SILVER ELECTROLYTE FOR DEPOSITING DISPERSION SILVER LAYERS AND CONTACT SURFACES WITH DISPERSION SILVER LAYERS

Abstract

The invention relates to a silver electrolyte for the deposition of silver layers on substrates, which comprises potassium silver cyanide, potassium cyanide with a content of at least 10 g/L, at least one grain refiner with a content of 0.2 to 10 g/L, at least one dispersant with a content of 1 to 10 g/L and at least one solid component with a content of 1 to 150 g/L, wherein the particles of the solid component have an average particle size (d.sub.50) of 10 nm-100 μm. Furthermore, contact surfaces and methods for the deposition of such contact surfaces are shown and the use of the electrolyte according to the invention in strip electroplating.

Claims

1. Silver electrolyte for the deposition of silver layers on substrates comprising a) Potassium silver cyanide with a content of at least 50 g/L, b) Potassium cyanide with a content of at least 100 g/L, c) at least one grain refiner with a content of 0.2 to 10 g/L d) at least one dispersant with a content of 1 to 10 g/L and e) at least one solid component with a content of 1 to 150 g/L, wherein the particles of the solid component have an average particle size (d.sub.50) of 10 nm-100 μm; and wherein the at least one grain refiner is selected from naphthalene sulphonic acid, naphthalene sulphonic acid derivatives or mixtures thereof.

2. (canceled)

3. Silver electrolyte according to any claim 1, wherein said at least one dispersant comprises alkyl sulfates having C.sub.1-C.sub.20 alkyl groups which may be unsubstituted or optionally substituted.

4. Silver electrolyte according to claim 1, wherein the particles of the at least one solid component have an average particle size (d.sub.50) of 1 μm to 20 μm.

5. Silver electrolyte according to claim 1, wherein the at least one solid component is selected a. from the group consisting of graphite, graphite fluoride, graphite oxide, diamond, Al.sub.2O.sub.3 coated graphite or mixtures thereof, preferably graphite, graphite fluoride, graphite oxide, Al.sub.2O.sub.3 coated graphite or mixtures thereof, more preferably graphite, graphite oxide or mixtures thereof and even more preferably graphite; or b. from the group consisting of MoS.sub.2, WS.sub.2, SnS.sub.2, NbS.sub.2, TaS.sub.2, hexagonal boron nitride, silver niobium selenide, TiN, Si.sub.3N.sub.4, TiB.sub.2, WC, TaC, B.sub.4C, Al.sub.2O.sub.3, ZrO.sub.2, cubic BN, MoSe.sub.2, WSe.sub.2, TaSe.sub.2, NbSe.sub.2, SiC, Al.sub.2O.sub.3 coated MoS.sub.2 and Al.sub.2O.sub.3 coated WS.sub.2 or mixtures thereof, preferably MoS.sub.2, WS.sub.2, hexagonal boron nitride or mixtures thereof and more preferably MoS.sub.2, WS.sub.2 or mixtures thereof or c. from the group consisting of MoS.sub.2, WS.sub.2, SnS.sub.2, NbS.sub.2, TaS.sub.2, hexagonal boron nitride, silver niobium selenide, TiN, Si.sub.3N.sub.4, TiB.sub.2, WC, TaC, B.sub.4C, Al.sub.2O.sub.3, ZrO.sub.2, cubic BN, MoSe.sub.2, WSe.sub.2, TaSe.sub.2, NbSe.sub.2, SiC, Al.sub.2O.sub.3 coated MoS.sub.2 and Al.sub.2O.sub.3 coated WS.sub.2 or mixtures thereof, preferably MoS.sub.2, WS.sub.2, hexagonal boron nitride or mixtures thereof and more preferably MoS.sub.2, WS.sub.2 or mixtures thereof.

6. Method of depositing a dispersion silver layer on a substrate comprising the steps a) providing of a silver electrolyte according to claim 1, b) introducing a substrate into the silver electrolyte, and c) performing the deposit.

7. Method according to claim 6, wherein the temperature in step c) is 15° C. to 30° C.

8. Method according to claim 6, wherein the current density in step c) is from 2.0 A/dm.sup.2 to 25.0 A/dm.sup.2 and preferably 2.5 A/dm.sup.2 to 20.0 A/dm.sup.2

9. Method according to claim 6, wherein the process is a strip electroplating.

10. Contact surface, wherein an electrochemically deposited dispersion silver layer is arranged on a substrate, wherein the dispersion silver layer comprises particles of at least one finely dispersed solid component with an average particle size (d.sub.50) of 10 nm-100 μm; wherein the dispersion silver layer comprises the at least one finely dispersed solid component in a quantity in the range from 0.5 to 10% by weight, based on the total weight of the dispersion silver layer; and wherein the contact surface has a micro-roughness, described by the average roughness Ra, in the range of 0.05 μm to 20 μm.

