KR20180072774A - Additives for Silver-Palladium Alloy Electrolytes - Google Patents

Abstract

The present invention relates to an electrolyte containing a reducing agent suitable for adjusting the composition of the silver-palladium layer. This reducing agent also contributes to the appearance improvement of the layer and to the increase of the brightness of the deposited layers (L value of CIE Lab). The present invention also discloses a method for electrodepositing silver-rich silver-palladium alloys. The alloy may be deposited on the conductive surface over a wide current density range.

Description

Additives for Silver-Palladium Alloy Electrolytes

The present invention relates to an electrolyte containing a reducing agent suitable for adjusting the composition of the silver-palladium layer. This reducing agent also contributes to the appearance improvement of the layer and to the increase of the brightness of the deposited layers (L value of CIE Lab). The present invention discloses a method for electrodepositing silver-rich silver-palladium alloys.

Electrical contacts are used in almost all electrical devices today. Their applications range from simple plug connectors to safety-related and sophisticated switching contacts in the automotive or aerospace technology field. Here, the contact surface is required to have good corrosion resistance and wear resistance, which combines good electrical conductivity, low contact resistance combined with long-term stability, and a minimally low insertion force. In electrical engineering, plug contacts are often coated with a hard gold alloy layer comprised of gold-cobalt, gold-nickel, or gold-iron. These layers have good abrasion resistance, good solderability, low contact resistance combined with long term stability and good corrosion resistance. Due to the rising cost of gold, we are looking for cheaper alternatives.

As an alternative to hard gold plating, silver-rich has been shown to be advantageous in coating with alloys (hard silver). Double silver and silver alloys are the most important contact materials in electrical engineering, not only because of their high electrical conductivity and good oxidation resistance. Such silver-alloy layers have layer properties similar to those of recently used hard gold layers and layer combinations such as, for example, palladium-nickel and gold flashes, depending on the metal added to the alloy. Also, the price of silver is relatively low compared to other precious metals, especially hard gold alloys.

One limitation to the use of silver is the fact that in an atmosphere containing, for example, sulfur or chlorine, silver has less corrosion resistance than hard gold. Except for visual surface changes, the discoloration film of silver sulfide in most cases does not represent any significant risk because the silver sulfide is reversible, soft, and if the contact force is strong enough, It is wiped and removed. On the other hand, the discoloration film of silver sulfide is nonconductive, hard, and not easily removed. Thus, a relatively high proportion of silver sulfide in the discoloration layer poses a problem in contact properties (Marjorie Myers: Interconnect & Process Technology, Tyco Electronics, Harrisburg, February 2009).

US 3980531 discloses cyanide-free electrolytes for galvanic deposition of alloys containing gold, silver and / or palladium. The bath contains thiosulfate, sulfite and borate or phosphate. The alloy is deposited at a slightly acidic to highly alkaline pH range. The electrolyte may optionally comprise a salt of a basic metal such as arsenic or cadmium. The deposition is carried out at a current density of 0.1 to 5 A / dm < ^{2 &} gt ;. In a bath according to US 3,980,531, the composition of the deposited alloy depends on the concentration of the metal salts used and the current density used. The appearance of the alloy varies from matt to high gloss. Due to the use of arsenic and cadmium, these electrolytes are no longer available today due to existing regulations (REACH).

US 6,251,249 B1 discloses an electrolyte for depositing a noble metal on a solid substrate. Such an electrolyte is iodide-free and contains a noble metal to be deposited in the form of an alkanesulfonate, an alkanesulfonamide and / or an alkanesulfonimide. Further, the electrolyte contains an organic sulfur compound and / or a carboxylic acid. The noble metal is preferably deposited in the temperature range of 20 to 60 占 폚. The pH value may be from 0 to 12. The electrolyte is suitable for electroless and electrolytic deposition of noble metal layers and for immersion plating. Embodiments of US 6,251,249 B1 relate only to immersion plating, where silver or palladium is deposited but silver-palladium alloy is not deposited. Information about the electrolytic deposition of the silver-palladium alloy or the composition of the alloy is not provided.

In EP 0 065 100 A1, the galvanic palladium electrolyte is disclosed as containing palladium sulfite and an acid. The electrolyte contains sulfuric acid and / or phosphoric acid and can be used at 20 to 40 占 폚. 80 to 95% of the palladium content may be added to the palladium sulfate, and the remainder may be added to the palladium sulfide. However, EP 0 065 100 A21 does not mention the deposition of palladium alloys.

