WO2012022689A1

WO2012022689A1 - Electrolyte and process for the deposition of copper-tin alloy layers

Info

Publication number: WO2012022689A1
Application number: PCT/EP2011/063923
Authority: WO
Inventors: Bernd Weyhmueller; Klaus Bronder; Uwe Manz; Frank Oberst; Mario Tomazzoni; Sascha Berger
Original assignee: Umicore Galvanotechnik Gmbh
Priority date: 2010-08-17
Filing date: 2011-08-12
Publication date: 2012-02-23
Also published as: KR20130098304A; DE102011008836A1; CN103069054A; EP2606164A1; CN103069054B; US20130140185A1; DE102011008836B4; JP2013534276A

Abstract

The present invention relates to an electrolyte and a process for depositing bronze alloys on consumer goods and industrial articles. The electrolyte of the invention comprises, in addition to the metals to be deposited and additives such as wetting agents, complexing agents and brighteners, in particular sulfur compounds which have a positive effect in the corresponding process for the deposition of the bronzes.

Description

Electrolyte and process for the deposition of copper- tin alloy layers

The present invention relates to an electrolyte and a process for depositing bronze alloys on consumer goods and industrial articles. The electrolyte of the invention comprises, in addition to the metals to be deposited and additives such as wetting agents, complexing agents and brighteners, in particular thioether derivatives which have a positive effect in the corresponding process for the deposition of the bronzes .

Consumer goods or consumer articles as are defined in the consumer articles regulations are upgraded by means of thin, oxidation-stable metal layers for decorative reasons and to prevent corrosion. These layers have to be mechanically stable and should also display no tarnishing or wear phenomena on prolonged use. Since 2001, the sale of consumer goods coated with nickel- containing upgrading alloys has no longer been permitted in Europe under EU guideline 94/27/EC or been possible only with observance of strict conditions since nickel and nickel-containing metal layers are contact allergens. Bronze alloys in particular have become established as a replacement for nickel- containing upgrading layers, and mass-produced consumer goods can be upgraded inexpensively in electrochemical barrel or rack plating processes to produce allergen- free, attractive products by means of these.

In the production of bronze layers for the electronics industry, the solderability of the resulting layer and if appropriate its mechanical adhesion are the critical properties of the layer to be produced. For use in this field, the appearance of the layers is generally less important than their functionality. For the production of bronze layers on consumer goods, on the other hand, the decorative effect (gloss and brightness) and durability of the resulting layer combined with an ideally unchanged appearance are the important target parameters .

Known processes for producing bronze layers include the conventional processes using cyanide-containing and thus highly toxic, alkaline baths and also various electrochemical processes which can, according to the composition of their electrolytes, usually be assigned to one of two main groups observed in the prior art: processes using electrolytes based on organosulfonic acid or processes using baths based on diphosphoric acid (pyrophosphoric acid) .

For example, EP1111097A2 describes an electrolyte which contains an organosulfonic acid and ions of tin and of copper together with dispersants and brighteners and also optionally antioxidants.

EP1146148A2 describes a cyanide-free copper-tin electrolyte which is based on diphosphoric acid and contains the reaction product of an amine and an epichlorohydrin in a molar ratio of 1:1 together with a cationic surfactant. The amine can be hexamethylene- tetramine. It is used in electrolytic deposition at current densities of 0.5, 1.5, 2.5 and 3.0 A/dm².

WO2004/005528 concerns a cyanide-free diphosphoric acid-copper-tin electrolyte which contains an additive composed of an amine derivative, an epichlorohydrin and a glycidyl ether compound in a molar ratio of 1:0.5-2:0.1-5. It was an object of this document to widen the current density range in which uniform deposition of the metals in a shiny layer can be achieved. It is explicitly stated that such deposition can only be achieved when the additive added is made up of all three of the abovementioned components. Cyanide-free acidic bronze electrolytes are likewise known. As such baths often contain one or more alkylsulfonic acids, usually in combination with further additives such as wetting agents, complexing agents, brighteners, etc.

