Patent ID: 7767074

Claim:
A method of etching copper on boards, comprising: applying an electric voltage between a cathode and a board, which constitutes an anode, the cathode and the board being immersed in an electrolyte, wherein: the electrolyte comprises at least a first component, which can be reduced from a first state in the form of an ion comprising a metal atom with a first positive oxidation number, to a second state in the form of an ion comprising the metal atom with a second positive oxidation number, the second positive oxidation number being smaller than the first positive oxidation number; the electrolyte includes a first redox potential for reducing the first component from the first state to the second state and a second redox potential for reduction of divalent copper ions to metallic copper, the first redox potential being greater than the second redox potential; and metallic copper on the board is oxidized and converted into positively charged copper ions while the first component is reduced from its first state to its second state, wherein precipitation of the copper ions on the cathode does not occur.