DE 10 2013 215 476 B3 discloses cyanide-free acidic and aqueous electrolytes for depositing silver-palladium alloys. In addition to silver and palladium salts, the electrolyte contains selenium or tellurium compounds, urea and / or one or more amino acids and sulfonic acid. With such an electrolyte, a silver-palladium alloy having a predominant silver content can be deposited over a wide current density range. However, only semi-matt alloy coatings can be made with such electrolytes. As the current density increases, the resulting layers are distinctly brownish. At the same time, the electrolyte shows a pronounced dependence of the alloy composition on the applied current density. Alloys may be affected only by concentration transitions of alloying metals or by temperature changes of the electrolyte during deposition.

Electrolytes known from the prior art for electrolytic deposition of silver-palladium alloys are characterized in that the deposition of the alloy over a wide current density range is not only highly polished, but also a silver-palladium alloy having a uniform ratio of silver to palladium It does not allow deposition. Similarly, the alloy composition can be scaled to a very limited scale only by shifting the bath parameters. In previously known baths, the palladium content in the deposited layers decreases with increasing current density. The appearance of the deposited layers also changes at the same time: as the current density increases, the layers become increasingly distinctly brownish. Heterogeneity in layers such as haze and speckle is simultaneously increased.

Thus, although a number of electrolytes are already known for the electrolytic deposition of silver-palladium alloys, there is still a need for electrolytes that are superior to prior art electrolytes in practical applications. These electrolytes should be sufficiently stable for industrial use and should permit deposition of stable and bright alloy compositions over a wide range of available current densities. A simple adjustment of the alloy composition is equally important. The electrolyte must remain fully functional even after high current density loading, and the layers deposited with such electrolytes must be homogeneous and advantageous for use in contact materials. The composition of the deposited alloy is particularly advantageously 90 + 3 wt% silver, 10 + -3 wt% palladium and 0-3 wt% tellurium and / or selenium.

These and other problems that occur apparently to those skilled in the art from the closest relevant prior art are addressed by the electrolyte according to claim 1 of the present invention. Protection against more favorable aspects in the dependent claims of claim 1 is pursued. The ninth aspect relates to a preferred silver-palladium alloy deposition method using an electrolyte according to the present invention. 10 to 12 relate to preferred aspects of the method of the present invention.

The challenge of providing a cyanide-free acidic and aqueous electrolyte for electrolytic deposition of a lustrous silver-palladium alloy with a predominant silver content is solved by a water electrolytic solution in dissolved form containing the following components in accordance with the invention:

a) a silver compound having a silver concentration of 1 to 300 g / l;

b) a palladium compound with a palladium concentration of 0.1 to 100 g / l;

c) a tellurium and / or selenium compound with a tellurium and / or selenium concentration of 0.002 to 10 g / l, based on the total amount of tellurium and selenium in said electrolyte;

d) a urea and / or urea derivative having a concentration of from 0.05 to 1.5 mol / l based on the total amount of urea and urea derivatives in said electrolyte, and / or from 0.005 to 0.5 at least one amino acid selected from the group consisting of alanine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, lysine, leucine, methionine, phenylalanine, phenylglycine, proline, serine, tyrosine and valine in a mol / l concentration;

e) at least one sulfonic acid, in a concentration of from 0.25 to 4.75 mol / l, based on the total amount of sulfonic acids;

f) salts and / or esters of sulfuric acid, gaseous sulfite, sulfinic acid and sulfuric acid in a concentration of from 1 to 100 mmol / l, based on the total amount of reducing agents, of formic acid, oxalic acid, ascorbic acid, hydrazine, hexamethylenetetramine, Salts and / or esters, formaldehyde, sodium formaldehyde sulfoxylate, benzaldehyde, benzaldehyde derivatives, hydroxybenzenes and esters thereof, polyphenols and esters thereof, phenol sulfonic acids and their salts and / or esters and glutathione and At least one reducing agent selected from the group consisting of salts and / or esters thereof.

Surprisingly, it has been found that by using the electrolytes disclosed herein, it is possible to deposit a lustrous silver-palladium alloy layer homogeneously on a conductive substrate over a wide range of current densities and very suitable for use in contact materials. As a result, the electrolyte according to the invention is suitable as a substitute for the hard gold alloy in the contact material. At the same time, the palladium content in the layer can be simply adjusted by a reducing agent (polish) added as a function of the amount of reducing agent added. As the reducing agent concentration increases, the palladium content of the deposited layer also increases. The electrolyte according to the present invention exhibits relatively high stability, which makes it particularly advantageous in industrial applications. With the electrolyte of the present invention, high quality electrical contact materials can be advantageously produced also in racks and high speed coating systems. Preferably, the electrolyte contains only those components.

The electrolyte according to the present invention can be used at a current density ranging from 0.1 to 100 A / dm ² . A current density range of 0.5 to 20 A / dm ² is preferred.