EP1408141 Al discloses a process for the electro^¬ chemical deposition of bronzes, in which an acidic electrolyte containing tin and copper ions together with an alkylsulfonic acid and an aromatic, nonionic wetting agent is used.

EP1874982A1 describes the deposition of bronzes from an electrolyte comprising copper and tin ions together with alkylsulfonic acids and a wetting agent. Sulfur compounds can advantageously also be present in the electrolyte proposed here. However, these are used here in combination with nonionic aromatic wetting agents.

EP1325175B1 likewise advises the presence of particular sulfur compounds of the general formula -R-Z-R'- in acidic bronze electrolytes. The aim is to achieve equalization of the standard potentials of Cu(II) and Sn(II) ions by selective complexation of the copper. Despite the thio compounds used in this document, the addition of antioxidants appears to be indispensable in order to prevent damaging Sn(II) oxidation. Different coating processes are usually used in the electroplating industry as a function of the type and nature of the parts to be coated. The processes differ, inter alia, in respect of the current densities which can be employed. Mention may be made of essentially 3 different coating processes.

1. Barrel plating for loose material and mass- produced parts: in this plating process, relatively low working current densities are employed (order of magnitude: 0.025-0.5 A/dm²)

Rack plating for individual parts:

in this plating process, medium working current densities are employed (order of magnitude: 0.2-5 A/dm²)

3. High-speed plating for strips and wires m continuous plants:

in this field , very high working current densities are employed (order of magnitude: 5-100 A/dm²)

For coatings with copper-tin, the first two plating processes (barrel and rack) are of greatest importance. Depending on different types of electrolyte, either barrel plating (relatively low current densities) or rack plating (mean current densities) is possible (see "Praktische Galvanotechnik", Eugen G. Leuze Verlag 1997, page 74 ff.)

In view of the above mentioned prior art, it can be determined that, especially for barrel applications, deposition processes which ensure uniform deposition of metals over the current density range normally considered and also employ electrolytes which appear less complicated in terms of the composition and are, in particular, stable to Sn(II) oxidation are particularly advantageous.

It was therefore an object of the present invention to provide a deposition process and a further electrolyte which is advantageous from both an ecological and economic point of view compared to the electrolytes disclosed in the prior art. Particular attention should be paid to the deposition of ideally white, shiny bronze layers in the low current density range by means of an electrolyte which is stable and has a simple composition . These objects and further objects which have not been mentioned here but can be derived in an obvious way by a person skilled in the art from the prior art are achieved by an electrolyte and a corresponding process for the deposition of bronzes according to the present claim 1 and claim 10, respectively. The dependent claims referring back to claim 1 and claim 10, respectively, represent preferred embodiments of the electrolyte or of the process. The proposal of a cyanide-free electrolyte for the deposition of copper-tin bronzes on consumer goods and industrial articles, which contains the metals to be deposited, e.g. copper, tin and optionally zinc, in the form of water-soluble salts and is characterized in that

the electrolyte comprises the following further constituents :

a) one or more alkylsulfonic acids;

b) an ionic wetting agent in the form of a salt of a sulfonated or sulfated aromatic alkyl aryl ether compound;

c) a complexing agent; and

d) a compound selected from the group consisting of dialkyl thioether derivatives,

extremely advantageously but nonetheless surprisingly enables the stated object to be achieved. This electrolyte makes it possible to produce very uniform and extremely bright deposits of copper-tin bronzes on consumer goods and industrial articles, especially in the low current density range. The electrolyte used has good stability, in particular in respect of Sn(IV) precipitates. This leads, completely surprisingly, to the addition of further antioxidants to the electrolyte to be dispensed with. In a preferred embodiment, no further antioxidants, in particular hydroquinone, catechol, resorcinol, phenolsulfonic acid, cresolsulfonic acid, etc., are therefore present in the electrolyte of the invention. This would not have been expected by a person skilled in the art in the light of the prior art.

