Copper plating is generally used for the fabrication of printed circuit boards of electronic devices. The patterning is carried out by masking with insulator for the partial plating on the substrate. It is desirable to develop a new alternative technology that takes environmental issues into consideration because the partial plating with a mask involves very complicated processes and wastewater treatment. Solid Electro Deposition (SED) method with the solid electrolyte membrane was reported by Yanagimoto et al.¹⁾ as the way to resolve the problem. The SED can be performed by a simple electrochemical cell in which the solid electrolyte membrane is sandwiched by counter and working electrodes. Imposition of voltage between two electrodes enables electrodeposition on the working electrode. The advantages of SED are written as follows.

・The electrochemical cell is very simple because the electrolyte is solid.

・The post-processing is also simple．

・It can be high-rate plating because the driving force of mass transfer of reactant is migration.

Among these advantages, the principle for high-rate plating by SED is explained below. Figure 1 shows the conceptual diagrams of mass transfer of cupric ions on electrode surface in two electrolytes. The charge transfer rate increases depending on the overvoltage in the case of plating in liquid electrolyte. However, the concentration polarization occurs on the electrode surface when the charge transfer rate is higher than the mass transfer rate of reactant. In this case, the driving force of mass transfer in electrolyte is normally diffusion. On the other hand, the mass transfer of reactant is dominated by migration in the SED if the transport ratio of metal ions in the solid electrolyte is unity. In this condition, the charge transfer rate becomes equal to the migration rate and the concentration polarization of reactant in the vicinity of the electrode does not occur, even if the charge transfer rate is increased. Therefore, it is possible to realize high-rate plating because diffusion is not rate-limiting process. We report the relationship between mass transfer mechanisms in solid electrolyte membrane and potential-current curves and establish the theory of high-rate copper plating by the SED. Reference:

1) K. Akamatsu, Y. Fukumoto, T. Taniyama, T. Tsuruoka, H. Yanagimoto, H. Nawafune, Langumuir, 27, 11761-11766 (2011).