Method for regenerating a cupric chloride and/or ferric chloride containing etching solution in an electrolysis cell

Method and apparatus for regenerating etching solutions obtained by chemily processing metallic surfaces, which solutions contain cupric chloride and/or ferric chloride. The apparatus includes between the anode and the cathode a diaphragm or an ion exchange membrane. The etching solution is passed through the electrolysis cell for anodic oxidation of the cuprous and/or ferrous ions obtained by etching of the metallic surface of a workpiece. An effective quantity of activated pulverous carbon particles is suspended at least in the anode compartment of the electrolysis cell, which cell is in communication with an etching chamber in such a way so as to allow circulating flow of solution.

The present invention relates to a method for regenerating a solution for 
electrochemically processing metallic surfaces of workpieces, which 
solution contains cupric chloride and/or ferric chloride, in an 
electrolysis cell, which has a diaphragm or an ion exchange membrane 
between the anode and the cathode, through which cell a used etching 
solution is passed for anodically oxidizing the cuprous and/or ferrous 
ions obtained by etching of the metallic surfaces. The invention also 
relates to an apparatus for carrying out the method of regenerating such a 
used solution. 
Cupric chloride and/or ferric chloride are known as oxidizing agents in 
etching solutions for processing metallic surfaces. They are used in the 
manufacture of conductor plates or printed circuits. This manufacture 
involves plates of plastic or synthetic material which are provided on at 
least one side with a copper coating or layer which is removed by the 
etching solution in accordance with a template or coating which protects 
those parts of the copper layer which are to remain to be effective in the 
resultant circuitry. Such solutions are also used in the production of a 
surface pattern for printing rollers or cylinders. Aside from surfaces of 
copper or copper alloys, also steel and other hard metal surfaces are 
treated with etching solutions. 
In order to render those methods economically viable, used or spent etching 
solutions are regenerated and reconditioned, as described, for example, by 
Bruch et al. in "Leiterplatten", (conductor plates), Leuze Verlag, 
Saulgau, 1978 (Germany). Particularly in the case when etching copper 
surfaces, it is desirable to recover copper contained in an etching 
solution. 
Electrochemical processes are useful for a continuous reconditioning of the 
etching solution whereby the etching solution is introduced into an 
electrolysis cell, and the oxidation agent for etching is regenerated at 
the anode of the electrolysis cell. When ferric chloride (FeCl.sub.3) is 
used as the etching agent, the ferrous chloride (FeCl.sub.2), formed 
during etching, is oxidized to ferric chloride. Etching solutions which 
contain cupric chloride (CuCl.sub.2) as the oxidation agent can be 
regenerated in a similar manner. Cuprous chloride (CuCl) or ferrous 
chloride, contained in the electrolyte solution after treating of the 
pertaining copper surface, is passed to the anode of the electrolysis cell 
to be converted again into cupric chloride or ferric chloride. It is 
disadvantageous in such processes, however, that chlorine is produced at 
the anode which leads to substantial environmental problems and to 
consumption of the oxidizing agent. 
In order to prevent the formation of chlorine gas, it is known to 
regenerate an etching solution, containing copper chloride or ferric 
chloride as the oxidizing agent, by introducing it into the cathode 
compartment of an electrolysis cell, while adding hydrochloric acid and 
hydrogen peroxide. In such an electrolysis cell the anode compartment is 
separated from the cathode compartment by means of a diaphragm. The anode 
compartment contains a sodium hydroxide solution. The sodium hydroxide 
serves to absorb or receive the chlorine which is produced at the anode 
during regeneration of the etching solution. This chlorine reacts with the 
sodium hydroxide while forming sodium hypochlorite. A high consumption of 
chemicals is disadvantageous in this method. Aside from sodium hydroxide 
also hydrochloric acid and hydrogen peroxide have to be added in order to 
maintain the etching conditions constant in the etching chamber. The toxic 
effect of the sodium hypochlorite formed in the anode compartment is 
furthermore disadvantageous since it requires further treatment. 
A further method has become known for regenerating an etching solution, 
containing copper chloride as oxidizing agent, in an electrolysis cell. To 
prevent the formation of chlorine gas at the anode, the copper content of 
the etching solution to be regenerated and the ratio of cuprous ions to 
cupric ions is limited within a narrow range. In addition, high current 
densities are necessary in the electrolysis cell. Aside from the 
considerable efforts for a control to adjust the predetermined 
concentration limits, as a result, also the deposition at the cathode of 
the electrolysis cell, of the copper etched away, is difficult. Generally, 
only sludge-like precipitates are formed. 
It is accordingly an object of the present invention to regenerate an 
etching solution by introduction thereof into an electrolysis cell while 
avoiding the formation of chlorine in such a way that no toxic substances, 
which would deleteriously affect the environment, are produced. 
It is furthermore an object of the present invention to provide a method 
which is easily carried out. 
It is still another object of this invention to provide an apparatus for 
carrying out the method of the invention.

