IE44205B1 - Process for the selective electrodepostion of metal - Google Patents

Abstract

In this method the solutions are applied to the surface to be treated in the form of a free jet which is preferably built up between a nozzle (1) and the surface (3) to be treated which takes the form of a target plate. This procedure makes possible the partial electroplating of surfaces without using masks.

Description

This invention relates to a process for the selective electrodeposition of metals onto conductive surfaces, or surfaces rendered conductive from electrolyte solutions and to an apparatus for carrying out the process.

Selective electrodeposition processes, also known as partial electroplating, have already been proposed. Such processes have hitherto been based on one or other of two basic principles.

On the one hand, avoiding bath containers, the parts to be electroplated are brought in contact with the electrolyte only at desired places, which is achieved, for example, by using rollers (German Patent Specification 186,654), wheels (German Patent Specification 2,324,834) or open hollow bodies (German Patent Specification 1,807,481). According to another principle of operation the conventional containers are used, but the supply of metal ions and the electrical field distribution on the surfaces to be treated is influenced by the interposition, for example, of screens (German Patent Specification, 2,263,642), covering devices (German Patent Specification 2,362,489), electrically insulated bands running on rollers (German Patent Specification 2,009,118), cages (German Patent Specification 2,230,891) or lacquer coatings (German Patent Specification 2,253,196).

However, such previously proposed processes are disadvantageous in that they either generally provide only an insufficient supply 44203 of metal ions, which leads to inadequate metal coating, or are extravagent in material, cost and time, since the coverings used must in each case first be applied and then removed or renewed owing to wear phenomena.

It is accordingly an object of the present invention to provide a process and an apparatus which, while avoiding the disadvantages of the previously proposed processes, enable surfaces to be partially electroplated with an optimum supply of metal ions and without the use or interposed coverings. ϊθ The present invention provides a process for the selective electrodeposition of metal onto a conductive surface or a surface that has been rendered conductive, from an electrolyte solution, which comprises applying the solution to a part of the surface to be treated in the form of a free jet emitted from a nozzle, and establishing a potential difference between the electrolyte and the surface.

It will be understood that the term free jet as used herein means a jet of liquid issuing from a suitable nozzle in such a manner that the jet is surrounded by gas over at least part O A of its travel from the nozzle to the surface to be electroplated. Although the form of the jet can be influenced in various ways (for example, by means of lowing gases or liquids, electric or magnetic fields, or guide members), it is a primary characteristic of a free jet that its form is not determined ? ζ wholly by any fixed boundary. 3. 4 8 0 5 Advantageously, the process of the invention is operated with one or more of the following variants:a. the free jet is built up dynamically between a nozzle and the surface to be treated which acts as a baffle plate; b. the potential difference is established by connecting the nozzle or a part of the nozzle or electrolyte supply means as the anode. c. a nozzle having a variable shape or diameter is used; d. relative pivotal movement of the nozzle and the surface that is to be electroplated, that is to say, the nozzle and/or the surface to be electroplated perform pivoting movements; e. the free jet is shaped with regard to direction and cross-section partly by a guide member, a flowing gas, or liquid and/or by an electric and/or magnetic field; f. the free jet is surrounded by a tubular jacket; g. the solutions on the surfaces to be electroplated are removed during the treatment by suction, especially with the use of a tubular suction jacket; h. the quantity of solution on the surface to be electroplated is continuously varied; i. the electrical current density at the cathode is varied; j. electrolyte solutions having different compositions are used in continuous or discontinuous alternation; and k a plurality of surfaces, especially of one workpiece, are treated simultaneously. 4. 3 0 s The or each electrolyte solution may be one known per se.

The process may be used to deposit a metal or a metal alloy, advantageously gold, silver, platinum, ruthenium, rhodium, palladium, osmium or iridium or an alloy thereof, more especially gold or silver or an alloy thereof.

The invention is illustrated by the following Examples: EXAMPLE 1.

Gold-plating of contact combs.

The base material of the contacts is in almost all cases an alloy 0 in which copper is the main component. For a contact capable of functioning for a long time a sufficiently thick diffusion barrier of nickel must be built up to prevent known copper/gold diffusion mechanisms.

The apparatus described below enables the deposition of both the 5 nickel and gold layers and the preliminary gold-plating to be carried out without the need for a transport path.

