Heat-stable silver alloy coating

Abstract

The present invention relates to the electrolytic deposition of an alloy containing primarily silver. Further components of the deposited alloy layer are palladium, tellurium, and one or more of the following metals: Ce, Dy, Pb, Bi, Al, Ga, Ge, Fe, In, Co, Ni, Cu, Sn, Sb, Rh, Ru, Ir, Pt, Au. The invention also relates to a method for the electrolytic deposition of a corresponding coating using a suitable electrolyte. The use of the electrolytically deposited alloy coating is also claimed.

Description

DETAILED DESCRIPTION

[0001] The present invention relates to the electrolytic deposition of an alloy containing primarily silver. Further components of the deposited alloy layer are palladium, tellurium, and one or more of the following metals: Ce, Dy, Pb, Bi, Al, Ga, Ge, Fe, In, Co, Ni, Cu, Sn, Sb, Rh, Ru, Ir, Pt, Au. The invention also relates to a method for the electrolytic deposition of a corresponding coating using a suitable electrolyte. The use of the electrolytically deposited alloy coating is also claimed.

[0002] Electrical contacts are used in practically all electrical appliances today. Their applications range from simple plug connectors to safety-critical, delicate switching contacts in the communications industry, for the automotive industry, or for aerospace technology. These contact surfaces must have good electrical conductivity, a low contact resistance with long-term stability, good corrosion and wear resistance with the lowest possible insertion force, and good resistance to thermal stresses. In electrical engineering, plug contacts are often coated with a hard-gold alloy layer consisting of gold-cobalt, gold-nickel, or gold-iron. These coatings have good wear resistance, good solderability, a low contact resistance with long-term stability, and good corrosion resistance. Due to the rising price of gold, the search for cheaper alternatives continues.

[0003] As an alternative to hard gold plating, coating with silver-rich silver alloys (hard silver) has demonstrated benefits. Silver and silver alloys are some of the most important contact materials in electrical engineering, not least for their high electrical conductivity and good oxidation resistance. Depending on the metals added to the alloy, these silver alloy coatings have coating properties similar to currently used hard gold coatings and coating combinations, such as palladium nickel with gold flash. Furthermore, silver is relatively inexpensive compared to other precious metals, especially hard gold alloys.

[0004] One limitation of using silver is that it has a lower corrosion resistance than hard gold, for example in atmospheres containing sulfur or chlorine. Aside from visible surface changes, tarnished silver sulfide films generally do not present any significant risk, as silver sulfide is semiconductive, soft, and, provided the contact force is strong enough, can be easily erased during the insertion process. Tarnished silver chloride films, on the other hand, are nonconductive, hard, and not easily dislodged. The relatively high proportion of silver chloride in the tarnish layer can therefore lead to problems with contact quality (see Marjorie Myers: Overview of the use of silver in connector applications; Interconnect & Process Technology, Tyco Electronics, Harrisburg, February 2009).

[0005] Other metals can be alloyed with silver to increase corrosion resistance. A possible alloying agent for silver in this connection is metallic palladium. For example, silver-palladium alloys are resistant to sulfur if the palladium content is correspondingly high (DE 29 14 880 A1).

[0006] Palladium-silver alloys have long been used successfully as contact materials in the form of wrought alloys. In relay switching contacts, a 60 / 40 palladium-silver alloy is preferably used as an inlay. Today, these coatings of electrical contact materials based on precious metals are also preferably produced galvanically. Although the electrochemical deposition of palladium-silver alloy coatings in most alkaline electrolytes has been well studied, no viable electrolytes have yet been developed, partly because the deposited palladium-silver alloy coatings do not meet the quality and composition requirements. The acidic electrolytes previously used, as described in the literature and patents, are mostly based on thiocyanate, sulfonate, sulfate, sulfamic acid, or nitrate electrolytes. However, many electrolytes still generally suffer from a lack of stability of the electrolyte system (Edelmetallschichten, H. Kaiser, 2002, p. 52, Eugen G. Leuze Verlag).

[0007] DE 10 2013 215 476 B3 describes the electrolytic deposition of alloys containing primarily silver. Additional alloying components are palladium, tellurium, or selenium. The alloy coatings described there exhibit aging effects, particularly at high temperatures, which lead to increased cracking.

[0008] It is therefore an object of the present invention to provide a novel and temperature-stable alloy coating which can be produced solely by electrolytic deposition and which is superior to corresponding alloys of the prior art. In particular, when producing the alloy coating according to the invention, it should have advantages over known alloy coatings which primarily contain silver and also include palladium and tellurium as components.

