EP0046522A1 - Method for the regeneration of an ammoniacal etchant - Google Patents

Abstract

In addition to catalyzing the reoxidization of spent alkaline etching agent, the suspension of activated carbon powder in the etching solution also increases the speed of etching when the etching solution is recirculated in the etching of printed circuit boards. The ammonium sulfate etching solution is set to a pH of about 9 by the addition of ammonia gas. In the recirculation of the etching solution, a part of the solution can be freed by filtration from suspended carbon particles and passed through the cathode and anode chambers of an electrolysis cell for the recovery of the etched metal by deposition on the cathode. The activated carbon powder for this purpose is calcined before use, at a temperature of between 900 DEG and 1200 DEG C. in vacuum or in an atmosphere that is inert, reducing, or only slightly oxidizing as in the case of an atmosphere containing carbon dioxide, water vapor or both, in a concentration that does not appreciably oxidize the carbon particles.

Description

The invention relates to a method for regenerating an ammoniacal etching solution which is supplied with oxygen for the reoxidation of the etchant contained in the etching solution.

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. Not only are the chemicals used used up, waste solutions are also created that cannot be removed without prior detoxification treatment. Compare, for example, H. Bruch et al., "Printed circuit boards", Eugen G. Leutze-Verlag, Saulgau / Württemberg, 1978.

When the alkaline etching solution is reoxidized by blowing in oxygen, regeneration is quicker with alkaline etching solutions than with acidic etching solutions, but the reaction speed lags behind the reaction rate achieved using chemical oxidizing agents.

The object of the invention is to provide a method for regenerating alkaline etching solutions in which no toxic residual solutions are obtained and in which the etching solution rapidly reoxidizes.

From DE-PS 27 14 075 a method is known in which activated carbon powder particles suspended in aqueous solution are used as a catalyst for the oxidation of pollutants, such as nitrite, cyanide or sulfite, for the removal of oxygen. The invention is based on this known effect of the activated carbon powder particles.

The object is achieved in the above-mentioned method according to the invention by the measures specified in claim 1. Activated carbon powder particles are suspended in the etching solution, which act as a catalyst when the etching agent reduced during the etching of the metal is oxidized back. Surprisingly, it has been found that after suspension of activated carbon powder particles in the alkaline etching solution and after their action as a catalyst, the etching process also occurs speed is increased significantly.

The activated carbon powder particles effective in the etching solution are previously annealed in a vacuum, in an inert, reducing atmosphere containing CO ₂ or water vapor at a temperature between 900 and 1200 ° C. When glowing in an atmosphere containing 00 ₂ or water vapor, the content of CO ₂ and water vapor is adjusted so that only a slight degradation of the activated carbon powder takes place during the treatment. It has proven to be advantageous to glow the activated carbon powder particles in the aforementioned manner for over an hour, claim 2. At concentrations of the activated carbon powder particles in the etching solution between 5 and 25% by weight, preferably between 10 and 12% by weight, is obtained one has a viscosity suitable for transport and for spraying the etching solution, claims 3 and 4.

For the deposition of metal ions dissolved in the etching solution, measures specified in patent claims 5 and 6 are used in an embodiment of the method according to the invention. After the metal has been etched and the activated carbon powder particles suspended in the etching solution have been separated off, part of the etching solution is passed through the cathode compartment of an electrolysis cell. The partial amount of the etching solution passed through the electrolytic cell and * adjusted so that the metal concentration which results from the deposition of the metal ions on the cathode becomes within the etching solution containing the suspended activated carbon powder for one of the electrolysis streams optimal etching speed is sufficient. The part of the etching solution passed through the electrolytic cell is returned to the etching solution circuit after flowing through the cathode space.

• Figur 1 Abhängigkeit der Ätzgeschwindigkeit vom Kupfergehalt einer Ammoniumsulfat enthaltenden Ätzlösung zum Ätzen von Kupfer ohne (Kurve I) und mit in der Ätzlösung suspendierten Aktivkohlepulverteilchen (Kurve II).
• Figur 2 Zeitlicher Verlauf des Potentials einer Ätzlösung für das Ätzen von Kupfer ohne (Kurve I) und mit suspendierten Aktivkohlepulverteilchen (Kurve II) bei Rückoxidation in Gegenwart von Sauerstoff
• Figur 3 Abhängigkeit der Ätzgesohwindigkeit einer Ätzlösung für Kupfer vom Potential der Ätzlösung ohne (Kurve I) und mit suspendierten Aktivkohlepulverteilchen (Kurve II),
• Figur 4 Ätzanlage mit Elektrolysezelle (schematisch)

