Silver Electrolyte for Separating Silver Dispersion Layers

Abstract

The present invention is directed to a silver electrolyte and a corresponding method for galvanic deposition of silver on conductive substrates. The silver electrolyte is characterized by specific additives which help to prevent a foaming of the electrolyte without at the same time negatively influencing the electrodeposition.

Description

[0001] The present invention is directed to a silver electrolyte and a corresponding method for galvanic deposition of silver on conductive substrates. The silver electrolyte is characterized by specific additives which help to prevent a foaming of the electrolyte without at the same time negatively influencing the electrodeposition.

[0002] Electrical contacts are used today in virtually all electrical appliances. Their applications range from simple plug connectors to safety-relevant, sophisticated switching contacts in the communications sector, for the automotive industry or for aerospace technology. Here the contact surfaces are required to have good electrical conductivity, low contact resistance with long-term stability, as well as good corrosion and wear resistance with insertion forces that are as low as possible. In electrical engineering, plug contacts are often coated with a hard-gold alloy layer, consisting of gold-cobalt, gold-nickel or gold-iron. These layers have a good resistance to wear, a good solderability, a low contact resistance with long-term stability, and good corrosion resistance. Due to the rising price of gold, less expensive alternatives are being sought.

[0003] As a substitute for hard-gold plating, coating with silver has proven advantageous. Silver and silver alloys are amongst the most important contact materials in electrical engineering not only on account of their high electrical conductivity and good oxidation resistance. These silver layers have layer properties similar to those of the hard-gold layers and layer combinations used hitherto, such as palladium-nickel with gold flash. In addition, the price for silver is relatively low compared with other precious metals, in particular hard-gold alloys.

[0004] Special silver electrolytes are used for silver-coating of substrates and for producing contact surfaces. These are usually cyanide-containing or cyanide-free silver-containing solutions, which serve for the electrochemical, in particular galvanic, silvering of surfaces. In this case, silver electrolyte solutions can contain a wide variety of further additives, for example grain refiners, dispersants, brightening agents, or solid components. For applications in the electrical and electronics sector, especially in plugs and plug and switching contacts, the conductivity, the contact resistance, and the coefficient of friction are particularly relevant.

[0005] If two silver-coated surfaces are moved over one another, a comparatively high force is necessary for this purpose, which force is dependent on the respectively applied normal force and the material-specific coefficient of friction of the surface. The disadvantage of contacts having silver surfaces is evident here, since these have a relatively high coefficient of friction which, in particular in the case of plug contacts, leads to high plugging and pulling forces. Due to the high coefficients of friction, wear occurs in the case of silver surfaces, as a result of which the number of possible plug cycles is severely limited. In addition, the problem arises that silver surfaces are prone to galling. However, the lowest possible contact resistance of a system of two silver-coated surfaces is particularly advantageous.

[0006] Various cyanide-containing silver electrolytes for producing contact surfaces have already been acknowledged in the prior art (DE2543082A1, WO9114808A1, DE10346206A1, DE102008030988A1, DE102015102453A1, CN105297095A). DE102018005352A1 also describes cyanide-containing silver electrolytes for producing contact surfaces into which solid components are dispersed as dry lubricant. These solids are intended to be incorporated into the silver layer in a manner as highly dispersed and readily distributed as possible. The aim is to ensure the highest possible self-lubricating properties of the silver layer, by way of the uniform dispersion therein of solid components (Arnet, R. et al, “Silberdispersionsschichten mit selbstschmierenden Eigenschaften” [Silver dispersion layers with self-lubricating properties], Galvanotechnik 2021, Vol. 1, p. 21 et seq.). It is problematic that the known silver electrolytes tend to foam, in particular when significant electrolyte movements are used, for example when using dispersing devices (total volume increase of the electrolyte about 40%). However, significant electrolyte movements are necessary for a high usable current density and thus rapid deposition. This adversely affects, in the coating process, inter alia:

[0007] a) the uniform incorporation of the solid into the silver layer;

[0008] b) by electrolyte losses due to the foam exiting from the process vessel; and

[0009] c) by marbling effects on the partial surface due to adhering foam during extension and during the lifting of the parts;

[0010] and thus leads to disadvantageous products or process problems. The object of the present invention is therefore to specify a possibility by which the foam formation is maximally suppressed in such electrolytes during the deposition of silver, and at the same time the homogeneous deposition of a silver dispersion layer is as far as possible not adversely affected.

