Effect of Chemical Additives in the Plating Bath on Surface Corrosion Resistance of Ni(P)

In this work, the effect of the chemical additives (surfactant, stabilizer) on the corrosion resistance of the Ni(P) layer was investigated. The average O content at the depth of 1 nm of the tested Ni(P) specimens was used as the indication of the corrosion degree for the tested Ni(P) specimen. The average O content at the depth of 1 nm of the tested Ni(P) specimens prepared with thiourea is 27.74 at.%, which is larger than the average O content (14.43 at.%) at the depth of 1 nm of the corrosion-tested Ni(P) layer. It can be concluded that the corrosion resistance of the Ni(P) layer would be greatly reduced two times with adding thiourea in the Ni(P) plating bath. The effect of the solder mask was also investigated on the corrosion resistance of the Ni(P) layer. We found that S impurities leaching from the solder mask might be co-deposited into Ni(P), and decrease the corrosion resistance of the Ni(P) layer. Yet, its influence is relatively lower than the effect of thiourea on the corrosion resistance of the Ni(P) layer. With adding CTAB, as a surfactant, in the Ni(P) plating bath, the average P content in the Ni(P) layer increases. The high P content further improves the corrosion resistance of the Ni(P) layer. Moreover, the positive effect of adding CTAB in the plating solution on the corrosion resistance of the Ni(P) layer would suppress the negative effect of the thiourea additive and solder mask in the plating solution. The main innovation finding of the work is that we found that adding CTAB in the Ni(P) plating solution can reduce the co-deposition of S impurities, from thiourea in the Ni(P) plating bath and the solder mask, in the Ni(P) layer. Consequently, the corrosion resistance of the Ni(P) layer can be further improved.