RU2696381C2 - Reagent method for regeneration of copper-ammonia solution of copper etching - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: one pre-calculated part of total volume of spent solution of etching of copper subject to regeneration is mixed with solution of hydrazine for reduction of ions of mono- and bivalent copper to metal copper, sediment of which is separated by decantation or filtration. Process of reducing divalent copper ions can be limited by obtaining univalent copper ions, which are precipitated by adding ammonium salts to the solution, and the precipitated residue of the univalent copper compound is separated from the solution. After separating copper precipitate or univalent copper compound, volume of etching solution of copper, which has been treated with hydrazine, is mixed with another pre-calculated part of total volume of spent solution of etching copper, which is not treated with solution of hydrazine. After mixing, obtained solution is subjected to aeration with air oxygen. After aeration copper-ammonium-chloride or copper-ammonium-sulphate solution of copper etching is ready for repeated use.

EFFECT: invention relates to a method of regenerating a copper-ammonium-chloride or copper-ammonium-sulphate solution of etching copper using hydrazine or an aqueous solution of hydrazine with concentration of 1–99 % by weight.

3 cl, 2 ex

Description

Usage: in the manufacture of printed circuit boards.

The invention relates to a method for regeneration (restoration of performance) of a copper-ammonia solution of copper etching by the reagent method.

The proposed method allows to regenerate a copper-ammonia solution of etching copper.

The purpose of the invention: to develop a method for the regeneration of a copper-ammonia solution of etching copper reagent method. It is desirable that the regeneration method does not significantly increase the volume of the initial solution and does not introduce any substances into the etching solution that will then be difficult to remove. The method, first of all, should provide a high rate of regeneration of copper-ammonia solutions of copper etching, which are often used in industry, in particular: copper-ammonia-chloride and less commonly used copper-ammonia-sulfate solutions of copper etching.

Copper-ammonia-chloride solutions of copper etching obtained by the action of an excess of ammonia solution on divalent copper chloride are known from the prior art. The concentration of divalent copper ions in such a fresh solution is 31-52 g / l, pH = 8.5-10.5 [1]. In the process of copper etching, an spent solution is formed in which the total concentration of copper ions (monovalent and divalent) can increase to 100-150 g / l, which leads to a decrease in the etching rate of metallic copper, despite the chemical oxidation of monovalent copper ions to divalent ions copper with atmospheric oxygen, which occurs during the etching process of printed circuit boards in an etching machine by the jet method [1]. The spent copper pickling solution is regenerated. A known reagent method for restoring the health of the spent copper-ammonia-chloride solution of copper etching, which consists in adding to it an oxidizing agent - a solution of hydrogen peroxide [2]. This method allows the oxidation of monovalent copper ions to divalent copper ions and at the same time to reduce the concentration of divalent copper ions due to dilution of the solution, since a dilute solution of hydrogen peroxide is used for regeneration. The disadvantages of the method is the excess (excess) of the volume of the copper etching solution containing a toxic component — copper ions, which will have to be neutralized. The method cannot be used for the regeneration of waste solutions containing a high (100-150 g / l) ion concentration of divalent copper only (such solutions have a lower etching rate and, correspondingly, etching quality due to the increased density and lower pH [1]) due to the absence of monovalent copper ions in them. Thus, the regeneration of the spent copper-ammonia-chloride solution of copper etching containing monovalent ions by the introduction of an oxidizing solution leads not only to the restoration of its performance, but also to the formation of excess volumes of a copper etching solution containing toxic copper ions.

The essence of the invention: the required volume to be regenerated spent copper-ammonia-chloride solution of etching copper (including containing only bivalent copper ions) is divided into two calculated parts. The calculated amount of a strong reducing agent, hydrazine, N ₂ H ₄ , is added to the first part of the solution with stirring, while the following reactions proceed fairly quickly at room temperature (1-3):

Reactions (1) - (3) proceed because the standard electrode potential for reducing the ammonia complex compound of monovalent copper to metallic copper is -0.12 V, the standard electrode potential for reducing the ammonia complex compound of divalent copper to metallic copper is -0.05 V [3 ], the standard electrode potential for the reduction of the ammonia complex compound of divalent copper to the ammonia complex compound of monovalent copper is -0.01 V [5], and the electrode oxidation potential of hydrazine p veins -1.16 V (pH = 14), -0.923 V (pH = 10) and -0.805 V (at pH = 8) [4].

