In situ TEM characterization of interfacial reaction in Sn–3.5Ag/electroless Ni(P) solder joint

This study examined the interfacial reaction in Sn–3.5Ag/electroless Ni(P) solder joints using in situ transmission electron microscopy (TEM). In situ TEM confirmed that the thickness of the ternary layer increased by approximately 70 nm. A new interfacial reaction layer (Ni3P) formed in the P-rich Ni layer/Ni(P) interface. Several Ni–P compounds that formed in the reflow process changed into the stable Ni3P phase. This suggests that the P-rich Ni layer acts as a diffusion barrier layer between the intermetallic compounds and the Ni(P) layer during the annealing process.