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Deep via filling is one of key technologies of 3D packaging. Vias are commonly filled by electroplating. Since cupric transportation in vias is limited by diffusion, Current density is one of the most influential factors for copper plating in vias. We investigated new additive of accelerator, suppressor and leveler. Simulation of the competitive adsorption ability of accelerator and suppressor at different potential was studied. It was found that accelerator has more powerful adsorption ability than suppressor at high potential. Suppressor would form a passivating layer at the surface in the electroplating process, but the layer is easily disrupted by accelerator at high potential. We also investigated vias filling at different current density to prove our assumption. 0.4 ASD was the best condition which got a fulfilled via without voids or seams. Conformal growth performance was attained at low current density and large current density would sealed the opening quickly, leaving seam at the bottom.