Ammoniacal etchants

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. 

Yang, Q. and Kocherginsky, N.M. (2006) Copper recovery and spent ammoniacal etchant regeneration based on hollow fiber supported liquid membrane technology From bench-scale to pilot-scale tests. Journal of Membrane Science, 286, 301. 

CEER process — (Capenhurst electrolytic etchant regeneration process) Electrochemical process for continuous copper removal from printed circuit board etching solutions employing either cupric chloride or ammoniacal etchant. In a cell divided by a cation exchange membrane the etching process is essentially reversed. In case of the cupric chloride etchant the etchant solution is pumped to the anode, the processes are at the... 

In the etching process employing a slightly acidic ammoniacal etchant the etching reaction is... 

FIGURE 4.15 Industrial installation for copper recovery from spent ammoniacal etchant solution by an SLM in a 160 m module processing 100 L/day. (From Sirkar, K.K., Ind. Eng. Chem. Res., 47, 5250, 2008.)... 

Jieh-Hwa Shyu, Electrochemical Studies of Etching Mechanisms in Ammoniacal Etchants, IPCTP-751, October 1988. 

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. 

Modern ammoniacal etchants are mildly alkaline solutions containing ammonium carbonate, cupric and chlorite ions together with proprietary additives. Metallic etch resists including tin-lead are not usually attacked but the pH and solution composition must be maintained in order to preserve the etch rate and prevent sludge formation. A possible set of reactions is ... 

The CEER process has also been used for ammoniacal etchants (Fig. 9.12(b)] when a sulphuric acid anolyte is preferred together with platinized titanium anodes graphite cathodes are retained. In this case the anode reaction is oxygen evolution etchant oxidation readily takes place chemically via dissolved oxygen in the etching machine ... 

Fig. 9.12 The Capenhurst Electrolytic Etchant Regeneration (CEER) process, (a) Cupric chloride etchant, (b) Ammoniacal etchant.

Concentrated waste solutions are obtained from spent metal plating baths and etchants. However, the majority of metal wastes are soflds or sludges obtained from the hydrolysis of metal-bearing solutions and industrial process effluents. Most of these water-insoluble wastes are composed of hydroxides or basic salts of the contained metals. Eor processing by hydrometallurgical routes the materials must be brought into solution usually by acid or ammoniacal or alkaline digestion. 

Ferric chloride solutions are used as etchants for copper, copper alloys, Ni/Fe alloys, and steel in PC applications, electronics, photoengraving arts, and metal finishing. Current use of ferric chloride etchant in printed wiring fabrication is extremely limited in the United States because of costly disposal of the copper-containing etchant, and the much better commercial support for ammoniacal and cupric chloride etchants. There is still considerable use for alloy etching and photochemical machining applications. 

A number of etchants are in use, depending upon the nature of the process and, to an extent, personal preference or tradition. These include (1) ammonium persulphate (2) sodium persulphate (3) potassium peroxysulphate (4) cupric chloride (5) FeClj (6) H2Cr04 (7) ammoniacal chlorite and (8) hydrogen peroxide/sulphuric acid. 

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