The invention is explained in more detail below on the basis of exemplary embodiments. The diagrams shown in the drawing show in detail:

• 1 dependence of the etching rate on the copper content of an etching solution containing ammonium sulfate for etching copper without (curve I) and with activated carbon powder particles suspended in the etching solution (curve II).
• FIG. 2 Time course of the potential of an etching solution for the etching of copper without (curve I) and with suspended activated carbon powder particles (curve II) during reoxidation in the presence of oxygen
• FIG. 3 dependence of the etching speed of an etching solution for copper on the potential of the etching solution without (curve I) and with suspended activated carbon powder particles (curve II),
• FIG. 4 etching system with electrolysis cell (schematic)

In the diagrams, in comparison with etching solutions which do not contain any active carbon powder particles, those with the addition of activated carbon powder particles to the etching solutions are shown illustrated effects. The suspended activated carbon powder particles were previously annealed in a vacuum or reducing atmosphere at 1000 ° C for one hour. Comparable results were also achieved with activated carbon powders which were annealed in an inert atmosphere containing CO ₂ or water vapor at temperatures above 900 ° C. The C0 ₂ or water vapor content in the atmosphere was adjusted so that the activated carbon powder was only slightly oxidized.

All of the diagrams shown in FIGS. 1 to 3 show the improvements achieved in the etching of copper using activated carbon powder. An ammonium sulfate solution with a content of 150 g ammonium sulfate per liter is used as the etching solution, which is adjusted to a pH of 9 by adding gaseous ammonia.

To measure the etching rate as a function of the copper content in the solution, different copper contents are set and the rate of dissolution of a copper plate sprayed with air in an etching solution is measured. The etching speeds achieved with etching solutions without activated carbon powder particles are inEig. ₁ in curve _I, the etching rate with 12% by weight of suspended activated carbon powder particles are shown in curve II. From the curve of curves I and II it can be seen that solutions with a copper content of about 20 g copper per liter or more when adding activated carbon powder have a considerably higher etching rate than etching solutions without activated carbon powder. It is particularly advantageous that the maximum of the etching speed in etching solutions with carbon powder parts compared to etching solutions without carbon powder parts is shifted towards higher copper contents in the solution.

The following exemplary embodiments were carried out in order to determine the influence of the activated carbon powder on the reoxidation of an etching solution:

Embodiment 1

A solution of 150 g ammonium sulfate and 30 g copper per liter was adjusted to a pH of 9 by adding gaseous ammonia. The solution was sprayed into air by means of a nozzle for oxidation, collected in an upwardly open solvent tank and circulated. The overpressure in the solution was 0.7 bar in front of the nozzle. The potential of the solution was measured using a platinum pen against a mercury / mercury oxide reference electrode. 1.5 liters of this solution, which had been heated to 50 ° C., were circulated.

40 g of copper powder were then dissolved in the solution, which resulted in a reduction of the potential in the solution by 330 millivolts. The time course of the potential in the solution is shown in FIG. 2, curve I. 80% of the initial potential in the solution was reached again after about 32 minutes.

An etching solution of the same composition was measured under the same conditions, in which an additional 12% by weight of activated carbon powder was suspended. After adding 40 g of copper powder to the 1.5 liters of the etching solution, the potential of the solution decreased by 310 millivolts. After about 15 minutes, 80% of the initial potential in the etching solution was reached again. The course of the potential of the solution is shown in Figure 2, curve II.

Embodiment 2

At a temperature of 48 ° C and a pH of 9.2, 1.5 liters of an aqueous solution with 150 g of ammonium sulfate and 35 g of copper per liter were sprayed in air at a pressure of 1.5 bar using a nozzle and in Cycle. Depending on the potential of the solution measured against a mercury / mercury oxide reference electrode, the etching rate was measured when etching copper. The dependence of the etching speed and potential of the solution is shown in FIG. 3. Curve I in FIG. 3 shows the dependence of the etching speed on the potential of an etching solution without activated carbon powder particles. If 12% by weight of activated carbon powder is added to an etching solution of the same composition, a much higher etching rate is achieved with the same potential of the solution, curve II in FIG. 3.

In the presence of activated carbon powder in the etching solution, it is not only the reoxidation of the etching solution accelerated, higher etching speeds are also achieved.