[0011] These and other objects evident from prior art are achieved by the use of an electrolyte according to the present claim 1. Advantageous embodiments relating to the electrolytes according to the invention are listed in dependent claims 2-7, which are dependent on claim 1. Claims 8-11 relate to a method including its preferred embodiments.

[0012] By providing an aqueous silver electrolyte for the galvanic deposition of silver layers on conductive substrates, which comprises the following components:

[0013] a) at least one soluble silver compound;

[0014] b) free cyanide in an amount of 20-200 g / l;

[0015] c) at least one luster additive in an amount of 0.2-10 g / l;

[0016] d) at least one wetting agent in an amount of 0.1-15 ml / l;

[0017] e) at least one solid component in an amount of 2-200 g / l;

[0018] wherein the electrolyte additionally has:

[0019] f) at least one defoamer in an amount of 0.2-20 g / l,

[0020] it is, surprisingly, it is easy to achieve the stated object.

[0021] During the deposition of silver layers from the electrolyte according to the invention, the electrolyte is to be kept constantly in motion in order to prevent sedimentation of the solid components and to ensure the highest possible current density. Foam formation is reliably prevented / largely reduced by means of the defoamers. It is also surprising that the addition of corresponding defoamers does not significantly negatively influence the layer composition (solids incorporation) and the desired properties of the silver layer, such as the contact resistance.

[0022] In principle, all compounds available to a person skilled in the art having a defoaming effect, and which are inert in the given system, can be used as defoamers (HypertextTransferProtocol: / / de.wikipedia.org / w / index.php?title=Entsch % C3% A4umer&oldid=187879609). Examples include defoamers from the group consisting of polyethers (BASF Pluriol® E Series), fatty alcohol alkoxylates (BASF Degressal® SD20), phosphoric acid esters (BASF Degressal® SD40), or alkyl polyglycol ether carbonates (CLARIANT COL® 100). The use of defoamers based on polyethers is particularly advantageous. In this context, those selected from the group of polyalkylene glycols, in particular polyethylene glycols, are advantageous (HypertextTransferProtocol: / / de.wikipedia.org / w / index.php?title=Polyethylen glycol&oldid=210432692). These are commercially available under different trade names, e.g., Pluriol® Series E200 to E9000, the number designator corresponding to the average molecular mass of the substance. It has also proven to be advantageous if the polyalkylene glycols used, in particular polyethylene glycol, have a higher average molar mass of greater than 200 g / mol, preferably at least 400 g / mol. The average molar mass of the polyethylene glycols used is very preferably between 1000 and 9000 g / mol and very particularly preferably between 4000 and 8000 g / mol. The average molar mass (HypertextTransferProtocol: / / de.wikipedia.org / w / index.php?title=Mittlere_mo lare Masse&oldid=188125754) of a polymer is determined by methods known to a person skilled in the art (HypertextTransferProtocol: / / www.chemgapedia.de / vsengine / vlu / vsc / de / ch / 9 / mac / charakterisierung / d3 / gpc / gpc.vlu / Page / vsc / de / ch / 9 / mac / charakterisie rung / d3 / gpc / auswertung.vscml.html). The amount of defoamer in the electrolyte can be defined by a person skilled in the art. This ranges between 0.2 and 20 g / l, preferably 1 and 10 g / l, and particularly preferably between 1 and 5 g / l.

[0023] In the context of the present invention, luster additives are substances which shift the grain size of the silver deposition to smaller grain sizes. Luster additives selected from the group consisting of substituted and unsubstituted mononuclear arylsulfonic acids, and thioalkylcarboxylic acids, thiocarbamides, have proven successful as said additives. Particularly preferred in this context are arylsulfonic acids, such as phenolsulfonic acid and benzenesulfonic acid, toluenesulfonic acid. However, in particular thiolactic acid, thiobarbituric acid and 1-phenyl-1H-tetrazol-5-thione have also proven to be advantageous. Those compounds are advantageous which have no negative influence on the solids deposition. The brightening agent B is used in a concentration of 0.2-10 g / l, preferably 0.5-10 g / l, and particularly preferably 1.0-5 g / l in the electrolyte according to the invention. It is in particular extremely advantageous if no naphthalene sulfonic acid, naphthalenesulfonic acid derivatives (for example naphthalene sulfonic acid condensation products with aldehydes) or mixtures thereof are present in the electrolyte according to the invention. In contrast, Na or K salts of arylsulfonic acids, in which the aryl group is a benzene ring, for example benzenesulfonic acid, are extremely preferred. The aryl group may optionally be substituted. In particular in connection with the polyether-based defoamers specified above, in particular polyethylene glycol ethers, the latter lead to only a small amount of foam occurring despite high current densities and resulting significant electrolyte movement, and the solids components can thus be dispersed well in the silver deposition (see examples).