In the electrolyte of the invention, the metals copper and tin or copper, tin and zinc to be deposited are present in solution as their ions. Preference is given to the embodiment in which the metals are used as salts with anions which are either already present in the electrolyte or do not lead to any increase in the concentration of an anion constituent in the electrolyte by further introduction of the corresponding metal salt. They are therefore very preferably introduced in the form of water-soluble salts which are preferably selected from the group consisting of alkylsulfonates, carbonates, hydroxidecarbonates , hydrogencarbonates , hydroxides, oxidehydroxides , oxides or combinations thereof. It may be pointed out that the metals can also be introduced in the form of a soluble anode into the electrolyte in a preferred embodiment. In this respect, reference may be made to the embodiments of the process of the invention which are correspondingly mentioned here as advantageous . The type and amount of salts introduced in the electrolytes can be decisive for the color of the resulting decorative bronze layers and can be set according to customer requirements. The metals to be deposited are, as indicated, present in ionically dissolved form in the electrolyte for the application of decorative bronze layers on consumer goods and industrial articles. The ion concentration of copper can be set in the range from 0.2 to 10 g/1 of electrolyte, preferably from 0.3 to 4 g/1 of electrolyte, the ion concentration of tin can be set in the range from 1.0 to 30 g/1 of electrolyte, preferably 2-20 g/1 of electrolyte, and, if present, the ion concentration of zinc can be set in the range from 0.5 to 20 g/1 of electrolyte, preferably 1-3 g/1 of electrolyte .

The electrolyte of the invention is an acidic electrolyte based on one or more alkylsulfonic acids. The concentration of the acids in the electrolyte can vary in the range 100-300 ml/1 of electrolyte, preferably 150-250 ml/1 and very particularly preferably about 200 ml/1. As alkylsul fonic acids in the electrolyte, it is possible to use those which would be considered by a person skilled in the art for such purposes. In the present case, the term alkyl refers to a linear or any type of branched alkyl radical having from 1 to 10, preferably from 1 to 5 and very particularly preferably from 1 to 3, carbon atoms. Very particular preference is given to using alkylsulfonic acids selected from the group consisting of methanesulfonic acid, ethanesulfonic acid and n-propanesulfonic acid. The abovementioned metals to be deposited are advantageously used in the form of the water-soluble alkanesulfonate salts. For upgrading consumer goods, very particular preference is given to introducing the metals to be deposited as salts of methanesulfonic acid in such a way that the resulting ion concentration is in the range from 0.3 to 4 gram of copper, from 2 to 20 gram of tin and from 0 to 3 gram of zinc, in each case per liter of electrolyte.

As mentioned above, the electrolyte used contains ionic wetting agents/brighteners . The wetting agents are formed from salts of a sulfonated or sulfated aromatic alkyl aryl ether compound. Such wetting agents are adequately known to those skilled in the art ("Die galvanische Abscheidung von Zinn und Zinnlegierungen", Manfred Jordan, Eugen G. Leuze Verlag, Bad Saulgau) . The sulfonated or sulfated aromatic alkyl aryl ether compounds used contain an alkyl group joined via an oxygen bridge to an aryl radical. For the purposes of the invention, the term alkyl refers to a radical which in the present case contains a linear or a type of branched alkyl radical having from 1 to 10, preferably from 1 to 5 and very particularly preferably from 1 to 3, carbon atoms. As aryl radicals, it is possible for a person skilled in the art to select those which can be subsumed under the formulae (C7-C19) -alkylaryl, (C6-Ci₈)- aryl, (C7-C19) -aralkyl, (C₃-Ci₈) -heteroaryl, (C4-C19) - alkylheteroaryl , (C4-C19) -heteroaralkyl . Particular preference is given to those selected from the group consisting of phenol, naphthol, benzene, toluene, xylene, cumene, anisole, aniline. It is very particularly advantageous to use an alkyl aryl ether compound selected from the group consisting of aryl ethoxylates, in particular β-naphthol ethoxylate, nonylphenol ethoxylate. The sulfonated or sulfated position can be present either in the aromatic or in the aliphatic part of the compound. It is preferably present in the aromatic part of the compound. As counterions, it is possible to select all cations which a person skilled in the art would consider for this purpose. Preference is given to using the alkali metal salts or ammonium ions of the corresponding acids. These are particularly advantageously selected from the group consisting of sodium and potassium. This additive (e.g. sodium salt of sulfonated or sulfated aryl ethoxylates, in particular Na salt of sulfonated and sulfated alkylphenol ethoxylates) increases the shininess of the deposited layers, broadens the current density range in the direction of higher current densities and increases the whiteness of the deposited layers in the combination according to the invention by about 2 L units. At the same time, this brightener acts as wetting agent. The wetting agents mentioned are advantageously used in a concentration of 0.01-10 ml/1 of electrolyte, preferably 0.2-5 ml/1 of electrolyte and particularly preferably 0.5-1 ml/1 of electrolyte.

