WO2008023339A2 - Method and composition for the deposition of palladium layers and palladium alloy layers - Google Patents

Method and composition for the deposition of palladium layers and palladium alloy layers Download PDF

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Publication number
WO2008023339A2
WO2008023339A2 PCT/IB2007/053356 IB2007053356W WO2008023339A2 WO 2008023339 A2 WO2008023339 A2 WO 2008023339A2 IB 2007053356 W IB2007053356 W IB 2007053356W WO 2008023339 A2 WO2008023339 A2 WO 2008023339A2
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Prior art keywords
palladium
acid
electrolytic composition
diamminepalladium
source
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PCT/IB2007/053356
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French (fr)
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WO2008023339A3 (en
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Stefan Schafer
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Enthone Inc.
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Publication of WO2008023339A3 publication Critical patent/WO2008023339A3/en

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    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00Electroplating: Baths therefor
    • C25D3/02Electroplating: Baths therefor from solutions
    • C25D3/56Electroplating: Baths therefor from solutions of alloys
    • C25D3/567Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of platinum group metals
    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00Electroplating: Baths therefor
    • C25D3/02Electroplating: Baths therefor from solutions
    • C25D3/50Electroplating: Baths therefor from solutions of platinum group metals
    • C25D3/52Electroplating: Baths therefor from solutions of platinum group metals characterised by the organic bath constituents used

Definitions

  • the present invention relates to a composition and a method of using the composition to deposit a palladium layer or a palladium alloy layer on a substrate surface.
  • the invention relates to a composition and a method of using the composition to deposit palladium layers having a variety of colors, including black, grey, and white.
  • Metallic surface coatings comprising palladium may be deposited on substrates for both functional and decorative purposes.
  • palladium-based surface coatings may be applied to contact surfaces in lead frames and electronic connectors to increase their corrosion resistance and resistance to mechanical loads.
  • palladium-based surface coatings may be applied as a final finish in jewelry in place of white gold layers to achieve significant cost savings.
  • U.S. Pat. No. 4,411,743 discloses an aqueous nitrate-free electrolytic composition for the deposition of palladium layers.
  • the composition includes sulfuric acid and/or phosphoric acid and a source of palladium ion. 80% to 95% of the palladium ions are from palladium sulfate, and the balance is from palladium sulfite.
  • the layers deposited therefrom are glossy and free of cracks.
  • European patent specification EP 0 512 724 Bl discloses a method for plating electrically conductive surfaces with at least two successive layers, wherein the first layer is a palladium pre-galvanizing layer and the second layer is a cover layer.
  • Disclosed cover layers include palladium nickel alloy, palladium, gold, rhodium, ruthenium, platinum, silver and alloys thereof.
  • the electrolytic composition for the deposition of the palladium pre-galvanizing layer includes a source of palladium ions and a complexing agent selected from among 1, 2-diaminobutane; 1, 2-diaminopropane; 1, 2-diamino-2-methylpropane; 1,2- diaminopentane; 1, 2-diaminohexane; 2, 3-diaminobutane; 2,3- diaminopentane; 2, 3-diaminohexane; 3, 4-diaminohexane and higher aliphatic diamines with adjacent primary, secondary or tertiary amino groups.
  • the as-deposited layers serve as galvanic pre-coatings for the subsequent deposition of palladium or palladium alloys on metal surfaces like for instance chromium, nickel, bronze, steel and others.
  • Japanese patent application JP 11153650 discloses a pyridine-containing electrolytic composition for the deposition of palladium-copper alloys on surfaces .
  • Palladium is advantageous as a functional coating since it possesses high mechanical resistance and good conductivity.
  • conventional processes are capable of depositing palladium layers or palladium alloy layers as white surface coatings.
  • different surface colors may be desired, with the additional requirement that the coating layer retain the advantageous functional properties.
  • Dark coatings, in particular, are en vogue as surfaces in decorative applications.
  • palladium-nickel layers are increasingly used in both intermediate layers and final layers. Moreover, palladium-nickel alloys absorb less hydrogen than do pure palladium layers, so that thicker layers having less internal stress may be deposited.
  • nickel is a known allergen, its use in surface layer is preferably avoided in products that directly contact skin. Therefore, there is an increasing interest in palladium alloy layers where nickel can be replaced by physiologically harmless elements, such as for example, copper .
  • an electrolytic composition and a method for using the composition to deposit palladium coatings or palladium alloy coatings, which overcome the shortcomings of processes known in the prior art.
  • the present invention is directed to an electrolytic composition for the deposition of a metallic surface coating comprising palladium.
  • the composition comprises a source of palladium ion; a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene sulfonic acid formaldehyde polycondensate, and a combination thereof.
  • the present invention is further directed to a method for the electrolytic deposition of a metallic surface coating comprising palladium on a surface of substrate.
  • the method comprises contacting the surface of the substrate with an electrolytic composition comprising (1) a source of palladium ion; (2) a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and (3) a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene sulfonic acid formaldehyde polycondensate, and a combination thereof; and applying an electric current at a current density sufficient to deposit the metallic surface coating on the surface of the substrate.
  • an electrolytic composition comprising (1) a source of palladium ion; (2) a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and (3) a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene
  • the present invention is directed to an electrolytic composition and a method of using the electrolytic composition for depositing a metallic surface coating comprising palladium.
  • the surface coating may be a relatively pure palladium coating or a palladium alloy coating.
  • the electrolytic composition may be used to deposit a palladium surface coating which comprises no alloying metal, with the proviso that metals may be present in trace amounts that may be considered impurities.
  • the electrolytic composition may be used to deposit a palladium alloy surface coating comprising a substantial weight percentage of an alloying metal.
  • the electrolytic composition comprises a source of palladium ions, a sulfonic acid, and a surfactant.
  • the electrolytic composition further comprises a source of an alloy metal ion.
  • the components of the electrolytic composition and the concentrations of the components in the electrolytic composition may be tailored to influence the color of the as-deposited palladium-based surface coating.
  • the electrolytic composition may comprise sulfur-containing compounds, which has been discovered to darken the palladium-based surface coating to allow for the deposition of surface coatings having a wide variety of colors, ranging from white to grey to black.
