JPH073476A - Method for regenerating copper etching liquid - Google Patents

Abstract

PURPOSE:To provide the method which regenerates an etching waste liq. by a convenient method and is capable of recovering excess copper ion. CONSTITUTION:The cuprous chloride etching waste liq. containing copper (I) chloride is fed to the cathode chamber of an electrolytic cell, and the copper ion is deposited on the cathode as a metallic copper to separate from the etching waste liq., moreover, the etching waste liq. is fed to an anode chamber and the copper (I) chloride is oxidized electrolytically to return almost copper (I) chloride to cupric (II) chloride, and the etching liq. having almost the same composition with that at starting time is regenerated. In this way, the recovering of copper and the regeneration of the etching liq. is executed simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reclaiming a waste liquid used for copper etching, and more particularly to a method for reclaiming a copper chloride etching waste liquid used for pattern formation of a subtracted printed circuit board.

[0002]

2. Description of the Related Art The so-called subtract method of forming a circuit pattern from a copper clad laminate by etching is most widely used in the manufacture of printed circuit boards. This method is to form through holes on a copper clad laminate and conduct conductive plating, then draw a wiring pattern using a resist and remove unnecessary parts by etching. There are merits such as that it can be manufactured and that the waste liquid treatment is relatively easy. The etching is so-called chemical etching, in which copper is eluted as copper ions by an oxidizing action associated with a change in valence of a transition metal.

The etching solution used for this etching is a mixed solution of ferric chloride (FeCl ₃ ) and cupric chloride (CuCl ₂ ), each of which dissolves copper according to the following chemical formula. 2 Cu + 2 FeCl ₃ → 2 FeCl ₂ + Cu ₂ Cl ₂ Cu + CuCl ₂ → Cu ₂ Cl ₂ Ferric chloride has no special selectivity and can be used by dissolving copper in a very wide range for use in etching printed circuit boards. Is widely used as. However, there has been a problem that the maintenance and management of the etching solution must always be performed, and the side etching becomes large due to excess hydrochloric acid. Furthermore, when the etching solution is regenerated, it is necessary to separate copper and iron by a chemical treatment, and there is also a problem that the regeneration is not easy.

On the other hand, copper chloride is difficult to use as a printed wiring board due to the problem that it reacts slightly to solder plating (Pb-Sn), but it was not always widely used at the beginning. However, replacing tin (Sn) in the solder plating with nickel (Ni) has completely solved the above problem, and copper chloride has also been used for copper etching. The etching product of cupric chloride (CuCl ₂ ) is cuprous chloride (Cu ₂ Cl ₂ ), and unlike ferric chloride, there is no need to separate metals from each other. Chemically, for example, by bubbling air, it is easily oxidized and converted to cupric chloride, which has the advantage that it only adjusts the balance of hydrochloric acid and does not require special preparation of liquid, and its utilization increases. ing.

However, the dissolution of copper from the printed circuit board due to etching causes an excess of copper in the etching solution, resulting in a serious problem in its treatment. Usually, a part of the etching solution is taken out and electrolytically reduced to deposit metallic copper. That ^{_{CuCl 2 + 2e - → Cu +}} 2 Cl - The reaction to perform the, or collected to obtain copper carbonate by the reaction of removing the collection and copper hydrochloric copper powder, or by chemical reaction eg with carbonates, Medium Obtaining copper oxide by the sum was performed. Copper is easily recovered by these recovery operations and the etching solution is stabilized, but the recovery operation is troublesome, and continuous operation is difficult.

[0006]

It is an object of the present invention to solve the above-mentioned problems of the prior art and to regenerate the copper chloride etching solution without using chemicals by a simple method, and at the same time, recover excess copper as pure metallic copper and use it as a resource. It is an object of the present invention to provide a method for reclaiming a copper etching solution that enables the effective utilization of the above.

[0007]

According to the present invention, a copper chloride etching waste liquid containing cuprous chloride is supplied to a cathode chamber of an electrolytic cell which is divided by a diaphragm into an anode chamber and a cathode chamber to supply excess copper ions. Is deposited on the cathode surface as metallic copper, the etching waste liquid is supplied to the anode chamber and the cuprous chloride is converted into cupric chloride to be regenerated as a copper etching liquid. .

