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.