EN plating (electroless nickel plating) allows even plating, regardless of the geometry and surface area. Plating occurs through the autocatalytic reaction between nickel and hypophosphite. Over time, orthophosphite builds up in the tank. This can affect the appearance of the EN deposit and the corrosion protection it delivers. While the bath can tolerate some orthophosphite build-up, other contaminants such as nitrate affect the EN deposit already at the trace level. Ion chromatography allows monitoring both trace level inorganic impurities and higher concentrated bath components like hypophosphite and orthophosphite.
For every gram of nickel that is reduced, about four grams of orthophosphite are formed. If the orthophosphite concentration becomes too large, free nickel will precipitate as nickel phosphide. Therefore, tracking of the orthophosphite content helps to monitor the EN plating bath’s age. While the baths can tolerate larger amounts of orthophosphite, a few ppm of nitrate already negatively affect the EN deposit and, in the worst case, stop deposition.
Ion chromatography (IC) is ideally suited for the analysis of these anionic species in EN plating baths. Conductivity detection is used to determine hypophosphite, orthophosphite, and phosphate. For the nitrate analysis in the trace level range, UV/VIS detection is used. With Inline Cation Removal, nickel is automatically removed from the sample prior to analysis. In combination with Inline Dilution, the analysis becomes even more convenient, as the sample is automatically diluted, reducing sample preparation to a minimum. To learn more about these determinations, download our free Application Notes.
AN-S-247 Hypophosphite, phosphite and phosphate in a nickel bath