[0009] These and other tasks, which are obvious to a person skilled in the art based on the background art, are achieved by an alloy coating having the features of claims 1 and 7 and a corresponding method for its production. The dependent claims attached to these claims relate to preferred embodiments of the invention. Claim 11 relates to preferred uses.

[0010] The present object was surprisingly achieved by producing an electrolytically deposited silver-palladium alloy coating, which contains primarily silver and less than or equal to 20 at% tellurium, relative to the total alloy coating, and furthermore comprises one or more of the following metals: Ce, Dy, Pb, Bi, Al, Ga, Ge, Fe, In, Co, Ni, Cu, Sn, Sb, Rh, Ru, Ir, Pt, Au. This alloy coating has high corrosion resistance. Furthermore, it has improved temperature stability, and during the electrolytic deposition of the alloy according to the invention, even at high current densities, the corresponding electrolyte does not cause cracks (see Table 1).

[0011] Those skilled in the art are familiar with electrolytically deposited silver-palladium alloy coatings (AgPdTe alloys) that primarily contain silver and also include tellurium. However, electrolytically produced silver-palladium alloy coatings that primarily contain silver and have less than or equal to 20 at% tellurium, relative to the total alloy coating, and that additionally contain one or more of the following metals: Ce, Dy, Pb, Bi, Al, Ga, Ge, Fe, In, Co, Ni, Cu, Sn, Sb, Rh, Ru, Ir, Pt, Au, are novel to those skilled in the art. Preferably, such AgPdTe alloy coatings additionally include the metals Ce, Dy, Pb, Bi, In, Sn, and / or Fe. In this context, metals belonging to the group of Bi, Pb, and Ce are particularly preferred as the additional metal. Bi is very particularly preferred in this context.

[0012] In an advantageous embodiment, the additional metal or metals should be present in the AgPdTe alloy coating in an amount of less than or equal to 40 at%. Preferably, only one additional metal is present in this amount. A particularly preferred amount of the additional metal is 0.1 at% to 20 at%, more preferably 0.5 at% to 10 at%, and very particularly preferably 0.5 at% to 5 at%. In individual cases, smaller amounts of less than 2 at% may also be sufficient.

[0013] Silver is the main component of this electrolytically produced alloy. The alloy deposited according to the present invention has a composition comprising approximately 50 at% to 95 at% silver (preferably the sole remainder being palladium and tellurium and an additional metal). According to the present invention, the concentration of the metal to be deposited in the electrolyte is set within the framework given above so that the result is a silver-rich alloy. It should be noted that the silver concentration in the deposited alloy is influenced not only by the concentration of the metal to be deposited, but also by the current density used, the amount of sulfonic acid used, and the amount of tellurium compound added. However, those skilled in the art will know how to set the corresponding parameters to obtain the desired target alloy or will be able to determine this through routine experimentation. Preferred target alloys are those in which the silver concentration exceeds 60 at%, more preferably between 70 at% and 99 at%, further preferably between 75 at% and 97 at%, and most preferably between 85 at% and 95 at%.

[0014] The alloy coating according to the present invention preferably contains 0.1 to 30 at% palladium. However, sufficient palladium should be present to provide the desired corrosion resistance. Generally, alloy coatings with a palladium content of 1 to 20 at%, more preferably 2 to 15 at%, and optimally 3 to 12 at% are suitable.

[0015] A further component of the alloy according to the invention is tellurium, which is preferably present in the alloy in a concentration of 0.1 to 10 at%, preferably 1 to 5 at%, and very preferably 2 to 4 at%.

[0016] The alloy coating according to the invention outperforms known electrolytically deposited AgPdTe alloys in terms of wear resistance and hardness (measured according to DIN EN ISO 6507-1:2018). The alloy coating according to the claims has a hardness of >250 Hv, preferably >260 Hv, and very preferably >270 Hv, depending on the alloy composition.

[0017] In a further embodiment, the present invention relates to a method for the electrolytic deposition of a silver-palladium alloy coating containing mainly silver, the silver-palladium alloy layer containing less than or equal to 20 at % tellurium relative to the total alloy coating. The method is characterized by using an aqueous, acidic, cyanide-free electrolyte having the following composition:

[0018] a) a soluble silver salt, preferably a sulfonate,

[0019] b) a soluble palladium salt, preferably a sulfate,

[0020] c) soluble tellurium salts in which tellurium has the oxidation state +4 or +6,

[0021] d) a soluble salt, preferably a sulfonate, of one or more of the additional metals Ce, Dy, Pb, Bi, Al, Ga, Ge, Fe, In, Co, Ni, Cu, Sn, Sb, Rh, Ru, Ir, Pt, and Au;

[0022] e) at least one amino acid selected from the group consisting of:

[0023] Alanine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, lysine, leucine, methionine, phenylalanine, phenylglycine, proline, serine, tyrosine, valine.

