TECHNICAL FIELD

The present invention relates to an environmentally friendly cyanide-free solution suitable for coating in general and electroplating in particular. Further, the present invention provides a method for the preparation of fully stable cyanide-free copper or gold solutions, which can be used either directly or in combination with already existing solutions suitable for plating, in particular electroplating of difficult to plate substrates.

BACKGROUND

Copper electroplating has been used in applications as different as electronics and other technical uses, as well as decorative, which is mainly due to the ease to produce mirror- bright deposits either using so-called levelers in the electrolyte or mechanical polishing of the resulting copper plate. Basically, there are two types of copper electrolytes, acid copper based on sulfuric acid, and alkaline copper based on sodium or potassium cyanide. More recently, alkaline copper electrolytes have been developed, containing strong complexing agents, stabilizing copper in the +II oxidation state, which is in contrast to cyanide, which stabilizes the +l oxidation state.

For many applications, acid copper plating is the method of choice as it is simple to handle and easy to control, giving excellent results particularly in terms of brightness at fast deposition rates. Substrates to be plated may include copper, brass, and certain iron- based materials. Other substrates, such as aluminum, magnesium and zinc dye cast are destroyed in acidic media and require alkaline processes to be plated, most reliably with cyanide-based ones. Due to the extremely high toxicity of cyanides, non-cyanide electrolytes are preferred and have found widespread acceptance in the industry. The Cu +II oxidation state of these electrolytes, however, bears the risk of unwanted immersion plating, leading to poor adhesion between the copper plate and the substrate. This is in particular true for parts that are prone to oxidation, which is why cyanide plating is still the preferred technology in this case. A cyanide-free alkaline electrolyte based on monovalent copper would therefore be highly desirable, addressing both, the high toxicity of cyanide and the immersion problem of divalent copper electrolytes.

Over the last two decades, mercapto-tetrazoles have found increasing interest in stabilizing copper +l mainly in the context of white bronze plating (Egli and Chen US 7'780'839, Foyetetal. US 2016/298249). Surprisingly, such electrolytes have not found much attention for pure copper plating. On one part this is due to missing registration in important industrial countries, namely the US, for the most promising and commercially available mercapto-tetrazole, 1-(2-dimethylamino-ethyl)-5-mercapto-1,2,3,4-tetrazole. On the other part, this can also be attributed to the scarce solubility of such copper complexes in alkaline media, whereas in acidic media mercapto-tetrazole based plating processes do not provide substantial advantages over the well-established sulfuric acid processes.

Similar observations have been made with the closely related mercapto-triazole and mercapto-thiadiazole compounds that generate thermodynamically stable, but poorly soluble monovalent copper complexes.

Gold electroplating has been conventionally used in jewelry but found, due to its excellent electric characteristics and corrosion resistance, a broad application range in the electronics industry over the last decades.

To date, most gold electrolytes are still based on cyanide, which is mainly owing to its high stability constant as compared to other well-known gold complexes used in electroplating, such as sulfite, thiosulfate and thiourea and its derivatives.

Over the last two decades, mercapto-triazoles and mercapto-tetrazoles have found increasing interest in stabilizing low valent metal cations for electroplating purposes. Examples include copper (Egli SE 2150946-8), copper in white bronze plating (Egli and Chen US 7'780'839, Foyet et al. US 2016/298249) and silver plating (Foyet at al. US 10'889'907). In gold electroplating this class of ligand has not yet been used as a major complexing agent, but only as anti-immersion or anti-displacement agent to reduce unwanted immersion plating on reactive substrates (Zhang et al EP 2'309'036, Breitfelder et al. US 2017/0159195) with a concentration maximum of 1 g/L of the mercapto compound. As with other low valency cations and analogously to the above mentioned copper, this limited use can be attributed to the scarce solubility of such complexes in aqueous media.

Therefore, there exists a need in the industry today for improved electroplating compositions and methods.

SUMMARY OF THE INVENTION

It is an object to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solve at least the above mentioned problem. This and other objects, that will become apparent in the following, are accomplished by an electroplating solution as described herein.

An object of this invention is to provide reliable and preferably fully adherent application of electroplates, more specifically copper or gold electroplates, on difficult-to- plate substrates, such as zinc dye cast, aluminum and magnesium and alloys thereof.

Another object is to provide copper or gold electroplates from a nontoxic electroplating bath that is substantially free of cyanide, while providing the same deposit quality, which is expected from cyanide-based electrolytes.

