Through-Hole Copper Electroplating Using Nitrotetrazolium Blue Chloride as a Leveler

The interaction between nitrotetrazolium blue chloride (NTBC) and copper surface was investigated using atomic force microscope (AFM) and X-ray photoelectron spectra (XPS). NTBC was employed as a leveler in the through-hole (TH) electroplating experiments. The electrochemical behaviors of NTBC were evaluated using rotating disk electrode. The results indicate that NTBC is an effective leveler used for TH electroplating. NTBC could be adsorbed on copper surface to form an adsorption layer. The adsorption behavior of NTBC on copper surface indicates that NTBC could inhibit the copper electrodeposition, which provides favorable conditions used as a leveler. In the TH electroplating experiments, a flat copper plating with uniform thickness in the TH was obtained when 3 ppm NTBC was added. The addition of NTBC could increase the cathodic polarization, which is attributed to the adsorption of NTBC on the cathode in the process of TH electroplating. The increase of potential difference at 100 and 1000 rpm with the addition of NTBC proves that NTBC is an effective additive used for TH electroplating.