The present invention will be described in detail below. Part of the copper chloride in the etching waste liquid dissolves the copper of the printed circuit board and is converted into cuprous chloride (Cu ₂ Cl ₂ ) as described above, and the etching waste liquid contains cupric chloride (CuCl ₂ ) and chloride. Copper (Cu ₂ Cl ₂ )
And the copper ion concentration is higher than at the beginning. In the present invention, first, the excess copper ions in the etching waste liquid are electrolytically reduced in the cathode chamber to be converted into metallic copper to be deposited on the cathode surface to deposit the copper ion concentration in the etching waste liquid to the initial level. Further, cuprous chloride, which is unnecessary for etching in the etching waste liquid, is oxidized to cupric chloride in the anode chamber to regenerate the etching waste liquid into an etching liquid having the same composition as the original.

[0009] leads to the cathode chamber side of the 2-chamber electrolytic cell the etching waste liquid which is the mixture, a portion of the copper CuCl ₂ + 2e ^- →
It is converted into copper by the reaction of Cu + 2 Cl ⁻ or Cu ₂ Cl ₂ + 2e ⁻ → 2Cu + 2 Cl ⁻ , is deposited on the cathode surface, and produces chlorine ions. In addition to this reaction on the cathode chamber side, 2CuCl ₂ +
^{_{2e - → Cu 2 Cl 2 +}} 2 Cl - of the reaction there is a possibility of occurring, actually decreases slightly pH generation occurs stable metallic copper in said potential by maintaining the cathode potential to zero or less noble To do. However, if the pH is 4 or less, the deposition of metallic copper takes place preferentially regardless of the pH and regardless of the potential.

The amount of copper ions to be deposited by the reduction in the cathode chamber in the method of the present invention is copper ions in excess of the initial copper ions, that is, the amount of copper corresponding to the amount of copper eluted from the material to be plated such as a printed circuit board. Therefore, excessive energization to deposit a large amount of metallic copper to reduce the copper ion concentration excessively should be avoided. Since the reduction reaction in the cathode chamber includes two kinds of reactions, that is, reduction of monovalent copper and reduction of divalent copper as described above, the theoretical amount of electricity required for depositing a necessary amount of copper ions as metallic copper can be accurately measured. It cannot be calculated. Therefore, during actual operation, the amount of current versus the amount of copper deposition is empirically determined in advance, and the amount of electricity required to deposit an excessive amount of copper ions in the etching waste liquid is calculated,
A corresponding amount of electricity is applied by (current amount per hour) × (hour) to remove excess copper ions from the etching waste liquid and deposit a predetermined amount of metallic copper on the cathode surface.

The metallic copper deposited on the cathode surface may be scraped off from the surface, or the cathode may be formed into a drum shape to form a foil and continuously peeled off. It is also possible to make the cathode slightly smaller than the anode to increase the actual current density, deposit in the liquid in the form of dendrite, and remove by filtration. The mixed solution of cuprous chloride and cupric chloride whose concentration has been optimized in the cathode chamber of the electrolytic cell is then supplied to the anode chamber of the electrolytic cell. The cuprous chloride in the mixed solution is converted into cupric chloride is anodized _{(Cu 2 Cl 2 + 2 Cl} - →
₂ CuCl 2 + 2e ^-). The potential required for causing this anodic oxidation reaction is about 0.3 to 0.4 V. At this potential, chlorine and oxygen are not normally generated on the anode side. Since it is used for the oxidation of cuprous chloride, substantially the oxidation of cuprous chloride proceeds at a current efficiency of 100%.

Therefore, almost all of the cuprous chloride in the etching waste liquid from which excess copper ions have been removed is oxidized to cupric chloride. Since the amount of electricity required at this time varies slightly depending on the ratio of monovalent copper and divalent copper in the etching waste liquid, electrolysis conditions, and the like, it is appropriately set according to the etching waste liquid and electrolysis conditions used. The regeneration method of the present invention may be carried out by collecting the etching waste liquid, but it is desirable to connect the above-mentioned regeneration electrolytic bath to the etching bath to circulate the etching waste liquid for continuous regeneration and reuse. The control in the method of the present invention may be performed by the copper ion concentration or the hydrogen ion concentration (pH).

Next, the electrolytic cell for regeneration which can be used in the method of the present invention will be described. The material of the electrolytic cell body to be used is not particularly limited, and corrosion-resistant materials such as hard vinyl chloride, acrylic resin, polypropylene, polyethylene, etc. may be appropriately selected according to the temperature at the time of etching to reduce and oxidize copper, and a wide range is available. Under the conditions, the objective can be achieved with almost 100% efficiency. Although the material is expensive, it is possible to use fluororesin or glass fiber reinforced resin.
However, it is desirable not to use a metallic material because it elutes into the etching waste liquid and causes contamination of the liquid.