In the present invention, a 'homogeneous' silver-palladium alloy coating means a uniform layer with respect to color and layer properties. The layer properties in this case are gloss, gloss, hardness and corrosion resistance. The silver-palladium alloy layer is homogeneous in two respects herein. First, the silver-palladium alloy layer deposited on a particular electrically conductive substrate is homogeneous according to the definition above. Secondly, the appearance of the deposited silver-palladium alloy can be improved when the layers are deposited using a different current density from the same electrolyte to a plurality of identical electrically conductive substrates, without any change in composition, temperature or movement of the electrolyte In other words, the layers, that is, the deposited layers, having the same alloy composition and the same visual appearance, are homogeneous in this case regardless of the current density.

It is known to those skilled in the art that the color and luster of the metallic coating can be measured with the aid of a so-called L * a * b * measurement according to CIE L * a * b (www.cielab.de) , And the L * value indicates glossiness. The gloss value (L * value) of the silver-palladium alloy layer according to the present invention is L * a * b * of 80 to 90 (measuring instrument X-Rite SP62, light source D65 / 10).

The gloss can be evaluated by measuring the reflectance. In the silver-palladium alloy layer according to the present invention, the addition of the reducing agent increases the reflectance of 5 to 40% of the initial value according to the applied current density and the concentration of the reducing agent. The reflectance was measured with a BYK-Gardner micro-TRI-gloss meter. The measurement was carried out in accordance with EN ISO 7668 with a light beam at an incident angle of 20 ° and a reflected light of 20 °. Methods of measuring surface gloss and related information known to those skilled in the art are described, for example, in Schriftenreihe Galvanotechnik und Oberflaechenbehandlung. Pruefung von funktionellen metallischen Schichten [Publication series: Electroplating and surface treatment: Section 4.3: Glanz- und Reflexionsmessung an Oberflaechen ', Eugen G Leuze-Verlag, Saulgau, 1st ed. 1997, pp. 117-125.

A galvanic bath is a solution containing an electrochemical metal precipitate (coating) that can be deposited on a substrate (object). This type of galvanic bath is often referred to as an 'electrolyte'. Accordingly, the cyanide-free and water-soluble galvanic bath according to the present invention is hereinafter referred to as an " electrolyte ".

An electrolyte according to the present invention for electrolytically depositing a lustrous and homogeneous silver-palladium alloy having a predominant silver content, and a method for depositing such a silver-palladium alloy, are described below, wherein the invention encompasses all The embodiments are included individually or in combination with each other.

Those of skill in the art will generally be familiar with metal compounds that may be added to the electrolyte.

The silver compound contained in the electrolyte according to the present invention is preferably a silver salt soluble in such an electrolyte. The silver salt in the present invention is preferably composed of methanesulfonic acid silver, carbonic acid silver, sulfuric acid silver, phosphoric acid silver, pyrophosphoric acid silver, silver nitrate, silver oxide, lactic acid silver, fluoride silver, silver bromide, silver chloride silver, silver azide silver, silver sulfide and sulfuric acid ≪ / RTI > Silver nitrate, silver carbonate, methane sulfonic acid, silver chloride and silver oxide are particularly preferred for use in the electrolyte according to the present invention. As used herein, the skilled artisan follows the principle that additional materials should be added as little as possible. For this reason, those skilled in the art will most desire to select methane sulfonic acid, silver carbonate or silver oxide as the silver salt to be added. With regard to the concentration of the silver compound used, the skilled artisan will be in accordance with the provided limits. The concentration of silver in the electrolyte is preferably from 1 to 300 g / l, more preferably from 2 to 100 g / l, and most preferably from 4 to 15 g / l.

The palladium compound used is preferably a salt or soluble complex soluble in the electrolyte. The palladium compound used herein is preferably selected from the group consisting of palladium hydroxide, palladium chloride, palladium sulfate, palladium pyrophosphate, palladium nitrate, palladium phosphate, palladium bromide, palladium P salt (diamine dinitrate palladium (II) (II) bromide, diamine dinitro palladium (II) chloride, diamine dinitro palladium (II) chloride, diamine dinitroxide (II) bromide, palladium acetate, palladium chloride, Palladium (II), bis (acetylacetonato) palladium (II), diamine dichloro palladium (II), potassium dioxalate palladium oxide, palladium iodide, tetraamine palladium (II), palladium oxide oxide, tetraamine palladium (II) hydrogencarbonate, bis (ethylenediamine) palladium (II) chloride, bis (ethylenediamine) palladium (II) Ethylene diamine) is selected from the group consisting of palladium (II). The palladium compound is advantageously selected from palladium hydroxide, palladium chloride, palladium glycine, palladium methanesulfonate and palladium sulfate.

