Electrochemical and in situ FTIR spectroscopic studies of gentian violet as a novel leveler in through-holes metallization for printed circuit board applications

An organic additive, gentian violet (GVT), is explored for the first time as a novel leveler with excellent property in through-holes (THs) metallization of Cu electronic plating in acidic medium for printed circuit board (PCB) applications. Studies of galvanostatic measurements with a platinum rotation disk electrode and density functional theory calculations demonstrate that the GVT behaves the fundamental leveler's characteristics of mass transfer adsorption, and displays a strong inhibition effect on electro-reduction of cupric ions at high rotating rate. Although the adsorption ability of GVT on Cu surface is weaker than that of commercial leveler Janus Green B (JGB), the potential difference of cupric ion reduction between low and high rotating rates is larger in case of GVT than that of JGB at same current density. Cyclic voltammetry measurements indicate that the Cu amounts of cathodic deposition and that of anodic stripping tend to the same at both low and high rotating rates when GVT, Cl−, polyethylene glycol (PEG) and bis-(sodium sulfopropyl)-disulfide (SPS) coexist in the solution, demonstrating excellent synergistic action of these additives and super leveling effect. In situ FTIR spectroscopic analysis combined with cyclic voltammetry measurements illustrate that the GVT adsorbs on Cu surface and thus affects the electro-reduction of cupric ions, which reveals the very complicated synergistic actions of these additives, i.e., the adsorption ability of GVT can be slightly enhanced by Cl−, while it has been greatly enhanced in the presence of PEG which nevertheless decreases slightly the inhibition effect of PEG on electro-reduction of cupric ions; the SPS plays an antagonistic effect with GVT due to their competitive adsorption. Based on the characterization of GVT as a novel leveler, we developed a GVT-based formula of THs metallization of Cu electronic plating, and demonstrated an excellent efficiency of a throwing power of 97.6% at 10 mA·cm−2 in a real PCB THs metallization of Cu electronic plating.