A Pd-free activation method for electroless nickel deposition on copper

In this work, a Pd-free activation method for electroless nickel deposition on copper via an immersion nickel technique was developed. In the very solution we studied, high concentration of thiourea resulted in a negative shift of the steady potential of copper, making it possible to realize immersion nickel. The obtained immersion nickel layers were characterized by scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy, demonstrating a co-deposition of sulfur in the nickel layer. Importantly, the post-treatment in 1.0 M NaH2PO2 + 1.0 M NaOH solution was able to eliminate the adsorbed thiourea and stimulate the catalytic activity of the immersion nickel layer for electroless nickel deposition. A combination of open circuit potential measurements and morphology studies indicated that an incubation step was required during the electroless nickel deposition on the immersion nickel layers after post-treatment. Although the catalytic activity of this Ni-activation method was slightly lower as compared to the conventional Pd-activation, both obtained electroless Ni-P layers exhibited similar morphology, chemical composition, corrosion resistance, and adhesion strength. Thus, this work demonstrated that the newly developed Ni-activation method was cost-effective and could be a promising replacement to expensive Pd-activation method currently used in printed circuit board industries.