The composition of an electrolyte and its operating conditions are, for example, as follows: Nickel sulphate, NiSO^-SHgO 300 grams per litre 20 Nickel chloride, NiCl2-6H20 45 grams per litre Boric acid, H3B03 40 grams pet litre Sodium lauryl sulpho-acetate 2 grams per litre pH value 4.0 Temperature 65°C.25 Cathodic current density 20 to 50 A/dm2.

, The duration of exposure for Ipm thickness is 10 seconds.

The nozzle is positioned at an angle of 90°to the part in order to nicket-plate as large a surface as possible. Pressure head of approximately 30 cm water column. The deposited nickel coatings have a silk mat finish. Their structure is of prismatic 2 form. The Vickers hardness of the coatings is 200 + 20 kp/mm .

After having been rinsed, the contacts undergo preliminary goldplating as a result of which an extremely good adhesion is obtai ned.

The electrolyte composition and the operating conditions for three different preliminary gold-plating processes according to the invention are described under (a), (b) and (c). (a) Gold as K Au (CN)2 Sodium citrate Tetraethylene pentamine Cobalt as the complex with the dispotassium salt of ethylene diamine tetracetic acid pH value Temperature Current density Duration of exposure Nozzle position 0.5 grams per litre 60 grams per litre 10 grams per litre. gram per litre. 3.8 to 25°C> to 10 A/dm2 seconds angle of 90° 4 2 0 5 (b) Gold as K Au (CN)2 Ammonium sulphate, (nh4)2so4 Boric acid, HgBOg Ethylene glycol, (H0-CH2-CH2-0H) Cadmium sulphate, CdS04.8/3H20 The dipotassium salt of ethylene diamine tetracetic acid Formaldehyde,(CHgO) Hydrazine sulphate, (n2h4.h2so4) Sodium arsenite, NagAsOg pH value Temperature Current density Duration of exposure for 1pm thickness is Nozzle position at an angle of 130°. 8.0 gram per litre. 30.0 grams per 1itre 60.0 grams per 1 itre 60.0 grams per 1 itre 3.5 grams per 1 itre 4.0 grams per 1 i tre .0 grams per litre. .0 grams per litre. 6.5 grams per litre. S.O 60°C. to 60 A/dm2 2 seconds.

The coatings are approximately 23.8 carat. The coatings deposited from the electrolyte have a high lustre and are tarnish-resistant. The distribution of layer thickness on the contact decreases upwards, and at the tip of the contact it is reduced to half the maximum layer thickness. On the sides of the contact, which do not serve as contact surfaces, there is 1/3 of the layer thickenss when using nozzles 0.5 mm in diameter, whereas 1/2 the layer thickness is deposited when using nozzles 1 mm in diameter. 7, 4420 5 (c) Gold as K Au (CN)2 Potassium dihydrogen citrate Cobalt as a chelate complex Wetting agent pH value Temperature Current density grams per litre. 150 grams per litre. 1.5 grams per litre 2.0 grams per litre 4.0 °C. to 100 A/dm2.= The duration of exposure for 1pm thickness is 1 to 10 seconds. Nozzle position at an angle of 110 to 130°to the part.

The coatings have very good electrical properties and are distinguished by an outstanding abrasion resistance resulting from the incorporation of 0.3 to 0.5% of Co. The distribution of layer thickness is just as good as in the preceding illustration.

EXAMPLE 2 Silver-plating of contact combs.

Instead of being gold- plated, the contacts may be silver-plated by either of the two processes (a) or (b). (a) Silver as silver thiosulphate Na3Ag (S203)2 Sodium thiosulphate Na2S2035 H20 Borax, Na2B^Oy 10 H.,0 Polyethylene imine, MW 500-1000 Sodium sulphite, Na2S03 grams 120 grams 10 grams per litre. per litre, per litre. 0,2 grams per litre grams per litre. 4 2 0 5 pH value Temperature Current density Deposition speed 1 pm in 1.5 to 2 seconds (b) Silver as potassium silver cyanide K Ag (CN)2 Potassium cyanide, KCN Antimony trichloride as a triethanolamine complex Wetting agent pH value Temperature Current density Deposition speed 1 pm in 5 seconds. 8.8 28°C. to 40 A/dm2. grams per litre. 120 grams per litre. grams per litre. 0.8 grams per 1itre. > 12 25°C to 30 A/dm2.

Since the abrasion resistance of the hard silver coatings is less than that of the gold-platings, it is necessary to silver-plate the contacts as uniformly as possible on the sliding zones of the plug connnectors. This is achieved by using as large a nozzle diameter as possible, say 1 to 2 mm, and by directing the jet of electrolyte vertically onto the part.