[0024] The present electrolyte contains solid components. The function thereof has been sufficiently acknowledged in the prior art. Within the meaning of the invention, “solid component” means a component which is not present in solution but is present in the electrolyte as a solid. In particular, such solid components can be used which are mentioned in DE102018005352A1 in this regard. These are preferably those selected from the group consisting of graphite, graphite fluoride, graphite oxide, enveloped graphite, graphene, carbon black, fullerene, diamond, Al2O3, cubic boron nitride, or mixtures thereof, preferably graphite, graphite fluoride, graphite oxide, Al2O3 enveloped graphite, or mixtures thereof, more preferably of graphite, graphite oxide, or mixtures thereof, and even more preferably of graphite. The manner of suitable conditioning of the substances is sufficiently described in the literature and has, if at all, only minor influence on the invention described here. The solid component is present in the electrolyte in a dispersed, in particular physically dispersed, manner. This is achieved in particular by corresponding devices, such as stirrers, dispersion devices (e.g., Ultraturrax®) or dispersing disks. The amount of solid component used can be specified by a person skilled in the art, according to their discretion. In general, the concentration here is 2-200 g / l, preferably 20-150 g / l, and particularly preferably 80-130 g / l. The diameter of the solid components must be selected by a person skilled in the art, according to the application profile. In principle, the average particle diameter (HypertextTransferProtocol: / / de.wikipedia.org / w / index.php?title=Partikelgr % C3% B6% C3% 9Fenverteilung&oldid=186369602) is between 1 and 50 μm, preferably 2 and 20 μm, and particularly preferably between 2 and 10 μm. For this purpose, the average particle diameter (d50 of the Q3 distribution) is measured according to ISO 13320-1 (latest version on the filing date) with a Tornado dry dispersion module from the company Beckmann. In the sense of the invention, the average particle size (d50) indicates that 50% of the particles of a solid component have a smaller diameter than the specified value.

[0025] Wetting agents are also present in the electrolyte. A person skilled in the art knows how these are selected. Typically, ionic and nonionic surfactants are used as wetting agents, for example polyethylene glycol adducts, fatty alcohol sulfates (e.g., sodium lauroyl sulfate), alkyl sulfates, alkyl sulfonates, aryl sulfonates, alkylarylsulfonates, sulfonated castor oils (see also: Kanani, N: Galvanotechnik; Hanser Verlag, Munich Vienna, 2000; page 84 et seqq.). Silver coatings that are deposited using baths equipped in this way are generally white and glossy to highly glossy. The wetting agents lead to a pore-free layer. Compounds based on alkyl sulfates are preferably used as wetting agents. These can be linear-chain or branched-chain alkyl sulfates having C1-C25 alkyl groups, and preferably linear-chain or branched-chain alkyl sulfates having C2-C20 alkyl groups which may be unsubstituted or optionally substituted. The wetting agent preferably contains a linear-chain or branched-chain alkyl sulfate having C3-C15 alkyl groups which may be unsubstituted or optionally substituted, and preferably a linear-chain or branched-chain alkyl sulfate having C3-C12 alkyl groups which may be unsubstituted or optionally substituted. The wetting agents can also be present in the form of their salts, e.g., sodium salt, potassium salt. Very particularly preferably, in this connection those selected from the group consisting of 2-ethylhexylsulfate-Na-salt, lauryl ether sulfate-Na-salt, sodium monoalkyl sulfates, for example sodium tetradecyl sulfate, sodium dodecyl sulfate, sodium ethylhexyl sulfate, sodium decyl sulfate, sodium octyl sulfate, and mixtures thereof are used. The content of the at least one wetting agent is between 0.1 and 15 ml / l, preferably between 0.2 and 10 ml / l, more preferably between 0.5 and 7 ml / l, and even more preferably between 1 and 6 ml / l.