The diaphragm may be appropriately selected from materials that allow the flow of electric current but impede the flow of the liquid, and ion exchange capacity is not particularly required. Therefore, asbestos diaphragm, polypropylene, filter cloth, and porous polytetrafluoroethylene non-woven fabric that are usually used are used. And the like are preferably used. However, an expensive cation exchange membrane known under the trade name Nafion or the like may be used.
When the ion exchange membrane is used, copper ions on the side of the anode chamber may move to the side of the cathode, but especially in the case of a cation exchange membrane having valence selectivity, monovalent ions mainly move. This is advantageous because monovalent copper ions in the regenerated cupric chloride are reduced.

The material of the cathode needs to be carefully selected. The cathode in the cathode chamber to which the etching waste liquid is supplied tends to be severely corroded in the case of hydrochloric acid or chloride bath, and it is better not to use nickel or iron which is usually used. Although carbon is less likely to be corroded and is suitable for the purpose, if copper deposition occurs in the pores of the carbon surface, the carbon itself may collapse. It is desirable to use a porous carbon-based material. Further, titanium tends to corrode the surface or form hydrides, but the amount thereof is so small that it can be substantially ignored and the impurity level of the liquid does not rise, so that it can be effectively used. Further, the copper deposited on the titanium cathode can be peeled off from the cathode very easily, and since it is deposited in the liquid as copper powder, it is more purposeful because the cathode need not be replaced.
Valve metals other than titanium, such as zirconium, tantalum, and niobium, are also effective, but are expensive and must be appropriately selected according to the purpose of use.

The material of the anode is preferably a metal electrode resistant to such hydrochloric acid aqueous solution. That is, it is a platinum group metal oxide electrode using titanium or a titanium alloy as a substrate and coating the surface thereof with an oxide such as ruthenium oxide. The electrode has extremely high resistance to the aqueous solution, and Cu ⁺ → Cu ²⁺ ( Cu
₂ Cl ₂ → CuCl ₂₎ reaction activity has enough for the side reactions chlorine evolution is chlorine even if the the cupric chloride monovalent oxidation results of copper ions in the unreacted (Cu ₂ Cl ₂ +
Cl ₂ → 2 CuCl ₂ ), so there is no substantial gas generation, which is extremely convenient. Further, a platinum-plated titanium electrode which is usually used in addition to the platinum group metal oxide electrode can be used in the present invention, but its corrosion resistance is inferior to that of the platinum group metal oxide electrode to a small extent.

Conventionally, a carbon electrode typified by graphite has been used, but this carbon electrode can also be used in the present invention. However, it is desirable to filter the liquid because carbon may partially collapse and float in the liquid. Also at a relatively low potential _{^{C + 4 OH - → CO 2}} + 2H 2 O + 4e - it should be noted that the reaction consumption of the carbon occurs at indicated by.
However, the decrease in current efficiency due to this is negligible.

The operating conditions of the regenerating electrolytic cell in the present invention, especially the current density, may be determined based on the above-mentioned electrode material and membrane resistance, and is usually 1 to 30 A / dm ² . When it exceeds 30 A / dm ² , the voltage rises, the efficiency at the cathode becomes unstable, and hydrogen generation sometimes occurs. If the current density is less than 1 A / dm ² , the desired reaction proceeds at a sufficiently low voltage, but the treatment amount becomes small, and the equipment must be made huge in order to increase the treatment amount.

[0019]

EXAMPLES Next, examples relating to the regeneration of copper etching waste liquid by the method of the present invention will be described, but the examples do not limit the present invention.

Example 1 A box-type electrolytic cell with a diaphragm made of hard vinyl chloride and having a length of 100 mm, a width (depth) of 60 mm, and a height of 120 mm (anode chamber) was prepared. A fluororesin membrane filter was used as the diaphragm, and a 70 mm × 70 mm polished titanium plate was used as the cathode, and the cathode was placed 30 mm away from the diaphragm. Also, a titanium electrode coated with ruthenium oxide having the same shape as the cathode is used as the anode, and 30 mm from the diaphragm.
It was installed separately and this regenerating electrolytic bath was connected to the etching bath.