  • the electrolytic composition according to the invention comprises a sulfur-based acid, for example a sulfonic acid, sulfuric acid, or a combination thereof. It is preferable to match the acid with the anion from the palladium ion source. In other words, if the source of palladium ion comprises a sulfonate anion, preferably the sulfonic acid is used. Similarly, if the source of palladium ions comprises a sulfate anion, it is preferred to use sulfuric acid. Matching the acid with the anion is not, however, necessary, and in some embodiments, a composition comprising a palladium ion source comprising sulfate may further comprise a sulfonic acid.
  • a composition comprising a palladium ion source comprising sulfonate may further comprise sulfuric acid. These acids are used to adjust the solution pH and achieve a high degree of solution conductivity. Suitable sulfonic acids include monosulfonic acid and disulfonic acid.
  • the electrolytic composition may comprise both a monosulfonic acid and a disulfonic acid. Particularly suited monosulfonic acids and disulfonic acids include alkyl sulfonic acids or alkyl disulfonic acids having from one to about four carbon atoms, more preferably having from one to two carbon atoms.
  • Exemplary sulfonic acids that may be added for pH adjustment/conductivity include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, and methane disulfonic acid, with methanesulfonic acid, ethanesulfonic acid, and methanedisulfonic acid particularly preferred.
  • the sulfonic acid may be added to the composition in a concentration sufficient to achieve a composition pH less than about 1. High acidity is preferred to achieve high plating efficiencies.
  • the acid adjustment is achieved by adding the sulfonic acid or sulfuric acid in high concentrations, such as at least about 75 mL/L, preferably at least about 150 mL/L.
  • the electrolytic composition further comprises a source of palladium ions.
  • Sources of palladium ions include any soluble palladium salt or palladium complex.
  • soluble palladium salts/complexes usable herein include ammine complex salts, nitrates, and chlorides of palladium.
  • suitable ammine complex salts of palladium include chlorides, bromides, iodides, nitrites, nitrates, and sulfates of palladium ammine complex salts.
  • Preferred ammine complex salts include diammine complex salts and tetraammine complex salts.
  • palladium ion sources include palladium dichloride (PdCl 2 ) , palladium dibromide (PdBr 2 ) , palladium sulfate (PdSO 4 ) , palladium nitrate (Pd(NOs) 2 ), palladium oxide (PdO), diamminepalladium hydroxide (Pd (NH 3 ) 2 (OH) 2 ) , dichlorodiamminepalladium (Pd (NH 3 ) 2 C1 2 ) , dinitrodiamminepalladium (Pd (NH 3 ) 2 (NO 3 ) 2 ) , dichlorotetraamminepalladium (Pd (NH 3 ) 4 Cl 2 ) , dibromotetraamminepalladium (Pd (NH 3 ) 4 Br 2 ) , tetraamminepalladium diiodide (Pd (NH 3 ) 4 I 2 ) , tetraamminepalladium din
  • the soluble palladium salt is selected from among palladium dichloride (PdCl 2 ) , palladium dibromide (PdBr 2 ) , palladium sulfate (PdSO 4 ) , palladium nitrate (Pd (NO 3 ) 2 ), palladium oxide (PdO), diamminepalladium hydroxide (Pd (NH 3 ) 2 (OH) 2 ) , dichlorodiamminepalladium (Pd (NH 3 ) 2CI2) , dinitrodiamminepalladium (Pd (NH 3 ) 2 (NO 3 ) 2 ) , and dichlorotetraamminepalladium (Pd (NH 3 ) 4 CI 2 ) .
  • the source of palladium ions may be added to the electrolytic composition to yield a palladium ion concentration between about 0.5 g/L and about 20 g/L, preferably between about 1 g/L and about 15 g/L, more preferably between about 2 g/L and about 10 g/L.
  • the palladium ion source is palladium sulfate, added in a concentration of about 5.7 g/L to achieve a palladium ion concentration of about 3 g/L.
  • the electrolytic composition of the present invention further comprises a surfactant to enhance wetting of the substrate surface.
  • the surfactant may be selected from a sulfopropylated polyalkoxylated naphthol (available from Raschig GmbH (Ludwigshafen, Germany) under the trade name Ralufon NAPE 14-90; CAS number 120478-49-1; [ (3-Sulfopropoxy) -polyalkoxy] -beta-naphthyl ether, potassium salt) , a naphthalene sulfonic acid formaldehyde polycondensate (available from BASF Group (Ludwigshafen, Germany) under the trade name Tamol NN 9401), or a combination thereof.
  • the sulfopropylated polyalkoxylated naphthol surfactant has been discovered to darken the palladium deposit.
  • the naphthalene sulfonic acid formaldehyde polycondensate is added to increase the range of useful current densities.
  • the surfactants are used in the electrolyte composition according to the invention in the form of their alkali metal salts, in particular, the sodium and potassium salts. The use of the salts enhances the surfactant solubility in the electrolytic composition .
  • the sulfopropylated polyalkoxylated naphthol surfactant may be added to the electrolytic composition in a concentration between about 0.5 g/L and about 8 g/L, preferably between about 2 g/L and about 5 g/L.
  • the naphthalene sulfonic acid formaldehyde polycondensate surfactant may be added to the electrolytic composition in a concentration between about 1 g/L and about 20 g/L, preferably between about 2 g/L and about 5 g/L.
  • the electrolytic composition of the present invention further comprises a sulfur-containing compound.
  • the sulfur-containing compound is a sulfur- containing amino acid.
  • Sulfur-containing amino acids which can be advantageously used in the electrolyte composition according to the invention include cysteine (2-amino-3- sulfanyl-propanoic acid) , methionine (2-amino-4- (methylsulfanyl) -butanoic acid), homocysteine (2-amino-4- sulfanyl-butanoic acid) , cystathionine (lanthionine) , alliin (2-amino-3-prop-2-enylsulfinyl] propanoic acid), allyl cysteine (2-propenylcysteine) , cystine, ethionine (2-Amino-4- ethylsulfanylbutyric acid or Ethyl-homocysteine) , N- Formylmethi
  • each amino acid is not critical to the efficacy of the invention.
  • the amino acid may be added in the R form, the L form, or as a racemic mixture.