[0026] Optionally, salts comprising Se or Te can also be present in the electrolyte. The selenium or tellurium compound which is used in the electrolyte can be selected accordingly by a person skilled in the art. Suitable selenium and tellurium compounds are those in which selenium or tellurium is present in oxidation states +4 or +6, in the form of an anion. Selenium and tellurium compounds are advantageously used in the electrolyte in which selenium or tellurium in oxidation state +4 is present. The selenium and tellurium compounds are particularly preferably selected from tellurites, selenites, tellurous acid, selenious acid, telluric acid, selenium acid, selenocyanates, tellurocyanates and selenate and tellurate. In this case, the use of selenium compounds rather than tellurium compounds is generally preferred. The addition of selenium to the electrolyte in the form of a salt of the selenic acid, for example in the form of potassium selenite, is very particularly preferred. Extremely preferred is the addition as potassium selenocyanate. The amount of these compounds in the electrolyte can be selected as required by a person skilled in the art. It is in the range of 0.1 mg-500 mg / l, preferably 0.5 mg-100 mg, and particularly preferably between 0.5 mg-10 mg / l, based on selenium or tellurium.

[0027] In addition to the ingredients indicated above, the electrolyte also contains a certain amount of free cyanide. This is preferably added to the electrolyte in the form of a water-soluble salt of hydrocyanic acid. The alkali salts are advantageous, and potassium cyanide is very particularly preferably used. The amount of free cyanide can be set in the electrolyte according to values known to a person skilled in the art. In general, the free cyanides are present in the electrolyte in a concentration of 20-200 g / l, preferably 80-180 g / l, and particularity preferably 100-150 g / l (in each case based on the CN ion). The cyanide salt used can also serve as a conductive salt.

[0028] Another essential component of the electrolyte is the silver, to be deposited, in dissolved form. This can be introduced into the electrolyte as required by a person skilled in the art, in the form of a water-soluble salt. Those from the group consisting of silver methanesulfonate, silver carbonate, silver phosphate, silver pyrophosphate, silver nitrate, silver oxide, silver lactate, silver fluoride, silver bromide, silver chloride, silver iodide, silver thiocyanate, silver thiosulfate, silver hydantoins, silver sulfate, silver cyanide and alkali silver cyanide are possible as these. Potassium silver cyanide is very particularly advantageous in this context. The silver salts are used in a starting concentration in the electrolyte which is between 2-200 g / l, preferably 10-100 g / l, and particularly preferably 20-50 g / l (in each case based on the Ag metal).

[0029] It should be noted that, in a preferred embodiment, further ions can also be present in dissolved form in the electrolyte, in a low concentration. These are in particular those which lead to a harder layer compared to the deposition of a pure silver layer (known as hard silver). These are ions selected from the group consisting of Sb, Bi, In, Sn, W, Mo, Pb, As, Cu, Ni. These are generally added in a concentration of 0.001-30 g / l, preferably 0.01-20 g / l, and particularly preferably 0.1-10 g / l (in each case based on the corresponding metal).

[0030] The present invention also relates to a method for the galvanic deposition of silver layers on conductive substrates, in which an electrically conductive substrate is immersed in the electrolyte according to the invention and a current flow established between an anode in contact with the electrolyte, and the substrate, as the cathode.

[0031] The temperature prevailing during the deposition of the dispersion layer can be selected by a person skilled in the art as desired, or the temperature is established by itself due to external influence (friction heat from dispersing modules). This will be guided on the one hand by a sufficient deposition rate and the usable current density range, and on the other hand by economic considerations or the stability of the electrolyte. It is advantageous to set a temperature of the electrolyte of 10° C. to 70° C., preferably 15° C. to 40° C., and particularly preferably 20° C. to 30° C.

[0032] In principle, the pH of the electrolyte can be adjusted as required by a person skilled in the art. In this case, however, a person skilled in the art will be guided by the consideration of introducing into the electrolyte the fewest possible additional substances that could negatively influence the deposition of the corresponding layer. In a particularly preferred embodiment, the pH is therefore set solely by adding a base. As such, all compounds can be used which, in the view of the person skilled in the art, are suitable for a corresponding application. This preferably uses alkali hydroxides, oxides or carbonates. During the electrolysis, the electrolyte according to the invention is preferably set in a basic pH range of >8. Optimal results can be achieved at a pH in the electrolyte of 8-13, more preferably 9-11. In principle, the pH can be adjusted as required by a person skilled in the art. In this case, however, a person skilled in the art will be guided by the consideration of introducing into the electrolyte the fewest possible additional substances that could negatively influence the deposition of the corresponding layer. In a particularly preferred embodiment, the pH is therefore set solely by adding a base. As such, all compounds can be used which, in the view of a person skilled in the art, are suitable for a corresponding application. It may be that fluctuations with respect to the pH of the electrolyte occur during electrolysis. In one preferred embodiment of the present method, the person skilled in the art will therefore proceed so that they monitor the pH during electrolysis and adjust it to the setpoint value if necessary. A person skilled in the art knows how to proceed here.

