Electroless Deposition of Highly Solderable Fe-Ni Films

The simultaneous electroless-deposition of Fe and Ni is challenging because Fe has a more negative standard reduction potential than Ni. In this study, FeNiP electroless deposits with Fe content up to 97 at.% were prepared by complexing with disodium ethylene diamine tetraacetate (EDTA-2Na). The addition of ETDA-2Na complexing agent effectively reduced the difference in the electrode potential between Ni and Fe from 0.21 V to 0.156 V, resulting in Fe-Ni depositions with very high Fe concentrations. The iron concentrations of deposited films were systematically investigated as functions of bath temperature, concentrations of EDTA-2Na and DTPA, mole ratio of Fe2+/Ni2+ and contents of NH3*H2O in the plating bath. The solderability of electroless FeNiP deposits with Sn and SnAgCu solders was found to increase with the iron content in the deposits from 0 at.% to 85 at.%, and to be better than that of the electroless NiP.