  • Preferred sulfur-containing amino acids include cysteine (2-amino-3-sulfanyl-propanoic acid), methionine (2-amino-4- (methylsulfanyl) -butanoic acid), homocysteine (2-amino-4-sulfanyl-butanoic acid) , cystathionine (lanthionine) , salts thereof, and derivatives thereof.
  • the sulfur-containing amino acid has been discovered to alter the color of the palladium deposit. That is, inclusion of a sulfur-containing amino acid in the electrolytic composition achieves a darker deposit. Therefore, in order to achieve a white palladium coating, the electrolytic composition preferably does not contain a sulfur-containing amino acid. In order to darken the palladium coating to achieve a grey color, the concentration of the sulfur-containing amino acid is between about 0.1 g/L and about 0.6 g/L, preferably between about 0.2 g/L and about 0.4 g/L.
  • the concentration of the sulfur-containing concentration is between about 0.6 g/L and about 2 g/L, preferably between about 0.8 g/L and about 1.5 g/L.
  • the electrolytic composition is used to deposit a relatively pure palladium layer, i.e., the palladium surface coating does not comprise an alloying metal present in a substantial weight percentage.
  • a relatively pure palladium surface coating may comprise metal (s) in trace amounts that may be considered impurities.
  • the sources of some components of the electrolytic composition comprise alkali metal ions, sodium or potassium, for example, which may become entrained in the palladium deposit.
  • the weight percentage of such metal impurities is limited to less than about 5 weight percent, more preferably less than about 1 weight percent, even more preferably less than about 0.1 weight percent.
  • the weight percentage of palladium in a relatively pure palladium surface coating is preferably at least about 95 weight percent, more preferably at least about 99 weight percent, even more preferably at least about 99.9 weight percent.
  • the electrolytic composition can include an alloying metal, such as copper. In one preferred embodiment, the alloying metal is copper.
  • the electrolytic composition further comprises a source of copper ions.
  • the source of copper ions may be a copper salt or a copper complex, provided that the source of copper ions is soluble in the electrolytic composition.
  • Exemplary sources of copper ion include copper fluoroborate, copper pyrophosphate, copper cyanide, copper phosphonate, copper sulfate, copper chloride, and other copper metal complexes such as copper methanesulfonate .
  • Preferred copper sources for use in the electrolytic composition include copper methanesulfonate and copper sulfate.
  • the source of copper ions may be added to the electrolytic composition to yield a copper ion concentration between about 0.5 g/L and about 20 g/L, preferably between about 1 g/L and about 15 g/L, more preferably between about 2 g/L and about 10 g/L.
  • the relative percentages of palladium and copper in the final deposit depend upon the ratio of palladium ion concentration to copper ion concentration.
  • the method of the present invention may be used to deposit a palladium: copper alloy comprising anywhere from about 0.1 weight percent to about 99.9 weight percent palladium, preferably between about 40 weight percent palladium to about 90 weight percent palladium, even more preferably between about 50 weight percent palladium and about 80 weight percent palladium. Copper is a preferred alloying metal since its inclusion yields a darker deposit.
  • an inventive method by which it is possible to deposit both white pure palladium and palladium alloys as well as grey to black pure palladium or palladium alloys.
  • the method according to the invention can be used in a kind of modular system which is built up on a constant chemical basis.
  • the basic components including acid and surfactants are substantially similar when depositing a white deposit to a dark, black deposit.
  • the color is influenced by varying the ratio of palladium ions to copper ions, and by modifying the concentrations of the sulfur-containing amino acids.
  • the problem is solved by a method for the electrolytic deposition of a palladium or palladium alloy layer on a substrate, which method is characterized in that substrate to be plated is contacted with an electrolyte composition which at least includes a palladium source, an acid, a surfactant, and sulfur- containing amino acid, wherein an electric current is applied at least temporarily between the substrate surface to be plated and a counter electrode.
  • the counter electrode may be an inert electrode, such as, for example, a platinum-coated titanium electrode.
  • the current density of the current to be applied in this case may, according to the invention, vary between about 0.25 A/dm 2 and about 1.0 A/dm 2 , preferably between about 0.3 A/dm 2 and about 0.8 A/dm 2 .
  • the substrate to be plated with a palladium or palladium alloy layer can be contacted with the inventive electrolytic composition which is maintained at a temperature between about 20 0 C and about 45°C.
  • a wide variety of substrates may be coated with a palladium-based surface coating according to the method of the present invention.
  • Parts to be coated may comprise, for example, brass, bronze, gold, silver, or nickel substrates. Pre-plating of the substrates with a gold strike or a palladium strike is particularly advantageous.
  • An electrolytic composition was prepared comprising the following components and concentrations:
  • Naphthalene sulfonic acid formaldehyde polycondensate (2.5 g/L, Tamol NN 9401, BASF)
  • a gold-plated brass plate was contacted with the above-described electrolytic composition at 40 0 C for 5 minutes.
  • the current density was 0.8 A/dm 2 .
  • An electrolytic composition was prepared comprising the following components and concentrations:
  • Copper ions (0.6 g/L, from about 2.4 g/L copper methanesulfonic acid)
  • Naphthalene sulfonic acid formaldehyde polycondensate (2.5 g/L, Tamol NN 9401, BASF)
  • a palladium-copper alloy layer was deposited having a palladium content of 80% and a copper content of 20% and having an appearance in the color of stainless steel.
  • An electrolytic composition was prepared comprising the following components and concentrations:
  • Naphthalene sulfonic acid formaldehyde polycondensate (2.5 g/L, Tamol NN 9401, BASF)
  • a brass plate was contacted with the above- described electrolytic composition at 35°C for 5 minutes.
  • the current density was 0.8 A/dm 2 .
  • a palladium-copper alloy layer having a thickness of 0.8 ⁇ m was deposited.
  • the deposited layer had the color of stainless steel and had a composition of 70% palladium and 30% copper.
  • An electrolytic composition was prepared comprising the following components and concentrations:
  • Naphthalene sulfonic acid formaldehyde polycondensate (5 g/L, Tamol NN 9401, BASF)
  • a white palladium-plated brass plate was contacted with the above-described electrolytic composition at 30 0 C for 5 minutes.
  • the current density was 0.3 A/dm 2 .

