NICKEL-BASED ELECTRICAL CONTACT DEVICE

Abstract: Device having an electrically conducting member having a contact surface consisting of a nickel-based contact material. In accordance with the invention, the nickel-based material at least in a surface region (e.g. 23) comprises controlled amounts of hydrogen and has low electrical contact resistance even after prolonged exposure to an oxidizing ambient. When used as a surface layer (e.g. 22) on an electrically conducting member (e.g. 21), such material is suitable as a contact material and represents an inexpensive alternative to gold. And, when prepared in the form of microscopic flakes, such material is suitable for use in electrically conductive inks and adhesives.

Description: NICKEL-BASED ELECTRICAL CONTACT DEVICE Technical m Field The invention is concerned with devices having an electrically conducting member having electrical contact surface of nickel-based materials. Background of the Invention Typically, the manufacture of high-quality electrical contacts has involved the usage of gold whose properties of low contact resistance and high chemical stability are key advantages in such usage. However, as the price of gold remains high, efforts continue at finding alternative materials for contact manufacture. Prominent among such alternatives are precious metals other than gold; e.g., silver-palladium alloys have been found suitable for certain applications. While such alternate alloys are less expensive than gold, still further cost reduction is desired, and nonprecious metal alloys such as, e.g., copper-nickel alloys have been investigated for contact resistance and stability over time. See S. M. Garte et al., "Contact Properties of Nickel-Containing Alloys", Electrical Contacts, 1972, Illinois Institute of Technology. Summary of..the ^ .Invention It has been discovered that a material consisting essentially of nickel and a controlled amount of hydrogen has contact properties comparable to those of gold such as, in particular, low and stable contact resistance. Preferred amounts of hydrogen in nickel are regarded to be such as to associate atoms of hydrogen with nickel atoms on dislocations, thus blocking oxidation at critical sites. Typically, surface contact resistance of the material is significantly less than 100 milliohms even after prolonged exposure to an oxidizing ambient. "Brief Description of.the p.rawing FIG. 1 is a perspective view of an electrical connector device in accordance with the invention; and FIG. 2 is a schematic cross-sectional view of a portion of a device in accordance with the invention. Detailed . Description The electrical connector device shown in FIG. 1 comprises housing 11 and contact pins 12. Housing 11 is ■ made of " an electrically insulating material, and contact pins 12 have contact surfaces in accordance with the invention. Shown in FIG. 2 are, in cross section, an electrically conducting member 21 on which layer 22 is situated. Member 21 may consist of a copper conductor material, and surface layer 22 is a nickel material which comprises hydrogen at least in a surface region 23. The incorporation of controlled amounts of hydrogen into nickel material results in enhanced contact properties such as low contact resistance and long-term stability of such resistance. Hydrogen may be incorporated in a nickel material in a variety of ways such as, e.g., in the course of electroplating, by sputtering in an argon-hydrogen atmosphere, and by indiffuεion at a bulk surface which, preferably, has been subjected to plastic deformation by cold working. Preferred concentrations of hydrogen depend on conditions under which layers or bodies of nickel are produced and processed, and it is postulated that preferred concentrations increase in direct relationship , with the cumber of nickel atoms on dislocations. In particular, greater amounts of hydrogen are beneficial for cold worked material, preferred amounts being directly related to level of cold working. In the case of electrodeposited layers, preferred amounts are in the range of from 0.0004 to 0.0009 atom concentration of hydrogen in nickel; when severe cold work is applied up to 0.01 atom concentration is preferred. Fortuitously, as dislocation slip bands produced by cold working also facilitate indiffusion of hydrogen, contact properties of cold-worked bulk nickel material are most favorably affected by hydrogen indiffusion. Accordingly, applications are preferred in which nickel material is plastically deformed by a significant amount, such as, e.g., corresponding to at least 50 percent reduction of cross-sectional area prior to hydrogen diffusion, the latter being carried out at a temperature which is less than the recrystallization temperature of Hi. Hydrogen indiffusion is typically effected over a time of a few minut_.es, and indiffusion is facilitated by heating at a temperature below the recrystallization temperature of Ni. Among applications of cold-worked material are those involving the use of microscopic flakes dispersed or embedded in a non-conductive matrix material as, e.g., in electrically conducting inks, pastes, and adhesives. Conveniently, hydrogen can be incorporated in nickel layers by electroplating out of a suitable nickel bath, solutions of nickel salts being considered most suitable where the anion is but weakly oxidizing. While a contact material of the invention may be free or essentially free of elements other than nickel and hydrogen, impurities may be present and additional elements may be included such as, e.g., boron, silicon, germanium, phosphorus, arsenic, antimony, cr bismuth. When present in solid solution or, in other words, when incorporated in the nickel structure, impurities and additives are considered not to interfere with the beneficial effect of hydrogen in nickel. Amounts of at least 70 atom percent nickel-hydrogen are preferred in the contact material. Contacts of the invention may receive a final coating of "flash" comprising a significant amount of a coating material such as gold, one or several platinum- group elements, or gold and one or several platinum-group elements, tne amount being sufficient to impart to the coated surface the appearance of such coating material. The structure of such coating may be essentially homogeneous or layered, and coating thickness typically is in a range from 0.01 to 0.05 micrometer. For example, a cobalt-hardened gold coating may be electro-deposited from a slightly acidic solution (pH 5) comprising potassium gold cyanide, cobalt citride , and a citric buffer. (The presence of cobalt, nominally in a range of from 0.2 to 0.5 percent by weight, enhances surface hardness especially in the case of thicker coatings.) Preferred temperature of the plating bath is approximately 35 degrees C, and a plating current of approximately 5 millia peres per cm is convenient. Typical plating times are of the order of half a minute. Prior to plating, a surface may be cleaned, e.g., by electrolytic scrubbing in an alkaline solution, rinsing in de-ionized water, and dipping in dilute hydrochloric acid at elevated temperature. Example 1. A layer having a thickness of approximately 1.68 micrometer and having approximately 0.005 atom concentration of hydrogen in nickel was deposited on a copper substrate by sputtering from an essentially pure nickel target in an atmosphere of approximately 10 percent by volume hydrogen, remainder essentially argon. The layer was exposed to atmospheric test conditions at 75 degrees C and 95 percent relative humidity for 65 hours. After such exposure contact resistance was determined to be in the range of from 7 to 10 milliohms. Example 2. A layer having a thickness of approximately 0.48 micrometer was deposited as further described in Example 1 above. Ultimate contact resistance was in the range of from 10 to 13 milliohms. Example..3» A layer having a thickness of approximately 4.5 micrometers was deposited on a copper substrate by electroplating from a 2-molar nickel chloride solution at a temperature of approximately 75 degrees C, pH of the solution was approximately 3 as obtained by the addition of ammonium hydroxide, and current density during 2 deposition was approximately 150 milliamperes/cm . The layer was exposed to atmospheric test conditions as described in Example 1 above, and contact resistance was determined to be in the range of from 1 to 10 milliohms. Example 4. A layer was deposited as described in Example 3 above except that a 2-molar nickel citrate solution was used at a pH of approximately 6. Contact resistance of the layer was found to be in the range of from 0.3 to 10 milliohms. Exampl 5. A layer was deposited as described in Example 3 above except that a 1/2-molar nickel acetate solution was used at a pH of approximately 8. Contact resistance of the layer was in the range of from 2 to 15 milliohms.

