GB2129441A

GB2129441A - Plated electrical contacts

Info

Publication number: GB2129441A
Application number: GB08231656A
Authority: GB
Inventors: Henley Frank Sterling
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-11-05
Filing date: 1982-11-05
Publication date: 1984-05-16
Also published as: GB2129441B

Abstract

In an electrical contact (eg a contact blade for a connector or a relay contact), the contact making portion is a precious metal (eg gold) deposited on the surface of an amorphous metal. The contact can be made by plating a contact blade fabricated from metallic glass (eg of 40% Ni, 40% Fe, 20%B or of 92% Ni, 8% Si) with gold or alternatively the contact area of a phosphor bronze connector blade may be melted by a laser and fast-refrozen to provide an amorphous area to receive the gold plate. Because the surface of the amorphous metal is very smooth, the thickness of precious metal needed is less than that needed with conventional contacts. The nickel underlayer usually used with gold plated contacts is no longer necessary.

Description

SPECIFICATION Gold plating The present invention relates to the selective plating of metal parts with precious metal, and especially (but not exclusively) where the metal is gold.

Gold is chosen as an electrical contact material because of its chemical inertness and its low and stable electrical contact resistance. No other material has been discovered with these excellent properties. It is expensive and so must be used as efficiently as possible. Gold is usually deposited by electroplating and much successful work has been done in the past ten years to enable gold to be selectively deposited. Only very thin layers of gold are necessary in theory to protect less noble (base) metals from the effects of troublesome environmental corrosion. In practice, however, imperfections and pores in the plated layer mean that protection is less than complete. Generally, closure of pores-proceeds as gold thickness is increased.

To meet some British Telecom specifications, four micrometres or more of gold is needed in the contact area of connectors. Other less stringent specifications are met with a micrometre or less of the metal. Testing of the "quality of gold coverage" and the number of pore type defects present is usually carried out by an electrographic test and by the assessment of the quantity of corrosion products formed in a corrosive gas atmosphere, designed as an accelerated environmental test As previously stated, in theory, only very thin layers of gold are needed, provided that they are continuous and free from imperfections. These imperfections are initiated at the substrate surface interface with the plating solution during the first nucleation of the deposited metal.In the commercial manufacture of connectors, for example, a typical metal used is phosphor bronze sheet, stamped-out and plated with gold in the contact area. The processes used in the casting, rolling and heat treatment of this sheet and the subsequent stamping and progressive-die work, leave the surface to be electroplated far from perfect. The most cursory examination under the microscope reveals many scratches, distorted grains, inclusions of foreign materials, etc., and a more detailed metallurgical analysis can reveal discontinuities of a more subtle nature. All these surface faults are potential initiators of pores in the subsequent plated layers and as such have been termed "pore-precursors". Many efforts have been made to improve the substrate surface for plating by pretreatments, for example, by electropolishing.However, for economical and practical reasons, it has not been possible to effect meaningful improvement in the surface quality of available substrate metal strip and sheet.

An object of the invention is to provide a selective precious metal plating technique in which the above difficulties are at least partly mitigated.

According to the invention, there is provided a metal part for electrical use, which includes a precious metal contacting region deposited on an amorphous metal surface.

This exploits the fact that in recent years, a new class of metals has become available, namely-amorphous metals or metallic glasses. In the preferred method of manufacture, mixtures of molten metals are jetted onto cooled drums to form ribbons or sheets of material which is frozen at an extremely high rate (supercooled at 106 degrees C per second). The material so formed is non-crystalline and absolutely homogeneous, exhibiting the same random atomic arrangement as the molten alloy. The surface therefore can be looked upon as a pseudo-liquid, which does not show the faults associated with rolled crystalline metals.

A useful article on these materials is "Materials with a magnetic future", by Campbell Grant and Richard McKim, in the "New Scieptist", June 3rd 1 982, pp 637-640.

These metals are being developed mainly as magnetic materials, but we have found that striking results are obtained when these glassy metals are used as substrates for gold plating. In some cases electrographic and gas corrosion tests show very good protection with gold layers as thin as 1000 Angstrom units (0.1 microns), when compared with the relatively poor protection obtained on a phosphor bronze substrate with such a thickness.

Metallic glasses can also be deposited by other means such as electroplating, sputtering or laser treatment. For example, a portion of the surface of a phosphor bronze connector blade coterminous with the contact area may be melted and fastrefrozen by a laser to provide an amorphous area to receive the gold plate.

A number of commercially available metallic glasses have been tried and have been shown themselves to be excellent substrates for gold plating because of their homogeneity, with no grain boundaries, and no inclusion; pin-hole counts are more favourable than obtained when conventional phosphor bronze rolled metal sheet is used as the base onto which the gold is plated.

Pin-hole counts are difficult to quantify, but attempts are made in plating and testing to use similar conditions for controls and samples.

In the manufacture of connectors, properties other than porosity are also important, such as the hardness of the substrate, its springiness, its wear resistance, etc. Electrical contact resistance and its constancy in life is linked strongly with corrosion resistance and therefore the porosity in the gold protecting layer.