When the calculated amount of hydrazine is added, either in pure form or in the form of an aqueous solution with a concentration of 1-99% (mass%), to the spent copper-ammonia-chloride solution of copper etching, the ions of mono- and divalent copper are reduced to metallic copper which precipitates as a brown precipitate according to reaction equations (2) and (3). Depending on the conditions, in addition to the deposition of metallic copper, precipitation of Cu ₂ O is also possible. After completion of reactions (2) and (3), a colorless transparent aqueous solution containing mainly ammonium chloride, ammonia and a possible residual amount of hydrazine is separated (decanted or is quickly filtered off) from a brown precipitate of powdered copper and mixed with the second calculated part of the spent copper-ammonia-chloride solution of etching of copper, not subjected to hydrazine treatment. If initially the estimated volume of the part of the spent copper etching solution to be treated with hydrazine was equal to the calculated volume of the second part of the initial spent copper-ammonia-chloride etching solution that would not be treated with hydrazine, then when the volumes of these solutions are mixed, the total concentration of copper ions will decrease twice in relation to the initial total concentration of copper ions in the spent solution of copper etching (excluding dilution when using hydrazine in the form of a solution and the residual concentration of copper ions in the solution subjected to hydrazine treatment). Hydrazine residues in the solution obtained by mixing the treated and the initial solution will react with an excess of divalent copper ions with the formation of monovalent copper ions according to reaction (1). Next, the resulting solution is loaded into an etching machine with a jet etching function, but the printed circuit boards are not loaded into this etching machine. In this case, when the pickling machine is turned on, the oxygen in the air has good contact with the pickling solution, and the copper ions are oxidized by the oxygen in the air to divalent copper ions. After a certain time, the pickling machine is stopped, and the regenerated solution is poured into an appropriate container.

Below we list the features of the regeneration process.

The amount of added hydrazine should be sufficient and take into account the possibility of the reaction of incomplete reduction of divalent copper ions to monovalent copper ions by reaction (1).

The amount of hydrazine added should be sufficient (it is recommended to take hydrazine in a small 1-10% excess against stoichiometry) so that reactions (2) and (3) are completely completed. The absence of noticeable amounts of monovalent copper ions in the solution treated with hydrazine will sharply slow down the oxidation of metallic copper by atmospheric oxygen, since the intermediate oxidizing agent is divalent copper ions, which are able to react with metallic copper.

To minimize the dilution (increase in volume) of the regenerated copper etching solution, it is recommended to use hydrazine in the form of hydrazine hydrate, N ₂ H ₄ × H ₂ O, containing N ₂ H ₄ at a concentration of 20.6 M.

To minimize the consumption of hydrazine hydrate, it is possible to limit the process to reaction (1), however, in this case, it is necessary to select a precipitating reagent that converts monovalent copper ions into a precipitate (having a low solubility product, PR <10 ^-12 ) in an ammonia-reducing medium . Such reagents include sulfide, hydrosulfide, cyanide, rhodanide, and, to a lesser extent, iodide ions, which are recommended to be added to the regenerated solution in the form of compounds with an ammonium cation according to reaction (4).

,

,

where An = S ^2- , HS ^- , CN ^- , SCN ^- , I ^- .

The precipitate obtained in this case containing monovalent copper ions should be separated from the ammonia solution under conditions of limited access to air oxygen.

In the course of reactions (1), (2), (3) and (4), ammonium chloride and ammonia are released, which are necessary for the etching of copper.

Since hydrazine and ammonia are toxic, the regeneration process must be carried out under a well-functioning exhaust device.

The access of air oxygen must be limited, since air oxygen oxidizes monovalent copper ions to divalent copper ions, and divalent copper ions oxidize metallic copper to monovalent copper ions. In this regard, the regeneration process is recommended to be carried out in a container made of chemically resistant material (plastic, glass), which must be loosely closed (covered) with a lid to prevent an increase in pressure in the container due to nitrogen gas. The evolved nitrogen gas interferes with the access of air oxygen to the regenerated solution.

After completion of reactions (2) and (3), the solution treated with hydrazine, which is practically free of copper ions, is separated from the precipitate of metallic copper and mixed with the calculated volume of the initial spent solution. The resulting solution is loaded into an etching machine with a jet etching function without loading printed circuit boards. When the etching machine is turned on, oxygen in the air oxidizes trace residual amounts of hydrazine, as well as monovalent copper ions into divalent copper ions. After a certain amount of time, the pickling machine is turned off and a fully regenerated copper-ammonia-chloride solution of pickling of copper is poured into an appropriate container.

The above information on hydrazine regeneration of the spent copper-ammonia-chloride solution of copper etching is also valid for the implementation of the regeneration of the spent copper-ammonia-sulfate solution of copper etching.

Example 1. 200 ml of spent copper-ammonia-chloride solution of copper etching with a concentration of divalent copper ions of 120 g / l was divided into two parts: the first with a volume of 135 and the second with a volume of 65 ml. 6.5 ml of hydrazine hydrate was added to the first part of a 135 ml solution. After completion of the reaction, the copper precipitate was separated by decantation, and the resulting solution was mixed with the second part of the spent solution with a volume of 65 ml. The concentration of copper ions in the resulting solution was 39 g / L.

