Copper etchant baths

Copper Etchant Baths. One of the most promising applications of coupled transport is the renovation of circuit board etchant solutions that contain copper.61 The printed circuit board industry produces more than ten million gal-lons/year of spent etchant solutions in which copper, other salts and etchant chemicals are concentrated. Coupled transport permits continuous on-site removal of copper from the etchant solutions and simultaneous regeneration of the etchant solution. This represents a considerable savings in the costs of manufacturing circuit boards. 

Copper etchants do not directly influence the electroless plating process, but are used merely to remove unwanted copper, and should not affect the deposit properties. The costs of waste treatment and disposal have led to disuse of throw-away systems such as chromic—sulfuric acid, ferric chloride, and ammonium persulfate. Newer types of regenerable etchants include cupric chloride, stabilized peroxide, and proprietary ammoniacal etchant baths. 

Copper recovery from etchant baths is a particularly promising application of coupled transport because the high copper concentrations in the etchant solutions result in high fluxes. A relatively small unit is, therefore, able to process a large volume of solution. 

Raw materials for PC board manufacture that contain metals include the following o Copper foil (encasing the board) o Etchants chromic acid, cupric chloride, ferric chloride o Catalysts stannous tin, palladium chloride o Electroless copper bath copper sulfate... 

This process is more complicated because both hydrogen peroxide and hydrochloric acid add water in the reaction process. Since hydrogen peroxide is unsafe to store and handle in concentrations above 35 percent, there is considerable water added with both the oxidizer and the hydrochloric acid. The result hmits the copper-holding capacity of the etchant. The addition is reasonably and simply controlled as a direct ratio of HCl, and peroxide is added to the bath to maintain the copper oxidation. This formulation has been favored in Europe and to some extent in Asia. 

Spent Baths. Certain spent baths can be bled into the ion exchange system.These typically inclnde the copper sulfate electroplating dragout, acid cleaners, predips, microetch and rinses, rinses following cupric chloride and ammoniacal etchants, and copper waste from electrowinning after reduction to 1.0 ppm or less. 

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