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Abstract

An electrolytic composition and a method of using the electrolytic composition to deposit palladium or palladium alloy layers is provided which overcomes the problems known from prior art. The electrolytic composition and method of the invention comprises a palladium source, a sulfur-based acid, and a surfactant. To deposit a palladium alloy layer, the electrolytic composition further comprises a source of alloying metal ions. Moreover, the electrolytic composition according to the invention may include additional sulfur- containing amino acids for the deposition of dark palladium layers.

Description

METHOD AND COMPOSITION FOR THE DEPOSITION OF PALLADIUM LAYERS
AND PALLADIUM ALLOY LAYERS
FIELD OF THE INVENTION
[0001] The present invention relates to a composition and a method of using the composition to deposit a palladium layer or a palladium alloy layer on a substrate surface. In particular, the invention relates to a composition and a method of using the composition to deposit palladium layers having a variety of colors, including black, grey, and white.
BACKGROUND OF THE INVENTION
[0002] Metallic surface coatings comprising palladium may be deposited on substrates for both functional and decorative purposes. For example, in electronics applications, palladium-based surface coatings may be applied to contact surfaces in lead frames and electronic connectors to increase their corrosion resistance and resistance to mechanical loads. In the field of decorative coatings, palladium-based surface coatings may be applied as a final finish in jewelry in place of white gold layers to achieve significant cost savings.
[0003] Methods and compositions for depositing palladium-containing layers are known. For example, U.S. Pat. No. 4,411,743 discloses an aqueous nitrate-free electrolytic composition for the deposition of palladium layers. The composition includes sulfuric acid and/or phosphoric acid and a source of palladium ion. 80% to 95% of the palladium ions are from palladium sulfate, and the balance is from palladium sulfite. The layers deposited therefrom are glossy and free of cracks.
[0004] European patent specification EP 0 512 724 Bl discloses a method for plating electrically conductive surfaces with at least two successive layers, wherein the first layer is a palladium pre-galvanizing layer and the second layer is a cover layer. Disclosed cover layers include palladium nickel alloy, palladium, gold, rhodium, ruthenium, platinum, silver and alloys thereof. The electrolytic composition for the deposition of the palladium pre-galvanizing layer includes a source of palladium ions and a complexing agent selected from among 1, 2-diaminobutane; 1, 2-diaminopropane; 1, 2-diamino-2-methylpropane; 1,2- diaminopentane; 1, 2-diaminohexane; 2, 3-diaminobutane; 2,3- diaminopentane; 2, 3-diaminohexane; 3, 4-diaminohexane and higher aliphatic diamines with adjacent primary, secondary or tertiary amino groups. The as-deposited layers serve as galvanic pre-coatings for the subsequent deposition of palladium or palladium alloys on metal surfaces like for instance chromium, nickel, bronze, steel and others.
[0005] Japanese patent application JP 11153650 discloses a pyridine-containing electrolytic composition for the deposition of palladium-copper alloys on surfaces .
[0006] Palladium is advantageous as a functional coating since it possesses high mechanical resistance and good conductivity. In decorative applications, conventional processes are capable of depositing palladium layers or palladium alloy layers as white surface coatings. In certain decorative coating fields such as glasses frames, bathroom fittings, furniture fittings and in the automotive industry, different surface colors may be desired, with the additional requirement that the coating layer retain the advantageous functional properties. Dark coatings, in particular, are en vogue as surfaces in decorative applications.
[0007] Conventional methods for depositing white palladium surface coatings employ alkaline ammonium salt- containing electrolytic compositions. At high pH values and increased alkalinity, ammonia is accordingly frequently released as a vapor, which is problematic from an environmental and worker safety standpoint. Furthermore, the conventional methods are prone to bath contamination with cyanide, and the regeneration of the electrolytic compositions is rendered difficult in view of the high complexation constant for palladium cyanide complexes .
[0008] In addition to pure palladium layers, it is conventional to deposit palladium-nickel layers in the field of decorative surface coating. Palladium-nickel layers are advantageous since they possess high corrosion resistance. Moreover, inclusion of nickel in the alloy is advantageous from a cost perspective compared to pure palladium coatings.
In view of these advantages, palladium-nickel layers are increasingly used in both intermediate layers and final layers. Moreover, palladium-nickel alloys absorb less hydrogen than do pure palladium layers, so that thicker layers having less internal stress may be deposited.
[0009] Since nickel is a known allergen, its use in surface layer is preferably avoided in products that directly contact skin. Therefore, there is an increasing interest in palladium alloy layers where nickel can be replaced by physiologically harmless elements, such as for example, copper .
SUMMARY OF THE INVENTION
[0010] Among the aspects of the present invention, may be noted an electrolytic composition and a method for using the composition to deposit palladium coatings or palladium alloy coatings, which overcome the shortcomings of processes known in the prior art.
[0011] Therefore, the present invention is directed to an electrolytic composition for the deposition of a metallic surface coating comprising palladium. The composition comprises a source of palladium ion; a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene sulfonic acid formaldehyde polycondensate, and a combination thereof. [0012] The present invention is further directed to a method for the electrolytic deposition of a metallic surface coating comprising palladium on a surface of substrate. The method comprises contacting the surface of the substrate with an electrolytic composition comprising (1) a source of palladium ion; (2) a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and (3) a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene sulfonic acid formaldehyde polycondensate, and a combination thereof; and applying an electric current at a current density sufficient to deposit the metallic surface coating on the surface of the substrate.
[0013] Other objects and features will be in part apparent and in part pointed out hereinafter.
DESCRIPTION OF THE EMBODIMENT (S) OF THE INVENTION
[0014] The present invention is directed to an electrolytic composition and a method of using the electrolytic composition for depositing a metallic surface coating comprising palladium. The surface coating may be a relatively pure palladium coating or a palladium alloy coating. In one embodiment, therefore, the electrolytic composition may be used to deposit a palladium surface coating which comprises no alloying metal, with the proviso that metals may be present in trace amounts that may be considered impurities. In another embodiment, the electrolytic composition may be used to deposit a palladium alloy surface coating comprising a substantial weight percentage of an alloying metal. The electrolytic composition comprises a source of palladium ions, a sulfonic acid, and a surfactant. For depositing a palladium alloy surface coating, the electrolytic composition further comprises a source of an alloy metal ion. Moreover, in certain embodiments, the components of the electrolytic composition and the concentrations of the components in the electrolytic composition may be tailored to influence the color of the as-deposited palladium-based surface coating. In one embodiment, for example, the electrolytic composition may comprise sulfur-containing compounds, which has been discovered to darken the palladium-based surface coating to allow for the deposition of surface coatings having a wide variety of colors, ranging from white to grey to black.