There is, in one aspect of the present invention, provided an electroplating composition comprising one or more sources of a noble metal selected from a) Cu(l) and/or Cu(ll) and b) Au(l), and/or Au(lll); at least one strong base; at least one acid; and a combination of at least two different mercapto ligands, selected from the group of mercapto-tri azoles, mercapto-tetrazoles, mercapto-thiadiazoles, and derivatives thereof.

In one embodiment, the composition further comprises at least one compound selected from thioether, thiourea, or a compound having a thioether or thiourea functionality. In one embodiment, the at least one compound is present in a concentration that is allowed by the solubility of the individual at least one compound, such as in the range 0.5 to 500 g/L, such as in the range of 1 to 200 g/L.

In one embodiment, the electroplating composition is aqueous.

In one embodiment, said at least one mercapto-ligand is a terminal ligand in that it comprises no additional co-ordinating nitrogen- or sulfur-comprising functional groups, and at least one other mercapto-ligand is a cross-linking ligand in that it comprises one additional co-ordinating nitrogen- or sulfur-comprising functional group.

In one embodiment, each individual mercapto-ligand is present in a concentration that is allowed by solubility of the individual ligand, such as in the range of from 0.1 to 500 g/L, such as in the range of from 10 to 150 g/L. Such a concentration may suitably be used when the one or more sources of noble metal are selected from Cu(l) and/or Cu(ll).

Further, in one embodiment wherein the one or more sources of noble metal are selected from Cu(l) and/or Cu(ll), the copper concentration of the electroplating composition is in the range of from 0.1 to 100 g/L, such as in the range of from 1 to 20 g/L.

In one embodiment wherein the one or more sources of noble metal are selected from Cu(l) and/or Cu(ll), the stoichiometric ratio of the cross-linking mercapto-ligand and the terminal mercapto-ligand equals or closely equals 2 to 1.

In one embodiment wherein the one or more sources of noble metal are selected from Cu(l) and/or Cu(ll), the composition has a pH of from 0 to 14, such as from 7 to 14.

In one embodiment wherein the one or more sources of noble metal are selected from Cu(l) and/or Cu(ll), the acid is a strong acid.

In one embodiment wherein the one or more sources of noble metal are selected from Cu(l) and/or Cu(ll), the electroplating composition further comprises one or more Cu alloying elements selected from ions of silver, gold, zinc, nickel, palladium, platinum, cobalt, rhodium, iron, ruthenium, tin, indium, and bismuth.

In one embodiment, the one or more sources of noble metal are selected from Au(l) and/or Au(lll).

In one embodiment, wherein the one or more sources of noble metal are selected from Au(l) and/or Au(lll), the gold concentration of the electroplating composition is in the range of from 0.05 to 50 g/L, such as 0.5 to 15 g/L.

In one embodiment, wherein the one or more sources of noble metal are selected from Au(l) and/or Au(lll), the stoichiometric ratio of the cross-linking mercapto-ligand and the terminal mercapto-ligand equals or closely equals 1 to 1.

In one embodiment, wherein the one or more sources of noble metal are selected from Au(l) and/or Au(lll), the composition has a pH of from 0 to 14.

In one embodiment, wherein the one or more sources of noble metal are selected from Au(l) and/or Au(lll), the composition further comprises one or more Au alloying elements selected from ions of copper, silver, zinc, nickel, palladium, platinum, cobalt, rhodium, iron, ruthenium, tungsten, rhenium, osmium, tin, indium, and bismuth.

In another aspect, there is provided a method of electroplating copper, a copper alloy, gold or a gold alloy, comprising providing a substrate; providing an electroplating composition as disclosed herein, and electroplating the copper, copper alloy, gold or gold alloy onto the substrate.

In one embodiment of the method aspect, the method is for electroplating a copper or copper alloy using an electroplating composition as disclosed herein.

In one embodiment of the method aspect, the method is for electroplating a gold or gold alloy using an electroplating composition as disclosed herein.

In one embodiment of the method aspect, the substrate is selected from a. magnesium or magnesium alloy; b. a zinc or zinc alloy substrate; c. an aluminum or aluminum alloy substrate; d. an iron or steel substrate; e. a copper or copper alloy substrate; f. a nickel or nickel alloy substrate; g. a titanium or titanium alloy substrate, and h. a tungsten or a tungsten alloy substrate. DETAILED DESCRIPTION OF THE INVENTION

There is provided herein an electroplating composition. An electroplating composition as disclosed herein comprises of one or more sources of a noble metal, selected from a) copper +1 (Cu(l)) and/or copper +11 (Cu(ll)), and b) gold +1 (Au(l)), and/or gold +111 (Au(lll)). Further, the electroplating composition comprises a combination of at least two different compounds, chosen from the groups of mercapto ligands, such as mercapto-tetrazoles, mercapto-triazoles, mercapto-thiadiazoles, and derivates thereof.

