Method and apparatus for etching copper

In a method for etching copper from articles, which comprises contacting the articles with an etchant solution containing cupric tetramine ions to remove copper from the articles at an etching station whereby the concentration of copper in the etchant solution increases, transferring the etchant solution to an electrochemical cell, removing the copper from the etchant solution as metal by electrochemical reduction in the cell, and returning the etchant solution to the etching station, the improvement which comprises

• transferring the etchant solution to the cathode compartment only of the electrochemical cell, the cell being divided into anode and cathode compartments by an ion exchange membrane;
• wherein the electrochemical cell is arranged so as substantially to inhibit aerial oxidation of the copper metal and the electrochemically-reduced etchant solution therein;
• the depth of the etchant solution in the electrochemical cell being large relative to the surface area of the etchant solution exposed to air;
• wherein the etchant solution is transferred from the etching station to the electrochemical cell when the specific gravity thereof exceeds a threshold value;
• and
• wherein the pH of the etchant solution at the etching station is measured and maintained by a pH controller which can activate means to introduce ammonium ions into the etchant solution at the etching station.

In an apparatus for etching copper from articles comprising an etching station at which in use the articles are to be contacted with an etchant solution containing cupric tetramine ions to remove copper from the articles whereby the concentration of copper in the etchant solution will increase, an electrochemical cell adapted for the removal of copper from the etchant solution by electrochemical reduction, an ion-exchange membrane dividing the cell into anode and cathode compartments, means for transferring the etchant solution to the electrochemical cell from the etching station, and means for returning the etchant solution from the electrochemical cell to the etching station, the improvement which comprises

• arranging for the etchant solution to be transferred to and returned from the cathode compartment only of the cell;
• wherein the electrochemical cell is arranged so as substantially to inhibit aerial oxidation of the copper metal and the electrochemically-reduced etchant solution therein;
• the depth of a portion of the electrochemical cell for containing the etchant solution being large relative to the surface area of an open top thereof;
• means for measuring the specific gravity of etchant solution at the etching station, the said means for measuring being operable to activate the said means for transferring when the specific gravity of the etchant solution at the etching station exceeds a threshold;
• and
• a pH controller for measuring and maintaining the pH of the etchant solution at the etching station by activating means for introducing ammonium ions into the etchant solution at the etching station.