EXAMPLE 3.

Selective and unilateral gold-plating of meter frames.

The composition and working conditions of the electrolyte are 25 as follows:3. 4 2 0 5 Gold as K Au (CN)2 Potassium pyrophosphate, K4P207 to 16 grams per litre. grams per litre.

Potassium dihydrogen phosphate, KH2P04 pH value Temperature grams per litre. .5 70°C.

The deposition speed for 1 pm is 15 seconds at 10 A/dm .

The free jet is in this case surrounded by a jacket tube and removed from the surfaces to be electroplated by suction with the use of the jacket tube. By this process, layers of large or small thickness may be applied by the controlled distribution of metal.

The process of the invention may be used for the selective electrodeposition of metals or alloys thereof onto conductive surfaces, or surfaces rendered conductive, from electrolyte solutions that are known per se.

The conductive surface is preferably electron-conductive but an ion-conductive surface may also be partially electroplated by the process of the invention and the surface may accordingly be, for example, that of a metal a metal oxide and/or metal sulphide Instead, of being naturally conductive, the surface may be one which has been rendered conductive, for example, one made conductive by the application of a thin layer of metal, metal . 4 2 0 5 oxide and/or metal sulphide.

Several forms of apparatus suitable for carrying out the process of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of one form of apparatus; Figures 2 and 3 are similar views, partly in section, of two different forms of apparatus; and Figure 4 shows (upper drawing) a part-diagrammatic vertical section of a further form of apparatus and (lower drawing) a side elevation of the same apparatus viewed from the right of the upper drawing.

Referring to the drawings, Figure 1 shows a fundamental arrangement for carrying out the process of the invention.

The free jet is formed between the nozzle (1), which is disposed on a tube (2) for supplying the electrolyte and a work-piece (3) which acts as a baffle plate, In the arrangement of Figure 1, the electroplated area is of indeterminate size because of the electrolyte flowing away. A defined surface shape may be obtained by removing the electrolyte by suction from the surface of the workpiece, especially by means of a tubular jacket. Figure 2 and Figure 3 show two basic embodiments including such suction arrangements, in each of which 11. 4 2 0 5 a free jet of electrolyte is directed from below against the work-piece. A tubular jacket (4) surrounds the nozzle (1) so as to be concentric therewith and terminates in a suction connector (5) .

In the apparatus shown in Figure, 2 the upper edge of the jacket and the work-piece (3) define an annular gap (6). When air is sucked out through the connector (5) the air flowing in through the gap (6) limits the area wetted by the electrolyte. A similar effect can be produced if, as shown in Figure 3, the tubular jacket is provided with a sealing ring (7) and pressed against the work-piece.

In this way the jacket tube is sealed off at this position from the atmosphere and, in operation, the partial vacuum created in the jacket tube causes the electrolyte to flow back.

In the apparatus shown in Figure 4 there is a supporting device for the work-piece. The apparatus can be used, for instance, in partial electroplating of pin combs, by selective deposition on the pins e.g., gold-plating at the lower end on two opposing sides in a certain region to improve the contact properties.

Referring to Figure 4, a work-piece (8) is disposed in a supporting device (9) which consists of a holding plate (10) and a cover (11) The supporting device is adjustably connected to a cross-piece (12) made of insulating material which is itself adjustably connected to two supports (13). The supports stand on a base plate (14).

Supply tubes (2) having nozzles (1) are located in pivotable holding devices (15) mounted in journals (15) having a common centre line which passes through the pins at the level of the surfaces to be 1? electroplated, so that the free jet is always incident substantially at the same place on the pins even when the nozzles are pivoted.

A predetermined shape of the area to be electroplated can be 5 obtained by adopting one or more of the following measures: a. variation of the shape or diameter of the nozzle and thus the cross-sectional shape of the free jet and of the size of the area to be electroplated: b. relative pivotal movement between the nozzle and the 10 surfaces to be electroplated; c. shaping the free jet with regard to direction and crosssection by means of conductive bodies and/or flowing gases, liquids, electric and/or magnetic fields; d. centering the conductive jet by means of a tubular jacket; e. removing the electrolyte solution by suction from the surface, especially with the use of a tubular section jacket tube; f. relative translational motion between the nozzle and the work-piece. Further, the thickness profile of the deposited 2° metal layer(s) can be influenced by controlling the electrolyte supply as follows: g. production of jet having a flow profile that does not vary with time in accordance with measures (a) to (f); h. continuous variation of the quantity of solution on the 25 surfaces to be electroplated; i. variation of the electrical current density at the cathode. 13. 4420 5 The sequence of layers may be varied, if desired, by using solutions of different composition in continuous or discontinuous alternation.

