The deposition process of an electroless copper plating solution using sodium citrate as the main complexing agent and sodium hypophosphite as the reducing agent has been investigated. The deposit composition, structure, and catalytic activity for the oxidation of hypophosphite during the process have been investigated. Formamidine disulfide (fd) has been shown to accelerate the deposition rate of the electroless plating just as it does with electroless plating solutions using N-(2-hydroxyethyl) ethylenediaminetriacetic acid trisodium salt hydrate (HEDTA) as the complexing agent. For solutions with the Cu2+/Ni2+ mole ratio of 42, the deposition rate decreased with time and terminated after 90 min plating because the surface catalytic activity of the deposit had decreased with thickness. A copper deposit with total thickness of 6.48-6.59 mum was obtained after 90 min plating. The decrease in the deposition rate with time was mitigated by decreasing the Cu2+/Ni2+ mole ratio, holding the concentration of copper ions constant. An optimized electroless copper plating process with sustained deposition rate with time and high metal conductivity was developed. The bath was used in a fully additive high density wiring process. (C) 2003 The Electrochemical Society.