CS257673B1 - A method of regenerating spent copper etching baths - Google Patents

Abstract

A method of regenerating spent copper etching baths containing copper in a complex form, based on the electrolytic reduction of the copper content in the bath to the required value. The required etching rate in the electrolytically processed bath is achieved by treatment consisting of acidification to a pH value lower than 5.5 and subsequent alkalization to a pH value suitable for etching. In this treatment, it is advantageous to carry out acidification and subsequent alkalization by adding an acid and a base containing ions that form the basis of the etching bath.

Description

The invention relates to a process for the regeneration of depleted copper etching baths in which the copper is contained in a complex form.

The active ingredient of etching solutions; used, for example, in the manufacture of electrical printed circuits or in the chemical machining of copper articles are copper ions which, when etched, react with copper metal:.

Cu ^{+ 2} + Cu - * 2 Cu ⁺

During the process, the ionic ions are oxidized again to copper (I) ions by air oxygen or by an etching agent present in the etching bath.

Since the cuprous salts are generally poorly soluble, and moreover, they are usually operated in pH ranges where cupric hydroxide or other sparingly soluble compounds are also precipitated from the cuprous salt solutions, complexing agents which bind mono- and divalent me3 in soluble form are common components of the etching solutions. Ammonium or organic amines are most commonly used as the complexing agent. Substances which are capable of oxidizing monovalent to bivalent are also a further component of the solution. During use of the bath, the copper content of the etching solution increases, or the concentration of the oxidizing component decreases, thereby decreasing the etching rate and, at the end of the bath's usability, the copper compounds may also be separated from the solution. The etching solutions used cannot be discharged into the waste due to the toxicity of the copper and, moreover, valuable raw materials would be lost. Therefore, various methods have been proposed for the treatment of the etching solutions used, with the aim of either merely obtaining copper in a commercially viable form or obtaining copper and at the same time reusable solutions for etching.

A considerable disadvantage of the methods of the first group is that after removal of the copper, the resulting solutions cannot be discharged into the waste water because they contain a residual copper concentration and have a considerably high salinity.

One method of the first group is to reduce the copper content of the etching bath by cementing with less noble metals (such as iron or aluminum), i.e. by adding metal chips to the bath which will reduce the copper solution. which cannot yet be discharged into waste.

Among the methods of the second group, the procedure of Ger.Offen 2,651,675 is of interest. The addition of HCl precipitates insoluble copper compounds from the solution, which are filtered off and, after addition of ammonia or water, the etching solutions can be reused. The disadvantage of the process is the difficulty of filtering the resulting suspensions or the need for further processing of the obtained precipitates to pure copper or to another commercially desired form of copper compounds.

According to US Pat. No. 4,083,758, the copper salt is extracted from the spent etching bath containing ammonium hydroxide and ammonium chloride first. The inorganic phase can be reused after the addition of ammonia. Copper (II) chloride is precipitated from the organic phase with dilute sulfuric acid, which is then converted into a solution from concentrated sulfuric acid from which pure copper is prepared by electrolysis.

The copper content of the etching baths can also be very effectively reduced by direct electrolysis.

By this procedure, the copper concentration in the exhausted etching bath can be reduced from an initial 100-150 g / dP to a value of about 5 g / dm, which is common in fresh etching baths. The solution obtained by electrolysis could be used as a fresh Reptace bath after the addition of active ingredients which have decomposed upon etching and electrolysis (oxidizing or complexing agents). ·

However, using an electrolytically regenerated etching bath, it was found that the etching rate in this solution was significantly lower than in the new etching bath. It has been shown that the carbonate is the cause of the process slowing down, thereby reducing the solubility of complex copper compounds in the etched copper layer of solution. Carbonates arise both

- 3 in the etching itself and in particular in the electrolysis by the anodic oxidation of the organic substances present in the baths as oxidizing agents or complexing substances.

Increasing the etching rates to the values typical of fresh etching baths can be achieved by the process of the present invention, which relates to a method of regenerating depleted copper etching baths in which it is contained in a complex form. SUMMARY OF THE INVENTION The present invention relates to a process in which exhausted etching baths in which the copper content has been reduced by electrolysis to the value of the newly prepared etching bath are acidified to a pH lower than 5.5 and then basified to a pH suitable for etching. Acidification and subsequent alkalization. of the solution is preferably carried out by the addition of an acid and a base with the ions forming the base of the etching bath. ’

Acidification to a pH of less than 5.5 produces carbonates from carbonates, which decompose into water and carbon dioxide. The carbon dioxide is released from the solution in gaseous form and only a small portion remains dissolved. The solution is again brought to a state suitable for etching by addition of components which have been decomposed by electrolysis (oxidizing and complexing agents), optionally by dilution with water, and by addition of alkali, thereby raising its pH to the prescribed value.

