EP1408141B1 - Process and electrolyte for the galvanic deposition of bronze - Google Patents

Description

The present invention relates to a process for the electrodeposition of bronzes, with which the substrate to be coated in an acidic electrolyte, which comprises at least tin and copper ions, an alkyl sulfonic acid and a wetting agent is metallized, and the representation of such an electrolyte.

Methods for the deposition of tin as well as tin alloys are known from the prior art and are already widely used in practice based on different electrolyte types. Widely used is the use of methods for the deposition of tin and / or tin alloys from cyanide electrolytes. However, such electrolytes are disadvantageously highly toxic, which makes their use from an environmental point of view problematic, so that for some years the development of cyanide electrolytes such as electrolytes based on pyrophosphate or oxalate, which operate in a pH range of 5 to 9 promoted becomes. However, such methods also have economic and technical disadvantages, of which the relatively slow deposition rates are mentioned here.

For these reasons, development is now increasingly in the direction of providing methods for depositing tin and / or tin alloys from acidic electrolytes since divalent tin in acidic electrolytes can be reduced very easily to metallic tin, resulting in better deposition rates with qualitatively equivalent ones Coatings leads, and the other As a result, the adverse influence of the alkaline electrolyte on the substrates, such as ceramic components of assemblies prevented.

So are from the EP 1 111 097 A2 and the US 6,176,996 B1 Acid electrolytes and methods for the separation of high quality tin or tin alloys with a higher deposition rate known. These are electrolytes which have at least two divalent metal salts of an organic sulfonic acid and from which solderable and corrosion-resistant coatings are deposited, which are used, for example, as a replacement for lead-containing, solderable coatings, in electrical engineering for the production of printed circuit boards.

The European patent application EP 1 091 023 discloses a method for depositing tin-copper alloys for electrical engineering applications. The electrolytes known from said patent application may contain between 5 and 100 g / l of tin, 0.01 and 10 g / l of copper and an aromatic nonionic surfactant and an alkylsulfonic acid. From the German patent application DE 100 46 600 For example, there is known an electrolyte for depositing tin-copper alloys containing one or more alkylsulfonic acids and / or alkanolsulfonic acids, one or more soluble stannous salts, one or more soluble copper (II) salts, and one or more organic sulfur compounds or more thioether functions and / or ether functions of the general formula -RZ-R '- (R and R' are identical or different non-aromatic organic radicals, Z is S or O). From the US 5,443,714 discloses a method for the deposition of lead or predominantly lead-containing metal alloys from acidic electrolytes, which may contain alkanesulfonic acids.

From the EP 1 001 054 For example, an electrolyte for depositing tin-copper alloys is known which contains water-soluble tin salts, water-soluble copper salts, inorganic or organic acids or their water-soluble salts, and one or more compounds selected from the group consisting of thioamides and thiols. The thus deposited tin-copper alloys can serve as a replacement for lead-containing tin solders. From the EP 1 111 097 For example, an electrolyte is known for the deposition of specularly lustrous tin-copper alloys, wherein the electrolyte is an aqueous cyanide-free solution comprising organosulfonic acids, bivalent tin and copper salt and a brightener. From the US 4,565,608 For example, there is known an alkaline cyanide bath for depositing copper-tin alloys containing as organo-constituents either a fatty acid amidoalkyldialkylamine oxide, a fatty acid amidoalkyldialkylamine betaine or an ethoxylated naphthol.

From the Japanese Patent Abstract 11181589 a solution for the deposition of tin alloys and a corresponding deposition method is known, wherein the solution comprises an organic sulfonic acid, tin salts of organic sulfonic acid and sulfonates of metals of the group consisting of zinc, bismuth, silver, indium and copper. From the Japanese Patent Abstract 08013185 For example, an electrolyte for depositing low-melting tin alloys is known, wherein the electrolyte may comprise tin as methanesulfonates or isopropanol sulfonates. As further alloying metals to be deposited. For example, the electrolyte may contain copper, silver, indium, zinc or thallium.

The US patent US 6,176,996 discloses an electrolyte for depositing a tin-based binary alloy, wherein the electrolyte is 20 to 500 g / L of a tin salt, 1 to 100 g / L of a metal salt selected from the group consisting of zinc, cobalt, bismuth and copper, 20 to 200 g / L a methanesulfonic acid, 10 to 300 g / l of a lead compound and 0.5 to 50 g / l of a complexing agent.