In this case, the palladium compound is added to the electrolyte at the above-indicated concentrations. The palladium compound is preferably used in a concentration of 0.1 to 100 g / l palladium, most preferably 2 to 20 g / l palladium in the electrolyte.

The electrolyte according to the present invention is aqueous. The silver and palladium compounds used are preferably salts or soluble complexes which are soluble in the electrolyte. Thus, the terms ' soluble salts ' and ' soluble complexes ' refer to salts or complexes that dissolve in the electrolyte at the working temperature. Herein, the working temperature is the temperature at which the silver-palladium alloy is deposited. In the context of the present invention, when more than 0.002 g / l of material is dissolved in the electrolyte at the working temperature, such material is considered to be soluble.

The deposited alloy containing silver, palladium and selenium and / or tellurium herein comprises a composition comprising 70 to 99 wt% of silver, 1 to 30 wt% of palladium and 0.1 to 5 wt% of selenium and / or tellurium, I have. Here, the ratio of silver, palladium and selenium and / or tellurium is 100 wt%. According to the present invention, the concentration of the metal to be deposited in the electrolyte is set within the framework provided above, resulting in a-rich alloy. Note that not only the concentration of the metal to be deposited has an influence on the silver concentration and the gloss of the alloy to be deposited, but also the amount of tellurium compound and / or selenium compound to which the current density is used and the addition of the reducing agent. Skilled artisans will appreciate that corresponding parameters must be set to achieve the desired target alloy, or will determine these parameters by repeated experimentation. Preferably, efforts are made to obtain an alloy having a concentration of 70 to 99 wt% silver, more preferably 80 to 95 wt%, and most preferably 87 to 94 wt%. The palladium content of the alloy according to the present invention is 1 to 30 wt%, preferably 5 to 20 wt%, particularly preferably 6 to 13 wt%. The content of selenium or tellurium in the alloy according to the present invention is 0.1 to 5 wt%, preferably 0.5 to 4 wt%, particularly preferably 1 to 3 wt%.

The alloys according to the invention containing silver, palladium and selenium and / or tellurium are hereinafter referred to as 'silver-palladium alloys'.

The selenium or tellurium compound used in the electrolyte may be suitably selected by those skilled in the art within the composition of the indicated concentrations. Concentrations of tellurium and / or selenium in the range of 0.002 to 10 g / l may be selected in the preferred concentration range, with the concentrations of tellurium and / or selenium in the range of 0.1 to 5 g / l being the most preferred range. The concentration data herein relate to the total amount of tellurium and selenium in the electrolyte. Suitable selenium and tellurium compounds are selenium or tellurium present in the oxidation state +4 or +6. Selenium and tellurium compounds are advantageously used in electrolytes in which there is a selenium or tellurium compound in oxidation state +4. The selenium and tellurium compounds are particularly preferably selected from the group consisting of atelutrate, selenite, atelic acid, aselenic acid, telluric acid, selenic acid, selenocyanide, tellurium cyanide and selenate and tellurate. The use of tellurium compounds instead of selenium compounds is generally preferred herein. The addition of tellurium to the electrolyte, in the form of a salt of atelerium acid, for example in the form of potassium attenuate, is preferred.

The electrolyte according to the present invention acts as a complexing agent for a compound selected from the group consisting of urea, urea derivatives, thiourea, thiourea derivatives and mixtures thereof and / or palladium and is useful for increasing the stability of the electrolyte of the present invention Lt; RTI ID = 0.0 > a-amino < / RTI >

The urea derivatives are selected from dimethylurea, ethyleneurea, N, N'-dimethylpropyleneurea, and N- (2-hydroxyethyl) ethyleneurea. The thiourea derivatives are, for example, 3-S-isothiuronium propane sulfonate and n-ethyl thiourea.

In one advantageous embodiment, component (d) which is a complexing agent for palladium of the electrolyte according to the invention is urea.

Wherein at least one alpha -amino acid is selected from the group consisting of alanine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, lysine, leucine, methionine, phenylalanine, phenylglycine, proline, serine, tyrosine and valine. Preferably, the amino acid used herein has only alkyl groups at various residues. In one advantageous embodiment, the alpha -amino acid is selected from alanine, glycine and valine. The use of glycine and / or alanine is most preferred.

Urea, urea derivatives, thiourea, thiourea derivatives and mixtures thereof are used at a concentration of 0.05 to 2 mol / l, preferably 0.2 to 1.5 mol / l, based on the total amount of urea and urea derivatives in the electrolyte do. The concentration of? -Amino acid in the electrolyte according to the present invention is 0.005 to 0.5 mol / l, preferably 0.01 to 0.2 mol / l. In the case of alpha -amino acids, this concentration data indicates the total amount of alpha -amino acids or alpha -amino acids, whether or not the electrolyte contains more than one alpha -amino acid.