In addition, several different areas, especially on one work-piece, may be treated simultaneously, and optionally also in different manners, when more than one nozzle is installed and used in accordance with the invention.

The process of the invention is of particular benefit when coating material is to be economized or when the function of the coating makes a particular shape necessary. Thus, for example, the process may be used in electrical technology for the coating of contact springs with noble metal in the region of the contact surfaces or for applying conductor paths for the production of printed circuits. Furthermore, selective coating with metal by electroplating of thin wires and bands can be carried out with special advantage.

The supply of metal ions to the surfaces to be electroplated is very favourable when carrying out the process of the invention, and is, surprisingly, generally equal to or can even be greater than in the case of electrolytes operated in bath containers. Moreover, since the process operates without the installation of any interposed coverings, it offers economies in material, cost and time.

A further advantage is that cathodic current densities may be 14, 44305 used which are greater by a factor of 10 to 100 than in the case of conventional electroplating apparatus, which results in a very marked increase in the speeds of deposition.

Therefore, the process of the invention makes possible, in a 5 technically extremely simple manner and with a product quality which has hitherto not been obtained, the controlled metal coating of selected surface regions, which may be even the finest lines, annular surfaces or a series of points and lines. A further surprising advantage is that it is possible to deposit, )° simultaneously onto several different areas, layers of metal of different, alternating composition.

Claims (22)

1. A process for the selective electrodeposition of metal onto a conductive surface or a surface that has been rendered conductive, from an electrolyte solution, which comprises 5 applying the solution to a part of the surface to be treated in the form of a free jet emitted from a nozzle and establishing a potential difference between the electrolyte and the surface.

2. A process according to Claim 1, wherein the surface to be treated acts as a baffle plate. Ίθ

3. A process according to Claim 1 or Claim 2, wherein the potential difference is established by connecting the nozzle or a part of the nozzle or the electrolyte supply as the anode.

4. A process according to any one of Claims 1 to 3, 15 wherein the nozzle has an outlet orifice of variable diameter and/or shape.

5. A process according to any one of Claims 1 to 4, wherein the nozzle and/or the surface to be electroplated perform a pivoting movement. pn

6. A process according to any one of Claims 1 to 5 wherein the free jet is shaped with regard to direction and crosssection by a guide member, flowing gas or liquid and/or by an 16, electric and/or magnetic field.

7. A process according to Claim 6, wherein the free jet is surrounded by a tubular jacket.

8. A process according to any one of Claims 1 to 7 , wherein 5 electrolyte solution is removed from the said surface by suction.

9. A process according to any one of Claims 7 and 8 wherein the suction is applied through the tubular jacket.

10. A process according to any one of Claims 1 to 9, wherein the quantity of electrolyte solution on the surface to be electroplated is continuously varied.

11. A process according to any one of Claims 1 to 10, wherein the electrical current density at the cathode is varied.

12. A process according to any one of Claims 1 to 11, wherein electrolyte solutions of different composition are used in continuous or discontinuous alternation.

13. A process according to any one of Claims 1 to 12, wherein a metal alloy is selectively deposited onto the said surface.

14. A process according to any one of Claims 1 to 12, wherein gold, silver, platinum, ruthenium, rhodium, palladium, osmium, iridium or alloy thereof is deposited on the said surface. 17. 442θ3

15. A process according to Claim 14, wherein gold or silver or an alloy thereof is deposited.

16. A process according to any one of Claims 1 to 15, wherein the said surface comprises a metal, metal sulphide or metal 5 oxide.

17. A process according to any one of Claims 1 to 16, wherein a plurality of surfaces a're electroplated simultaneously.

18. A process according to Claim 17, wherein each surface is a surface of a single work-piece.

19. A process according to Claim 1, conducted substantially as described in any one of the Examples herein.

20. A process according to Claim 1, conducted substantially as described herein with reference to any one of Figures 1 to 4 or the accompanying drawings.

21. An article having a surface on which metal has been selectively electrodeposited by a process according to any one of Claims 1 to 20.

22. An article according to Claim 21, which is a thin wire or a band.