EP0122963B1 - Apparatus for regenerating an ammoniacal etching solution - Google Patents

Abstract

1. Equipment for regenerating an ammoniacal etching solution which contains catalyst particles for reoxidation with supply of oxygen, having a feed line for etching solution taken from an etching chamber to a filter which is impermeable to catalyst particles in the etching solution, and a return line, connected to the filter, for etching solution, containing catalyst particles, to the etching chamber, and having an electrolytic cell, in which a connecting line, connected to the filter, for catalyst particle-free etching solution obtainable as the filtrate ends and which has an outlet, connectable to the etching chamber, for etching solution which has been deplected of metal ions, characterized in that a liquid-jet pump (10) is inserted into the return line (9), the working medium of the pump being the etching solution and the suction branch (11) of the pump being connected to an oxygen line (12) which carries oxygen or an oxygen-containing gas mixture and which can be fed with oxygen generated at the anode (17) of the electrolytic cell (13), and that teh oxygen line (12) is connected to the gas space above the electrolyte in the electrolytic cell (13) and passes to the suction branch (11) via a condenser (42) for precipitating water vapour from the gas mixture carried in the oxygen line (12), and that a condensate line (44) discharging condensate produced on the condenser (42) ends in washing chamber (2) downstream of the etching chamber (1).

Description

The invention relates to a system for regenerating an ammoniacal etching solution. Oxygen is fed to the etching solution for the re-oxidation of the etchant contained in the etching solution, optionally in the presence of a catalyst contained in the etching solution. In order to recover etched metal, at least part of the etching solution flows through an electrolysis cell, metal being deposited cathodically and oxygen being produced at the anode of the electrolysis cell. The system features from which the invention is based are specified in the preambles of claims 1 and 8.

Alkaline etchants are used for etching metallic objects, in particular for the production of printed circuit boards, which are also known under the name “printed circuits”, especially when the printed circuit boards to be etched are metal parts which are not resistant to acidic etching media, for example made of lead, tin or nickel, exhibit. A reoxidation of the alkaline etching solution after etching off the metal is carried out with the addition of ammonia gas and / or ammonium chloride in the presence of oxygen or air.

From DE-A 3 031 567 it is known to suspend catalyst particles in the etching solution, which accelerate the etching itself, but also the reoxidation of the etching solution and thus save the addition of chemical oxidizing agents, which lead to toxic residual solutions. In this known device, the etched metals are deposited in an electrolysis cell. For this purpose, part of the etching solution, which has ammonium sulfate, flows through the electrolytic cell. The etched metals are deposited on the cathode of the electrolytic cell, oxygen is generated on the anode.

In the known device, the etching solution containing the catalyst particles is sprayed in air for reoxidation. This is done directly in the etching chamber by spraying the etching solution onto the workpieces to be processed. The reoxidation with air is not an advantage in all cases. This is particularly not the case because ammonia is added to the etching solution to adjust the pH and odor nuisances and environmental problems caused by evaporating ammonia should be kept as low as possible.

The object of the invention is to mix the etching solution intensively in a simple manner with a gas having a high oxygen content in a system of the type mentioned.

This object is achieved according to the invention by the design of the system specified in claim 1. The oxygen formed at the anode of the electrolytic cell is fed to the etching solution. The gas fractions introduced into the etching solution, which do not contribute to the reoxidation, such as the nitrogen fractions in air, are low. At the same time, oxygen is advantageously used which arises in the electrolysis cell when the etched metal is recovered. A liquid jet pump serves for the entry, the working medium of which is the etching solution and the suction nozzle of which is connected to an oxygen line connected to the electrolysis cell. With the liquid jet pump, rapid reoxidation is achieved through intensive mixing and fine distribution of the gases containing oxygen.

In order to separate water vapor that is entrained when the oxygen and ammonia are sucked out of the gas space of the electrolysis cell, even before the gas mixture is introduced into the etching solution, the oxygen line connected to the gas space above the electrolyte of the electrolysis cell is guided over a condenser in which the gas mixture is cooled and Water vapor is excreted. The condensed water is used as rinsing water for the etched workpieces and thus reduces the total amount of detergent required. The condensate line leading away the condensate from the condenser expediently opens into the last rinsing chamber of the system. It is advantageous that the water separated in the condenser contains ammonia. When the condensate enters the rinsing chamber, hydrolysis of the copper tetrammine complex, for example when etching copper in the etching solution, with the deposition of copper hydroxide or basic copper salt on the machined workpiece surface cannot occur.