[0033] The current density that is established in the electrolyte according to the invention between the cathode and the anode during the deposition process can be selected by a person skilled in the art on the basis of the efficiency and quality of deposition. Depending on the application and type of coating system, the current density in the electrolyte is advantageously set to 0.2 to 100 A / dm2. If necessary, current densities can be increased or reduced by adjusting the system parameters, such as the design of the coating cell, flow rates, anode or cathode relationships, etc. A current density of 0.2-50 A / dm2 is advantageous, 0.2-10 A / dm2 is preferred, and 1-5 A / dm2 is very particularly preferred.

[0034] Instead of direct current, pulsed direct current or reverse pulse plating can also be applied. In this case, the current flow is thereby interrupted for a certain period of time (pulse plating), or the current flow reverses. The use of pulse plating in the form of current interruptions and reverse pulse plating for silver graphite dispersion deposition is described in the literature (Arnet, R. et al, “Silberdispersionsschichten mit selbstschmierenden Eigenschaften”, [Silver dispersion layers with self-lubricating properties], Galvanotechnik 2021, Vol. 1, p. 21 et seq.).

[0035] The electrolyte according to the invention and the method according to the invention can be used for the galvanic deposition of silver layers, preferably for technical applications, for example electrical plug connections and printed circuit boards. For technical applications, coating in continuous-flow systems can also be used.

[0036] Layer thicknesses in the range from 0.1 to 100 μm are typically deposited in rack operation, in particular for technical applications having current densities in the range from 0.5 to 50 A / dm2. For technical applications, up to 200 μm or even 500 μm thick layer thickness is sometimes also deposited in continuous plants. For this purpose, the current densities are in the range indicated above.

[0037] Various anodes can be employed when using the electrolyte. Soluble or insoluble anodes are just as suitable as the combination of soluble and insoluble anodes. If a soluble anode is used, it is particularly preferred if a silver anode is used (DE1228887, Praktische Galvanotechnik, 5th edition, Eugen G. Leuze Verlag, p. 342 et seq., 1997).

[0038] Preferred insoluble anodes are those made of a material selected from the group consisting of platinized titanium, graphite, stainless steel, mixed metal oxides, glass carbon anodes, and special carbon material (“diamond-like carbon,” DLC), or combinations of these anodes. Insoluble anodes of platinized titanium or titanium coated with mixed metal oxides are advantageous, wherein the mixed metal oxides are preferably selected from iridium oxide, ruthenium oxide, tantalum oxide and mixtures thereof. Iridium-transition metal mixed oxide anodes composed of iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide, or iridium-tantalum mixed oxide are also advantageously used for execution of the invention. More information may be found in Cobley, A. J et al. (The use of insoluble anodes in acid sulphate copper electrodeposition solutions, Trans IMF, 2001, 79 (3), pp. 113 and 114).

[0039] Possible electrically conductive substrates are those which can be coated with the electrolyte according to the invention in the acidic pH range. These are preferably noble metal-containing substrates or even non-noble substrates, such as nickel or copper surfaces. Preferably, the silver layer according to the invention is deposited on a nickel or nickel alloy layer, or a copper or copper alloy layer. Suitable substrate materials which are advantageously used here are copper base materials such as pure copper, brass, bronze (e.g., CuSn, CuSnZn) or special copper alloys for plug connectors, such as alloys comprising silicon, beryllium, tellurium, phosphorus, or iron-based materials such as iron or stainless steel or nickel or a nickel alloy such as NiP, NiW, NiB, gold or silver. The substrate materials may also be multilayer systems that have been galvanically coated or coated using other coating techniques. This relates, for example, to ferrous materials which have been nickel-plated or copper-plated and subsequently optionally gold-plated, pre-palladiumed, pre-platinumed, or coated with pre-silver. The intermediate layers for nickel plating or copper plating can thereby also be made from corresponding alloy electrolytes—e.g. NiP, NiW, NiMo, NiCo, NIB, Cu, CuSn, CuSnZn, CuZn etc. A further substrate material can be a wax core which has been pre-coated with conductive silver lacquer (electroforming).

