GB2147311A

GB2147311A - Electrodepositing precious metal alloys

Info

Publication number: GB2147311A
Application number: GB08326126A
Authority: GB
Inventors: James Brian O'hara
Original assignee: Hara J B O
Current assignee: Hara J B O
Priority date: 1983-09-29
Filing date: 1983-09-29
Publication date: 1985-05-09
Also published as: GB8326126D0; GB2147311B

Abstract

A method of electrodepositing an alloy of a precious metal, which comprises electrodepositing a first layer with a first precious metal content from a first plating bath and thereafter electrodepositing a second layer with a second precious metal content directly on to the first layer from a second plating bath, the first and second baths being compatible such that no intermediate treatment e.g. rinsing of the first layer is required before applying the second layer from the second bath. The method may be used in the manufacture of printed circuits. For example, a Pd-Ni alloy may be electrodeposited by depositing a first 4 micron thick layer of 20/80 or 10/90 Pd/Ni followed by a second 1 micron layer of 90/10 Pd/Ni without any intermediate treatment. The method may also be used in the manufacture of jewellery or costume jewellery. For example a first gold alloy layer relatively poor in gold may be directly followed by a thin rich gold alloy or pure gold layer. Further applications of the invention are in the plating of electrical conductors and in electroforming.

Description

SPECIFICATION Electrodeposition of precious metal alloys This invention relates to the electrodeposition of precious metal alloys. Because of the inherent expense of precious metals, it is always a problem to find methods of reducing costs in applications which call for the use of precious metals.

According to the present invention there is provided a method of electrodepositing an alloy of a precious metal, which comprises electrodepositing a first layer with a first precious metal content from a first plating bath and thereafter electrodepositing a second layer with a second precious metal content directly on to the first layer from a second plating bath, the first and second baths being compatible such that no intermediate treatment of the first layer is required before applying the second layer from the second bath.

It is normal to require a number of intermediate treatments between plating baths for plating out different alloys, such as neutralising, washing and rinsing, because of the incompatibility of successive baths in multiple stage electrodeposition processes. These intermediate stages necessitate costly additions to the process in terms of time, equipment and raw materials. The present invention avoids such treatment stages and their attendant disadvantages.

In many applications of electrodeposited precious metal alloys, a high precious metal content is required to give specific properties in only one part of the deposit, such as at the metal surface (eg oxidation resistance, solderability conductivity and high frequency applications, or aesthetic appearance), while a minimum thickness is required for such reasons as adequacy of mechanical strength.

In such applications the present invention provides a a means of achieving both the required thickness and the required local, eg surface, properties while reducing the overall precious metal content of the alloy and thereby effecting valuable cost savings.

It is frequently preferred that the second layer be the higher in precious metal content and thinner than the first, to maximise the advantages gained by the invention.

Advantageously the alloys of the first and second layers are sufficiently compatible that the second layer welds to the first by intermetallic diffusion. The layers may accordingly lose any sharply defined boundaries and become indistinct in the final product, with a gradual change in composition through the alloy.

Generally speaking, plating conditions in the first and second baths will be adapted to ensure that in each case an alloy of the desired proportions is deposited therefrom, and the compositions of the baths will reflect the alloy compositions to be electrodeposited therefrom.

The method according to the invention may be varied by increasing the number of baths and the numbers of layers of precious metal alloy deposited, in accordance with the alloy properties and gradations of composition ultimately required.

Each subsequent bath in accordance with the invention should be compatible with the previous bath, such that no intermediate treatment of the previous layer is required before applying the subsequent layer from that bath.

Precious metals which may be present in the alloys electrodeposited in accordance with the invention include gold, silver and the platinum group metals (ruthenium, rhodium, palladium, osmium, iridium and platinum).

For example, alloys may be deposited in accordance with the invention in substitution for the palladium/nickel alloys used in printed circuit manufacture, as disclosed in my British Patent Application No. 8235929 (Publication No. 2113477).

Such alloys may contain 65-95% palladium and 355% nickel; an exemplary weight ratio is 80/20 Pd/ Ni. Instead of electroplating a uniform layer of say 5 micron thickness to achieve the necessary combination of mechanical strength and surface alloy composition, a first layer 4 micron thick of 20/80 or 10/90 Pd/Ni deposited from a first plating bath may be followed by a second layer 1 micron thick of 90/ 10 Pd/Ni from a compatible second plating bath without the need for any intermediate neutralising, washing, rinsing or other treatment bath, the two layers blending at their junction by intermetallic diffusion to yield an electrodeposited alloy layer having the required mechanical strength and high palladium content at the surface where it is required for achieving the advantages set out in the aforesaid patent application yet with valuable savings in palladium content.