The electroplating composition as disclosed herein is substantially free from cyanides. In other words, the electroplating composition comprises no cyanide.

In one embodiment, at least one mercapto-ligand provides one co-ordination site to the noble metal, whereas at least another mercapto-ligand provides two co-ordination sites to the noble metal, thereby bearing the potential of cross-linking two noble metal cations. The mercapto ligand providing one co-ordination site is also referred to herein as a terminal ligand, or a mono-dentate ligand. This mercapto ligand has no additional coordinating nitrogen- or sulfur-comprising functional group. The mercapto ligand providing two co-ordination sites is also referred to herein as a cross-linking ligand, or a bi-dentate ligand. This mercapto ligand has an additional nitrogen- or sulfur-comprising functional group, which makes the mercapto ligand suitable for cross-linking.

Depending on the specific noble metal, the at least two mercapto ligands may be present in different ratios. The one co-ordination site mercapto-ligand and the two coordination sites mercapto-ligand are preferably, but not limited, applied in a 1 to 2 molar ratio when the noble metal is copper. The one-co-ordination site mercapto-ligand and the two-co-ordination site mercapto-ligand are preferably, but not limited, applied in a 1 to 1 molar ratio when the noble metal is gold.

The electroplating composition, which is also referred to elsewhere herein as an electrolyte, may in some embodiments be combined with an ion source of another metal. For example, a copper electrolyte as described herein can be combined with any ion source of the following metals: silver, gold, zinc, nickel, palladium, platinum, cobalt, rhodium, iron, ruthenium, tin, indium, and bismuth. A gold electrolyte as described above can be combined with any ion source of the following metals: copper, silver, zinc, nickel, palladium, platinum, cobalt, rhodium, iron, ruthenium, tungsten, rhenium, osmium, tin, indium, and bismuth. The skilled person will understand that other metals may be used as ion sources. The electrolyte combining a noble metal with an ion source from another metal may advantageously allow for producing alloy deposits.

Mercapto ligands have previously been investigated as potential substitutes to cyanides since they constitute low-valent complexes of sufficiently high stability for electroplating. For a commercially successful application of metal-mercapto ligand compounds (MMLC), however, the metal concentration should preferably be sufficiently high to allow for economically reasonable plating rates, preferably at different pH-values.

In spite of favorable stabilities of MMLCs, their low solubility has been a limiting factor for a successful technical implementation.

The inventor has surprisingly found that the combination of at least two different mercapto ligands has a very favorable influence on the solubility of MMLCs, particularly if one of the mercapto ligands has cross-linking and another mercapto-ligand has terminal binding properties to the low-valent metal center. When the noble metal is copper, the stoichiometry of the cross-linking to the terminal mercapto-ligand is preferably 2 to 1.

When the noble metal is gold, the stoichiometry of the cross-linking to the terminal mercapto-ligand is preferably 1 to 1

In one embodiment, the solubility of the MMLCs is further improved by the addition of a thioether compound, and/or a thiourea compound, and/or a compound with thioether or thiourea functionality. The thioether and/or thiourea compound may be added in a suitable amount, the exact stoichiometric ratio is of less importance. It is the solubility of the individual compound in the composition that determines the maximum amount.

There is also no need to discriminate between different sources of noble metal. For instance, different cuprous or cupric copper sources may be introduced. Divalent copper is readily reduced to the monovalent oxidation state upon the addition of the corresponding copper salts.

Sources of copper ions include both cuprous and cupric metal salts, such as, but not limited to, Cu(ll)F ₂ , Cu(l)CI, Cu(ll)CI ₂ , (NH ₄ )2Cu(ll)CI ₄ , Cu(l)Br, Cu(ll)Br ₂ , Cu(l)l,