[0040] The term “electrolyte bath” is understood according to the invention to mean the aqueous solution which is put into a corresponding vessel and used with an anode and a cathode, under current flow, for electrolysis. In the present case, merely the solid component used represents the exception here.

[0041] The electrolyte according to the invention is aqueous. Except for the added solid components and possibly insoluble heterogeneous defoamers, the compounds used in the electrolyte are soluble in the electrolyte. The term “soluble” refers to those compounds which dissolve in the electrolyte at working temperature. The working temperature is thereby that temperature at which electrolytic deposition takes place. In the context of the present invention, a substance is deemed soluble if at least 1 mg / l of this substance dissolves in the electrolyte at the working temperature.

[0042] The electrolyte according to the invention has long-term stability. By combining the luster additives described for the deposition of silver, and the use of a defoamer, it was possible to obtain coatings suitable for the application described. These have sufficiently low contact resistances and, moreover, maintain a surprisingly high integrity of the surface, and thus low contact resistances, even after many plugging and friction processes, in contact circuits. This was not to be expected from the available state of the art.EXAMPLESElectrolyte Composition Aqueous A:30 g / l as potassium silver cyanide

[0044] 130 g / l potassium cyanide

[0045] 5 g / l potassium carbonate

[0046] 2 mg / l Se as potassium selenocyanate

[0047] 4 g / l ethylhexylsulfate

[0048] 1 g / l benzenesulfonic acid

[0049] 100 g / l graphite powder having an average particle size (d50) of 2-4 μm

[0050] Current density 1.5 A / dm2

[0051] Temperature: 25° C.

[0052] Anode: soluble fine silver anodesAddition Pluriol ® E 600 [ml / l]Polyethylene glycolGraphite incorporation inAverage molar mass 600the silver layer [wt. %]02.01.02.0

[0053] The graphite incorporation is not adversely influenced by addition of the defoaming component.Electrolyte Composition Aqueous B:30 g / l as potassium silver cyanide

[0055] 130 g / l potassium cyanide

[0056] 5 g / l potassium carbonate

[0057] 2 mg / l Se as potassium selenocyanate

[0058] 5 g / l ethylhexylsulfate

[0059] 1 g / l benzenesulfonic acid

[0060] 100 g / l graphite powder having an average particle size (d50) of 2-4 μm

[0061] Current density 1.5 A / dm2

[0062] Temperature: 25° C.

[0063] Anode: soluble fine silver anodesAddition Pluriol ® E 6000 [ml / l]Polyethylene glycolGraphite incorporation inAverage molar mass 6000the silver layer [wt. %]02.01.02.0

[0064] The graphite incorporation is not adversely influenced by addition of the defoaming component.

Claims

1. An aqueous silver electrolyte for the galvanic deposition of silver layers on conductive substrates, comprising:a) at least one soluble silver compound;b) free cyanide in an amount of 20-200 g / l;c) at least one luster additive in an amount of 0.2-10 g / l;d) at least one wetting agent in an amount of 0.1-15 ml / l;e) at least one solid component in an amount of 2-200 g / l;wherein the electrolyte additionally has:f) at least one defoamer in an amount of 0.2-20 g / l.

2. The aqueous silver electrolyte according to claim 1, wherein the defoamer is selected from the group of polyalkylene glycols.

3. The aqueous silver electrolyte according to claim 2, wherein the defoamer has an average molar mass of at least 200 g / mol.

4. The aqueous silver electrolyte according to claim 1, wherein the luster additive is selected from the group consisting of arylsulfonic acids.

5. The aqueous silver electrolyte according to claim 1, wherein the solid component is selected from the group consisting of graphite, graphite fluoride, graphite oxide, diamond, Al2O3 enveloped graphite, or mixtures thereof.

6. The aqueous silver electrolyte according to claim 1, wherein the wetting agent is selected from the group of alkyl sulfates.

7. The aqueous silver electrolyte according to claim 1, wherein it additionally comprises at least 0.1-500 mg / l of a salt of a Se— or Te anion (based on the selenium or tellurium).

8. A method for the galvanic deposition of silver layers on conductive substrates, wherein an electrically conductive substrate is immersed in the electrolyte of according to claim 1, and a current flow is established between an anode in contact with the electrolyte, and the substrate as the cathode.

9. The method according to claim 8, wherein the temperature of the electrolyte is 20° C.-90° C.

10. The method according to claim 8, wherein the current density during electrolysis is between 0.2-100 A / dm2.

11. The method according to claim 8, wherein the pH during electrolysis is continuously set to a value of >8.