A complexing agent should likewise be present in the electrolyte. The complexing agent has, inter alia, the task of preventing any Sn(IV) ions formed from being precipitated as tin dioxide. Without addition of complexing agents, the electrolyte becomes turbid due to the tin dioxide formed after only a short time. The bronze depositions become increasingly matt as a result. The turbidity caused by finely divided Sn0₂ significantly increases the consumption of other organic additives. The addition of the complexing agent greatly reduces the degree to which the electrolyte becomes turbid and the quality of the bronze layers remains constantly good (shiny and white) with increasing usage of the bath and the consumption of organic additives being minimized.

As complexing agents, it is possible to select those compounds which would be considered for this purpose by a person skilled in the art. The preferred compounds are based on (hydroxy) dicarboxylic or tricarboxylic acids. Particular preference is given to using complexing agents selected from the group consisting of oxalic acid, malonic acid, succinic acid, tartaric acid, malic acid, citric acid, maleic acid, glutaric acid, adipic acid. Very particular preference is given to malic acid in this context. The complexing agents mentioned are advantageously used in a concentration of 1-300 g/1 of electrolyte, preferably 20-200 g/1 of electrolyte, particularly preferably 50-150 g/1 of electrolyte.

As mentioned above, the electrolyte of the invention is also admixed with one or more dialkyl thioether derivatives. These agents lead to improved deposition of the bronze alloy, in particular in the range of low current densities. Symmetrically substituted dialkyl thioether derivatives, e.g. thiodiglycol propoxylate or thiodiglycol ethoxylate, are advantageous in this context. As alkyl radicals, it is again possible to use those mentioned above. The alkyl radicals may be substituted by further functional groups. The latter can preferably be selected from the group consisting of hydroxy, carboxylic acid (ester), thiol, amino. Very particular preference is given to, for example, compounds selected from the group consisting of thiodiglycol propoxylate, thiodiglycol, thiodiglycerol , thiodiglycol ethoxylate, thiodiethylene bis (3- (3,5- di-tert-butyl-4-hydroxyphenyl ) propionate ) , 2-amino-4- (methylthio ) butanoic acid, 2 , 2 ' -thiodiethanethiol , 3 , 3 ' -thiodipropanethiol , 2 , 2 ' -thiodiacetic acid,

3 , 3 ' -thiodipropionic acid, diethyl 2 , 2 ' -thiodiacetate, dimethyl 2 , 2 ' -thiodiacetate, dioctyl 2 , 2 ' -thiodiacetate, didodecyl 2 , 2 ' -thiodiacetate, didodecyl 3, 3' -thiodipropionate, dimethyl

