Effect of Rinsing on the Oxide Film Properties and Solder Wettability of Bright Nickel-Plated Surfaces

The effect of rinsing immediately after plating on the surface oxidation and solder wettability of bright nickel-plated surfaces has been studied. Nickel plating was carried out in a Watts bath with brightener by an electroplating technique, and the nickel-plated specimens were immediately dipped and rinsed in deionized water. The dissolved oxygen content in the deionized water was controlled by several methods such as aeration, exposure to open air and deaeration with nitrogen. Water temperature was varied from 5 to 100°C. The oxide films on the rinsed surfaces were examined by ellipsometry (ELL), X-ray photoelectron spectroscopy (XPS), and reflection high-energy electron diffraction (RHEED). The thickest oxide film was observed near 80°C with rinsing within 5 minutes. The amount of dissolved oxygen did not significantly affect oxide film thickness below 80°C. The surface oxide film was composed mainly of Ni2O3, its structure being controlled by water temperature. Oxide structure changed from amorphous to crystalline at about 40°C. Both the thickness and structure of the oxide films were found to be important factors for controlling the solder wettability of bright nickel-plated surfaces, and amorphous structure played a particularly decisive role in improving solder wettability. Rinsing in water containing ethyl alcohol dramatically improved solder wettability.