It is expedient to add ammonia to the etching solution at the same time as the oxygen (claim 2) in order to adjust the pH of the etching solution. As much ammonia must be added to the etching solution as is essentially lost through evaporation during the etching in the etching chamber and when the etching solution is regenerated.

The ammonia escaping into the gas space above the electrolyte during regeneration in the electrolysis cell can be returned to the etching solution with the extracted oxygen. The ammonia is introduced into the etching solution with the oxygen and, like the oxygen, is mixed intensively with the etching solution.

Further designs of the regeneration system are specified in claims 3 to 7. Thereafter, seen in the flow direction of the etching solution, a pressure relief line branches off from the return in front of the liquid jet pump and opens into a collecting container for etching solution, which is connected to the etching chamber for receiving the etching solution removed from the etching chamber. The collecting container is connected to the etching chamber in such a way that the etching solution flows into the collecting container in a natural gradient.

The intensive mixing of the oxygen with the etching solution and its fine distribution therein, which are achieved by introducing the oxygen from the gas space of the electrolytic cell by means of the liquid jet pump, accelerate the reoxidation of the etching solution in such In such a way that the catalyst particles additionally introduced into the etching solution are unnecessary for those cases in which it is not also important that the metal profile formed during the etching is not slightly undercut. This simplifies the etching process. A corresponding system is specified in claim 8.

If there are no catalyst particles in the etching solution, the filter protecting the electrolytic cell from the ingress of catalyst particles is not required.

The amount of water vapor generated in the electrolysis cell depends on the temperature in the electrolysis cell. With increasing electrolyte temperature, the water vapor content in the gas space above the electrolyte increases, and more condensate can then be obtained in the condenser. By adjusting the temperature in the electrolysis cell, the amount of condensate to be generated can be regulated, claim 6. The maximum temperature in the electrolysis cell is limited by the required pH in the electrolyte. The pH value drops with increasing temperature because the ammonia content in the electrolyte drops. The electrolyte must remain alkaline, especially to protect the electrodes.

• Fig. 1 Ätzanlage für eine Ätzlösung mit Katalysatorteilchen
• Fig. 2 Ätzanlage für eine katalysatorteilchenfreie Ätzlösung mit Kondensator zur Erzeugung von Spülwasser
• Fig. 3 Rückoxidationszeit für eine Ätzlösung, in die Sauerstoff mittels einer Flüssigkeitsstrahlpumpe eingetragen wird, im Vergleich mit einer durch Versprühen in der Ätzkammer oxidierten Ätzlösung.

The invention and further refinements of the invention are explained in more detail below on the basis of exemplary embodiments which are shown schematically in the drawing. The individual shows:

• Fig. 1 etching system for an etching solution with catalyst particles
• Fig. 2 etching system for a catalyst particle-free etching solution with a capacitor for generating rinsing water
• 3 reoxidation time for an etching solution, into which oxygen is introduced by means of a liquid jet pump, in comparison with an etching solution oxidized by spraying in the etching chamber.

A regeneration system connected to an etching chamber 1 with a rinsing chamber 2 is shown schematically in FIG. The ammoniacal etching solution to be regenerated, which contains ammonium sulfate in conjunction with copper tetrammine complex as an etchant and catalyst particles suspended in the etching solution, flows from the etching chamber 1 via an inlet 3 to a filter 4. The catalyst particles contained in the etching solution serve to increase the etching speed and / or to accelerate the reoxidation of the etching solution. For example, activated carbon particles as described in DE-A 3 031 567 are suitable for catalysis.

In the exemplary embodiment, the inlet 3 is connected to the etching chamber 1 in such a way that the etching solution can first of all flow out of the etching chamber into a collecting container 5. It is guided from the collecting container to the filter 4 by means of a pump 6 via a pressure line 7. In the exemplary embodiment, the supply of the etching solution to the filter thus includes the supply 3 itself, the collecting container 5, the suspension pump 6 and the pressure line 7.

The filter 4 is provided with a filter insert 8 which is impermeable to the catalyst particles suspended in the etching solution. The filter insert 8, which is cylindrical in the exemplary embodiment, is shown in broken lines in the drawing. The filter 4 is arranged vertically and the etching solution flows through it with catalyst particles from top to bottom. A return 9 from the filter 4 leads back to the etching chamber 1. In the reflux 9, an etching solution containing catalyst particles is passed.