Within the composition of the provided concentrations, one skilled in the art can freely choose the optimum concentration for the amino acid used. The skilled artisan will appreciate that too small an amount of amino acid can not produce the desired stabilizing effect, while too high a concentration may inhibit the deposition of palladium.

The electrolyte according to the present invention is used within an acidic pH range. Optimum results at a pH value of < 2 in the electrolyte can be obtained. One of skill in the art will know how to set the pH value of the electrolyte. The skilled artisan will follow the idea of introducing as few as possible additional materials that can adversely affect the deposition of the alloy. In one most preferred embodiment, the pH value is measured only by the addition of sulfonic acid. Preferably, then, this results in a strong acid deposition condition wherein the pH value is less than 1, possibly reaching 0.1, or 0.01 for the limit. The optimum pH value will be between 0.3 and 0.6.

In the electrolyte according to the invention, at least one sulfonic acid is used for the addition at a concentration of 0.25 to 4.75 mol / l, the concentration being based on the total amount of sulfonic acids used. The concentration is preferably 0.5 to 3 mol / l, and most preferably 0.8 to 2.0 mol / l. The at least one sulfonic acid serves to first establish an appropriate pH value of the electrolyte. Secondly, this leads to further stabilization of the electrolyte according to the invention. The upper limit of the sulfonic acid concentration is due to the fact that only silver is deposited at too high a concentration. In principle, sulfonic acids known to those skilled in the art for use in electroplating techniques may be used. The sulfonic acid is preferably selected from the group consisting of ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid, and methanesulfonic acid. They may be used herein individually or as a mixture. Propanesulfonic acid and methanesulfonic acid are more particularly preferred in this context. Methane sulfonic acid is most particularly preferred.

The at least one reducing agent is selected from the group consisting of formic acid, oxalic acid, ascorbic acid, hydrazine, hexamethylenetetramine, salts and / or esters of sulfurous acid, gaseous sulfites, sulfinic acid and its salts and / or esters, formaldehyde, sodium formaldehyde sulfoxylate, Benzaldehyde, benzaldehyde derivatives, hydroxybenzenes and esters thereof, polyphenols and esters thereof, phenol sulfonic acid and its salts and / or esters, and glutathione and its salts and / or esters.

In one advantageous embodiment, the reducing agent is selected from hydroxybenzene, sodium formaldehyde sulfoxylate and ascorbic acid.

In another advantageous embodiment, the reducing agent is selected from salts and / or esters of sulfurous acid.

The salt of the sulfurous acid may be a sulfite or a hydrogen sulfite. The sulfites and hydrogen sulfites are advantageously lithium, sodium, potassium, or ammonium salts.

The ester of sulfurous acid is a compound having the formula R1-OS (= O) -O-R2 wherein R1 and R2 are linear or branched bicyclic alkyl groups having 1 to 10 carbon atoms, cyclic alkyl groups having 3 to 10 carbon atoms Group, an aryl group, and a benzyl group.

Within the context of the present invention, a linear or branched aliphatic cyclic alkyl group of 1 to 10 carbon atoms is methyl, ethyl, n-propyl, isopropyl, 1-butyl, Pentyl, 3-pentyl, 3-methylbutyl, 2,2-dimethylpropyl and all isomers of hexyl, heptyl, octyl, nonyl and decyl. It is known to those skilled in the art that the cyclic alkyl group should contain at least 3 carbon atoms. In the context of the present invention, the cyclic alkyl group advantageously will comprise a propyl, butyl, pentyl, hexyl, heptyl and octyl ring. The cyclic alkyl groups for the purposes of the present invention are selected from the above-mentioned cyclic alkyl groups without any other substituents, and the above-mentioned cyclic alkyl groups wherein some of them are bonded to one or more non-cyclic alkyl groups . In the latter case, the cyclic alkyl group may be, according to the above, a chemical bond that is bonded to an oxygen atom through a cyclic non-cyclic carbon atom of the cyclic alkyl group. According to the provided definition of the term &quot; alkyl group &quot;, the cyclic alkyl group may have up to 10 carbon atoms. In the case of groups R1 and R2, when an aryl group is contemplated, it will be selected from phenyl, naphthyl and anthracenyl.

In the case of gaseous sulfites, the gas introduced into the electrolyte is SO ₂ .

Sulfinic acid is a compound having the formula R3-S (= O) -OH, wherein R3 is a linear or branched bicyclic alkyl group having 1 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, Group, and these groups are defined as described above for R &lt; 1 &gt; and R &lt; 2 &gt;.