However, such processes have their limits in the deposition of tin-copper alloys with high copper contents, such as the so-called "real" bronzes, which have a copper content of at least 10%. Thus, for example, the high potential difference between tin and copper can lead to higher oxidation rates of divalent tin, as a result of which it is very easily oxidized to tetravalent tin in acidic electrolytes. In this form, however, tin in the acidic is no longer electrodepositable and thus removed from the process, which leads to an uneven deposition of both metals and to lowering the deposition rate. In addition, the oxidation to tetravalent tin is associated with a strong sludge formation, which can prevent a stable operation and a long life of the acidic electrolyte. In addition, the formation of an adherent and non-porous coating is no longer guaranteed by such impurities.

Due to such procedural disadvantages, there is hitherto no large field of application for electrolytically deposited bronze coatings. Occasionally bronze coatings are used in the jewelry industry as a substitute for expensive silver or allergies triggering nickel. Likewise, processes for the electrolytic deposition of bronzes are gaining in importance also in some technical areas, for example in electrical engineering for the coating of electronic components or in the field of mechanical engineering and / or process technology for the coating of running and friction layers. As a nickel substitute here, however predominantly white bronze or so-called "fake bronzes" deposited, the copper content can be kept very low process-related.

The invention is therefore based on the object of specifying a method for the deposition of bronzes, which allows a uniform deposition of at least tin and copper next to each other from an acidic electrolyte at much higher deposition rates over the methods known in the art. In addition, with the help of this method, adherent and non-porous bronze coatings with high copper contents and different decorative and mechanical properties should be deposited.

Furthermore, an acidic electrolyte is to be provided for the deposition of such bronze coatings, which may have a high content of bivalent copper ions, is stable to oxidation-induced sludge formation, is ready for use over a prolonged period and is economical and environmentally friendly.

The object is achieved by a process for the electrodeposition of bronzes with a copper content of> 10 wt .-%, wherein a substrate to be coated is metallized in an acidic electrolyte at a set current density between 0.1 to 120 A / dm ² , wherein the electrolyte has at least tin and copper ions, an aromatic nonionic surfactant and methanesulfonic acid dissolved, characterized in that the electrolyte has a tin ion concentration of 2 to 75 g / l, a copper ion concentration of 2 to 70 g / l and a methanesulfonic acid concentration of at least 238 g / l is adjusted and bismuth and / or zinc is added to the electrolyte.

The present invention provides a process for the electrodeposition of bronzes, wherein, using an electrolyte, an anode of a copper-tin alloy and a cathode connected to the substrate to be coated, the coating is carried out while passing through direct current. Furthermore, the invention provides an electrolyte which can be used in particular for this process and also the coatings obtainable by this process.

By the method according to the invention, the disadvantages known in the prior art become available with the provision of a novel composition of the electrolyte eliminated and achieved in this way significantly better deposition results. In addition, the implementation is simplified and made more economical. This too is mainly due to the advantageous composition of the electrolyte. Thus, for example, the process is carried out at room temperature or between 17 to 25 ° C and to be coated Substrate metallized in a strongly acidic medium at a pH of <1. In this temperature range, the electrolyte is particularly stable. In addition, there are no costs for heating the electrolyte and also the metallized substrates need not be cooled down in a time and cost intensive manner. In addition, deposition rates of 0.25 μm / min are achieved at a current density of 1 A / dm ² , inter alia due to the pH value and the advantageous addition of at least one aromatic, nonionic wetting agent. This can be increased by the increase of the metal content up to 7 A / dm ² in the rack application and for pass-through systems even up to 120 A / dm ² . Thus, applicable current densities in a range of 0.1 to 120 A / dm ^{2 are} achieved depending on the type of system.

In particular, by the addition of at least one aromatic, nonionic wetting agent to the electrolyte, the wetting of the surfaces to be metallized, especially of more complex substrates, is surprisingly improved considerably. This advantageously has the consequence that not only significantly higher deposition rates are achieved by the use of the method according to the invention, but also that the coatings obtained by the process are uniform and of high quality, have a very good adhesion and are completely non-porous.