[0015] The electrolytic composition according to the invention comprises a sulfur-based acid, for example a sulfonic acid, sulfuric acid, or a combination thereof. It is preferable to match the acid with the anion from the palladium ion source. In other words, if the source of palladium ion comprises a sulfonate anion, preferably the sulfonic acid is used. Similarly, if the source of palladium ions comprises a sulfate anion, it is preferred to use sulfuric acid. Matching the acid with the anion is not, however, necessary, and in some embodiments, a composition comprising a palladium ion source comprising sulfate may further comprise a sulfonic acid. Likewise, a composition comprising a palladium ion source comprising sulfonate may further comprise sulfuric acid. These acids are used to adjust the solution pH and achieve a high degree of solution conductivity. Suitable sulfonic acids include monosulfonic acid and disulfonic acid. The electrolytic composition may comprise both a monosulfonic acid and a disulfonic acid. Particularly suited monosulfonic acids and disulfonic acids include alkyl sulfonic acids or alkyl disulfonic acids having from one to about four carbon atoms, more preferably having from one to two carbon atoms. Exemplary sulfonic acids that may be added for pH adjustment/conductivity include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, and methane disulfonic acid, with methanesulfonic acid, ethanesulfonic acid, and methanedisulfonic acid particularly preferred.
[0016] The sulfonic acid may be added to the composition in a concentration sufficient to achieve a composition pH less than about 1. High acidity is preferred to achieve high plating efficiencies. The acid adjustment is achieved by adding the sulfonic acid or sulfuric acid in high concentrations, such as at least about 75 mL/L, preferably at least about 150 mL/L.
[0017] The electrolytic composition further comprises a source of palladium ions. Sources of palladium ions include any soluble palladium salt or palladium complex. Examples of soluble palladium salts/complexes usable herein include ammine complex salts, nitrates, and chlorides of palladium. Among them, suitable ammine complex salts of palladium include chlorides, bromides, iodides, nitrites, nitrates, and sulfates of palladium ammine complex salts. Preferred ammine complex salts include diammine complex salts and tetraammine complex salts. Specific examples of palladium ion sources include palladium dichloride (PdCl2) , palladium dibromide (PdBr2) , palladium sulfate (PdSO4) , palladium nitrate (Pd(NOs)2), palladium oxide (PdO), diamminepalladium hydroxide (Pd (NH3) 2 (OH) 2) , dichlorodiamminepalladium (Pd (NH3) 2C12) , dinitrodiamminepalladium (Pd (NH3) 2 (NO3) 2) , dichlorotetraamminepalladium (Pd (NH3) 4Cl2) , dibromotetraamminepalladium (Pd (NH3) 4Br2) , tetraamminepalladium diiodide (Pd (NH3) 4I2) , tetraamminepalladium dinitrite (Pd (NH3) 4 (ONO) 2) , tetraamminepalladium dinitrate (Pd (NH3) 4 (NO3) 2) , tetraamminepalladium disulfite (Pd (NH3) 4 (SO3) 2) , tetraamminepalladium disulfate (Pd (NH3) 4 (SO4) 2) , dinitrotetraamminepalladium (Pd (NH3) 4 (NO2) 2) , dibromodiamminepalladium (Pd (NH3) 2Br2) , diamminepalladium diiodide (Pd (NH3) 2I2) , diamminepalladium dinitrite (Pd (NH3) 2 (ONO)2), diamminepalladium dinitrate (Pd (NH3) 2 (NO3) 2) diamminepalladium disulfite (Pd (NH3) 2 (SO3) 2) , diamminepalladium disulfate (Pd (NH3) 2 (SO4) 2) , and dinitrodiamminepalladium (Pd (NH3) 2 (NO2) 2) • These salts may be synthesized, or alternatively, commercially available products may be used. In a preferred embodiment of the present invention, the soluble palladium salt is selected from among palladium dichloride (PdCl2) , palladium dibromide (PdBr2) , palladium sulfate (PdSO4) , palladium nitrate (Pd (NO3) 2), palladium oxide (PdO), diamminepalladium hydroxide (Pd (NH3) 2 (OH) 2) , dichlorodiamminepalladium (Pd (NH3) 2CI2) , dinitrodiamminepalladium (Pd (NH3) 2 (NO3) 2) , and dichlorotetraamminepalladium (Pd (NH3) 4CI2) .
[0018] The source of palladium ions may be added to the electrolytic composition to yield a palladium ion concentration between about 0.5 g/L and about 20 g/L, preferably between about 1 g/L and about 15 g/L, more preferably between about 2 g/L and about 10 g/L. In one embodiment, for example, the palladium ion source is palladium sulfate, added in a concentration of about 5.7 g/L to achieve a palladium ion concentration of about 3 g/L.
[0019] The electrolytic composition of the present invention further comprises a surfactant to enhance wetting of the substrate surface. Preferably, the surfactant may be selected from a sulfopropylated polyalkoxylated naphthol (available from Raschig GmbH (Ludwigshafen, Germany) under the trade name Ralufon NAPE 14-90; CAS number 120478-49-1; [ (3-Sulfopropoxy) -polyalkoxy] -beta-naphthyl ether, potassium salt) , a naphthalene sulfonic acid formaldehyde polycondensate (available from BASF Group (Ludwigshafen, Germany) under the trade name Tamol NN 9401), or a combination thereof. The sulfopropylated polyalkoxylated naphthol surfactant has been discovered to darken the palladium deposit. The naphthalene sulfonic acid formaldehyde polycondensate is added to increase the range of useful current densities. Advantageously, the surfactants are used in the electrolyte composition according to the invention in the form of their alkali metal salts, in particular, the sodium and potassium salts. The use of the salts enhances the surfactant solubility in the electrolytic composition .
[0020] The sulfopropylated polyalkoxylated naphthol surfactant may be added to the electrolytic composition in a concentration between about 0.5 g/L and about 8 g/L, preferably between about 2 g/L and about 5 g/L. The naphthalene sulfonic acid formaldehyde polycondensate surfactant may be added to the electrolytic composition in a concentration between about 1 g/L and about 20 g/L, preferably between about 2 g/L and about 5 g/L.
