A nitrogen-containing heterocyclic compound N-(3-(5-Mercapto-1H-tetrazol-1-yl) phenyl) acetamide (named L) was investigated as a new leveler to develop the microvias Cu filling with or without cracked plating in blind via. The synergistic effects of L with other plating additives were investigated by galvanostatic measurements (GMs) and cyclic voltammetry (CV) measurements. The GMs show that the Δη values (Potential difference at different speeds of Cu rotating disk electrode) are approximately 24 mV which usually suggests better Cu filling performance for the corresponding electrolyte additives. In addition, the optical microscope (OM) measurements indicated that microvias cracked plating was more likely to occur when there is no accelerator in the copper plating solution. The results of OM experiments also show that the microvia super-filling would not appear although the copper plating rate at the bottom of the blind hole is higher than that of the outer copper layer of the blind hole if there is no air agitation in the copper plating solution. The finest copper electroplating formula made up of the virgin acid solution (VAS) only added the PEP, L, SPS, Cl⁻ was found and applied to carry out superfilling of microvias.