[0024] The electrolyte used according to the present invention contains salts of silver, palladium, and tellurium, and one or more of the additional metals Ce, Dy, Pb, Bi, Al, Ga, Ge, Fe, In, Co, Ni, Cu, Sn, Sb, Rh, Ru, Ir, Pt, and Au, also in the form of salts. Preferred are salts of the additional metals Ce, Dy, Pb, Bi, In, Sn, and / or Fe. In this context, it is particularly preferred to use a metal belonging to the group consisting of Bi, Pb, and Ce as the additional metal. Bi is very particularly preferred in this context.

[0025] The electrolyte according to the present invention is used in an acidic pH range. The best results are obtained with a pH value in the electrolyte <2. Those skilled in the art will know how to set the pH value of the electrolyte. Preferably it is in the strongly acidic range, more preferably <1. It is most advantageous to choose very strongly acidic deposition conditions, where the pH value is less than 0.8, and it is possible to even reach 0.1 or even 0.01 in special cases. Ideally, the pH value will be around 0.6. It is possible that the pH value of the electrolyte fluctuates during the electrolysis. In a preferred embodiment of the present invention, those skilled in the art will therefore take the step of monitoring the pH value during the electrolysis and, if necessary, adjusting it to the set point value.

[0026] In principle, the pH value can be adjusted according to the knowledge of those skilled in the art. However, those skilled in the art will be guided by the concept of minimizing the introduction of additives into the electrolyte that could adversely affect the deposition of the alloy. Therefore, in a particularly preferred embodiment, the pH value is adjusted solely by adding sulfonic acid. The added free sulfonic acid is used in a sufficient concentration of 0.25 mol / l to 4.75 mol / l. This concentration is preferably 0.5 mol / l to 3 mol / l, and optimally 0.8 mol / l to 2.0 mol / l. The sulfonic acid primarily serves to establish a suitable pH value in the electrolyte. Secondly, its use further stabilizes the electrolyte according to the present invention. The upper limit of the sulfonic acid concentration is set because excessively high concentrations result in the deposition of only silver. In principle, any sulfonic acid known to those skilled in the art for use in electroplating technology can be used. The sulfonic acid is preferably selected from the group consisting of ethanesulfonic acid, propanesulfonic acid, benzenesulfonic acid, and methanesulfonic acid. Propanesulfonic acid and methanesulfonic acid are particularly preferred in this context. Methanesulfonic acid is particularly preferred.

[0027] The electrolyte used in the method according to the present invention has a specific electrolyte density, which can be determined by one skilled in the art. It is preferably between 1.0 and 1.5 at 23°C. Densities of 1.0 to 1.3, and optimally 1.0 to 1.2, are particularly preferred. Density is determined gravimetrically.

[0028] The temperatures generally used during the deposition of the alloy according to the invention can be selected by a person skilled in the art as needed. This person will be guided, on the one hand, by suitable deposition rates and applicable current density ranges, and, on the other hand, by the cost and stability of the electrolyte. It is advantageous to set a temperature in the electrolyte of 30°C to 90°C. Using an electrolyte at temperatures of 45°C to 75°C, very preferably 50°C to 70°C, and optimally >60°C, is particularly preferred.

[0029] The current density established in the electrolyte between the cathode and the anode during the deposition process can be selected by a person skilled in the art according to the deposition efficiency and quality. Depending on the application and the type of coating equipment, the current density in the electrolyte is advantageously set to 0.1 A / dm 2 Up to 100A / dm 2 If necessary, the current density can be increased or decreased by adjusting system parameters such as coating cell design, flow rate, anode or cathode settings, etc. 0.25A / dm 2 Up to 50A / dm 2 , preferably 0.5A / dm 2 Up to 20A / dm 2, and more preferably 1A / dm 2 Up to 15A / dm 2 The current density is favorable. Optimally, the current density is 2A / dm 2 Up to 12A / dm 2 .

[0030] Those skilled in the art will be generally familiar with metal compounds that can be added to the electrolyte. Preferably, a silver salt that is soluble in the electrolyte can be used as the silver compound to be added to the electrolyte. Particularly preferred salts are selected from the group consisting of: silver methanesulfonate, silver carbonate, silver sulfate, silver phosphate, silver pyrophosphate, silver nitrate, silver oxide, and silver lactate. In this context, those skilled in the art should also be guided by the principle of minimizing the addition of additives to the electrolyte. Therefore, those skilled in the art will preferably select a sulfonate, more preferably a methanesulfonate, as the silver salt to be added. Regarding the concentration of the silver compound to be used, those skilled in the art should be guided by the limits given above for the alloy composition. Preferably, the silver compound will be present in the electrolyte at a concentration of 0.01 mol / l to 2.5 mol / l, more preferably 0.02 mol / l to 1 mol / l of silver, and most preferably between 0.05 mol / l and 0.2 mol / l of silver.