Cu(l) ₂ 0, Cu(ll)0, CU(II)(OH) ₂ , CU(II)(S0 ₄ ), CU(II)C0 ₃ * CU(II)(OH) ₂ , CU(II)(N0 ₃ ) ₂ , Cu(ll) ₃ (P0 ₄ ) ₂ , Cu(ll)P ₂ C>7, Cu(l)acetate, Cu(ll)acetate, and Cu(ll)(BF ₄ ) ₂ . All copper sources can be applied in their anhydrous as well their hydrated forms. Cuprous or cupric salts can be introduced in an amount into the electroplating compositions, or electrolyte, that the copper concentration ranges from 0.1 to 100 g/L, and more preferably from 1 to 20 g/L. Similarly, there is no need to discriminate between aurous or auric gold sources. Trivalent gold is readily reduced to the monovalent oxidation state upon the addition of the corresponding gold salts. Sources of gold ions include both aurous and auric metal salts, such as, but not limited to, Au(l)CI, Au(lll)CI ₃ , HAu(lll)CL, NaAu(lll)CL, KAu(lll)CL, (NH ₄ )AU(III)CI ₄ , Au(lll)Br ₃ , HAu(lll)Br ₄ , Au(l)l, Au ₂ (lll)0 ₃ , Au(lll)(OH) ₃ , NaAu(lll)(S0 ₃ ) ₂ , Na ₃ Au(l)(S ₂ 0 ₃ ) ₂ , HAU(III)(N0 ₃ ) ₄ , Au(lll)acetate, Au(l)thiomalate, and any method to generate in situ mono- or trivalent gold solutions from solid gold. All gold sources can be applied in their anhydrous as well their hydrated forms. Aurous or auric salts can be introduced in an amount into the electroplating composition, or electrolyte, that the gold concentration ranges from 0.05 to 50 g/L, and more preferably from 0.5 to 15 g/L.

The inventor has surprisingly found that the combined application of at least two different mercapto ligands provides improved electroplating compositions. As set out above, one mercapto ligand is preferably cross-linking and one is preferably terminal in a stoichiometric ratio specific for the noble metal. Each one by itself shows very high complex stability with the noble metal (I), i.e. Cu(l) or Au(l). Moreover, the solubility in water is relatively good initially. However, overtime precipitation or gel formation can be observed, pointing to a dynamic mechanism, where different intermediate compounds are soluble, but one (not necessarily the most stable one) is insoluble, consuming ultimately all other species in the equilibrium. Precipitation or gel formation can largely be reduced by the combination of at least two different mercapto ligands. It is possible that already the combination of two different mercapto ligands reduces the formation-probability of a low solubility product. The inventor has observed, however, that this effect is particularly pronounced by the simultaneous addition of a cross-linking and a terminal mercapto- ligand.

In this context, solubility, i.e. the ability of a particular compound to dissolve in a solvent, refers to a particular compound’s ability to dissolve in the electroplating composition. Solubility is preferably visually determined, however, the skilled person is aware of other means for determining solubility.

Mercapto ligands include mercapto-triazoles, mercapto-tetrazoles and mercapto- thiadiazoles and have the general formula, Formula I: where X is either S and Y is CR (thiadiazole), X is NR and Y is CR (triazole), or X is NR and Y is N (tetrazole). R can be hydrogen, a saturated or unsaturated organic side chain, but also any heteroatom or a salt forming cation.

Derivatives of mercapto-triazoles include, but are not limited to, 1/-/-1,2,4-triazole-3-thiol, 4-methyl-4/-/-1,2,4-triazole-3-thiol, 4-amino-5-hydrazino-1,2,4-triazole-3-thiol and 5-(4- pyridyl-1 /-/-1 ,2,4-triazole-3-thiol. 4-methyl-4/-/-1,2,4-triazole-3-thiol is shown in Formula II as an illustrative example of a mercapto-triazole compound: ( II )

Derivatives of mercapto-thiadiazoles include, but are not limited to, 5-methyl-1,3,4- thiadiazole-2-thiol, 2,5-dimercapto-thiadiazole and 5-a ino-1,3,4-thiadiazole-2-thiol, the latter being shown in Formula III as an illustrative example of a mercapto-thiadiazole compound:

H ₂ N

( ill )

Derivatives of mercapto-tetrazoles include but are not limited to 5-mercapto-1/-/-tetrazole- 1 -acetic acid, 5-mercapto-1/-/-tetrazole-1-methanesulfonic acid, 1 -methyl- 1 /-/-tetrazole-5- thiol, 5-mercapto-1 -phenyl-1 /-/-tetrazole, 1-(2-dimethylaminoethyl)-5-mercapto-1/-/- tetrazole, illustrated in Formula IV, 1-(2-diethylaminoethyl)-5-mercapto-1 /-/-tetrazole and 1- (2-hydroxyethyl)-5-mercapto-1 /-/-tetrazole.

( IV )

All mercapto ligands can be used in any concentration that is allowed by the solubility of the individual compound, but for example in the range of 0.1 to 500 g/L, and preferably between 10 and 150 g/L.