To reoxidize the etching solution flowing back to the etching chamber, oxygen is introduced into the etching solution. For this purpose, a liquid jet pump 10 is inserted in the return 9, the suction port 11 of which is connected to an oxygen line 12. The liquid jet pump uses the etching solution flowing out of the filter 4 and containing catalyst particles as the working medium.

The oxygen line 12 starts from an electrolysis cell 13. A portion of the etching solution flows through the electrolytic cell to deposit metal etched off in the etching chamber at cathode 14. Catalyst particle-free etching solution is to be fed to the electrolytic cell. A connecting line 16, 16 ′, 16 ″ connected to the filter 4 and the electrolysis cell 13 is used for this purpose. Oxygen is produced at the anode 17 of the electrolysis cell. The oxygen line 12 opens into the gas space above the electrolyte of the electrolysis cell and thus becomes operational when the liquid jet pump 10 is in operation In addition to oxygen, there is also ammonia and water vapor in the gas space, which evaporate from the electrolyte according to its vapor pressure.

An ammonia line 18 leads to the supply of ammonia in the oxygen line 12 and is connected to a storage container 20 for ammonia which can be closed by means of a shut-off device 19. Fresh liquid ammonia can thus be introduced into the etching solution containing the catalyst particles from the liquid jet pump 10 with the oxygen drawn off from the electrolytic cell in order to regulate the pH of the etching solution. For this purpose, the shut-off device 19 is operatively connected to a pH value measuring device 21 inserted in the connecting line 16 with a measuring electrode. If the pH falls below a predetermined permissible limit value, the shut-off device 19 is opened and ammonia is introduced into the etching solution. The pH value measuring device switches the shut-off device 19 with the aid of electrical control units.

Between the filter 4 and the liquid jet pump 10, a pressure relief line 22 opens into the return line 9 and is led to the drainage of etching solution in the collecting container 5.

An overflow 24 of etching solution depleted in metal ions leads from the outlet 23 of the electrolytic cell to the etching chamber. The depleted Ätzlö solution is mixed in the etching chamber as a fresh etching solution with the etching solution containing catalyst particles.

Underneath the electrolysis cell 13 there is a drain container 25. It serves to empty the electrolysis cell and is connected to the bottom of the electrolysis cell 13 via an outlet 26 which can be shut off by means of a solenoid valve 27. Etching solution can also flow from the electrolysis cell 13 into the drain container 25 via a second overflow 28.

In addition to the pH value measuring device 21, there is also a device 29 for measuring the metal ion concentration and a flow meter 30 in the connecting line 16.

The quantity of etching solution to be conducted to the electrolytic cell 13 is measured by the flow meter 30. In the exemplary embodiment, the flow meter 30 is operatively connected to two controllable shut-off devices 31 and 32. The flow meter 30 can effect the adjustment of the shut-off devices, for example mechanically, hydraulically, but also electrically. If the latter is desired, solenoid valves 31, 32 are used as shut-off devices. Of the two shut-off elements, the shut-off element 31 is inserted in the connecting line 16, the shut-off element 32 in a bypass 33 branching off from the connecting line 16 in front of the shut-off element 31. The two shut-off elements are set in such a way that there is a constant in the connecting line part 16 'leading to the electrolysis cell Etching solution current sets. The volume of etching solution to be introduced into the electrolysis cell per unit of time depends on the amount of metal that can be deposited in the electrolysis cell in the same unit of time.

The metal ion concentration in the etching solution measured by the device 29 determines the mode of operation of the electrolysis cell. The device 29 is operatively connected to a three-way valve 34 inserted at the end of the connecting line part 16 ', to which on the one hand the end piece 16 "of the connecting line 16 leading to the electrolytic cell 13 is connected and on the other hand a bypass line 35 which opens into the bypass 33. The three-way valve 34 opened toward the electrolysis cell 13. If the metal ion concentration of the etching solution falls below a predetermined value, the three-way valve 34 is switched over, and the etching solution then flows off via the bypass line 35. The electrolysis cell is switched off.

