Influences of forced convection during acid copper electroplating on microvia fill of printed circuit boards were studied. The plating formula was composed of polyethylene glycol (PEG), chloride ion, 3-mercapto-1-propanesulfonate, and Janus green B (JGB). The filling performances under various plating conditions were examined with scanning electron microscopy and optical microscopy. Chemical and physical interactions between these additives and fluid dynamics were characterized by cyclic linear sweep voltammetry, steady-state current-potential measurements, linear sweep voltammetry, and galvanostatic measurements using different rotation speeds of working electrode. Experimental results indicated that the potential-dependent adsorption of chloride ion on the copper surface determined and governed the electrochemical effect of these organic additives on the cathode, resulting in a convection-dependent adsorption of inhibiting reagents and an asymmetrical fill of copper deposit in the microvias. A synergistic inhibition effect on the copper deposition caused by a composite suppressor composed of PEG, Cu+, Cl-, and JGB was demonstrated. The dominance of the competitive adsorption between the accelerator and the composite suppressor was shown to depend significantly on the chloride ion concentration and on the forced convection. © 2005 The Electrochemical Society. All rights reserved.