The noble metal or noble metal alloy electroplating composition may further include one or more compounds out of the class of thioethers or compounds having thioether functionality. Such compounds extend the applicable noble metal concentration range and specify the applicable pH range of the electroplating composition. These substances may have one or more thioether functionalities, with the general formula,

( V ) where R and R' are aliphatic or arylic carbons, which by themselves may have other functional groups. Furthermore, the thioethers may be open-chained, branched, or cyclic. Typical thioethers as described above are 2,2'-dithioethanol, 2,2'-dithioacetic acid, 3,6- dithia-1,8-octanediol or 1,4,7-trithiacyclononane. As observed with mercapto ligands, the upper concentration limits of the thioether compounds are determined by the solubility of the individual compounds. Suitable concentrations of the thioether compounds range from 0.5 to 500 g/L, and more preferably from 1 to 200 g/L.

Similarly to thioether compounds, thiourea compounds can be added to the electroplating composition or electrolyte, the general formula of which are depicted below. R, R', R", R'" are hydrogen, aliphatic or arylic carbons, which by themselves may have other functional groups. Furthermore, the thioureas may be open-chained, branched, or cyclic. Typical members are thiourea, N,N'-dimethyl-thiourea, N,N'-diethyl-thiourea and N- allyl-thiourea.

( VI )

As described with mercapto ligands and thioethers, the upper concentration limits of the thioureas are determined by the solubility of the individual compounds. Reasonable concentrations range from 0.5 to 500 g/L, and more preferably from 1 to 100 g/L.

As well known in the art, wetting agents may be added to the electroplating composition in a concentration from 0.1 to 20 g/L. Conventional wetting agents may be used for copper and gold electroplating. For example, wetting agents known from cyanide copper plating, e.g., alkoxylated amine oxides, may be used for copper electroplating. For example, wetting agents known from gold cyanide plating, e.g., alkyl ether phosphates and sulfates, and alkoxylated amine oxides, may be used for gold electroplating.

A copper electroplating composition as disclosed herein may be produced by mixing the copper salt with the at least two mercapto ligands and optionally thioether. Subsequently, the pH is adjusted to 12 or higher. This can be done by any chemical with alkaline character such as a base. Preferably the chemical has strong alkaline character, such as a strong base, and examples include the well-known KOH or NaOH. The skilled person is aware of other bases or strong bases that can be used. Moreover, as the skilled person will understand, a strong base is a base that is completely dissociated into the cation and OH in water.

To acidify the copper electroplating composition, any known moderate to strong proton donator can be applied and in particular oxo-acids, such as sulfuric acid, alkyl sulfonic acids, aryl sulfonic acids, phosphoric acid, oligomeric phosphoric acids, phosphorous acid, organo-phosphonic and -biphosphonic acids, e.g., etidronic acid, boric acid, nitric acid, amidosulfonic acid and carboxylic acids, such as formic acid, acetic acid, lactic acid, succinic acid, to mention only a few typical members, as well as amino- carboxylic and amino-phosphonic acids. The skilled person is aware of other moderate or strong acids that can be used. Moreover, as the skilled person will understand, a strong acid is an acid that is typically completely dissociated into a proton and an anion in water. The final pH of the copper electroplating composition can be anywhere between 0 and 14 and may be affected by the applied thioether and/or thiourea, if any, which defines the pH at which the copper electrolyte is fully clear.

A gold electroplating composition as disclosed herein may be produced by pre dissolving the at least two mercapto ligands in suitable stoichiometry, e.g. a one-to-one stoichiometry for gold electroplating, in alkaline water having a pH-value of 12 or higher. The pH of the alkaline water may be adjusted in advance by the addition of KOH or NaOH. To such a solution an appropriate amount of a water-soluble gold compound is added, either pre-dissolved in water or as a solid. The at least two mercapto ligands may be in at least a fivefold excess compared to the final gold concentration for plating at pH above 12.

Electroplating at neutral or acidic pH typically require higher mercapto-ligand excess. Too high gold concentrations may result in greenish to blueish gold plates from such under-stabilized solutions.

After the full dissolution of the gold compound in the alkaline mercapto-ligand solution, the electroplating composition can be acidified by any known moderate to strong proton donator and in particular by oxo-acids, such as sulfuric acid, alkyl sulfonic acids, aryl sulfonic acids, phosphoric acid, oligomeric phosphoric acids, phosphorous acid, organo-phosphonic and -biphosphonic acids, e.g., etidronic acid, boric acid, nitric acid, amidosulfonic acid and carboxylic acids, such as formic acid, acetic acid, lactic acid, succinic acid, to mention only a few typical members, as well as amino-carboxylic and amino-phosphonic acids. The final pH of the gold electroplating composition may be anywhere between 0 and 14 and may be affected by the applied thioether and/or thiourea, if any, which defines the pH at which the gold electrolyte is fully clear.

