US2887442A - Process for the electrolytic deposition of copper - Google Patents

Description

PROCESS FOR ELECTROLYTIC DEPOSITION OF COPPER 9 Claims. (Cl. 204-42) The aqueous copper ba'ths used so far can be distinguished in two groups, the acid and the alkaline copper baths. Of the acid copper baths the disadvantage is known that the deposition of contact copper on profiled objects cannot or only with difiiculty be prevented, whereas the alkaline copper baths always contain the copper complex bound to the cyanide ion. The disadvantages of cyanidic copper baths are evident; they are toxic, give off toxic vapors and are unstable, i.e. the cyanide decomposes while forming substances which collect in thebaths, whilst moreover CO is taken up from the air. When the cyanide bath has become useless, its removal forms a problem per se.

The process according to the present "invention relates to an electrolytic deposition of copper fromaqueousco'pper salt solutions in the presence of a diamine. For the sake of completeness it is remarked that copper baths containing a diamine are known per's'e fr'om Transactions Electrochemical Society 71 (1937), 255-261;73 (1938), 371376, and 78 (1940) 303-307. Accordin'g to the invention a diamine is used, the boiling point of which at atmospheric pressure lies between approximately 100 and 150 C., in an amount of at least 1 :molper liter. The thus prepared baths do not have the disadvantagesof the acid and alkaline copper baths; the copper deposits are very resistant and free oftpores,'whilst the metal distribution of the bath is good. The depositalso has a good tarnish resistance. The concentration of the baths prepared according to the invention can be chosen high, namely up to approximately 250 g. of copper sulfateper liter, so that quick operation is possible. With a cathode density of 5 to 7 a./dm. more than 11 micron of copper is deposited per minute.

It has been observed that the diamine copper complex formed obtains its greatest solubility when per mol of copper salt approximately 2 mols of diamine are added.

In the preferred amine concentration a part of the amine gets lost relatively quickly by evaporation. Such losses are expensive, the evaporated amines moreover are obnoxious to health and finally one does not know the concentration of the amine in the bath at any moment.

Furthermore it has now been found that the disadvantage of the volatility of the amine used can be obviated by adding to the bath also a monoamino carboxylic acid the complexity constant of which is higher than that of the diamine used. These baths have all advantages adhering to the use of baths with a high diamine concentration, but they yield moreover a deposit which can very easily be polished, which means a considerable saving of expenses in the mechanical treatment.

In Table I some diamines are indicated the boiling point of which lies between 100 and 150 C., together with their boiling points and the negative logarithm of the complexity constant, pK

2,887,442 Patented May 19, 1959 2 in'which K (Cu"+).(En) (Cu'Enl Herein Enre'presents the concentration Ofthe diamine, e.g. of the ethylene diamine, (Cu represents the concentration of the free cupric .ions and (CuEn represents the. concentration of the cupric ion bound to the diamine.

In Table II some amino acids are mentioned together with the negative logarithm of the complexity constant of the association reaction with the free cupric ion, 'in which Herein AZ represents the amino acid and CuAZ the cupric amino acid complex.

TABLE II P a-Alanine =a-c -c c c c. 15.0 fl-Alanine 12.8 Glycine 15.4 Glutamic acid l 15.0

'y-Aminobutyric acid 8.6

Preferably amino acids are usedthecomplexity constant of which is at least some tenth powers greater than that of the diamine with which it is combined, in other words the pK of which is at least 2 smaller than the pK of the diamine used. In that case namely the greater part of the cupric ion isbound to adiamine complex and for a much smaller part (with adilference of2 approximately one-thousandth of the above-mentioned part) asan amino acid complex. The amino acid complexes namely, in general, are less soluble in the usedsolutions than the diamine 'complexes,sotlrat in the reversed case insoluble amino acid complexes may be formed.

An advantage of the copper baths prepared according to the invention is the following. When a small excess of the diamine (about 2.2 mols) per mol of copper salt is used, the copper as well as the greater part of the diamine are bound to a complex of slight volatility, evaporation of the excess of diamine, however, still being possible. This evaporation is controlled according to the invention in the copper bath by replacing the previously necessary excess of diamine by a non-volatile amino acid which binds only a low percentage of the copper and is rather well soluble itself.