Another advantage of the aromatic, nonionic wetting agent used is that due to the advantageous wetting properties during the process, the electrolyte and / or the substrate in the electrolyte has little or no need to be moved in order to achieve the desired deposition results, so that the use of additional devices for moving the electrolyte can be dispensed with. In addition, due to the advantageous use of the aromatic, nonionic wetting agent when removing the metallized substrates from the electrolyte, the electrolyte residues run better from the substrates, which leads to reduced carry-over losses and thus to lower process costs.

Particularly advantageous is the addition of 2 to 40 g / l of one or more aromatic, nonionic wetting agents, particular preference being given to using β-naphthol ethoxylate and / or nonylphenol ethoxylate.

The proposed method is thus advantageously economical and environmentally friendly with respect to the cyanidic processes.

Optionally, the additional use of one or more known in the art anionic and / or aliphatic, nonionic wetting agents is possible, provided that they support the advantageous mode of action of the aromatic, nonionic wetting agent or even reinforce. Polyethylene glycols and / or anionic surfactants are preferably added to the electrolyte as anionic and / or aliphatic, nonionic wetting agents in this regard.

As already described above, the method according to the invention is characterized in particular by the particular composition of the electrolyte. This contains essentially tin and copper ions, an alkyl sulfonic acid and an aromatic nonionic wetting agent. Optionally, stabilizers and / or complexing agents, anionic and / or nonionic, aliphatic wetting agents, antioxidants, brighteners and other metal salts may additionally be present in the electrolyte.

The metals introduced mainly for the deposition of bronze according to the invention in the electrolyte - tin and copper - may be present primarily as salts of alkylsulfonic acids, preferably as methanesulfonates or as salts of mineral acids, preferably as sulfates. The tin salt used is particularly preferably the tin methanesulfonate in the electrolyte, which is advantageously added to the electrolyte in an amount of 5 to 195 g / l of electrolyte, preferably 11 to 175 g / l of electrolyte. This corresponds to a use of 2 to 75 g / l, preferably 4 to 67 g / l of divalent tin ions. The copper salt used is particularly preferably the copper methanesulfonate in the electrolyte, which is advantageously added to the electrolyte in an amount of 8 to 280 g / l of electrolyte, preferably 16 to 260 g / l of electrolyte. This corresponds to a use of 2 to 70 g / l, preferably 4 to 65 g / l of divalent copper ions.

Since the deposition rate in the acidic medium is significantly higher, the electrolyte is an acid, preferably a mineral and / or an alkyl sulfonic acid in Quantities of 140 to 382 g / l electrolyte, preferably 175 to 245 g / l electrolyte added. The use of methanesulphonic acid turned out to be particularly advantageous, since on the one hand it causes advantageous solubility of the metal salts and, on the other hand, prescribes or facilitates the adjustment of the pH required for the process due to its acidity. In addition, the methanesulfonic acid has the advantageous property of contributing significantly to the stability of the bath.

According to a further feature of the invention, at least one additional metal and / or chloride is added to the electrolyte. Advantageously, the metals are in the form of their soluble salts. In particular, the addition of zinc and / or bismuth influences the properties of the deposited coatings to a particular extent. The zinc and / or bismuth metals introduced into the electrolyte may be predominantly present as salts of alkylsulfonic acids, preferably as methanesulfonates or as salts of mineral acids, preferably as sulfates. As the zinc salt, the zinc sulfate is particularly preferably used in the electrolyte, which is advantageously added to the electrolyte in an amount of 0 to 25 g / l electrolyte, preferably 15 to 20 g / l electrolyte. As bismuth salt, the bismuth methanesulfonate is particularly preferably used in the electrolyte, which is advantageously added in an amount of 0 to 5 g / l electrolyte, preferably 0.05 to 0.2 g / l electrolyte to the electrolyte.

Furthermore, various additives such as stabilizers and / or complexing agents, antioxidants and brighteners, which are commonly used in acidic electrolytes for the deposition of tin alloys, may be added to the electrolyte.

In particular, the use of suitable compounds to stabilize the electrolyte is an important prerequisite for rapid and high-quality deposition of bronzes. Advantageously, gluconates are added to the electrolyte as stabilizers and / or complexing agents. Here, the preferred use of sodium gluconate has been found to be particularly advantageous in the process according to the invention. The concentration of the stabilizers and / or complexing agents is 0 to 50 g / l of electrolyte, preferably 20 to 30 g / l of electrolyte. As the antioxidant compounds are preferred from the class of Dihydroxybenzenes, for example, mono- or polyhydroxyphenyl such as catechol or phenolsulfonic acid used. The concentration of the antioxidants is 0 to 5 g / l of electrolyte. Advantageously, the electrolyte contains hydroquinone as an antioxidant.