In one embodiment, the electroplating composition comprises any type of pH- buffering compound, for example aromatic nitrogen compounds, e.g., imidazole, or Good's buffers to stabilize near-neutral pH-values.

Optionally, the electroplating composition may comprise allyl-type brighteners such as butyne-diol or propargylic alcohol and their derivatives. Carbon-disulfide-adducts, such as trithio-carbonate, dithio-carboxylic acids, xanthogenates and carbamates can also be introduced as grain refiners. Also well-known in the art metallic grain refiners may be included into the composition such as selenium, antimony, bismuth, cobalt, thallium, indium, and others in the form of their commercially available salts. The concentration range of brighteners and grain refiners may be between 0.5 to 1000 ppm, preferably between 5 and 100 ppm.

An electroplating composition is preferably prepared by any of the methods disclosed above in a tank, suitable for electroplating. Pure copper anodes, known from copper cyanide plating, can be used, as well as insoluble anodes and copper-alloy anodes. Although not common in practice, pure gold anodes can be used. Preferably, however, platinized titanium anodes or mixed metal oxide anodes, well-known from gold cyanide plating, are used.

The following examples are intended to further illustrate the invention but are not intended to limit its scope.

EXAMPLE 1

An electrolyte of the composition according to table 1 was been mixed in the order as listed.

Table 1: electrolyte composition according to example 1

After the addition of KOH, the electrolyte was heated up to a temperature >50° C to expedite the process of dissolution and conversion of Cu(ll) to Cu(l). The make-up can also be done at ambient temperature. Ultimately, the product of this procedure was a fine beige dispersion at both temperatures. At elevated temperatures, however, the period, when all components are in solution, lasts significantly longer, which is why higher temperatures are preferred. Having said that, pH adjustment with methanesulfonic acid to a pH value of 8, results in a clear faint lemon yellow and, after the addition of propargylic alcohol and wetting agent, ready to use solution in both cases.

Subsequently, the solution was used in a Hull cell to plate polished brass panels applying the following parameters: temperature 55° C, paddle agitation, 0.5 A per panel and soluble copper anodes. After conventional pre-treatment (2 minutes cathodic electrocleaning, 30 seconds alkaline pickling) the panels were plated for 10 minutes, resulting in a bright copper plate over the whole current density range indicating a strong- bonded and even plating.

In another example, the above described process was repeated with the only differences being phosphoric acid replacing the methanesulfonic acid and the copper sulfate pentahydrate concentration being 20 g/L. The repeated process resulted in a similarly bright copper plate over the whole current density range indicating a strong- bonded and even plating.

EXAMPLE 2

1.8 liters of the electrolyte of example 1 were transferred into a 2 liter beaker, equipped with two pure copper anodes and a stir bar, rotating at 300 rpm, and heated up to 55° C. A magnesium AZ31 sheet with dimensions of 50 x 100 x 5 mm was pre-treated like a conventional brass panel, i.e. , cathodic degreasing and alkaline pickling. The only difference was a very short pickling time of 2 seconds to minimize smut formation. The sheet was subsequently contacted to the cathodic side of a rectifier and, with 2 A current on, immersed into the beaker. After 2 minutes the current was reduced to 0.75 A. After 30 minutes plating time, the sheet was removed from the solution, rinsed, and dried by air-jet. The resulting copper plate showed a uniform satin-bright appearance. A taping test with common Scotch® tape showed full adhesion of the copper plate to the AZ31 substrate. The sheet was then subjected to 100° C for one hour and the taping test was repeated showing the same full adhesion of the copper plate to the AZ31 substrate.

EXAMPLE 3

The procedure described in Example 2 was repeated, using AZ91 substrate. In contrast to AZ31, the AZ91 substrate had be mechanically pre-cleaned, using Scotch-Brite® in order to remove already existing smut on the surface of the substrate. All other steps were performed identically, resulting in the same appearance and adhesion properties, described for AZ31.

EXAMPLE 4

The procedure described in Example 2 was repeated using a common zinc dye cast material, a Zamak 3 substrate with dimensions of 75 x 100 x 3 mm. The pre-treatment was extended by an anodic electrocleaning of 15 seconds after two minutes of cathodic electrocleaning. Pickling time was approximately 10 seconds. All other steps were performed identically, resulting in the same appearance and adhesion properties, described for AZ31.