The method of the present invention is characterized primarily therein that 
an effective amount of activated pulverous carbon particles is suspended 
at least in the anode compartment of the electrolysis cell. 
The pulverous activated carbon particles suspended in the etching solution 
in the anode compartment of the electrolysis cell react with the chlorine, 
which chlorine results after regeneration of the oxidizing agent, while 
forming chloride ions, whereby the activated carbon powder is oxidized. 
The respective concentrations of cupric chloride and/or ferric chloride in 
the etching solution can be maintained relatively high in the presence of 
the active carbon particles. It is furthermore of advantage that metal 
coated workpieces which are etched with an etching solution in accordance 
with the present invention exhibit only a low extent of underetching (side 
etching) of the covered or protected surface regions. The metals removed 
by the etching agent, which metals are dissolved in the solution, are 
recoverable at the cathode of the electrolysis cell which cathode is 
separated from the anode compartment by a diaphragm or an ion exchange 
membrane. The diaphragm or ion exchange membrane is impermeable to the 
activated carbon powder. This is particularly of economic importance in 
the recovery of copper. 
Activated pulverous carbon powder of a concentration of from about 5 to 24% 
by weight is preferred to be added to the etching solution. It is 
furthermore preferred to add activated carbon powder which has been heat 
treated in a vacuum at a temperature of from about 900.degree. to about 
1200.degree. C., whereby heat treating can be carried out in an inert 
atmosphere or in a reducing atmosphere, with the heat treating being 
preferably carried out for about at least one hour. 
The apparatus in accordance with the present invention is characterized 
primarily therein that in the anode compartment of the electrolysis cell 
the etching solution contains suspended in it activated pulverous carbon 
particles. 
The etching solution containing activated pulverous carbon particles or 
activated carbon powder particles is circulated in a circuit including the 
etching chamber and the anode compartment of the electrolysis cell, so 
that at a continuous etching with an etching solution which remains 
constant in composition, particularly in the case of working of 
copper-containing surfaces, a continuous recovery of the copper will be 
possible. Dissolved copper is separated at the cathode of the electrolysis 
cell. 
The invention will be further described with reference to the accompanying 
drawing and on the basis of the examples. 
As indicated in the drawing, the apparatus includes an etching chamber 1 
and an electrolysis cell 2. An etching solution 3 is circulated through 
the apparatus. 
In the etching chamber 1 the etching solution is brought into contact, by 
means of a spray nozzle 4, with the surface of a workpiece 5 which is to 
be processed in the apparatus. The spent or used solution flows to the 
bottom of the etching chamber 1. By suction it is brought from here 
through a suction line or conduit 6, by means of a pump adapted to convey 
the solution, this pump generally designated by the numeral 7, and is 
pumped into the electrolysis cell 2. A partition 10, either a diaphragm or 
ion exchange membrane, is positioned in the electrolysis cell 2 between 
the pertaining anode 8 and the pertaining cathode 9, so that there is 
provided a cathode compartment 11 and an anode compartment 12 which are 
separated by the partition 10. An overflow conduit 13 for the solution 
contained in the cathode compartment is arranged at the cathode 
compartment 11. This overflow conduit 13 is in communication with the 
etching chamber 1. In the embodiment shown, the anode 8 is made of 
graphite and has a tubular configuration, whereby etching solution can 
flow through the tubular anode. The wall of the graphite tube is provided 
with bores or passages 14 which allow movement of the etching solution so 
as to contact the diaphragm or the ion exchange membrane and to allow for 
ion exchange between the anode compartment 12 and the cathode compartment 
11. The oxidizing agent of the etching solution is regenerated at the 
anode 8, while copper, removed from the workpiece 5 when the surface of 
the workpiece is comprised of copper or a copper alloy, is recoverable at 
the cathode 9. The regenerated etching solution flows through the anode 
compartment 12 and through a pressure line or conduit 15 again into the 
etching chamber 1. 
EXAMPLE 1 
In etching solutions with varying iron chloride content, there were 
suspended activated pulverous carbon particles of a concentration of 15% 
by weight, based on the weight of the etching solution. A total of 1.4 
liter etching solution was circulated through the apparatus. At the 
graphite anode a constant current of 5 A was maintained by means of a 
supply of constant current. Etching solution at a temperature of about 
50.degree. C. was removed from the anode compartment and was sprayed at a 
pressure of about 1.5 bar, by means of nozzle 4, from a distance of about 
4 cm onto a stainless steel sheet. 
The weight loss per minute of the stainless steel sheet as a function of 
the iron content in the etching solution was measured. 
At an iron content of 5 g/l in the etching solution, stainless steel was 
removed by etching at a rate of 42 mg/min. The etching velocity increased 
as the iron content of the solution increased; at an iron content of 50 
g/l the metal removal rate was 221 mg/min. During all tests, even after 
complete oxidation of ferrous ions to ferric ions, at a constant current 
of 5 A, no escape of chlorine from the electrolysis cell could be 
observed. The weight loss of activated pulverous carbon particles during 
the test period of 5 hours was below 1%. 
EXAMPLE 2 
In an etching solution containing copper chloride there were suspended 15% 
by weight of activated pulverous carbon particles. 1.4 liter of etching 
solution were circulated through the apparatus in the manner described in 
the foregoing example. At the graphite anode a constant current of 5 A was 
maintained. Etching solution removed from the anode compartment of the 
electrolysis cell was heated to a temperature of about 50.degree. C. and 
was sprayed onto a copper sheet at a pressure of 1.5 bar by means of the 
nozzle 4. 
Even after complete oxidation of cuprous ions to cupric ions, at a constant 
current of 5 A, no chlorine gas development was observed at the 
electrolysis cell. After 5 hours of operation the weight loss of activated 
pulverous carbon particles was below 1%. 
A development of chlorine after regeneration of an iron and copper chloride 
containing etching solution, in which activated pulverous carbon particles 
were suspended, could not be noticed, even after the addition of 1 Mol/l 
sodium chloride. 
The present invention is, of course, in no way restricted to the specific 
disclosure of the specification and drawing, but also encompasses any 
modifications within the scope of the appended claims.