11. Contact surface according to claim 10, wherein the at least one finely dispersed solid component is selected a. from the group consisting of MoS.sub.2, WS.sub.2, SnS.sub.2, NbS.sub.2, TaS.sub.2, hexagonal boron nitride, silver niobium selenide, TiN, Si.sub.3N.sub.4, TiB.sub.2, WC, TaC, B.sub.4C, Al.sub.2O.sub.3, ZrO.sub.2, cubic BN, MoSe.sub.2, WSe.sub.2, TaSe.sub.2, NbSe.sub.2, SiC, Al.sub.2O.sub.3 coated MoS.sub.2 and Al.sub.2O.sub.3 coated WS.sub.2 or mixtures thereof, preferably of MoS.sub.2, WS.sub.2, hexagonal boron nitride or mixtures thereof and more preferably of MoS.sub.2, WS.sub.2 or mixtures thereof or b. from the group consisting of graphite, graphite fluoride, graphite oxide, diamond, Al.sub.2O.sub.3 coated graphite or mixtures thereof, preferably graphite, graphite fluoride, graphite oxide, Al.sub.2O.sub.3 coated graphite or mixtures thereof, more preferably graphite, graphite oxide or mixtures thereof and even more preferably graphite; or c. from the group consisting of MoS.sub.2, WS.sub.2, SnS.sub.2, graphite, graphite oxide, graphite fluoride, hexagonal boron nitride, silver niobium selenide, SiC, Al.sub.2O.sub.3 coated graphite, Al.sub.2O.sub.3 coated MoS.sub.2 and Al.sub.2O.sub.3 coated WS.sub.2 or mixtures thereof, preferably of MoS.sub.2, WS.sub.2, graphite and hexagonal boron nitride or mixtures thereof.

12. Contact surface according to claim 10, wherein the dispersion silver layer comprises the at least one finely dispersed solid component in a quantity in the range from 1.0 to 10% by weight and preferably from 3.1% by weight to 10% by weight, based on the total weight of the dispersion silver layer.

13. Use of the contact surface according to claim 10 for electrical contacts in plug connections.

14. Use of a dispersion silver electrolyte according to claim 1 for coating a substrate by strip application.

Description

EMBODIMENTS

Materials

[0103] For the tests, copper sheets (material: CuFe2P) from Wieland-Werke AG were used. The average roughness Ra of the uncoated sheets is 0.47 μm.

[0104] KCN was purchased from Bücherl and K[Ag(CN).sub.2] was purchased from Umicore.

[0105] SLOTOSIL SG 1911 and SLOTOSIL SG 1912 are additives for silver electrolytes based on KCN/potassium silver cyanide for the dispersion separation of the company Dr.-Ing. Max Schlötter GmbH & Co. KG. SLOTOSIL SG 1911 comprises a naphthalene sulphonic acid derivative as grain refining additive. SLOTOSIL SG 1912 comprises an alkyl sulfate as dispersion stabilizing additive.

[0106] CUPRUM 11, a brightener, CUPRUM 12, a wetting agent, and the anti-tarnish concentrate AG 111 were purchased by Dr.-Ing.Max Schlötter GmbH & Co KG.

[0107] The graphite particles used come from Graphit Kropfmühl AG. The graphite powder used of the UF2 grade has a mean particle size of d.sub.50=4.5 μm

Measurement Methods

[0108] Determination of Solid Content

[0109] The solid content (in weight %) was determined by energy dispersive X-ray spectroscopy (EDX). For this purpose, measurements on the deposited thin films were carried out with an X-Flash Detector 410-M (Bruker AXS Microanalysis GmbH), which was mounted in a JSM-6610 LV electron microscope (manufacturer: JEOL) with an excitation voltage of 25 kV. The measurements were evaluated with the program Esprit (Bruker).

[0110] Determination of the Diameter of the Solid Components (d.sub.50)

[0111] The diameters of the particles of the solid components in the form of the average particle size d.sub.50 were determined by laser diffraction with a Helos instrument from Sympatec.

[0112] Measurement of Micro Roughness (as Centre Roughness Ra)

[0113] The microroughness (as mean roughness Ra) was determined by means of an optical measuring method with a VKX100 confocal 3D laser scanning microscope (manufacturer: Keyence Corporation) and subsequent evaluation with the Multi file analyzer program (Keyence Corporation).