[0021] The electrolytic composition of the present invention further comprises a sulfur-containing compound. In particular, the sulfur-containing compound is a sulfur- containing amino acid. Sulfur-containing amino acids which can be advantageously used in the electrolyte composition according to the invention include cysteine (2-amino-3- sulfanyl-propanoic acid) , methionine (2-amino-4- (methylsulfanyl) -butanoic acid), homocysteine (2-amino-4- sulfanyl-butanoic acid) , cystathionine (lanthionine) , alliin (2-amino-3-prop-2-enylsulfinyl] propanoic acid), allyl cysteine (2-propenylcysteine) , cystine, ethionine (2-Amino-4- ethylsulfanylbutyric acid or Ethyl-homocysteine) , N- Formylmethionine (2-formamido-4-methylsulfanyl-butanoic acid), Methylmethionine ( (3-Amino-3-carboxy-propyl) -dimethyl- sulfanium or Methyl-methionine or Vitamin U) , salts thereof, and derivatives thereof. The stereochemistry of each amino acid is not critical to the efficacy of the invention. Simply stated, the amino acid may be added in the R form, the L form, or as a racemic mixture. Preferred sulfur-containing amino acids include cysteine (2-amino-3-sulfanyl-propanoic acid), methionine (2-amino-4- (methylsulfanyl) -butanoic acid), homocysteine (2-amino-4-sulfanyl-butanoic acid) , cystathionine (lanthionine) , salts thereof, and derivatives thereof.
[0022] The sulfur-containing amino acid has been discovered to alter the color of the palladium deposit. That is, inclusion of a sulfur-containing amino acid in the electrolytic composition achieves a darker deposit. Therefore, in order to achieve a white palladium coating, the electrolytic composition preferably does not contain a sulfur-containing amino acid. In order to darken the palladium coating to achieve a grey color, the concentration of the sulfur-containing amino acid is between about 0.1 g/L and about 0.6 g/L, preferably between about 0.2 g/L and about 0.4 g/L. In order to darken the palladium coating yet more to achieve a dark or black color, the concentration of the sulfur-containing concentration is between about 0.6 g/L and about 2 g/L, preferably between about 0.8 g/L and about 1.5 g/L.
[0023] In some embodiments, the electrolytic composition is used to deposit a relatively pure palladium layer, i.e., the palladium surface coating does not comprise an alloying metal present in a substantial weight percentage.
A relatively pure palladium surface coating may comprise metal (s) in trace amounts that may be considered impurities.
These metal impurities may be present since the sources of some components of the electrolytic composition comprise alkali metal ions, sodium or potassium, for example, which may become entrained in the palladium deposit. Preferably, the weight percentage of such metal impurities is limited to less than about 5 weight percent, more preferably less than about 1 weight percent, even more preferably less than about 0.1 weight percent. Stated another way, the weight percentage of palladium in a relatively pure palladium surface coating is preferably at least about 95 weight percent, more preferably at least about 99 weight percent, even more preferably at least about 99.9 weight percent. [0024] Alternatively, the electrolytic composition can include an alloying metal, such as copper. In one preferred embodiment, the alloying metal is copper. Accordingly, the electrolytic composition further comprises a source of copper ions. The source of copper ions may be a copper salt or a copper complex, provided that the source of copper ions is soluble in the electrolytic composition. Exemplary sources of copper ion include copper fluoroborate, copper pyrophosphate, copper cyanide, copper phosphonate, copper sulfate, copper chloride, and other copper metal complexes such as copper methanesulfonate . Preferred copper sources for use in the electrolytic composition include copper methanesulfonate and copper sulfate.
[0025] The source of copper ions may be added to the electrolytic composition to yield a copper ion concentration between about 0.5 g/L and about 20 g/L, preferably between about 1 g/L and about 15 g/L, more preferably between about 2 g/L and about 10 g/L. The relative percentages of palladium and copper in the final deposit depend upon the ratio of palladium ion concentration to copper ion concentration. The method of the present invention may be used to deposit a palladium: copper alloy comprising anywhere from about 0.1 weight percent to about 99.9 weight percent palladium, preferably between about 40 weight percent palladium to about 90 weight percent palladium, even more preferably between about 50 weight percent palladium and about 80 weight percent palladium. Copper is a preferred alloying metal since its inclusion yields a darker deposit.
[0026] Accordingly, by the addition of suitable additives there is provided an inventive method by which it is possible to deposit both white pure palladium and palladium alloys as well as grey to black pure palladium or palladium alloys. The method according to the invention can be used in a kind of modular system which is built up on a constant chemical basis. In other words, the basic components including acid and surfactants are substantially similar when depositing a white deposit to a dark, black deposit. The color is influenced by varying the ratio of palladium ions to copper ions, and by modifying the concentrations of the sulfur-containing amino acids.
[0027] Concerning the method, the problem is solved by a method for the electrolytic deposition of a palladium or palladium alloy layer on a substrate, which method is characterized in that substrate to be plated is contacted with an electrolyte composition which at least includes a palladium source, an acid, a surfactant, and sulfur- containing amino acid, wherein an electric current is applied at least temporarily between the substrate surface to be plated and a counter electrode. The counter electrode may be an inert electrode, such as, for example, a platinum-coated titanium electrode.
[0028] The current density of the current to be applied in this case may, according to the invention, vary between about 0.25 A/dm2 and about 1.0 A/dm2, preferably between about 0.3 A/dm2 and about 0.8 A/dm2.
[0029] The substrate to be plated with a palladium or palladium alloy layer can be contacted with the inventive electrolytic composition which is maintained at a temperature between about 200C and about 45°C.
[0030] A wide variety of substrates may be coated with a palladium-based surface coating according to the method of the present invention. Parts to be coated may comprise, for example, brass, bronze, gold, silver, or nickel substrates. Pre-plating of the substrates with a gold strike or a palladium strike is particularly advantageous.
[0031] Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. EXAMPLES
[0032] The following non-limiting examples are provided to further illustrate the present invention.
