Experimental and theoretical study of high-flat and stable leveler tetrazolium blue chloride in the thickening process of copper through holes

In the through hole plating of printed circuit board (PCBs), the development of highly quality flattening machine has become the core task of the development of through hole thickening. In this paper, tetrazolium blue chloride (TB) with stable structure of tetrazolium is selected as the through-hole plating agent to achieve high plane thickening of PCB through-hole. A series of electrochemical tests show that TB has good adsorption characteristics at the cathode, can effectively suppress copper deposition, and has a convective adsorption effect, and has the potential to be used as a leveler. Its adsorption on the copper surface and interaction with PEG and SPS are confirmed by in situ Raman and in situ electrochemical FTIR spectroscopy. Through quantum chemical calculation, it is analyzed that TB is adsorbed on the surface of copper layer through tetrazolium structure and forms ph···Cu2+ ionic bond, thus co-suppressing copper deposition. Finally, through the throwing force (TP) measurement and atomic force microscope (AFM) experiments, it is confirmed that at the current density of 1.5 A·dm−2, TB has high thickening performance (TP = 136.7 %) and excellent leveling ability (Ra = 22.2 nm) in PCB through hole plating.