3, 3' -thiodipropionate, diethyl 3, 3' -thiodipropionate, dioctyl 3, 3' -thiodipropionate, 3 , 3 ' -thiodipropanol , 2 , 2 ' -thiodiethanol , 4 , 4 ' -thiodibutanol , 1 , 1 ' - ( thiodi- 2 , 1-ethanediyl ) 2-propionate, dioctadecyl

3 , 3 ' -thiodipropionate in this context, with 2-amino- 4- (methylthio ) butanoic acid appearing to be very preferred . The above mentioned dialkyl thioether derivatives are advantageously used in a concentration of 0.01-20 g/l of electrolyte, preferably 0.1-5 g/l of electrolyte, particularly preferably 0.3-1 g/l of electrolyte. The pH of the electrolyte is in the strongly acidic range because of the addition of the acids. It is set so that a range from -1 to 4, preferably a range from -0.5 to 2 and very particularly preferably a pH of about 1, results.

Furthermore, the present invention proposes an electrolytic deposition process for the electrochemical application of bronze alloy layers to consumer goods and industrial articles, in which the substrates to be coated are dipped into an electrolyte according to the invention and an appropriate flow of current is provided. The preferred embodiments of the electrolyte which have been discussed above apply analogously to the process presented here.

The electrolyte is preferably heated to a temperature in the range from 20 to 40°C, preferably about 30°C. It is possible to set a current density which is in the range from 0.01 to 100 Ampere per square decimeter [A/dm²] and is dependent on the type of the plating facility. Thus, current densities in the range from 0.01 to 0.75 A/dm² are preferred, from 0.025 to 0.5 A/dm² are more preferred and about 0.1-0.3 A/dm² are very particularly preferred, in barrel plating processes. In rack plating processes, current densities in the range from 0.2 to 10.0 A/dm², particularly preferably from 0.2 to 5.0 A/dm² and very particularly preferably from 0.25 to 1.0 A/dm², are preferably selected. However, the barrel application (see introduction and "Praktische Galvanotechnik", Eugen G. Leuze Verlag 1997, page 74 ff.) is preferred. When using the electrolyte of the invention, it is possible to use various anodes. Soluble anodes are particularly advantageous. As soluble anodes, preference is given to using anodes composed of a material selected from the group consisting of electrolytic copper, phosphorus-containing copper, tin, copper-tin alloy, copper-zinc alloy and copper-tin-zinc alloy. Particular preference is given to combinations of different soluble anodes composed of these materials .

Pure copper anodes can also be used in this electrolyte system. However, the preferred anodes for the copper- tin electrolyte based on alkylsulfonic acid are copper- tin alloy anodes having a copper content of from <90% by weight to >50% by weight and a tin content of from >10% by weight to <50% by weight. The anodes more preferably comprise 85-60% by weight of copper and 40-15% by weight of tin. The copper content of the anode is very preferably about 4 times the tin content. This is also the case when other elements such as, preferably, zinc are optionally present in the soluble anode .

The electrolyte also does not contain any materials which are harmful to health, which is a further advantage over other copper-tin electrolyte systems based on methanesulfonic acid. In methanesulfonic-acid copper-tin electrolytes, antioxidants, inter alia, are normally used to prevent oxidation of tin. As antioxidants, hydroquinone (carcinogenic) , catechol and resorcinol (both harmful to health) are often used. None of the chemicals mentioned are used in the electrolyte system of the invention. The electrolyte is stable enough to make do without the addition of further antioxidants.

For the purposes of the invention, (C6-Cis) -aryl is an aromatic system which is made up entirely of from 6 to 18 carbon atoms. In particular, such systems are selected from the group consisting of phenyl, naphthyl, anthracenyl, etc. (C7-C19) -Alkylaryl radicals are radicals which bear a (Ci-Cs) -alkyl radical on the (C6-Cis) -aryl radical.

(C7-C19) -Aralkyl radicals are radicals which have a (C6-Cis) -aryl radical on a (Ci-C₈) -alkyl radical by which the radical is bound to the molecule concerned.

