni-Sn-P layer as a diffusion barrier in the Sn-Ag solder/electroless Ni-P system

This study examined the ternary Ni₂SnP layer in Sn-3.5Ag/EN-P solder joints by using in situ transmission electron microscopy (TEM). The TEM analyses confirmed that Sn from the solder diffused into the P-rich Ni layer through the ternary Ni-Sn-P layer. However, Ni was neither detected in the solder region nor formed an additional Ni₃Sn₄ IMC layer at the interface between the solder and the ternary layer during the in situ annealing in the TEM. This suggests that the ternary Ni-Sn-P layer acts as a diffusion barrier to Ni during the aging process.