The present invention accordingly, extends to producing a printed circuit by a method comprising the step of electrodepositing a precious metal alloy by the method of this invention. More particularly, the method of this invention may be used to deposit the metal alloy, particularly a palladium/ nickel alloy, in step (b) of the method of producing a printed circuit set out in the aforesaid patent application, namely:: (a) printing a plating resist onto the clean surface of a layer of electrically conductive material on at least one side of a substrate so as to leave exposed only the required track areas of the surface, (b) electroplating over the track areas a metal alloy which will act as an etch resist for the underlying electrically conductive material, which has good solderability, which has a melting point higher than 250 C, and which will provide a base for gold plate, (c) removing the plating resist, and (d) removing the layer of electrically conductive material from the non-track areas by etching.

As a further example, the method of this invention may be applied to the manufacture of jewellery or costume jewellery, for instance to substitute for the application of a rolled gold layer. A first gold alloy layer relatively poor in gold may be electrodeposited from a first bath and directly thereafter a relatively thin rich gold alloy or pure gold layer may be electrodeposited from a second bath without intermediate treatment baths. The first and second layers are preferably of compositions selected to be of similar colour, so that any wearing through of the second layer will not leave an unsightly appearance. Again, the richer second layer may merge with the first layer by diffusion.

The present invention accordingly also extends to producing an article of jewellery or costume jewellery by a method comprising the step of electrodepositing a precious metal alloy by the method of this invention.

The method of the invention may be applied both to electroplating a precious metal alloy on to a permanent substrate and to electroforming an article of a precious metal alloy on a removable conductive mould or matrix.

The Present invention further extends to the plating of wire or other electrical conductors to impart specific properties at or near the surface thereof, e.g., properties of conductivity or suitability for high frequency application.

Claims

1. A method of electrodepositing an alloy of a precious metal, which comprises electrodepositing a first layer with a first precious metal content from a first plating bath and thereafter electrodepositing a second layer with a second precious metal content directly on to the first layer from a second plating bath, the first and second baths being compatible such that no intermediate treatment of the first layer is required before applying the second layer from the second bath.

2. A method according to claim 1, wherein the second layer is higher in precious metal content and is thinner than the first layer.

3. A method according to claim 1 or 2, wherein the first and second layers are sufficiently compatible that the second layer welds to the first layer by intermetallic diffusion.

4. A method according to claim 1, 2 or 3, wherein the alloys of the first and second layers comprise the same constituents present in the alloys in different proportions.

5. A method according to claim 4, wherein plating conditions in the first and second baths are adapted to ensure that in each case an alloy of the desired proportions is deposited therefrom, and the compositions of the baths reflect the alloy compositions to be electrodeposited therefrom.

6. A method according to any one of the preceding claims, raised by increasing the number of baths and the number of layers of precious metal alloy deposited, each subsequent bath being compatible with the previous bath such that no intermediate treatment of the previous layer is required before applying the subsequent layer from the subsequent bath.

7. A method according to any one of the preceding claims, wherein the precious metal alloys of the different layers are alloys of gold, silver or a platinum group metal.

8. A method according to any one of the preceding claims, wherein the alloys of the first and second layers are compatible palladium/nickel alloys with the alloy of the first layer high in nickel content and the alloy of the second layer high in palladium content.

9. A method of producing a printed circuit, comprising the steps of: (a) printing a plating resist onto the clean surface of a layer of electrically conductive material on at least one side of a substrate so as to leave exposed only the required track areas of the surface, (b) electroplating over the track areas a metal alloy which will act as an etch resist for the underlying electrically conductive material, which has good solderability, which has a melting point higher than 250 C, and which will provide a base for gold plate, (c) removing the plating resist, and (d) removing the layer of electrically conductive material from the non-track areas by etching, wherein step (b) is carried out by the method according to any one of claims 1 to 8.

10. A method of producing an article of jewellery, the method comprising the step of electrodepositing a precious metal alloy by the method of any one of claims 1 to 8.

11. A method according to claim 10, wherein the alloy is a gold alloy with the first layer being relatively poor in gold and the second layer relatively thin and rich in gold.

12. A method according to claims 10 or 11, wherein the first and second layers are of compositions selected to be of similar colour.

13. A method according to claims 10, 11 or 12 which comprises electroplating the precious metal alloy onto a permanent substrate or electroforming an article of a precious metal alloy on a removable conductive mould or matrix.

14. A method of plating wire or other electrical conductors to impart specific properties at or near the surface thereof, comprising the step of electrodepositing an alloy of a precious metal on the wire or other electrical conductor by the method of any one of claims 1 to 8.

15. A method of electrodepositing an alloy of a precious metal, substantially as herein described.