Benzaldehyde derivatives include benzaldehyde sulfonic acid, its salts and esters, for example, benzaldehyde-2-sulfonic acid sodium salt, dimethylaminobenzaldehyde, 3-chlorobenzaldehyde, 4- chlorobenzaldehyde, 2- Is selected from aldehyde, 2-methylbenzaldehyde, 2-nitrobenzaldehyde, 3,5-dibromobenzaldehyde, 3-nitrobenzaldehyde and 3,5-dimethoxybenzaldehyde.

Hydroxybenzene is selected from phenol, catechol, resorcinol, hydroquinone, pyrogallol, hydroxyquinone and phloroglucinol.

If the at least one reducing agent is a salt of an organic compound, sodium, potassium, lithium or ammonium salts will be advantageously selected. For organic acids having multiple protons, single, multiple or all acidic hydrogen atoms may be replaced by sodium, potassium, lithium, or ammonium ions. When one or more acidic hydrogen atoms are replaced by sodium, potassium, lithium, or ammonium ions, these cations may be the same or different.

In the case of one or more reducing agents, it may be an ester of an organic compound. It is known to those skilled in the art that esters are condensation products of alcohols and carboxylic acids. Thus, the esters of the alcohols in the list of suitable reducing agents provided above are the condensation products of the carboxylic acids R4-COOH with one of the alcohols mentioned above, and the esters of the carboxylic acids in the list provided above are obtained by reacting one of the above-mentioned carboxylic acids with the alcohol R5- OH. &Lt; / RTI &gt;

Herein, R4 and R5 are independently selected from linear or branched bicyclic alkyl groups having 1 to 10 carbon atoms, cyclic alkyl groups having 3 to 10 carbon atoms, aryl groups or benzyl groups, As defined above.

Particularly advantageously, the at least one reducing agent is selected from a salt or ester of sulfurous acid and a gaseous sulfite.

The at least one reducing agent is contained in the electrolyte at a concentration of from 1 to 100 mmol / l, advantageously from 5 to 30 mmol / l, wherein the concentration is based on the total amount of the above-mentioned reducing agents in the electrolyte.

In addition, the electrolyte according to the present invention contains at least one sulfonic acid in a concentration of 0.25 to 4.75 mol / l. The concentration is preferably 0.5 to 3 mol / l, and most preferably 0.8 to 2.0 mol / l. The one or more sulfonic acids serve to first establish an appropriate pH value of the electrolyte. Secondly, its use causes additional stabilization of the electrolyte according to the invention. The upper limit of sulfonic acid is due to the fact that only silver is deposited when the concentration is too high. The sulfonic acid has the formula R6-S (= O) 2-OH, wherein R6 is a linear or branched bicyclic alkyl group having 1 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, Group, these groups being defined as described above for R &lt; 1 &gt; and R &lt; 2 &gt;. The sulfonic acid is preferably selected from the group consisting of methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and benzenesulfonic acid. Methanesulfonic acid and propanesulfonic acid are more particularly preferred in this context. Methane sulfonic acid is most preferred.

Optionally, the electrolyte according to the present invention may further contain a surfactant. These surfactants are selected from anionic surfactants and nonionic surfactants. Examples include polyethylene glycol adducts, fatty alcohol sulfates, alkylsulfates, alkylsulfonates, arylsulfonates, alkylarylsulfonates and heteroarylsulfonates, betaines, fluorosurfactants, and salts and derivatives thereof. Suitable surfactants are known to those skilled in the art, e. Kanani: Galvanotechik [Electroplating], Hanser-Verlag, Munich and Vienna, 2000, pp. 84 ff]. Prior to the addition of the surfactant, the electrolyte according to the present invention has a surface tension of at least 70 mN / m. When a surfactant is added, its concentration is advantageously chosen such that the surface tension of the electrolyte will be reduced to a value of less than 50 mN / m. The surface tension can be measured by the bubble pressure surface tensiometer.

In a further aspect, the present invention relates to a method for electrolytically depositing a silver-palladium alloy having a predominant silver content from an electrolyte according to the present invention, wherein an electrically conductive substrate is immersed in the electrolyte, A current flow is established between the anode and the substrate as a cathode. It is noted that the embodiments referred to as being preferred for the electrolyte can be applied with only minor modifications to the methods discussed herein.

The predominant temperature during the deposition of the silver-palladium alloy can be selected as desired by those skilled in the art. The skilled person will be guided, on the one hand, by a suitable deposition rate and an acceptable current density range, on the other hand by cost or electrolyte stability. Advantageously, a temperature of 25 to 75 占 폚, preferably 30 to 65 占 폚, is set in the electrolyte. The use of electrolytes at temperatures of 45 to 55 占 폚 appears to be particularly preferred.

