Application of Electrodeposited Ni-P Film for the Improvement of Corrosion Resistance in Au-Co/Ni Processes

An electroplated Ni–P film with about 0.9 wt% co-deposited phosphorus was obtained using a sulfamic-acid-type Ni electroplating solution containing 0.05 mol/dm3 of phosphoric acid for improvement of corrosion resistance. However, crack-formation-deposited Ni–P films were often observed under operation at pH 4. This problem was resolved by operation at pH of 2.5. Furthermore, we were able to achieve crack-free Ni-P deposition with high current density. Moreover, bright Ni–P films were obtained using acetic acid or formic acid as the organic acid. The phosphorus content might be controllable by changing the phosphorous acid concentration. Crack-free Ni–P films with about 4.0 wt% co-deposited phosphorus were formed by addition of 0.4 mol/dm3 phosphorous acid and 0.2 mol/dm3 acetic acid as the organic acids. Next, we plated various Ni(3 μm) and Au–Co(0.03 μm) films on test substrates for which the corrosion resistance of the resulting electroplated Au–Co/Ni films were examined. The electroplated Au–Co/Ni–P films were superior corrosion-resistant electroplated Ni films. Their corrosion resistance improved with the increase of phosphorus content.