[0031] The palladium compound to be used is preferably also a salt or a soluble complex that is soluble in the electrolyte. The palladium compound used here is preferably selected from the group consisting of palladium hydroxide, palladium chloride, palladium sulfate, palladium pyrophosphate, palladium nitrate, palladium phosphate, palladium bromide, palladium P salts (diamminedinitrito palladium(II) ammonia solution), palladium glycinate, palladium acetate, palladium EDA complex, and tetraammine palladium bicarbonate. The palladium compound is added to the electrolyte at a concentration that allows sufficient deposition in the alloy coating. The palladium compound is preferably used in the electrolyte at a concentration of 0.001 mol / l to 0.75 mol / l palladium, very preferably at a concentration of 0.01 mol / l to 0.2 mol / l palladium.

[0032] The tellurium compound used in the electrolyte can be appropriately selected by a person skilled in the art within the desired concentration framework. A concentration between 0.05 mmol / l and 80 mmol / l tellurium, and particularly preferably between 0.5 mmol / l and 40 mmol / l tellurium, can be selected as a preferred concentration range. Compounds containing tellurium in the +4 and +6 oxidation states of the element can be considered as compounds that can provide the electrolyte. Compounds in which such elements have the +4 oxidation state are particularly preferred. Particularly preferred in this context are compounds selected from the group consisting of tellurites, tellurous acid, and telluric acid. It is most preferred that the tellurium be added to the electrolyte in the form of a salt of tellurous acid.

[0033] Amino acids are used as complexing agents in the present electrolyte. It is preferred that the amino acids used herein have only alkyl groups in the variable residues. More preferably, amino acids such as alanine, glycine, and valine are used. The use of glycine and / or alanine is optimal. Within the concentration framework given above, those skilled in the art are free to choose the optimal concentration of the amino acid used. The person of ordinary skill will use the following reality as a guideline: if the amount of amino acid is too low, it will not produce the desired stabilizing effect, while too high a concentration may inhibit the deposition of palladium and other alloying metals. Therefore, it has been shown to be particularly advantageous if palladium is added directly to the electrolyte as the corresponding palladium amino acid complex.

[0034] A variety of anodes can be employed with this electrolyte. Soluble or insoluble anodes, as well as combinations of soluble and insoluble anodes, are equally suitable. If a soluble anode is used, a silver anode is particularly preferred.

[0035] Preferred insoluble anodes are made from a material selected from the group consisting of platinized titanium, graphite, iridium transition metal mixed oxides, and special carbon materials (DLC or diamond-like carbon), or combinations thereof. Platinized titanium or iridium tantalum mixed oxides are particularly preferred for practicing the present invention. For more information, see Cobley, AJ et al. (The use of insoluble anodes in acid sulphate copper electrolytic deposition solutions, Trans IMF, 2001, 79(3), pp. 113 and 114).

[0036] In the electrolyte according to the present invention, depending on the application, anionic and nonionic surfactants can generally be used as wetting agents, such as, for example, polyethylene glycol adducts, fatty alcohol sulfates, alkyl sulfates, alkyl sulfonates, aryl sulfonates, alkylaryl sulfonates, heteroaryl sulfates, betaines, fluorosurfactants, and their salts and derivatives (see: Kanani, N: Galvanotechnik; Hanser Verlag, Munich Vienna, 2000; pp. 84ff). The use of methanesulfonates, especially potassium salts, is preferred.

[0037] In a further embodiment, the present invention relates to the use of the alloy coating according to the invention as an end coating or as an intermediate coating in an electrical contact material to increase the corrosion resistance of such a contact material. Preferred embodiments of the alloy coating are also suitable for its use.

[0038] By adding certain additional metals (such as Bi, Pb, Ce, or In) to AgPdTe alloys, discernible advantages can be obtained in electrolytic deposition. The operating range of the electrolyte is significantly increased. Crack-free deposits can be deposited at significantly higher current densities and significantly higher coating thicknesses under the same deposition conditions. At the same time, the alloy compositions of these coatings are stable over a large operating range, which is of course a significant advantage for high-speed deposition. The alloy itself is significantly harder and is therefore destined for use as a contact material. This would not have been obvious to one skilled in the art at the priority date.