Example 1. Deposition of a "White" Palladium Layer
[0033] An electrolytic composition was prepared comprising the following components and concentrations:
[0034] Palladium ions (3 g/L, from about 5.7 g/L palladium sulfate)
[0035] Methane sulfonic acid (150 mL/L)
[0036] Naphthalene sulfonic acid formaldehyde polycondensate (2.5 g/L, Tamol NN 9401, BASF)
[0037] Sulfopropylated polyalkoxylated naphthol (2.5 g/L, Ralufon NAPE 14-90, Raschig GmbH) .
[0038] A gold-plated brass plate was contacted with the above-described electrolytic composition at 400C for 5 minutes. The current density was 0.8 A/dm2.
[0039] Under these conditions, a 0.9 μm thick pure palladium surface coating having the color of stainless steel was deposited.
Example 2. Deposition of a "White" Palladivim-Copper Alloy Layer
[0040] An electrolytic composition was prepared comprising the following components and concentrations:
[0041] Palladium ions (3 g/L, from about 5.7 g/L palladium sulfate)
[0042] Copper ions (0.6 g/L, from about 2.4 g/L copper methanesulfonic acid)
[0043] Methane sulfonic acid (100 mL/L)
[0044] Naphthalene sulfonic acid formaldehyde polycondensate (2.5 g/L, Tamol NN 9401, BASF)
[0045] Sulfopropylated polyalkoxylated naphthol (2.5 g/L, Ralufon NAPE 14-90, Raschig GmbH) . [0046] A bronze-plated brass plate was contacted with the above-described electrolytic composition at 35°C for 5 minutes. The current density was 0.8 A/dm2.
[0047] Under these conditions, a palladium-copper alloy layer was deposited having a palladium content of 80% and a copper content of 20% and having an appearance in the color of stainless steel.
Example 3. Deposition of a "White" Palladium-Copper Alloy Layer
[0048] An electrolytic composition was prepared comprising the following components and concentrations:
[0049] Palladium ions (4 g/L, from about 7.6 g/L palladium sulfate)
[0050] Copper ions (2 g/L, from about 8 g/L copper methanesulfonic acid)
[0051] Methane sulfonic acid (100 mL/L)
[0052] Naphthalene sulfonic acid formaldehyde polycondensate (2.5 g/L, Tamol NN 9401, BASF)
[0053] Sulfopropylated polyalkoxylated naphthol (2.5 g/L, Ralufon NAPE 14-90, Raschig GmbH) .
[0054] A brass plate was contacted with the above- described electrolytic composition at 35°C for 5 minutes. The current density was 0.8 A/dm2.
[0055] Under these conditions, a palladium-copper alloy layer having a thickness of 0.8 μm was deposited. The deposited layer had the color of stainless steel and had a composition of 70% palladium and 30% copper.
Example 4. Deposition of a "Grey" Palladium-Copper Alloy Layer
[0056] An electrolytic composition was prepared comprising the following components and concentrations:
[0057] Palladium ions (4 g/L, from about 7.6 g/L palladium sulfate) [0058] Copper ions (2 g/L, from about 8 g/L copper methanesulfonic acid)
[0059] Methane sulfonic acid (150 mL/L)
[0060] Methionine (1 g/L)
[0061] Naphthalene sulfonic acid formaldehyde polycondensate (5 g/L, Tamol NN 9401, BASF)
[0062] Sulfopropylated polyalkoxylated naphthol (2.5 g/L, Ralufon NAPE 14-90, Raschig GmbH) .
[0063] A white palladium-plated brass plate was contacted with the above-described electrolytic composition at 300C for 5 minutes. The current density was 0.3 A/dm2.
[0064] Under these conditions, a 0.3 μm thick palladium-copper alloy layer was deposited. The deposited layer appeared anthrazite-grey in its color and had a composition of 50% palladium and 50% copper.
[0065] When introducing elements of the present invention or the preferred embodiments (s) thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.
[0066] In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.
[0067] As various changes could be made in the above compositions and processes without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Claims

WHAT IS CLAIMED IS:
1. An electrolytic composition for the deposition of a metallic surface coating comprising palladium, the composition comprising: a source of palladium ion; a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene sulfonic acid formaldehyde polycondensate, and a combination thereof.
2. The electrolytic composition of claim 1 wherein the source of palladium ion is selected from the group consisting of palladium dichloride (PCICI2) , palladium dibromide (PdBr2) , palladium sulfate (PdSO4), palladium nitrate (Pd (NO3) 2), palladium oxide (PdO) , diamminepalladium hydroxide
(Pd (NH3) 2 (OH) 2) , dichlorodiamminepalladium (Pd (NH3) 2C12) , dinitrodiamminepalladium (Pd (NH3) 2 (NO3) 2) , dichlorotetraamminepalladium (Pd (NH3) 4CI2) , dibromotetraamminepalladium (Pd (NH3) 4Br2) , tetraamminepalladium diiodide (Pd (NH3) 4I2) , tetraamminepalladium dinitrite (Pd (NH3) 4 (ONO) 2) , tetraamminepalladium dinitrate (Pd (NH3) 4 (NO3) 2) , tetraamminepalladium disulfite (Pd (NH3) 4 (SO3) 2) , tetraamminepalladium disulfate (Pd (NH3) 4 (SO4) 2) , dinitrotetraamminepalladium (Pd (NH3) 4 (NO2) 2) , dibromodiamminepalladium (Pd (NH3) 2Br2) , diamminepalladium diiodide (Pd (NH3) 2I2) , diamminepalladium dinitrite (Pd (NH3) 2 (ONO)2), diamminepalladium dinitrate (Pd (NH3) 2 (NO3) 2) diamminepalladium disulfite (Pd (NH3) 2 (SO3) 2) , diamminepalladium disulfate (Pd (NH3) 2 (SO4) 2) , and dinitrodiamminepalladium (Pd (NH3) 2 (NO2) 2) , and combinations thereof .
3. The electrolytic composition of claim 1 wherein the source of palladium ion is selected from the group consisting of palladium dichloride (PdCl2) , palladium dibromide (PdBr2) , palladium sulfate (PdSO4), palladium nitrate (Pd (NO3) 2), palladium oxide (PdO) , diamminepalladium hydroxide
(Pd (NH3) 2 (OH) 2) , dichlorodiamminepalladium (Pd (NH3) 2C12) , dinitrodiamminepalladium (Pd (NH3) 2 (NO3) 2) , and dichlorotetraamminepalladium (Pd (NH3) 4Cl2) , and combinations thereof.