A solution pump 36 ensures circulation of the etching solution in the electrolysis cell 13. The solution pump dips with its suction line 37 into the drain container 25, into which the etching solution flows via the overflow 28, and conveys the etching solution back in its pressure line 39 via a filter 38 to the electrolytic cell. In the exemplary embodiment, the etching solution enters the electrolysis cell between cathode 14 and anode 17. After the electrolysis cell has been switched off, the etching solution is emptied into the drain container 25 by opening the solenoid valve 27. Before the electrolysis cell is operated again, the etching solution is conveyed back from the drain container into the electrolysis cell by means of the solution pump 36.

In the exemplary embodiment, an etching solution containing ammonium sulfate and copper tetrammine complex is used for etching copper. After the etched metal has been deposited on the cathode and oxygen has formed on the anode, the etching solution depleted of metal ions can serve as a rinsing solution for rinsing the workpieces etched in the etching chamber 1 after the end of the etching treatment. The etched workpieces are to be cleaned in particular of catalyst particles still adhering. The amount of etching solution required for this can be found in the overflow 24. A rinsing line 40 which can be connected to the overflow 24 and which leads to the rinsing chamber 2 is shown in broken lines in FIG. The rinsing chamber 2 and the etching chamber 1 are connected to one another in such a way that the etching solution can flow into the etching chamber after the rinsing process.

The system shown in FIG. 1 is to be supplemented by the condensation device shown in FIG. The condensation device is the subject of both exemplary embodiments. A condenser 42 is provided in the oxygen line 12 and a device 43 for regulating the electrolyte temperature is provided in the electrolysis cell 13. In the condenser 42, water vapor is precipitated, which is sucked out of the gas space above the electrolyte of the electrolysis cell with the gas mixture still containing oxygen and ammonia. A condensate line 44 leads from the condenser 42 to the rinsing chamber 2 of the etching system. The water separated in the condenser is used to rinse the etched workpieces.

So that a sufficient amount of condensate can be generated in the condenser 42 by cooling the extracted gas mixture, the temperature in the electrolyte is regulated in the electrolytic cell by means of the device 43. The amount of water vapor contained in the gas mixture increases with the electrolyte temperature. The device 43 essentially serves to cool the electrolysis cell, which heats up during its operation as a result of the passage of current. A high temperature constancy is achieved by designing the electrolysis cell with a cooling jacket through which cooling water flows, claim 14. The amount of cooling water is regulated as a function of the temperature of the electrolyte.

FIG. 1 shows a regeneration system for an etching solution in which catalyst particles are suspended. If the oxygen input via the liquid jet pump and the intensive mixing of the oxygen with the etching solution and its fine distribution achieved is sufficient for rapid reoxidation, the catalyst particles are unnecessary and the system is simplified. The filter 4 used in the pressure line 7 is omitted. Instead, as shown in the exemplary embodiment according to FIG. 2, a simple pipe connection 41 remains between the pressure line 7 and connecting line 16. Insofar as the regeneration system has individual parts which unchanged correspond to the design shown in FIG. 1, the same reference numerals as in FIG. 1 are entered in FIG.

In the exemplary embodiment, an etching solution containing ammonium sulfate and copper tetrammine complex is also used in the system according to FIG. 2 for etching copper. A temperature of 75 ° C. is set in the electrolysis cell by cooling the electrolyte when the etched copper is deposited. About 5 m ³ / h of gas mixture are sucked out of the gas space above the electrolyte by the liquid jet pump from the electrolysis cell. When the electrolysis cell is closed, around 1.25 l / h of condensate can be generated from the gas mixture in the condenser as a rinsing agent under these conditions. Approx. 500 l / h of oxygen are generated at the anode of the electrolysis cell at a current of 2400 A. The etching solution containing copper ions introduced into the electrolytic cell was adjusted to a pH of 9.

In FIG. 3, reoxidation times are given, curve A indicating the reoxidation of the etching solution when biospraying in the etching chamber, and curve B representing the reoxidation by additionally introducing oxygen into the etching solution by means of the liquid jet pump. The reoxidation in the etching solution is measured via the potential of the Cu ⁺⁺ / Cu ^{+ -} redox system against a calomel reference electrode (Hg / Hg ₂ Cl _{2 /} saturated KCI).