[0039] Example:

[0040] Deposition conditions, beaker test, aqueous electrolyte according to DE 10 2013 215 476 B3:

[0041] 100ml / l methanesulfonic acid 70%

[0042] 2g / l amino acids

[0043] 20 g / l silver (as soluble silver salt)

[0044] 12 g / l palladium (as a soluble palladium salt)

[0045] 500 mg / l tellurium (as tellurite)

[0046] 30g / l methanesulfonate

[0047] 65℃ / 300rpm 6cm / PtTi anode

[0048] Deposition conditions, beaker test, electrolyte according to the invention:

[0049] 100ml / l methanesulfonic acid 70%

[0050] 2g / l amino acids

[0051] 20 g / l silver (as soluble silver salt)

[0052] 12 g / l palladium (as a soluble palladium salt)

[0053] 300 mg / l alloying metals (cerium, bismuth, lead, indium) (as soluble salts)

[0054] 500 mg / l tellurium (as tellurite)

[0055] 30g / l methanesulfonate

[0056] Both electrolytes with a pH <1 were initially charged at 65°C. The stirring rate was 300 rpm using a 6 cm magnetic stirrer and a product movement rate of 6 cm / s. These experiments were performed in a beaker at a 1 liter scale. A PtTi anode was used. The substrate used was a Cu substrate pre-coated with Ni and gold. The electrolyte density was 1.1 g / cm 3 (23° C.) It was electrolyzed at various current densities (see Table 1).

[0057] Deposition results:

[0058] electrolytes <![CDATA[i[A / dm 2 ]]]> [%]Ag [%]Pd [%]Te [%]Bi AZ crack R 180℃120min old 1 87 9.5 3.5 X No cracks crack old 4 92.5 4.5 3.0 X No cracks crack old 6 93.5 4.0 2.5 X crack crack New 1 92.6 4.1 2.4 0.9 No cracks No cracks New 4 91.9 3.7 3.1 1.3 No cracks No cracks New 6 91.2 4.6 3.0 1.1 No cracks No cracks

[0059] Table 1: Comparison of old and new electrolytes at different current densities in terms of cracks and alloy composition .

[0060] By adding salts of, for example, Bi, Ce, Pb, or In to the electrolyte for depositing AgPdTe alloys containing primarily silver, the operating range of the electrolyte is significantly increased. Crack-free deposits can be deposited at significantly higher current densities and significantly higher coating thicknesses under the same deposition conditions. At the same time, the alloy compositions of these coatings are stable over a large operating range, a significant advantage for high-speed deposition. In addition, the alloys according to the present invention exhibit improved wear resistance and hardness properties. When adding, for example, 1.5 at% Bi, the hardness increases from 250 Hv to 300 Hv.

Claims

1. An electrolytically deposited silver-palladium alloy coating containing mainly silver, which contains less than or equal to 20 at% tellurium relative to the entire alloy coating, It is characterized by It additionally contains metallic Bi in an amount of 0.5 at % to less than 2 at %.

2. The alloy coating according to claim 1, in Silver is contained in the alloy coating in an amount greater than 60 at %.

3. The alloy coating according to claim 1 or 2, in Palladium is present in the alloy coating in an amount of 0.1 at % to 30 at %.

4. The alloy coating according to claim 1 or 2, in Tellurium is present in the alloy coating in an amount of 0.1 at % to 10 at %.

5. The alloy coating according to claim 1 or 2, in The alloy coating has a hardness of >250 Hv.

6. A method for the electrolytic deposition of a silver-palladium alloy coating containing mainly silver and having less than or equal to 20 at% of tellurium relative to the total alloy coating, It is characterized by Use an aqueous, acidic, cyanide-free electrolyte with the following composition: a) Soluble silver salts b) a soluble palladium salt, c) soluble tellurium salts, in which tellurium has an oxidation state of +4 or +6, d) a soluble salt of metallic Bi in an amount of 0.5 at% to less than 2 at% e) 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, valine.

7. The method according to claim 6, in During electrowinning, the pH of the electrolyte is below 2.

8. The method according to claim 6 or 7, in The electrolyte density at 23°C is between 1.0 and 1.

5.

9. The method according to claim 6 or 7, in The current density during electrolytic deposition was between 0.1 A / dm 2 and 100A / dm 2 Between, depends on the coating method and equipment technology.

10. The method according to claim 6 or 7, in The electrolytic deposition is carried out at a temperature of 30°C to 90°C.

11. Use of the alloy coating according to any one of claims 1 to 5 in an electrical contact material, the alloy coating being used as an end coating or as an intermediate coating to increase the corrosion resistance of such contact material.