The impact of the ferric/ferrous (Fe3+/Fe2+) redox couple on the behavior of polyethylene glycol (PEG) and bis-(3-sulfopropyl) disulfide (SPS) during copper electrodeposition is investigated. The Fe3+/Fe2+ couple is used in plating of copper onto printed circuit boards and may have advantages when implemented for on-chip metallization of copper. Experiments show that in the presence of Fe3+/Fe2+ the suppressing behavior of PEG does not change; in contrast, the accelerating activity of SPS increases when Fe3+/Fe2+ is present in a copper-plating bath. Furthermore, potentiostatic experiments suggest that SPS interacts with Fe2+ ions in the bulk electrolyte, probably to produce 3-mercapto-1-propane sulfonic acid (MPS) at low ppb levels. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3575638] All rights reserved.