Claims: Claims 1. Device comprising an electrically conducting member having a contact surface, said contact surface being the surface of a surface region of said member and consisting of a contact material, CHARACTERIZED IN THAT an amount of at least 70 atom percent of said contact material consists of nickel and hydrogen, said hydrogen being present in said amount in a significant small percentage so as to enhance an electrical contact property of said contact surface. 2. Device according to claim 1, CHARACTERIZED IN THAT hydrogen atoms in said contact material being in correspondence with nickel atoms on dislocations. 3. The method according to claim 1, CHARACTERIZED IN THAT said surface region being an electrodeposited layer in which atom concentration of hydrogen in said amount is in the range of from 0.0004 tc 0.0009. 4. Device according to claim 1, CHARACTERIZED IN THAT said surface region being a layer which has been plastically deformed and in which atom concentration of hydrogen in said amount is in the range of from 0.0004 to 0.01. 5. Device according to claim 4, CHARACTERIZED IN THAT said surface region has been plastically deformed so as to result in cross-sectional area reduction greater than or equal to 50 percent. 6. Device according to claim 1, CHARACTERIZED IN THAT the contact resistance at said surface is less than 100 milliohms. 7. Device according to claim 1, CHARACTERIZED IN THAT said contact surface is essentially the entire surface of said member. 8. Device according to claim 7, CHARACTERIZED IN THAT said member is a contact pin. 9. Device according to claim 7, CHARACTERIZED IN THAT said member is a conductive particle. 10. Device according to claim 9 , CHARACTERIZED IN THAT said particle is an ink particle. 11. Device according to claim 9, CHARACTERIZED IN THAT said particle is embedded in a non-conductive matrix material. 12. Device according to claim 11, CHARACTERIZED IN THAT said non-conductive matrix material is an adhesive material. 13. Device according to claim 1, CHARACTERIZED IN THAT said contact material has a surface coating which consists essentially of a coating material selected from the group consisting of gold, one or several platinum-group elements, and gold and one or several platinum-group elements. 14. Device according to claim 13, CHARACTERIZED IN THAT the amount of said coating material being sufficient to produce a surface appearance of said coating material. 15. Apparatus according to claim 13, CHARACTERIZED IN THAT — O - — said surface coating has a thickness in the range of from 0.01 to 0.05 micrometer. 16. Method for making a device having an electrically conducting member, comprising a step of providing said member with a contact surface which is the surface of surface region of a contact material, CHARACTERIZED BY producing said contact material so that at least a surface region thereof comprise an amount of at least 70 atom percent of nickel and hydrogen, with hydrogen being present in said amount in a significant small percentage so as to enhance an electrical contact property of said contact surface. 17. Method according to claim 16, CHARACTERIZED BY conducting said step as a step of electrodepositing or a step or sputtering or a step of diffusion of hydrogen into nickel. 18. Method of claim 17, CHARACTERIZED BY cold working said member prior to diffusion.

Inventors: HAUSER JOACHIM JACQUES, PLEWES JOHN TRAVIS, ROBBINS MURRAY, HAUSER, JOACHIM, JACQUES, PLEWES, JOHN, TRAVIS, ROBBINS, MURRAY
Applicants: AMERICAN TELEPHONE & TELEGRAPH, AMERICAN TELEPHONE & TELEGRAPH COMPANY
Application year: 1986
Main classification: H01R43
IPC codes: H01B1, H01R43