US 2897584 A
Description (OCR text may contain errors)
Aug- 4, 1959 K. scHuMPEL-r 2,897,584-
` GOLD PLATED ELECTRICAL CONTACT ND SIMILAR ELEMENTS Filed may 22. 1957 1N VENTOR. A64 n SUN/@0&7
WIM Y@ United States Patent GOLD PLATED ELECTRICAL CONTACT AND SllVIILAR ELEMENTS Karl Schumpelt, Union, NJ., assignor to Sel-Rex Corporation, Belleville, NJ., a corporation of New Jersey Application May 22, 1957, Serial No. 660,955
2 Claims. (Cl. 29-199) This invention relates to the improvement of gold plated products where the gold is plated over silver.
It is customary, for example, in the manufacture of slip ring assemblies and many electrical contacts to specify that a layer of gold, about 000010 to 000020" thick for example, be plated over a silver deposit (about .0002" thick for example). The gold layer is noncorrosive, attractive, is not fouled by electrical discharges, etc., and thus provides the best surface layer for such products. The silver layer beneath the gold layer cooperates with the latter to provide a double layer of noble metal of sutiicient thickness to prevent corrosion of the basis metal. After a certain time, however, such products discolor or tarnish showing, for example, large discolored blotches. This tarnishing is not due to porosity of the gold layer since it does not appear in small spots or specks` although with respect to some `gold deposits, the porosity of the deposit may be a contributing factor. One method that has been used heretofore to overcome this defect is to increase the thickness of the gold deposit.
One phase of this invention is based on the discovery that such surface tarnish in the gold plated products is due to the diffusion of silver through the gold layer.
Another phase of the invention is based on the discovery that the tarnish may be prevented by providing a very thin layer of barrier metal between the silver and gold layers. The metals which may be employed as barrier metals are platinum, ruthenium, rhodium or palladium. A very thin layer of the barrier metal is suicient, for example, a deposit of 0000025 to 000005 in thickness is very satisfactory. This thickness of palladium or other platinum metal does not interfere with the electrical properties. With such a layer of barrier metal on the silver deposit the thickness of gold may be safely reduced to 000010 without sacrificing the protective value thereof and without making the product susceptible to tarnishing.
In the drawing:
Fig. 1 shows a typical electrical contact which may be advantageously plated according to the present invention.
Fig. 2 is an enlarged cross sectional view of the surface region of a product similar to that of Fig. 1 made according to the present invention.
The shape of the electrical plug element of Fig. l is not a part of the invention as the invention is applicable to any such element where corrosion is to be prevented and where good electrical Contact with a cooperating element such as a jack is desirable. The plug element 10, however, has a plug end portion and a hollow portion 12 at the opposite end wherein an electrical conductor may be soldered. The surface layer 23 of said element as shown in Fig. 2 is of gold. Beneath the layer of gold is the barrier layer 22 of palladium. A layer of platinum, rhodium, or ruthenium may be substituted for the palladium layer 22. Beneath the palladium layer 22 is the silver layer 21. The basis metal 20 may be brass, copper, etc.
The following example further illustrates how the product is manufactured.
Example A copper plug similar to that shown in Fig. 1 is provided. This plug is rst plated with silver to a thickness of about .0002, from a silver electrolyte solution containing, for example:
Silver (as metal) g./liter 25-33 Free potassium cyanide do- 30-45 Potassium carbonate do 30-90 The resultant product is rinsed and then plated with a palladium to a thickness of about .0000025 to about .000005 from a palladium solution of the Pilet type (U.S. Patent 330,149) containing, for example,
Palladous chloride, PdCl2.2H-2O g./liter 3.7 Di-sodium` phosphate, Na2HPO4 do 100 Di ammonium phosphate,
2HPO4.12H2O ....d0 Boric acid do 2.5
or 4any other workable palladium plating bath that produces commercially acceptable deposits. Thereafter, the product is rinsed and a layer of gold 000010 to 000020" is deposited thereon. A satisfactory gold deposit is obtained from the cyanide gold baths such as disclosed in Modern Electroplating, The Electrochemical Society, 1942, pages 199-209. Such a bath, for example, contains the following ingredients:
Metallic gold (as cyanide) -..g/liter-- 4.2 KCN 0---- 15 Accelerated tarnishing tests show the resultant product to be resistant to tarnishing, whereas the same tests on commercially plated products, i.e., without palladium or other barrier metal layer, resulted in tarnishing of the parts.
Although the -gold formulation directly above gives good results, equivalent and better are obtained from other gold formulations, some of which are proprietary preparations.
The features and principles underlying the invention described above in connection with specific exempliiications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific feature or details thereof.
1. As an article of manufacture which is resistant to corrosion and to tarnishing by diffusion, a basis metal, a layer of silver deposited on said basis metal, a layer of gold about 00001 to 00002 thick on the outside surface thereof and a layer of about 0000025" to 000005" in thickness of a barrier metal selected from the group consisting of platinum, ruthenium, rhodium and palladiurn between the silver layer and the gold layer, said barrier metal layer being bonded to said silver at one side and to the gold layer at the other side thereof.
2. As an electrical contact element which is resistant to corrosion and to tarnishing by diffusion, a basis metal, a layer of silver deposited on said basis metal, a layer of gold about 00001" to 00002" thick on the outside surface thereof and a layer of about 0000025 to 000005" in thickness of palladitun between the silver layer and the gold layer, said palladium layer being bonded to said silver at one side and to the gold layer at the other side thereof.
References Cited in the le of this patent UNITED STATES PATENTS Jackson Dec. 10, 1929 Miller Jan. 23, 1951