Side Reactions in Electroless Copper Solutions with Formaldehyde as Reducing Agent

In alkaline electroless copper solutions with formaldehyde as reducing agent, side reactions between formaldehyde and hydroxide occur. In solutions of formaldehyde and sodium hydroxide below 70°C the only reaction found is the Cannizzaro reaction. The rate constant of this reaction was determined at different temperatures, yielding an activation energy of 87 kJ·mol−1. An increase of Na+ concentration leads to an increase of the rate of this reaction. The nature of the anion had no effect. Above 70°C a second reaction proceeds: aldol condensation. Oxygen suppletion inhibits the aldol condensation. Analyses of continuously operating electroless copper solutions showed that the kinetics found in alkaline HCHO solutions could be applied directly to real plating solutions.