Thus the porosity factor is of considerable significance for successful use of amorphous metals in electrical contact manufacture, and in fact low porosity factor has been shown to be advantageous.

One example of amorphous metal which has been studied uses an electrical contact blade fabricated from a metallic glass sold under the trade name "Metglas 2826" (Allied Chemical).

This was gold plated directly with a plating solution sold under the trade name "Autronex CC" (Sel Rex, Oxy-metal) according to the maker's instructions. 0.5 micrometres of gold were deposited in the contact area.

An electrical contact blade was also fabricated from phosphor-bronze and plated with 1.5 micrometres of nickel from a standard sulphamate bath followed by 0.5 micrometres of gold as detailed above.

These two contact blades were subjected to electrographic and gas tests as used in the trade, and the contact blade fabricated from "Metglas" showed significantly lower porosity and higher corrosion resistance than the control.

It should be noted that the nickel underlayer used in the control blade referred to above is necessary to prevent diffusion of gold into the bronze, and can provide an area for outgrowth of pin-holes generated at the substrate interface.

"Metglas 2826" contains approximately 40% nickel together with 40% iron and 20% boron. No nickel sub-layer is needed; in fact we found that if such an underlayer was used, porosity was increased slightly.

In a second example, all of the details were as set out for the first example, but using the amorphous metal sold under the trade name "Vitrovac 0080" (Vacum Schmelze) composition nickel 92%, silicon 8%.

Although the examples quoted were for the contact blades for connectors, the invention is usable for other electrical devices in which selective gold plating is required. Thus it is usable for selective plating or relay contacts, and also for such devices as electromechanical switching equipment used in telephone exchanges. In some cases the amorphous metal used is limited to the areas to be gold plated.

We have referred above to the fact that in order to meet some British Telecom specifications it is necessary to plate contact areas with relatively thick gold plating, i.e. four micrometres.

With conventional plating techniques such a thickness is needed to meet certain gas tests which are applied to the contact areas. With the present invention it is possible to produce contact blades and other parts which meet the technical requirements of such customers without needing such thick layers. As indicated above, layers as thin as half a micrometre, give excellent results.

Finally, it should be noted that the invention is applicable to selective plating of precious metals "used in the trade" other than gold.

Claims

1. A metal part for electrical use, which includes a precious metal contacting region deposited on an amorphous metal surface.

2. An electrical contact-making part such as a contact blade for a connector or a relay contact, in which the contact-making portion is a precious metal deposited on the surface of an amorphous metal.

3. A part as claimed in claim 1 or 2, and in which the precious metal is gold.

4. A part as claimed in claim 1, 2 or 3, and in which the amorphous metal is an alloy of 40% nickel, 40% iron and 20% boron, sold under the trade name "Metglas 2826".

5. A part as claimed in claim 1, 2 or 3, and in which the amorphous metal is an alloy 92% nickel and 8% silicon, sold under the trade name "Vitrovac 0080".

6. A part as claimed in claim 1, in which the amorphous metal surface is produced by treating the desired region of a substrate to melt that region, which is thereafter rapidly refrozen.

7. An electrical connector contact blade made from an alloy of 40% nickel, 40% iron and 20% boron sold under the trade name "Metglas 2826", having a layer of gold 0.5 micrometre thick deposited on it from a plating solution sold under the trade name "Autronex CC".

8. An electrical connector contact blade made from an alloy of 92% nickel and 8% silicon sold under the trade name "Vitrovac 0080" having a layer of gold 0.5 micrometre thick deposited on it from a plating solution sold under the trade name "Autronex CC".

9. An electrical connector contact blade made from a metal at least part of which is heat treated by a laser and then rapidly refrozen to render it amorphous, said metal having a layer of gold 0.5 micrometre thick deposited on its amorphous region from a plating solution sold under the trade mark "Autronex CC".

10. An electrical metal part having a contact making region of a precious metal, substantially as described herein.

New claims or amendments to claims filed on 7 February, 1 983.

New or amended claims

11. An electrical contact-making part, such as a relay contact or a contact blade for a connector, in which the contact-making portion is a precious metal deposited on to the surface of an amorphous metal, and in which the amorphous metal is one which was produced by melting the metal, and then supercooling the molten metal to give an amorphous homogeneous glass-like region to which the precious metal is deposited.

1 2. An electrical contact-making part, such as relay contact or a contact blade for a connector, in which the contact-making portion is a layer of gold whose thickness is one micron or less which is deposited directly to the surface of an amorphous nickel-containing alloy, in which the amorphous alloy is formed on the surface of the part to be treated, and in which the amorphous alloy is one which was produced by melting the metal and then supercooling the molten metal to give an amorphous homogeneous glass-like region to which the gold is deposited.

13. A method of making an electrical contact making part, such as a relay contact or a contract blade for a connector, which includes producing on the part to be treated a layer of an amorphous nickel-containing alloy, which alloy is made by melting the alloy and then supercooling it at a rate such as to give an amorphous homogeneous glass-like region, and then depositing a gold layer directly on to the amorphous alloy, the gold layer having a thickness of one micron or less.