The implementation of the method according to the invention enables the deposition of bronzes on different substrates. For example, all common materials for the production of electronic components can be used. Likewise, in particular hard and wear-resistant bronze coatings are deposited on materials such as plain bearings etc. by the method according to the invention. Also in the fields of decorative coating, for example of fittings and jewelry, etc., the inventive method is advantageously used, which is particularly advantageous in these areas, the deposition of multi-metal alloys containing tin, copper, zinc and bismuth, effects.

A very particular advantage is that with the method according to the invention so-called "real" bronzes can be deposited, which have a copper content> 60%, wherein the copper content can be up to 95 wt .-%, depending on the desired property. In addition, the ratio of the copper content to the tin content in the electrolyte has a significant influence on the properties such as hardness and color of the bronze coatings. Thus, with a tin / copper ratio of 40/60, silver-colored coatings, so-called white bronzes, are deposited, which are relatively soft. At a tin / copper ratio of 20/80, yellow gold-colored coatings, so-called yellow bronzes, are formed, and at a tin / copper ratio of 10/90, red-gold-colored coatings, so-called red bronzes, are formed.

In addition, the deposition of tin-rich white bronzes with a copper content ≥ 10% is possible.

Depending on the desired appearance of the bronze coatings, in addition to a different copper content, additives such as brighteners are added to the electrolyte. Advantageously, the electrolyte contains brighteners from the class of aromatic carbonyl compounds and / or α, β-unsaturated carbonyl compounds. The concentration of the brightener is 0 to 5 g / l electrolyte.

For a more detailed explanation of the invention, some preferred embodiments are presented below, to which, however, the invention can not be limited.

Electrolyte composition:

The base electrolyte of the strongly acidic electrolyte according to the invention essentially comprises (per liter of the electrolyte) 2 - 75 g divalent tin, 2 - 70 g divalent copper, 2 - 40 g an aromatic, nonionic wetting agent and 140 - 382 g a mineral and / or alkylsulfonic acid

Optionally, further constituents (per liter of the electrolyte) can be added to the electrolyte: 0-10 g an anionic and / or aliphatic, nonionic wetting agent, 0 - 50 g a stabilizer and / or complexing agent, 0 - 5 g an antioxidant, 0 - 5 g a shine agent 0 - 5 g trivalent bismuth 0 - 25 g divalent zinc

In order to achieve a certain color of the deposited bronze coatings, the electrolyte is prepared by variation of the individual components as exemplified below. Additional information on the corresponding process conditions and other properties of the individual coatings can be found in Table 1. Example 1 (red bronze) 4 g / l Sn ²⁺ 18 g / l Cu ²⁺ 286 g / l methane 3 g / l aromatic, nonionic wetting agent 0.4 g / l aliphatic, nonionic wetting agent 2 g / l Antioxidant 20 mg / l complexing Example 2a (yellow bronze) 4 g / l Sn ²⁺ 18 g / l Cu ²⁺ 240 g / l methane 32.2 g / l aromatic, nonionic wetting agent 2 g / l Antioxidant 25 g / l Stabilizer / complexing agent Example 2b (yellow bronze) 4 g / l Sn ²⁺ 18 g / l Cu ²⁺ 286 g / l methane 32.2 g / l aromatic, nonionic wetting agent 6 mg / l brightener 2 g / l Antioxidant 50 g / l Stabilizer / complexing agent Example 3 (white bronze) 5 g / l Sn ²⁺ 10 g / l Cu ²⁺ 240 g / l methane 32.2 g / l aromatic, nonionic wetting agent 6 mg / l brightener 2 g / l Antioxidant 25 g / l Stabilizer / complexing agent Example 4 (Matt white bronze) 18 g / l Sn ²⁺ 2 g / l Cu ²⁺ 258 g / l methane 9 g / l aromatic, nonionic wetting agent