The current density established in the electrolyte between the cathode and the anode during the deposition process can be selected by those skilled in the art depending on the efficiency and quality of deposition. Depending on the application and coating plant type, the current density of the electrolyte is advantageously set to 0.1 to 100 A / dm ² . If desired, the current density can be increased or decreased by adjusting system parameters such as design of the coating cell, flow rate, anode or cathode setup, and the like. A current density of 0.5 to 20 A / dm ² is advantageous, preferably 1 to 20 A / dm ² , and most preferably 1.5 to 15 A / dm ² .

As already indicated, the electrolyte according to the invention is of the acidic type. The pH value is preferably < 2, particularly preferably < 1. Variations in the pH value of the electrolyte may occur during electrolysis. Thus, in one preferred embodiment of the present invention, those skilled in the art will take steps to adjust the pH value during electrolysis, if necessary, to a set point.

A variety of anodes may be used when using electrolysis. Soluble or non-soluble anodes are suitable, such as a combination of soluble or non-soluble anodes. When a soluble anode is used, a silver anode is particularly preferred.

It is preferable to comprise a material selected from the group consisting of platinum titanium, graphite, iridium-transition metal mixed oxide and special carbon material (DLC or diamond-like carbon) or a combination of such anodes, such as a non-soluble anode. Particularly preferred is a mixed oxide anode comprising an iridium-ruthenium mixed oxide, an iridium-ruthenium-titanium mixed oxide or an iridium-tantalum mixed oxide for carrying out the present invention. Platinum-titanium anodes are more particularly preferred. 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).

The present invention provides a silver-palladium alloy electrolyte comprising a reducing agent added for alloy conditioning and as a polish agent and also for electrolytically depositing a silver-palladium layer, and a related method. The electrolyte contains at least one reducing agent for alloy conditioning and gloss imparting: the palladium content of the silver-palladium alloy deposited can be adjusted by the addition of the at least one reducing agent. As already indicated in the context above, the alloy deposited according to the invention has a composition comprising 70 to 99 wt% silver, 1 to 30 wt% palladium and 0.1 to 5 wt% selenium and / or tellurium, The ratio of silver, palladium and selenium and / or tellurium is 100 wt% in total. In addition, the electrolyte according to the present invention results in a more homogeneous deposition compared to conventional silver-palladium alloy electrolytes.

Layers deposited from conventional silver-palladium electrolytes have an L * value of 67 to 78, depending on the current density applied. Using the novel electrolyte system according to the invention, a significantly higher L * value is achieved for the deposited layers, and the deposited layers are uniform over the applied current density range. These values are 80 to 90, depending on the reducing agent used.

This could not be expected due to background knowledge known in the art.

mode

Various basic electrolytes were prepared and in each case the reducing agent was added at two different concentrations. The silver-palladium layer was then deposited, characterized, and compared with each other for these electrolytes containing a reducing agent and without a reducing agent.

Mode 1

Basic electrolyte:

100 ml / l methanesulfonic acid 70%

3 g / l glycine

10 g / l of palladium (as palladium hydroxide)

5 g / l silver (as silver nitrate)

0.5 g / l of tellurium (as telluric acid)

reducing agent:

- 0 g / l sodium formaldehyde sulfoxylate

- 0.95 g / l sodium formaldehyde sulfoxylate (8 mmol)

- 7.1 g / l sodium formaldehyde sulfoxylate (40 mmol)

Temperature: 30 ℃

Anode: PtTi

The palladium content of the deposited layer was measured using X-ray fluorescence analysis (XRF) (Fischerscope XDV-SDD, software WIN-FTM version 6.28-S-PDM).

The measurement results for the palladium content are as follows:

Figure 1 shows the results of palladium content measurements.

The gloss of the deposited layer was measured in the form of L * values according to CIEL * a * b.

Measurement results:

Mode 2

Basic Electrolyte:

80 ml / l methanesulfonic acid 70%

5 g / l of urea

10 g / l of palladium (as palladium chloride)

6 g / l silver (as methanesulfonic acid silver)

1.0 g / l of tellurium (as potassium tellurite)

reducing agent:

- 0 g / l ascorbic acid

- 0.14 g / l ascorbic acid

- 0.42 g / l ascorbic acid

Temperature: 60 ° C

Anode: PtTi

The palladium content of the deposited layer was measured using X-ray fluorescence spectrometry (XRF).

The measurement results for the palladium content are as follows:

Figure 2 shows the results of the palladium content measurement.

The gloss of the deposited layer was measured in the form of L * values according to CIEL * a * b.