The etching waste liquid discharged from the etching bath enters the electrolytic bath from the bottom of the cathode chamber, undergoes cathodic reduction, is taken out from the upper part of the cathode chamber, then enters the anode chamber from the bottom of the anode chamber, is anodized, and is then anodized. It was taken out from the upper part of the chamber. The height of the anode chamber is higher than that of the cathode chamber.
The height was increased by about 10 mm so that the pressure could be balanced even if gas was generated from the anode. Further, the regenerated liquid taken out from the anode chamber was thoroughly stirred in the stirring tank, and then circulated in the etching tank for reuse. Using a solution obtained by dissolving to saturation sodium chloride to 3 moles / liter CuCl ₂ .2H ₂ 0 as an etchant was used to etch the printed circuit board in the etching bath. The copper ion concentration after etching was about 2 mol / liter for both Cu ⁺ and Cu ²⁺ , and after adjusting the liquid temperature of this etching waste liquid to 30 ° C., 0.1 liter / hour was applied to the cathode chamber of the regeneration electrolytic cell. Feed at rate. The amount of current in the cathode chamber is excessive copper ion (about 1 mol /
It was set to about 17 A so that 1 liter) was deposited.

The etching waste liquid taken out from the upper part of the cathode chamber was supplied to the anode chamber through a membrane filter having an opening of 3 μm and electrolyzed at a current value of 17 A (about 35 A / dm ² ). A copper chloride solution having a black powder deposited and a Cu ²⁺ concentration of about 3 mol / l and a Cu ⁺ concentration of almost zero was obtained as an anolyte, and this copper chloride solution was directly usable as an etching solution. Since there was evaporation of water of about 5 ml / hour during the electrolysis, it was adjusted when the copper chloride solution was supplied to the etching tank. In this state, etching was continuously performed for 10 hours, but no deterioration of the etching solution occurred,
Neither was chlorine generated from the anode chamber. When the current efficiencies of the anode and cathode were calculated, both were about 95%.

[0022]

Industrial Applicability According to the present invention, a copper chloride etching waste liquid containing cuprous chloride is supplied to a cathode chamber of an electrolytic cell which is partitioned by a diaphragm into an anode chamber and a cathode chamber, and excess copper ions are converted into metallic copper into a cathode. After depositing on the surface, the etching waste liquid is supplied to the anode chamber, the cuprous chloride is converted to cupric chloride and regenerated as a copper etching liquid. The copper etching solution containing cupric chloride dissolves copper as the etching progresses, and copper ions become excessive, and cupric chloride is reduced and the etching waste solution of the mixed solution of cupric chloride and cuprous chloride is used. Become. Conventionally, a part of this etching waste liquid was taken out to recover copper, but copper recovery and regeneration of the etching waste liquid cannot be carried out at the same time, and the recycling operation is time-consuming and not an effective method.

On the other hand, in the method of the present invention, by the above-described configuration, the etching waste liquid in which copper ions are excessive and a part of cupric chloride is converted into cuprous chloride is used for the regeneration and the recovery of copper. Can be carried out by a relatively simple operation in the electrolytic cell, and the metal copper deposited in the cathode chamber can be recovered to obtain a regenerated etching solution containing substantially only cupric chloride in the anode chamber. When the cathode is drum-shaped, the drum-shaped cathode can be rotated to continuously obtain metallic copper deposited on the cathode in the form of a foil or the like.

Further, when the regenerating electrolytic bath of the method of the present invention is installed in the vicinity of the etching bath so that it can be connected to the etching bath, the etching waste liquid generated in the etching bath is circulated to the regenerating electrolysis bath as it is without being taken out to the outside. Since the etching waste liquid can be regenerated, the above-described etching waste liquid can be regenerated and copper can be recovered without the need for additional equipment.

Claims (3)

[Claims] 1. A copper chloride etching waste liquid containing cuprous chloride is supplied to a cathode chamber of an electrolytic cell partitioned by a diaphragm into an anode chamber and a cathode chamber to deposit excess copper ions as metallic copper on the cathode surface. After that, the etching waste liquid is supplied to the anode chamber, the cuprous chloride is converted into cupric chloride and regenerated as a copper etching liquid. 2. The method according to claim 1, wherein the cathode is a conductive drum, and the copper deposited on the surface of the cathode is scraped to continuously reproduce the copper. 3. The electrolytic bath is connected to an etching bath, and the etching waste liquid in the etching bath is supplied to the electrolytic bath for regeneration, and then circulated to the etching bath for reuse. Method.