To improve the hardness and / or ductility of the deposited bronze coatings, different contents of zinc and / or bismuth are added to the electrolyte as exemplified below. Additional information on the corresponding process conditions and other properties of the individual coatings can be found in Table 1. Example 5 (high ductility) (Example of the invention) 4 g / l Sn ²⁺ 18 g / l Cu ²⁺ 238 g / l methane 32.2 g / l aromatic, nonionic wetting agent 3 mg / l brightener 2 g / l Antioxidant 25 g / l Stabilizer / complexing agent 20 g / l ZnSO ₄ Example 6 (Hardness) (Example of the invention) 4 g / l Sn ²⁺ 18 g / l Cu ²⁺ 238 g / l methane 32.2 g / l aromatic, nonionic wetting agent 2 g / l Antioxidant 25 g / l Stabilizer / complexing agent 0.1 g / l Bi ³⁺ Example 7 (Yellow Bronze) (Example of the invention) 14.5 g / l Sn ²⁺ 65.5 g / l Cu ²⁺ 382 g / l methane 32.2 g / l aromatic, nonionic wetting agent 4 g / l Antioxidant 25 g / l Stabilizer / complexing agent 20 g / l ZnSO ₄

With the above exemplary electrolyte compositions, coatings having certain properties were deposited under the process conditions listed in the table below. Table 1 Example no. Coating /
Proportions in% by weight Properties of the coating sn Cu Zn Bi hardness ductility shine colour 1 10 90 - - 180 HV ₅₀ ++ Yes red 2a 20 80 - - 283 HV ₅₀ ± Yes yellow 2 B 20 80 - - 317 HV ₅₀ ± Yes yellow 3 40 60 - - 360 HV ₅₀ ± Yes White 4 90 10 - - - - No White 5 20 80 <1 - - +++ Yes yellow 6 20 80 - <1 345 HV ₅₀ - Yes yellow 7 20 80 <1 - - ++ Yes yellow

Claims (15)

1. Process for the electrochemical deposition of bronzes having a copper content of > 10% by weight, where a substrate to be coated is metallized in an acidic electrolyte at a set current density in the range from 0.1 to 120 A/dm² and the electrolyte comprises at least tin and copper ions, an aromatic nonionic wetting agent and methanesulphonic acid, characterized in that a tin ion concentration of from 2 to 75 g/l, a copper ion concentration of from 2 to 70 g/l and a methanesulphonic acid concentration of at least 238 g/l are set in the electrolyte and bismuth and/or zinc is added to the electrolyte.
2. Process according to Claim 1, characterized in that β-naphthol ethoxylate is added as aromatic nonionic wetting agent to the electrolyte.
3. Process according to Claim 2, wherein from 2 to 40 g/l of β-naphthol ethoxylate are added to the electrolyte.
4. Process according to any of the preceding claims, characterized in that the deposition is carried out at a temperature of from 17 to 25°C.
5. Process according to any of the preceding claims, characterized in that a pH of the electrolyte of < 1 is set for the deposition.
6. Acidic electrolyte for the electrochemical deposition of bronzes having a copper content of > 10% by weight, which contains at least tin and copper ions, methanesulphonic acid and an aromatic nonionic wetting agent, characterized in that the electrolyte has a tin ion concentration in the range from 2 to 75 g/l, a copper ion concentration in the range from 2 to 70 g/l and a methanesulphonic acid concentration of at least 238 g/l and contains bismuth and/or zinc.
7. Electrolyte according to Claim 6, characterized in that the electrolyte comprises β-naphthol ethoxylate as aromatic nonionic wetting agent.
8. Electrolyte according to Claim 7, characterized in that it comprises from 2 to 40 g/l of β-naphthol ethoxylate.
9. Electrolyte according to any of Claims 6 to 8, characterized in that it contains tin and copper in the form of a soluble alkylsulphonic acid salt.
10. Electrolyte according to any of Claims 6 to 9, characterized in that it contains polyethylene glycol and/or anionic surfactants as further wetting agent.
11. Electrolyte according to any of Claims 6 to 10, characterized in that it contains chloride.
12. Electrolyte according to any of Claims 6 to 11, characterized in that it contains gluconate as complexing agent.
13. Electrolyte according to any of Claims 6 to 12, characterized in that it contains an antioxidant from the class of dihydroxybenzenes.
14. Electrolyte according to any of Claims 6 to 13, characterized in that it contains brighteners from the class of aromatic carbonyl compounds and/or α,β-unsaturated carbonyl compounds.
15. Electrolyte according to any of Claims 6 to 14, characterized in that it has a pH of < 1.