Measurement results:

Mode 3

Basic Electrolyte:

100 ml / l methanesulfonic acid 70%

5 g / l valine

12 g / l of palladium (as palladium hydroxide)

25 g / l silver (as silver nitrate)

1.5 g / l of tellurium (as telluric acid)

reducing agent:

- 0 g / l hydroquinone

- 0.5 g / l of hydroquinone

- 1 g / l hydroquinone

Temperature: 60 ° C

Anode: Graphite

The palladium content of the deposited layer was measured using X-ray fluorescence spectrometry (XRF).

The measurement results for the palladium content are as follows:

Figure 3 shows the results of the palladium content measurement.

The gloss of the deposited layer was measured in the form of L * values according to CIEL * a * b.

Measured results for gloss:

Mode 4

Basic Electrolyte:

200 ml / l methanesulfonic acid 70%

2 g / l glycine

15 g / l of palladium (as palladium sulfate)

8 g / l of silver (as silver carbonate)

0.5 g / l of tellurium (as telluric acid)

reducing agent:

- 0 g / l sodium sulfite

- 1 g / l sodium sulfite

- 2 g / l sodium sulfite

Temperature: 40 ° C

Anode: PtTi

The palladium content of the deposited layer was measured using X-ray fluorescence spectrometry (XRF).

The measurement results for the palladium content are as follows:

Fig. 4 shows the results of the palladium content measurement.

The gloss of the deposited layer was measured in the form of L * values according to CIEL * a * b.

Measured results for gloss:

Claims (12)

A cyanide-free acidic and aqueous electrolyte for electrolytically depositing a bright silver-palladium alloy having a predominant silver content, wherein the electrolyte is in a dissolved form,
a) a silver compound having a silver concentration of 1 to 300 g / l;
b) a palladium compound with a palladium concentration of 0.1 to 100 g / l;
c) a tellurium and / or selenium compound with a tellurium and / or selenium concentration of from 0.002 to 10 g / l, based on the total amount of tellurium and selenium in said electrolyte;
d) a urea and / or urea derivative having a concentration of from 0.05 to 1.5 mol / l based on the total amount of urea and urea derivatives in said electrolyte, and / or from 0.005 to 0.5 at least one amino acid selected from the group consisting of alanine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, lysine, leucine, methionine, phenylalanine, phenylglycine, proline, serine, tyrosine and valine in a mol / l concentration;
e) at least one sulfonic acid, in a concentration of from 0.25 to 4.75 mol / l, based on the total amount of sulfonic acids;
f) salts and / or esters of sulfurous acid, gaseous sulfites, sulfinic acids and their salts, of formic acid, oxalic acid, ascorbic acid, hydrazine, hexamethylenetetramine, sulfurous acid, in a concentration of from 1 to 100 mmol / l, Salts and / or esters, formaldehyde, sodium formaldehyde sulfoxylate, benzaldehyde, benzaldehyde derivatives, hydroxybenzenes and esters thereof, polyphenols and esters thereof, phenol sulfonic acids and their salts and / or esters, and glutathione and And at least one reducing agent selected from the group consisting of salts and / or esters thereof. The electrolyte according to claim 1, wherein the silver compound is selected from silver nitrate, silver carbonate, methanesulfonic acid, silver chloride and silver oxide. 3. The electrolyte according to claim 1 or 2, wherein the palladium compound is selected from palladium hydroxide, palladium chloride, palladium glycine, palladium methanesulfonate and palladium sulfate. 4. The process according to any one of claims 1 to 3, wherein the selenium and / or tellurium compound is selected from the group consisting of atelutate, selenite, atelic acid, ascelenic acid, telluric acid, selenate and tellurate Electrolyte, characterized. The electrolyte according to any one of claims 1 to 4, wherein the? -Amino acid is selected from alanine, glycine and valine. The electrolyte according to any one of claims 1 to 4, wherein the component (d) is urea. 7. The electrolyte according to any one of claims 1 to 6, wherein the at least one sulfonic acid is selected from ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid and methanesulfonic acid. 8. The electrolyte according to any one of claims 1 to 7, characterized in that the at least one reducing agent is selected from salts and / or esters of hydroxyphenols, ascorbic acids, and sulfurous acids. A method for electrolytically depositing a silver-palladium layer predominantly containing silver from the electrolyte of any one of claims 1 to 8, comprising the steps of: immersing an electrically conductive substrate in the electrolyte; And establishing a current flow between the substrate and the substrate. 10. The method of claim 9, wherein the temperature of the electrolyte is between 25 and &lt; RTI ID = 0.0 &gt; 70 C. &lt; / RTI &gt; Claim 9 or claim 10 wherein, it characterized in that the electric current for electrolysis is 0.5 to 20A / dm ^2. 12. The method according to any one of claims 9 to 11, wherein during the electrolysis the pH value is set at a constant value < 2.

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