As an insoluble anode, the reaction process of titanium anode is significantly different from that of soluble anode (phosphocopper sphere). Take the usual oxygen evolution reaction as an example, the chemical reaction equation is as follows:
Insoluble anodes
Soluble anodes
The differences between the anodic chemical reactions of insoluble anodes and soluble anodes are mainly as follows:
The reaction products are different
As can be seen from the above reaction equation, the most convenient part of using soluble anode is that all the metal deposited at the cathode comes from the metal dissolved in the anode reaction, so as to achieve metal balance in the electroplating system. When insoluble anode is used, the anode not only does not produce corresponding metal ions, but also generates additional hydrogen ions. Therefore, for the insoluble anode, in addition to the copper ion also need to consume excess hydrogen ion, so that the whole electroplating system to maintain balance, the most important solution is to use copper oxide. Therefore, the use of titanium anode, almost all need to be matched with additional copper oxide powder adding system, which is the biggest difference with the phosphorus copper ball system.
The reaction process is different
The anodic reaction process of soluble anode is relatively simple. The final reaction is the conversion of copper (0 valence) to copper ion (+2 valence) and the side reaction will also partially produce copper ion (+1 valence). The anodic reaction of insoluble anode is an electrocatalytic reaction process through the noble metal oxide coating on the surface of titanium anode. The basic reaction is the anodic reaction of water electrolysis and the final products are oxygen and hydrogen ions. In this reaction process, not only the coating will lead to the bath of additives through contact caused by a large number of decomposition, at the same time the reaction will produce including oxygen atoms, hydroxyl radicals and other intermediates with strong oxidation, will also cause additional decomposition of additives. This presents A significant barrier to the use of insoluble anodes, which cause additional additive consumption compared to soluble anodes, resulting in significantly higher operating costs for PCB copper plating processes.
The reaction potential is different
The standard electrode potential of insoluble anode is obviously higher than that of soluble anode due to water electrolysis at the anode anode during electroplating. At the same time, the resistivity of titanium is higher than that of copper. Moreover, in general, the use of titanium anodes tends to employ higher current densities. This results in a significantly higher voltage across the plating system when titanium anodes are used than soluble anodes. This voltage difference is at least 1V, even 2V. Compared to the power supply suitable for the phosphocopper sphere, the voltage design of the power supply for the insoluble anode needs to be considered in advance. Of course, from the cost point of view, the cost of power supply will also have a corresponding increase.