Copper surfaces were etched with a copper tetrammine complex and ammonium sulfate containing etching solution with a copper content of 50 g / I and 150 g / I (NH ₄ ) ₂ S0 ₄ and with a pH value of 9 adjusted with ammonia at a temperature of 50 ° C. During the etching, the potential of the Cu ⁺⁺ / Cu + redox system dropped from an initial value of 125 mV to approximately -60 mV within 3% minutes of the etching time. The reoxidation began after this etching time.

It can be seen from FIG. 3 that with the same copper removal with the etching solution, the intensive introduction of oxygen into the etching solution by means of the liquid jet pump leads to a significantly faster reoxidation than is the case when the etching solution is simply sprayed into the etching space. . Thus, when applying oxygen by means of the liquid jet pump, a potential of +100 mV already after about 3 _^1/2 minutes reoxidation time (. Figure 3: after 7 min total time) is achieved, while the same potential value during spraying of the etching solution in the etching chamber is only after 10 ½ minutes. If air is sucked in with the liquid jet pump instead of oxygen from the gas space of the electrolytic cell, the reoxidation speed decreases with the same copper removal, but the reoxidation is still considerably faster than with reoxidation according to curve A. The intensive oxygen mixing with the etching solution therefore improves regeneration the etching solution by oxidation considerably.

Claims (8)

1. Equipment for regenerating an ammoniacal etching solution which contains catalyst particles for reoxidation with supply of oxygen, having a feed line for etching solution taken from an etching chamber to a filter which is impermeable to catalyst particles in the etching solution, and a return line, connected to the filter, for etching solution, containing catalyst particles, to the etching chamber, and having an electrolytic cell, in which a connecting line, connected to the filter, for catalyst particle-free etching solution obtainable as the filtrate ends and which has an outlet, connectable to the etching chamber, for etching solution which has been depleted of metal ions, characterized in that a liquid-jet pump (10) is inserted into the return line (9), the working medium of the pump being the etching solution and the suction branch (11) of the pump being connected to an oxygen line (12) which carries oxygen or an oxygen-containing gas mixture and which can be fed with oxygen generated at the anode (17) of the electrolytic cell (13), and that the oxygen line (12) is connected to the gas space above the electrolyte in the electrolytic cell (13) and passes to the suction branch (11) via a condenser (42) for precipitating water vapour from the gas mixture carried in the oxygen line (12), and that a condensate line (44) discharging condensate produced on the condenser (42) ends in a washing chamber (2) downstream of the etching chamber (1).

2. Equipment according to Claim 1, characterized in that an ammonia feed line (18, 19, 20) which can be isolated is connected to the oxygen line (12).

3. Equipment according to Claim 1 or 2, characterized in that a pressure relief line (22) ends in the return line (9) upstream of the liquid-jet pump (10), as viewed in the direction of flow of the etching solution.

4. Equipment according to Claim 3, characterized in that the pressure relief line (22) ends in a receiver vessel (5) which, for receiving etching solution taken from the etching chamber (1), is connected to the etching chamber (1).

5. Equipment according to Claim 4, characterized in that the receiver vessel (5) is connected to the etching chamber (1) in such a way that the etching solution flows into the receiver vessel (5) by gravity.

6. Equipment according to one of Claims 1 to 5, characterized in that, for producing a given condensate quantity, the electrolytic cell (13) is fitted with a device (43) for controlling the electrolyte temperature.

7. Equipment according to claim 6, characterized in that the electrolytic cell (13) is surrounded by a cooling jacket bearing a cooling water flow.

8. Equipment for regenerating an ammoniacal etching solution with supply of oxygen, having a feed line for etching solution taken from an etching chamber and a return line to the etching chamber for the etching solution, and having an electrolytic cell, in which a connecting line, connected to the feed, for a part of the etching solution ends and which has an outlet, connectable to the etching chamber, for etching solution which has been depleted of metal ions, characterized in that a liquid-jet pump (10) is inserted into the return line (9), the working medium of the pump being the etching solution and the suction branch (11) of the pump being connected to an oxygen line (12) which carries oxygen or an oxygen-containing gas mixture and which can be fed with oxygen generated at the anode (17) of the electrolytic cell (13), and that the oxygen line (12) is connected to the gas space above the electrolyte in the electrolytic cell (13) and passes to the suction branch (11) via a condenser (42) for precipitating water vapour from the gas mixture carried in the oxygen line (12), and that a condensate line (44) discharging condensate produced on the condenser (42) ends in a washing chamber (2) downstream of the etching chamber (1).

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