4. The electrolytic composition of any one of claims 1 through 3 wherein the sulfur-based acid is the sulfonic acid and wherein the sulfonic acid is a monosulfonic acid, a disulfonic acid, or a combination thereof.
5. The electrolytic composition of claim 4 wherein the sulfonic acid is an alkyl sulfonic acid or an alkyl disulfonic acid having from one to about four carbon atoms, preferably having from one to two carbon atoms.
6. The electrolytic composition of any one of claims 1 through 5 further comprising a sulfur-containing amino acid.
7. The electrolytic composition of 6 wherein the sulfur-containing amino acid is selected from the group consisting of cysteine, methionine, homocysteine, cystathionine, alliin, allyl cysteine, cystine, ethionine, N- Formylmethionine, Methylmethionine, salts thereof, derivatives thereof, and combinations thereof.
8. The electrolytic composition of 6 wherein the sulfur-containing amino acid is selected from the group consisting of cysteine, methionine, homocysteine, cystathionine, salts thereof, derivatives thereof, and combinations thereof.
9. The electrolytic composition of any one of claims 1 through 8 wherein the surfactant is in the form of an alkali salt.
10. The electrolytic composition of any one of claims 1 through 8 further comprising a source of alloying metal ions such that the metallic surface coating comprising palladium further includes an alloying metal.
11. The electrolytic composition of claim 10, wherein the source of alloying metal ions is a source of copper ions.
12. A method for the electrolytic deposition of a metallic surface coating comprising palladium on a surface of substrate, the method comprising: contacting the surface of the substrate with an electrolytic composition comprising (1) a source of palladium ion; (2) a sulfur-based acid selected from the group consisting of a sulfonic acid, a sulfuric acid, and a combination thereof; and (3) a surfactant selected from the group consisting of a sulfopropylated polyalkoxylated naphthol, a naphthalene sulfonic acid formaldehyde polycondensate, and a combination thereof; and applying an electric current at a current density sufficient to deposit the metallic surface coating on the surface of the substrate.
13. The method of claim 12 wherein the current density is applied between about 0.25 A/dm2 and about 1.0 A/dm2, preferably between about 0.3 A/dm2 and about 0.8 A/dm2.
14. The method of claim 12 or 13 wherein the surface of the substrate is contacted with the electrolytic composition maintained a temperature between about 200C and about 45°C.
15. The method of any one of claims 12 through 14 wherein the source of palladium ion is selected from the group consisting of palladium dichloride (PdCl2) , palladium dibromide (PdBr2) , palladium sulfate (PdSO4) , palladium nitrate (Pd (NO3) 2), palladium oxide (PdO), diamminepalladium hydroxide (Pd (NH3) 2 (OH) 2) , dichlorodiamminepalladium (Pd (NH3) 2C12) , dinitrodiamminepalladium (Pd (NH3) 2 (NO3) 2) , dichlorotetraamminepalladium (Pd (NH3) 4Cl2) , dibromotetraamminepalladium (Pd (NH3) 4Br2) , tetraamminepalladium diiodide (Pd (NH3) 4I2) , tetraamminepalladium dinitrite (Pd (NH3) 4 (ONO) 2) , tetraamminepalladium dinitrate (Pd (NH3) 4 (NO3) 2) , tetraamminepalladium disulfite (Pd (NH3) 4 (SO3) 2) , tetraamminepalladium disulfate (Pd (NH3) 4 (SO4) 2) , dinitrotetraamminepalladium (Pd (NH3) 4 (NO2) 2) , dibromodiamminepalladium (Pd (NH3) 2Br2) , diamminepalladium diiodide (Pd (NH3) 2I2) , diamminepalladium dinitrite (Pd (NH3) 2 (ONO)2), diamminepalladium dinitrate (Pd (NH3) 2 (NO3) 2) diamminepalladium disulfite (Pd (NH3) 2 (SO3) 2) , diamminepalladium disulfate (Pd (NH3) 2 (SO4) 2) , and dinitrodiamminepalladium (Pd (NH3) 2 (NO2) 2) , and combinations thereof.
16. The method of claim 15 wherein the source of palladium ion is selected from the group consisting of palladium dichloride (PdCl2) , palladium dibromide (PdBr2) , palladium sulfate (PdSO4), palladium nitrate (Pd (NO3) 2), palladium oxide (PdO) , diamminepalladium hydroxide
(Pd (NH3) 2 (OH) 2) , dichlorodiamminepalladium (Pd (NH3) 2C12) , dinitrodiamminepalladium (Pd (NH3) 2 (NO3) 2) , and dichlorotetraamminepalladium (Pd (NH3) 4C12) , and combinations thereof.
17. The method of any one of claims 12 through 17 wherein the sulfur-based acid is the sulfonic acid and wherein the sulfonic acid is a monosulfonic acid, a disulfonic acid, or a combination thereof.
18. The method of claim 17 wherein the sulfonic acid is an alkyl sulfonic acid or an alkyl disulfonic acid having from one to about four carbon atoms, preferably having from one to two carbon atoms .
19. The method of any one of claims 12 through 18 wherein the electrolytic composition further comprises a sulfur-containing amino acid.
20. The method of 19 wherein the sulfur-containing amino acid is selected from the group consisting of cysteine, methionine, homocysteine, cystathionine, alliin, allyl cysteine, cystine, ethionine, N-Formylmethionine, Methylmethionine, salts thereof, derivatives thereof, and combinations thereof.
21. The method of 19 wherein the sulfur-containing amino acid is selected from the group consisting of cysteine, methionine, homocysteine, cystathionine, salts thereof, derivatives thereof, and combinations thereof.
22. The method of any one of claims 12 through 21 wherein the surfactant is in the form of an alkali salt.
23. The method of any one of claims 12 through 21 wherein the electrolytic composition further comprises a source of alloying metal ions such that the metallic surface coating comprising palladium further includes an alloying metal .
24. The method of claim 23 wherein the source of alloying metal ions is a source of copper ions.
PCT/IB2007/053356 2006-08-22 2007-08-22 Method and composition for the deposition of palladium layers and palladium alloy layers WO2008023339A2 (en)

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