Corrosion behavior of electroless nickel/immersion gold plating by interfacial morphology

Pad discoloration is caused by Ni corrosion during electroless nickel immersion gold (ENIG) treatment, and here it was investigated by SEM, XPS and cross-sectional EDS analysis. Interestingly, we found that the corrosion occurred at two different sites. For relatively thinner Ni layers, the Ni corrosion occurred at the nodule boundary, whereas thicker Ni deposits caused pit corrosions. The electroless Ni had an amorphous structure and had isotropic surface energy. In other words, the domain boundary energy between two Ni nodules did not change during Ni growth. However, the intersection angle of the two surfaces gradually increases during film growth, and the cusp stress between the two nodules also decreases gradually during Ni growth. Hence, the corrosion mode changed from nodule boundary corrosion to pit corrosion. Promoting Ni nucleation as well as increasing the Ni thickness is expected to suppress the pad discoloration by reducing the nodule boundary corrosion. Open image in new window