For the purposes of the invention, (C₃-Ci₈) -heteroaryl radicals are aromatic systems having at least three carbon atoms. Further heteroatoms are additionally present in the aromatic system. These are preferably nitrogen and/or sulfur. Such heteroaromatics may be found, for example, in the Bayer-Walter, Lehrbuch der Organischen Chemie, S. Hirzel Verlag, 22nd edition, p. 703 ff.

For the purposes of the invention, (C4-C19) - alkylheteroaryl is a (C3-C18) -heteroaryl radical which is supplemented by a (Ci-C₈) -alkyl substituent. Bonding to the molecule concerned is via the heteroaromatics.

(C4-C19) -Heteroaralkyl, on the other hand, is a (C₃-Ci₈)- heteroaryl radical which is bound to the molecule concerned via a (Ci-C₈) -alkyl substituent.

Examples :

Electrolyte formulation according to the invention:

180 ml/1 of methanesulfonic acid (70%)

60 g/1 of malic acid

20 ml/1 of copper methanesulfonate solution (100 g/1)

= 2 g/1 of Cu in the electrolyte

20 ml/1 of tin methanesulfonate solution (300 g/1) =

6 g/1 of Sn in the electrolyte

1 g/1 of 2-amino-4- (methylthio ) butanoic acid

1 ml/1 of brightener (sodium salt of sulfonated and sulfated alkylphenol ethoxylates)

1. 200 ml/1 of deionized water are placed in a 1 1 glass beaker . 2. 180 ml/1 of methanesulfonic acid (70%) is then slowly added with vigorous stirring.

3. 60 g/1 of malic acid is then dissolved in the dilute methanesulfonic acid with vigorous stirring. After complete dissolution,

4. 20 ml/1 of copper methanesulfonate solution and 20 ml/1 of tin methanesulfonate solution are added and the volume is made up to 950 ml with deionized water.

5. 1 g/1 of 2-amino-4- (methylthio ) butanoic acid is then added. After this has dissolved completely,

6. 1 ml/1 of brightener is added to the electrolyte and the electrolyte is made up to the final volume (1000 ml) with deionized water.

Parameters for deposition: Temperature: electrolyte temperature: 30 °C pH: pH < 1

Current densities for barrel applications:

The optimal current density range for barrel applications is from 0.1 to 0.3 A/dm². Anodes :

The anodes for the copper-tin electrolyte based on methanesulfonic acid are copper-tin alloy anodes having a copper content of 80% by weight and a tin content of 20% by weight [commercially available from Goodfellow GmbH] .

Electrolyte properties:

Color light blue

Density 1.146 (25°C)

Current yield in the working current density range, virtually 100%

Degree of deposition mg/amine - 24 mg/amine

Deposition rate 0.025 μπι/min at 0.1 A/dm'

Properties of the coating:

Coating : copper-tin

Alloy composition: 70-55% of

(depending

conditions )

Density of the coating: about 8.2 g/cm³ (calculated)

Color : white, L* value about 82-85

Experiment using substitutes for dialkyl thioether derivatives : Formulation method for 1 1 of electrolyte:

See experiment using 2-amino-4- (methylthio ) butanoic acid Working parameters:

Temperature: 30°C

Anodes: Cu-Sn 80/20 1 liter glass beaker/200 rpm/6 cm magnetic stirrer bar/ movement of goods

The experimental depositions were carried out on 0.5 dm² brass plates at 0.2 A/dm²/10 min and 0.5 A/dm²/5 min.

The dialkyl thioether derivative was replaced by the following substances (see table) in these experiments.

Result: None of the substances tested worked as well as the dialkyl thioether derivatives, in particular 2-amino-4- (methylthio ) butanoic acid.

Claims

A cyanide-free electrolyte for the deposition of copper-tin bronzes on consumer goods and industrial articles, which contains the metals to be deposited in the form of water-soluble salts, characterized in that

the electrolyte comprises the following further constituents :

a) one or more alkylsulfonic acids;

c) a complexing agent; and

d) a compound selected from the group consisting of dialkyl thioether derivatives.

