Blind vias filling by direct-current copper electroplating is widely used in printed circuit boards (PCBs) to increase input/output (I/O) density due to high density interconnection. The blind vias of a PCB can be filled perfectly by copper electroplating using organic additives such as suppressor, leveler and accelerator in a copper plating bath. However, the current density cannot be raised too high because a void is easily formed at the blind via after filling plating at a high current density. Therefore, this work is to adjust the ratio of organic additives to fill the blind vias of a PCB by copper electroplating at 25℃~30℃ and at a high current density (i.e., 5 A/dm²). The filled blind vias were examined by cross-sectional analysis using an optical microscope (OM) and a scanning electron microscope (SEM). In addition, synergistic effect of organic additives on copper deposition was analyzed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) to explain how did these additives work for superfilling of the blind via at the high current density.