Example 2. 200 ml of spent copper-ammonia chloride etching solution of copper with a concentration of divalent copper ions of 120 g / l was divided into two parts: the first with a volume of 135 and the second with a volume of 65 ml. To the first part of the 135 ml solution was added 19.5 g of solid ammonium thiocyanate, and after its dissolution 3.2 ml of hydrazine hydrate. After completion of the reaction, the precipitate of copper rhodanide was separated by decantation, and the resulting solution was mixed with the second part of the spent solution with a volume of 65 ml. The solution was then aerated with air. The concentration of copper ions in the resulting solution was 39 g / L.

Information sources

1. Ilyin V.A. "PCB manufacturing technology." - L. Mechanical Engineering, 1984. - 77 p.

2. Ilyin V.A. Chemical and electrochemical processes in the manufacture of printed circuit boards. M., VINITI, 1994, 142 pp.

3. Handbook of a chemist. T. 3. Chemical equilibrium and kinetics, properties of solutions, electrode processes. M. - L. 1965, 1004 p.

4. A quick reference to chemistry. Under the total. ed. Kurylenko O.D., Kiev. Naukova Dumka 1974, 991 pp.

5. Handbook of electrochemistry. Under A.M. Sukhotina. - L. Chemistry, 1981.- 488 p.

Claims (16)

1. The method of regeneration of copper-ammonia-chloride or copper-ammonia-sulfate solution of etching of copper by the reagent method, characterized in that in one of the two previously calculated parts of the total volume of the spent solution of etching of copper, ions of mono- and divalent copper are removed from it or due to their recovery to a precipitate of metallic copper with hydrazine or its aqueous solution with a concentration of 1-99 wt.% according to the stoichiometry of the reaction equations: 4 [Cu (NH ₃ ) ₂ ] CI + N ₂ H ₄ = ₄ Cu ↓ + 4NH ₄ CI + 4NH ₃ + N ₂ ↑, 2 [Cu (NH ₃ ) ₄ ] CI ₂ + N ₂ H ₄ = 2 Cu ↓ + 4NH ₄ CI + 4NH ₃ + N ₂ ↑, or due to reduction with hydrazine or its aqueous solution with a concentration of 1-99 wt.% according to the stoichiometry of the reaction: 4 [Cu (NH ₃ ) ₄ ] CI ₂ + N ₂ H ₄ = 4 [Cu (NH ₃ ) ₂ ] CI + 4NH ₄ CI + 4NH ₃ + N ₂ ↑ divalent copper ions to monovalent copper ions, which are removed by adding to the solution sulfide or hydrosulfide or rhodanide or ammonium iodide according to the stoichiometry of the reaction: 4 [Cu (NH ₃ ) ₄ ] CI ₂ + N ₂ H ₄ + 4NH ₄ An = ₄ CuAn ↓ + 8NH ₄ CI + 12NH ₃ + N ₂ ↑, where An = S ^2- , HS ^- , SCN ^- , I ^- , a copper metal precipitate or a monovalent copper sulfide, rhodanide or iodide precipitate is separated, then the resulting solution, purified from copper ions, is mixed with the second part of the total volume of the spent copper etching solution that has not been treated with hydrazine, and a copper etching solution containing mono- and bivalent copper, which is subjected to aeration with atmospheric oxygen to oxidize possible hydrazine residues and monovalent copper ions to bivalent copper ions, and a copper etching solution containing two copper copper in a concentration corresponding to the range of values for a fresh solution of copper pickling. 2. The method according to p. 1, characterized in that aeration with atmospheric oxygen is carried out in an etching machine without loading printed circuit boards. 3. The method according to p. 1, characterized in that hydrazine or its aqueous solutions with a concentration of 1-99 wt.% Take in excess taken in 1-10% against the stoichiometry of the reaction equations: 4 [Cu (NH ₃ ) ₄ ] CI ₂ + N ₂ H ₄ = 4 [Cu (NH ₃ ) ₂ ] CI + 4NH ₄ CI + 4NH ₃ + N ₂ ↑, 4 [Cu (NH ₃ ) ₂ ] CI + N ₂ H ₄ = ₄ Cu ↓ + 4NH ₄ CI + 4NH ₃ + N ₂ ↑, 2 [Cu (NH ₃ ) ₄ ] CI ₂ + N ₂ H ₄ = 2 Cu ↓ + 4NH ₄ CI + 4NH ₃ + N ₂ ↑, 4 [Cu (NH ₃ ) ₄ ] CI ₂ + N ₂ H ₄ + 4NH ₄ An = ₄ CuAn ↓ + 8NH ₄ CI + 12NH ₃ + N ₂ ↑, where An = S ^2- , HS ^- , SCN ^- , I ^- .