EXAMPLE 5

The procedure described in Example 2 was repeated, using a 75 x 150 x 1 mm sheet of the magnesium alloyed aluminum substrate 5005. After two minutes cathodic electrocleaning the sheet was immersed for 30 seconds in 10% nitric acid, followed by standard zincate treatment for another 30 seconds. The sheet was then plated at 1 ASD for 10 minutes producing a fully bright and perfectly adherent copper plate.

EXAMPLE 6

An electrolyte of the composition described in table 2 was mixed in the order as listed. Table 2: electrolyte composition of example 6

The identic make-up procedure, as described in Example 1 to 5, was applied resulting in the same deposit and adhesion properties after plating.

EXAMPLE 7

It has further been observed that if the same molarity is used, both, cross-linking mercapto ligands between each other, and terminal mercapto ligands between each other, are fully interchangeable without any adverse effect on solution stability, plating performance, and deposit characteristics. Following to this, an electrolyte was mixed in the order as listed in table 3.

Table 3: electrolyte composition of example 7

The identic make-up procedure, as described in Example 1 to 5, was applied resulting in the same deposit and adhesion properties after plating.

EXAMPLE 8

As indicated above, several methods for the in situ preparation of a gold solution can be used for the make-up of a gold electrolyte or electroplating composition. In a well- ventilated hood, 1 liter of a gold cyanide plating solution (2 g/L Au) was refluxed and concentrated to one fifth of its original volume. The concentrate was then digested by 30 milliliter nitric acid and 100 milliliter hydrochloric acid. After the evolution of nitrous oxide gases had stopped, the solution was allowed to cool and a yellow slurry with lemon-yellow needle-like crystals of presumably HAu(lll)CL formed. The aqueous mother liquor was carefully decanted and the needles were collected without further purification.

At ambient temperature and under vigorous stirring the yellow needles were added in several portions to an aqueous solution of 11.79 g 3-Amino-5-mercapto-1, 2, 4-triazole, 11.69 g 4-Methyl-1,2,4-triazole-3-thiol, and 18 g KOH. Upon every addition, the solution turned shortly dark yellow and immediately changed back to the original yellow color. The pH of the clear solution was then adjusted to 11 and used without further additions for plating on a plain brass and on a bright nickel-plated brass Hull cell panel at room temperature, paddle agitation and at 1 A current for 5 minutes. The resulting panel showed an evenly bright gold deposit over the whole current density range.

EXAMPLE 9

An electrolyte of the composition presented in table 4 was prepared, by initially mixing the mercapto ligands and KOH, followed by the addition of the gold solution and the wetting agent and concluded by pH adjustment.

Table 4: electrolyte composition of example 9

Subsequently, the solution was used in a Hull cell to plate polished brass panels and polished iron panels applying the following parameters: ambient temperature, paddle agitation, 1 A per panel and mixed metal oxide anodes. After conventional pre-treatment (2 minutes cathodic electrocleaning, 30 seconds alkaline pickling for brass, diluted hydrochloric acid to remove the protecting zinc for iron panels) the panels were plated for 5 minutes, resulting in a deep yellow bright gold plate over the whole current density range indicating a strong-bonded and even plating.

EXAMPLE 10

An electrolyte of the composition according to table 5 was prepared, by initially mixing the mercapto ligands and KOH, followed by the addition of the gold solution and the wetting agent and concluded by pH adjustment.

Table 5: electrolyte composition of example 10

Subsequently, the solution was used in a Hull cell to plate polished brass panels and polished iron panels applying the following parameters: ambient temperature, paddle agitation, 1 A per panel and mixed metal oxide anodes. After conventional pre-treatment (2 minutes cathodic electrocleaning, 30 seconds alkaline pickling for brass, diluted hydrochloric acid to remove the protecting zinc for iron panels) the panels were plated for 5 minutes, resulting in a deep yellow bright gold plate over the whole current density range indicating a strong-bonded and even plating.

EXAMPLE 11

An electrolyte of the composition according to table 6 was prepared, by initially mixing the mercapto ligands and KOH, followed by the addition of the gold solution and the wetting agent and concluded by pH adjustment.

Table 6: electrolyte composition of example 11

Subsequently, the solution was used in a Hull cell to plate polished brass panels and polished iron panels applying the following parameters: ambient temperature, paddle agitation, 1 A per panel and mixed metal oxide anodes. After conventional pre-treatment (2 minutes cathodic electrocleaning, 30 seconds alkaline pickling for brass, diluted hydrochloric acid to remove the protecting zinc for iron panels) the panels were plated for 5 minutes, resulting in a deep yellow bright gold plate over the whole current density range indicating a strong-bonded and even plating.