Acidification of the electrolyzed etching bath and subsequent alkalinization slightly increases the salinity of the solution, but by diluting it it is possible to achieve the required salt concentration in the etching bath. There is no defect in the volume of the etching bath in the overall balance, because on the contrary the solution is lost by etching boards during etching.

For acidification and alkalization of the etching bath, it is preferable to use acids and bases containing ions forming the basis of the etching bath. For example, to treat laptops of baths containing ammonia and ammonium chloride, it is preferred to use ammonia to acidify the hydrochloric acid and to alkalinize. By simply diluting with water, a solution with a suitable salt concentration for etching can then be obtained.

It is particularly preferred to acidify the solution by adding an oxidizing or complexing component of the acid etching bath (e.g., trichloroacetic acid instead of its salt),

Thereby producing an effective etching bath without increasing the salinity of the solution.

An advantage of the proposed process is also that the resulting solution has the same composition and therefore the same density as the fresh etching bath after the addition of oxidizing or complexing components and optionally after dilution with water, so that the density sensors in the etching machines react as well as the newly prepared bath.

The process according to the invention and the effect achieved by it are illustrated in more detail in the following examples.

Example 1

A fresh etching bath was prepared from ammonium chloride, copper chloride, three sodium chloride, and ammonia. It contained 110 g / dm ^{J of} chloride, 5 g / dm ^{J of} cupric ions, 140 g / dp of trichloroacetic acid and was basified to pH 9.5 with ammonia. In this 50 ° C bath, a 1 cm copper loop etching test was performed at a speed of 500 rpm. The etching rate averaged 3.4 µm / min during the first 9 minutes, and increased with the etching time due to the increase in the copper ion concentration.

Example 2 * 3

A depleted etching bath of pH 8.8 contained 100 g / dm of cuprous ions, 135 g / dd of chlorides, 58 g / dd. trichloroacetic acids, ammonium salts and ammonia. Laboratory electrolysis with a copper vibrating cathode, graphite anodes and PVC diaphragms electrolysed the etching bath, reducing the copper content to 5.5 g / day, the chloride content to 144 g / day and the trichloroacetic acid content to less Trichloroacetic acid decomposed during etching and electrolysis at 50 g / dm < 3 >. After addition of trichloroacetic acid trichloroacetic acid, after dilution with water to a chloride concentration of 110 g / day dn? and after alkalization with ammonia to pH 9.5, an etching test was carried out in the above experimental setup. The etching rate in this solution was on average only 2.5 µm / min during the first 9 min, ie 25% lower than in a fresh etching bath.

- 5 Example 3

The electrolyzed etching bath of composition 3 -3 above (5.5 g Cu / dm, 144 g Cl / dm) was acidified with concentrated hydrochloric acid (36%) to pH 4.5. At pH below 7.5, there was a significant effervescence of the solution caused by the release of carbon dioxide. 8 cm @ 3 of acid were consumed to acidify the 100 cm etching bath. Then the solution was diluted with water to 150 cu cu to reduce the chloride concentration, 22 g of trichloroacetic acid in the form of sodium trichloroacetate was added and the pH of the solution was adjusted to 9.5 by the addition of aqueous ammonia (26%). The resulting solution was carbonate-free and contained the same amount of chloride and trichloroacetate ions as the fresh etching solution. Only the copper content was adjusted to the desired pH by adding 0.23 g of copper in the form of CuCl ₂ .2 HgO. In the etching test, the etching rate was found to be the same as in the fresh etching bath.

Example 4

The electrolyzed etching bath of the same composition as in Example 3 was acidified by the addition of trichloroacetic acid (18.3 g of acid was used per 100 cm bath), bringing the pH of the bath to 1.3. The carbonates were removed from the solution. The pH was then adjusted to 9.5 with ammonia, and the solution was diluted with water to a volume of 130 cm @ 3 to maintain the chloride concentration as in the fresh bath of Example 1. 0.1 g of copper chloride was added to equalize the copper content. The etching rate showed the same etching rate as in Examples 1 and 3.

Claims (2)

Method for the regeneration of depleted copper etching baths, in which the copper is contained in a complex form, in which the copper content is reduced by electrolysis to a desired value, characterized in that the solution is acidified to pH lower than 5.5 after electrolysis and basify to a pH suitable for etching, 2. A process according to claim 1, characterized in that the solution is acidified and then rendered alkaline by addition of an acid and a base with the ions forming the base of the etching bath.