As appears from Table II monoamino monocarboxylic acids as well as monoamino dicarboxylic acids, such as glutarnic acid can be used. If desired, a wetting agent may be added to the bath. This wetting agent may be of the usual nature, such as e.g. an alkaline salt of a benzene sulfonic acid or lauryl sulfonic acid, but a deposit with improved properties, especially in respect of the brightness is obtained when the sulfate of a primary aliphatic alcohol with a branched carbon chain with 6 to 16 carbon atoms is added to the bath as the wetting agent.

The invention is elucidated by way of the following examples: Example 1 In the thus prepared bath brushed iron objects were copper plated at a temperature of 58 C., a cathode density of 8 a./dm. and an anode density of 1.2 a./dm. The pH value of the bath was about 8.7. The cathode was continuously kept moving as usual.

After 30 minutes a copper layer with an average layer thickness of about 50 microns had deposited: 94 microns on the projecting portions of the object and 34 microns in the hollow portions. This points to an extremely uniform distribution of the metal. The deposit everywhere had the same high brightness and could immediately be nickel-plated without afterpolishing.

Example 2 A copper bath was prepared with the following composition:

Copper sulfate 5 aq 225 g./l. (0.9 mol). Propylene diamine-1.2 148 g./l. (2.0 mols).

Glutamic acid 66 g./l. (0.45 mol). 2.butyl-decanol sulfate 0.8 g./1.

With the aid of the thus prepared bath brushed iron objects were copper plated at 56 C. The cathode denwhich comprises electrolyzing an aqueous solution containing an acidic copper salt, at least one mol per liter of a diamine with a boiling point between about 100 C. and 150 C. at atmospheric pressure and a saturated aliphatic monoamino carboxylic acid suflicient in amount to complex the copper, the decomposition constant of the complex being greater than that of the complex of the copper with the diamine used.

2. The process of. claim 1, wherein the decomposition constant of the complex of the acid is at least times as great as that of the complex of the copper with the diamine used.

3. The process of claim 2, wherein a sulfate of a primary aliphatic alcohol with a branched carbon chain having from 6 to 16 atoms is added to the solution as a wetting agent.

4. A process for the electrolytic deposition of copper, which comprises electrolyzing an aqueous solution containing an acidic copper salt, at least one mol per liter of a diamine with a boiling point between about 100 C. and C. at atmospheric pressure and a monoamino carboxylic acid selected from the group consisting of rat-alanine, B-alanine, glycine, glutamic acid and 'yaminobutyric acid, the amount of the acid being sufiicient to complex the copper.

5. An aqueous electrolyte for the electrolytic depositionof copper consisting essentially of an aqueous solution of an acidic copper salt, at least one mol per liter of a diamine with a boiling point between about 100 C. and 150 C. at atmospheric pressure and a saturated aliphatic monoamino carboxylic acid sufiicient in amount complex being greater than that of the complex of the to complex the copper, the decomposition constant of the copper with the diamine used.

6. An aqueous electrolyte for the electrolytic deposition of copper consisting essentially of an aqueous solution of an acidic copper salt, at least one mol per liter of a diamine with a boiling point between about 100 C. and 150 C. at atmospheric pressure and a monoamino carboxylic acid selected from the group consisting of a-alanine, fl-alanine, glycine, glutamic acid and 'y-aminobutyric acid, the amount of the acid being sufficient to complex the copper.

7. The electrolyte of claim 6, comprising about one half mol per liter of the monoamino carboxylic acid.

8. The process of claim 4, wherein the molar proportion of the acid is 0.1 to 0.6 times the molar proportion of copper.

9. The electrolyte of claim 6, wherein the molar proportion of the acid is 0.1 to 0.6 times the molar proportion of copper.

References Cited in the file of this patent 'UNITED STATES PATENTS Greenspan Apr. 2, 1940 Harford Aug. 8, 1944

Claims (1)

1. A PROCESS FOR THE ELECTROLYTIC DEPOSITION OF COPPER, WHICH COMPRISES ELECTROLYZING AN AQUEOUS SOLUTION CONTAINING AN ACIDE COPPER SALT, AT LEAST ONE MOL PER LITER OF A DIAMINE WITH A BOILING POINT BETWEEN ABOUT 100* C. AND 150* C. AT ATMOSPHERIC PRESSURE AND A SATURATED ALIPHATIC MONOAMINO CARBOXYLIC ACID SUFFICIENT IN AMOUNT TO COMPLEX THE COPPER, THE DECOMPOSITION CONSTANT OF THE COMPLEX BEING GREATER THAN THAT OF THE COMPLEX OF THE COPPER WITH THE DIAMINE USED.