Further, the present invention provides for, without limitation, the following embodiments.

ITEMIZED LIST OF EMBODIMENTS

1. A copper electroplating composition comprising one or more sources of Cu(l) or Cu(ll), a strong base and a strong acid for solution make-up and for providing conductivity, and the combination of at least two different mercapto ligands, selected from the groups of mercapto-triazoles, mercapto-tetrazoles, and mercapto-thiadiazoles. A plating composition of item 1 in which the copper concentration in the electrolyte ranges from 0.1 to 100 g/L and more preferably from 1 to 20 g/L. A plating composition of any one of the preceding items, characterized in that at least one of the mercapto ligands has no additional nitrogen- or sulfur-comprising functional group, suitable for co-ordination and can therefore be considered as mono-dentate or terminal ligand and at least another one of the mercapto ligands comprising an additional nitrogen- or sulfur-comprising functional group, suitable for co-ordination and can therefore be considered as bi-dentate, not chelating but rather cross-linking ligand. A plating composition of item 3, characterized in that the stoichiometric ratio of the cross-linking mercapto-ligand and the terminal mercapto-ligand equals or closely equals 2 to 1. A plating composition of any one of the preceding items, in which the concentration of each individual mercapto-ligand is applied in any concentration that is allowed by the solubility of the individual compound, but mainly in the range of 0.1 to 500 g/L, and preferably between 10 and 150 g/L. A plating composition of any one of the preceding items, characterized in that at least one chemical with at least one thioether and/or thiourea functionality is added to the formulation. A plating composition of item 6 in which the concentration of the thioether and/or thiourea compound is applied in any concentration that is allowed by the solubility of the individual compound, but preferably from 0.5 to 500 g/L and more preferably from 1 to 200 g/L. A plating composition of any one of the preceding items characterized in that the pH ranges from 0 to 14, and more preferably from 7 to 14. A method of electroplating copper or a copper alloy using a formulation of any one of items 1 to 8 on a substrate. The method of item 9, wherein the substrate is a magnesium or magnesium alloy substrate. The method of item 9, wherein the substrate is a zinc or zinc alloy substrate. The method of item 9, wherein the substate is an aluminum or aluminum alloy substrate. The method of item 9, wherein the substrate is an iron or steel substrate. The method of item 9, wherein the substrate is a copper or copper alloy substrate. A gold electroplating composition comprising one or more sources of Au(l) or Au(lll), a strong base for solution make-up, an acid for pH adjustment and for providing conductivity, and the combination of at least two different mercapto ligands, selected from the groups of mercapto-triazoles, mercapto-tetrazoles, and mercapto-thiadiazoles. A plating composition according to item 16 in which the gold concentration in the electrolyte ranges from 0.05 to 50 g/L and more preferably from 0.5 to 15 g/L. A plating composition according to item 16 or 17 characterized in that at least one of the mercapto ligands has no additional nitrogen- or sulfur-comprising functional group, suitable for co-ordination and can therefore be considered as mono-dentate or terminal ligand and at least another one of the mercapto ligands comprising an additional nitrogen- or sulfur-comprising functional group, suitable for co-ordination and can therefore be considered as bi-dentate, not chelating but rather cross- linking ligand. A plating composition according to any one of items 15 - 17 characterized in that the stoichiometric ratio of the cross-linking mercapto-ligand and the terminal mercapto-ligand equals or closely equals 1 to 1. A plating composition according to any one of items 15-18 in which the concentration of each individual mercapto-ligand is applied in any concentration that is allowed by the solubility of the individual compound, but mainly in the range of 0.1 to 500 g/L, and preferably between 10 and 150 g/L. A plating composition according to any one of items 15 - 19 characterized in that at least one chemical with at least one thioether and/or thiourea functionality is added to the formulation. A plating composition according to item 20 in which the concentration of the thioether and/or thiourea compound is applied in any concentration that is allowed by the solubility of the individual compound, but preferably from 0.5 to 500 g/L and more preferably from 1 to 200 g/L. A plating composition according to any one of items 15-21 characterized in that the pH ranges from 0 to 14. A method of electroplating gold or a gold alloy using a formulation according to any one of items 15-21 on a substrate. A method of electroplating gold or a gold alloy according to item 23 wherein the substrate is selected from a. a magnesium or magnesium alloy substrate; b. a zinc or zinc alloy substrate; c. an aluminum or aluminum alloy substrate; d. an iron or steel substrate; e. a copper or copper alloy substrate; f. a nickel or nickel alloy substrate, and optionally g. a titanium or titanium alloy, and h. a tungsten or tungsten alloy substrate.