Coating Copper Sheets

[0114] Electroplating

[0115] Samples were coated with dispersion silver layers to obtain contact surfaces. The copper sheets were first copper-plated, then pre-silvered and finally coated with a dispersion silver layer.

[0116] Between each step was rinsed thoroughly with water.

[0117] The galvanisation of the copper sheets included the following steps: [0118] 1. and 2. step: degreasing of the substrates according to known methods; first alkaline degreasing step at 60° C. for 1 min with ultrasonic support. Second alkaline electrolytic degreasing step at room temperature (25° C.) for a treatment time of 2 to 3 min. [0119] 3. step: Etching of copper with bath of sulphuric acid, complexing agent-free copper activation. The activation is applied at room temperature (25° C.) for 0.5 min. [0120] 4. step: Treatment with bright copper bath, which was a cyanide electrolyte to deposit bright surfaces. The electrolyte, consisting of 10 g/l KOH, 115 g/l KCN, 64 g/l CuCN and 1.5 ml/l brightener CUPRUM 11; 2.5 ml/l base additive CUPRUM 12 was operated at 60° C. The electrolyte was used with 2 A/dm.sup.2. [0121] 5. step: The pre-silvering was carried out in a pre-silvering bath with a cyanide electrolyte with low silver content (120 g/l KCN; 3.7 g/l K[Ag(CN).sub.2]). The pre-silver plating was operated at room temperature (25° C.). As cathodic current density 2 A/dm.sup.2 was chosen. [0122] 6. step: Deposition of the dispersion silver layers

[0123] The sheets pre-treated according to the procedure described above were mounted on A rotary cell for coating.

[0124] The electrolyte had the following composition: [0125] KCN: 154 g/L [0126] K[Ag(CN).sub.2]: 56 g/L [0127] SLOTOSIL SG 1911: 20 mL/L [0128] SLOTOSIL SG 1912: 20 mL/L [0129] Graphite UF2: 70 g/L

[0130] The sheets were coated at different rotation speeds to simulate a belt speed of 30 m/min, 60 m/min and 100 m/min. The deposition was performed at a current density of 2.5 A/dm.sup.2 5 A/dm.sup.2, 10 A/dm.sup.2, 15 A/dm.sup.2 and 20 A/dm.sup.2 respectively. Detailed information on the individual tests is listed in Table 1. [0131] 7. step: Antitarnish aftertreatment; The antitarnish, 160 ml/l Antitarnish Concentrate [0132] AG 111, was applied at 50° C. and pH 5.3. The coated test specimens were immersed in the anti-tarnish for 2 min. Afterwards they were rinsed with deionised water and dried.

[0133] Table 1 shows the results of the characterisation of the deposited dispersion silver layers. The graphite contents of the graphite-containing silver layers were determined by EDX.

TABLE-US-00001 TABLE 1 Results strip electroplating Duration average Speed Current of Electrolyte Graphite rough- (m/ density coating temperature content ness Examples min) (A/dm.sup.2) (min) (° C.) EDX Ra (μm) 1 100 2.5 8 21 1.76 1.38 2 60 2.5 8 21 3.13 2.26 3 30 2.5 8 21 4.98 2.51 4 100 5 4 21 1.69 1.09 5 60 5 4 22 3.73 2.95 6 30 5 4 22 6.39 2.43 7 100 10 2 22 1.33 1.00 8 60 10 2 22 6.45 3.66 9 30 10 2 22 8.32 4.39 10 100 15 1.5 22 2.23 1.08 11 60 15 1.5 22 6.36 4.90 12 30 15 1.5 22 8.69 6.33 13 100 20 1 23 2.05 1.00 14 60 20 1 23 7.54 4.85 15 30 20 1 23 7.63 16.03

[0134] The results presented in Table 1 show the electrolyte according to the invention is suitable for the deposition of dispersion silver layers. In comparison, electrolytes known from the state of the, which are used for the production of dispersion silver layers, the achievable particle contents are much higher, which is a significant improvement.

[0135] In contrast to known electrolytes used for the production of dispersion silver layers, the electrolyte according to the invention is especially suitable for the deposition of dispersion silver layers by means of the reel-to-reel process.

[0136] By incorporating solid components, especially a dry lubricant into the dispersion silver layer, dispersion silver layers are obtained with considerably better sliding properties compared to pure silver layers especially at high concentrations solid components. A high concentration of solid particles in the layer is especially advantageous for wear caused by micro-vibrations (fretting). In the case of small contact points, high solid particle concentrations increase the probability that a sufficient amount of solid particles is present in the contact area to reduce wear. This property is particularly important for contact surfaces of connectors and, as the examples show, is achieved with the method according to the invention.