The electrolyte as claimed in claim 1, characterized in that it comprises copper and tin or copper, tin and zinc as metals to be deposited.

The electrolyte as claimed in claim 1 and/or 2, characterized in that the metals to be deposited are present in ionically dissolved form, with the ion concentration of copper being in the range from 0.2 to 10 g/1 of electrolyte, the ion concentration of tin being in the range from 1.0 to 20 g/1 of electrolyte and, if present, the ion concentration of zinc being in the range from 1.0 to 20 g/1 of electrolyte.

The electrolyte as claimed in one or more of claims 1 to 3, characterized in that alkylsulfonic acids selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, n-propanesulfonic acid are used.

5. The electrolyte as claimed in one or more claims 1 to 4, characterized in that the alkanesulfonates of the metals to be deposited are used as water-soluble salts.

The electrolyte as claimed in one or more of claims 1 to 5, characterized in that an alkyl aryl ether compound selected from the group consisting of β-naphthol ethoxylate, nonylphenol ethoxylate is used.

The electrolyte as claimed in one or more of claims 1 to 6, characterized in that the alkali metal salts of the corresponding acids are used.

The electrolyte as claimed in one or more of claims 1 to 7, characterized in that complexing agents selected from the group consisting of oxalic acid, malonic acid, succinic acid, tartaric acid, malic acid, citric acid, maleic acid, glutaric acid, adipic acid are used.

The electrolyte as claimed in one or more of claims 1 to 8, characterized in that a dialkyl thioether derivative selected from the group consisting of thiodiglycol propoxylate, thiodiglycol , thiodiglycerol , thiodiglycol ethoxylate, thiodiethylene bis ( 3- ( 3 , 5-di-tert- butyl-4-hydroxyphenyl ) propionate ) , 2-amino-4- (methylthio ) butanoic acid, 2 , 2 ' -thiodiethanethiol , 3 , 3 ' -thiodipropanethiol , 2 , 2 ' -thiodiacetic acid, 3 , 3 ' -thiodipropionic acid, diethyl 2 , 2 ' -thiodi- acetate, dimethyl 2 , 2 ' -thiodiacetate, dioctyl 2 , 2 ' -thiodiacetate, didodecyl 2 , 2 ' -thiodiacetate, didodecyl 3, 3' -thiodipropionate, dimethyl 3,3'- thiodipropionate, diethyl 3, 3' -thiodipropionate, dioctyl 3, 3' -thiodipropionate, 3,3'-thiodi- propanol, 2 , 2 ' -thiodiethanol , 4 , 4 ' -thiodibutanol , 1,1'- (thiodi-2, 1-ethanediyl ) 2-propionate, dioctadecyl 3 , 3 ' -thiodipropionate is used.

The electrolyte as claimed in one or more of claims 1 to 9, characterized in that the pH of the electrolyte is in the range from -1 to 4.

A process for the electrochemical deposition of copper-tin bronzes on consumer goods and industrial articles, which contains the metals to be deposited in the form of water-soluble salts, wherein the substrates to be coated are dipped into an electrolyte and an appropriate flow of current is provided, characterized in that an electrolyte as claimed in one or more of claims 1 to 10 is used.

The process as claimed in claim 11, characterized in that the electrolyte is heated to a temperature in the range from 20 to 40°C during the deposition of the metals.

The process as claimed in claim 11 and/or 12, characterized in that a current density which is in the range from 0.01 to 100 Ampere per square decimeter is set.

14. The process as claimed in one or more of claims 11-13, characterized in that the soluble anodes composed of a material selected from the group consisting of electrolytic copper, phosphorus-containing copper, tin, copper-tin alloy, copper-zinc alloy and copper-tin-zinc alloy or combinations of these anodes are used.