Suppressors play a significant role in microvia filling by copper electrodeposition to achieve electrical interconnection of the adjacent layers in printed circuit boards (PCBs). In this work, in order to investigate the adsorption behaviors of one type of triblock copolymer (with a structure of polyethylene oxide - polypropylene oxide - polyethylene oxide and a molecular weight of 2900, named as EPE2900) on the cathode during the copper electroplating process, electrochemical methods such as cyclic voltammetric stripping (CVS) was employed. The integrated value of the Cu stripping peak was marked as Q, the size of which can reflect the inhibiting strength of EPE2900 on the copper deposition. Then the dependence of Q/Q(0) values on EPE2900 and Cl- concentrations was studied systematically by the CVS measurements. Here Q(0) was the integrated value of the Cu stripping peak measured in the base electrolyte. The obtained results indicated that the inhibiting strength of EPE2900 monotonously increased with its concentrations. However, the inhibiting strength of EPE2900 only increased with Cl- concentration when EPE2900 concentration was higher than 20 ppm. Importantly, the critical concentrations of Cl- and EPE2900 in the solution to form an intact barrier layer adsorbing onto the cathode surface were calculated. Based on the results of CVS measurements, a possible adsorption model of EPE2900 was proposed, which was able to reasonably elucidate the CVS measurements. In the meantime, Cu+-EPE2900-Cl- complexes were formed and very likely involved in the adsorption model, further evidenced by rotating ring-disk electrode (RRDE) techniques. (C) 2013 Published by Elsevier Ltd.