The preferred insoluble anode is stainless steel and relatively little difficulty arises.
The archetype anode is graphite which is essentially cheap and which by reacting as an otherwise insoluble anode with the anode product oxygen can reduce the thermodynamic anode potential.
Insoluble anodes usually generate oxygen (chlorine is possible in chloride solutions) in completing the circuit but may also oxidise metal ions to a higher valency state, raise dissolved oxygen levels, oxidise additives and complexants (eg.
It is clearly necessary that insoluble anodes are not attacked, either physically by spalling or chemically by solution constituents, because this leads to solution contamination, and that they allow high conductivity passage of current.
* Anode material (copper anodes or insoluble anodes).
PCBs (size: 500 mm x 400 mm) with blind microvias ([empty set]: 100 [micro]m, depth: 80 [micro]m) were copper-plated in a 1400-litre test module equipped with insoluble anodes. This test module is identical in construction to the electroplating module of a vertical continuous plating line introduced into market a few years ago.
The electrolyte is used under direct current conditions and with insoluble anodes at a maximum temperature of 22[degrees]C.