The following exemplary embodiments 3 and 4 are carried out in an etching system shown schematically in FIG.

The etching system consists of an etching chamber 1, in which the objects 2 to be etched are sprayed with ammoniacal etching solution by means of a spray device 3. The etching solution is circulated by a solvent pump 4 from the bottom of the etching chamber 1 via a pipeline 5 connected to the spray device 3 '. A section of the pipeline 5 consists of a filter 6 which is permeable to the etching solution, but which retains the activated carbon powder particles suspended in the etching solution. The part of the etching solution which passes through the filter 6 is led to the cathode chamber 7 of an electrolytic cell 8 and, after the etched metal has been deposited, is returned through the anode chamber 9 of the electrolytic cell into the circuit of the etching solution, in the exemplary embodiment into the etching chamber 1.

Embodiment 3

In the etching system shown in FIG. 4, 15 liters of etching solution, which contained 150 g of ammonium sulfate and 50 g of copper per liter and activated carbon powder in an amount of 10% by weight, are circulated and by means of the spray device equipped with nozzles at an overpressure between cathodes and anode space of the electrolytic cell there is a diaphragm 10, sprayed in air at 0.8 bar. The etching solution had been heated to 50 ° C. and was adjusted to a pH of 9 by adding ammonia gas. Copper plates were etched. The etch rate was approximately 2.6 g copper per minute. About 20 milliliters of the solution were continuously separated from the circuit through a hinduroh diaphragm, which was used as a filter in the pipeline, and introduced into the cathode compartment of the electrolysis cell. Copper was deposited from the etching solution on a stainless steel cathode with 30 ampere direct current, corresponding to a current density of 5 ampere per dm ² . The copper solution-etched solution penetrated through the diaphragm separating the cathode and anode space of the electrolysis cell and into the anode space of the electrolysis cell. A plastic net resistant to the etching solution was used as the diaphragm. The etching solution was returned from the anode compartment to the circuit of the etching solution containing the suspended activated carbon powder particles.

In the course of 8 operating hours, 306 g of copper were removed continuously in the etching system, corresponding to an average amount of 0.64 g of copper per minute. During this time, 278 g of copper was deposited on the cathode, corresponding to an amount of copper of 0.62 g per minute. This amount of deposited copper corresponds to 98% of the theoretically possible depositable amount of 284.5 g based on the current flowing through the electrolytic cell.

With an electrode spacing of 2 μm in the electrolysis cell, the cell voltage was 2.3 volts.

Embodiment 4

Brass was etched in the etching system shown in FIG. 4 using an ammoniacal etching solution. A portion of the aqueous solution containing 150 g of ammonium sulfate, 21 g of copper and 44 g of zinc per liter was introduced into the cathode chamber of the stainless steel cathode electrolytic cell. At a pH of 9.5, a solution temperature of 20 ° C and a current density of 5 amperes per dm ² , an alloy of 66% copper and 34% zinc is separated in the electrolytic cell on the stainless steel cathode. The current efficiency for metal deposition was 92%.

For reoxidation, activated carbon powder particles were suspended in the etching solution in the same way as in the previous exemplary embodiments, and the etching solution was sprayed in air to come into contact with oxygen.

Claims (6)

1. A method for regenerating an ammoniacal etching solution, which is supplied for the reoxidation of the etching agent containing oxygen in the etching solution, characterized in that activated carbon powder particles are suspended in the etching solution, which previously contained in a vacuum, inert, reducing, C0 ₂ or water vapor atmosphere Temperature between 900 and 1200 ° were annealed. 2. The method according to claim 1, characterized in that the activated carbon powder was annealed for over an hour. 3. The method according to claim 1 or 2, characterized in that activated carbon powder particles are suspended in a concentration between 5 and 25 wt .-% in the etching solution. 4. The method according to claim 3, characterized in that activated carbon powder particles are suspended in a concentration between 10 and 12 wt .-% in the etching solution. 5. The method according to any one of the preceding claims, characterized in that a part of the etching solution after the etching of the metal and after separating the activated carbon powder particles suspended in the solution for metal recovery is passed through the cathode space of an electrolytic cell. 6. The method according to the preceding claim, characterized in that the etching solution containing the activated carbon powder particles is circulated and the part of the etching solution flowing through the cathode space of the electrolytic cell is re-introduced into the circuit of the etching solution after deposition of the metal.

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