NICKEL-BASED ELECTRICAL CONTACT

Abstract: Contacts comprising nickel and having a crystallographically disordered structure having electrical contact properties which render them suitable as replacements for gold contacts; disclosed contacts have low contact resistance even after prolonged exposure to an oxidizing ambient. Contacts comprising nickel and at least one glass-forming additive selected from boron, silicon, germanium, phosphorus, arsenic, antimony, or bismuth, are readily formed, e.g., as layers on substrates. A crystallographically disordered structure is produced in a contact surface layer at least upon exposure to an oxidizing ambient; alternatively, such desired structure can be produced by ion bombardement and even in the abscence of glass-forming additives.

Description: NICKEL-BASED ELECTRICAL CONTACT Technical Field The invention is concerned with electrical contact surfaces and, more specifically, with nickel-based contact surface materials. Background of the Invention Typically, the manufacture of high-quality electrical contacts has involved the use 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 also 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 certain nickel alloys have contact properties of high stability and low contact resistance comparable to those of gold. Devices in accordance with the invention comprise a contact surface which is the surface of such alloy comprising nickel and at least one glass-forming additional element such as boron, silicon, germanium, phosphorus, arsenic, antimony, or bismuth. The presence of such glass-forming element is considered to inhibit the formation of semiconducting nickel oxide and/or to result in the formation of a thermodynamically more stable compound, preserving metallic conductivity of a contact layer in an oxidizing ambient. The addition of one or several glass-forming elements results in a crystallographically disordered structure at least upon exposure of the layer to an oxidizing ambient, this as contrasted with the formation of crystalline nickel oxide in the absence of preferred addition of a glass-forming element. Alternatively, crystallographically disordered structure can be produced by ion bombardment, alpha particles being conveniently used for this purpose. Surface contact resistance less than 100 milliohms is typically maintained even after prolonged exposure to an oxidizing ambient. Brief Description of the Drawing 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 a surface layer 22 is situated. In accordance with the invention surface layer 22 is made of an alloy of nickel and at least one glass-forming additional element. Upon exposure to an oxidizing atmosphere, portion 23 of layer 22 further comprises oxygen. Preferred glass-forming additive elements are boron, silicon, germanium, phosphorus, arsenic, antimony, and bismuth, and their presence in the contact layer is in a preferred amount in the range of from 1 to 40 and preferably 2 to 10 atom percent relative to the combined amount of nickel and the additive element; preferred also in the range of from 25 to 35 atom percent where thermodynamically stable, stoichiometric compounds are formed. In combination, nickel and the glass-forming additive element or elements constitute a preferred amount of at least 70 atom percent of the contact layer material. In the interest of enhanced electrically and mechanical contact properties, the addition of cobalt is desirable, elements other than cobalt preferably being limited to amounts less than 5 atom percent in combination and preferably less than 1 atom percent. Particularly undesirable is the presence of Group VI elements such as sulfur, selenium, and tellurium, and their combined amount is preferably limited to less than 0.5 atom percent. In the case of non-stoichiometric aggregates, glass-forming additives to nickel are considered to inhibit the formation of semiconducting nickel oxide in an oxidizing ambient. Instead of such semiconducting nickel oxide, in the presence of the glass-forming additive, a surface layer of an aggregation including nickel, oxygen, and the glass-forming additive is believed to be formed in sufficiently large regions of the layer, such aggregation having essentially metallic conduction properties. Based on experimental evidence the thickness of the oxygencontaining surface layer is estimated to be on the order of 2.5 nm. Crystallographically disordered structure in nickel-containing layers is produced also upon ion bombardment which results in a crystallographically disordered structure even before exposure to an oxidizing ambient. Still, it is the disordered, quasi-amorphous, glass-like nature of an oxidized surface portion which is considered to be conducive to desired low contact resistance of a contact layer for use in an oxidizing ambient. A crystallographically disordered nickel aggregate preferably comprises nickel in an amount of at least 50 atom percent. The following examples specifically illustrate the suitability of contacts in accordance with the invention. Example 1. A layer consisting essentially of 95 atomic percent nickel and 5 atomic percent antimony was deposited by getter-sputtering approximately 3 micrometers thick on a copper substrate. Standard four-point probes were used to determine surface contact resistance; such resistance was found to be in the range of from 5 to 7 milliohms. The deposited film was then subjected to a test for stability at elevated temperature and humidity (65 hours at a temperature of 75 degrees C, relative humidity of 95 percent), and contact resistance was then found to be in the range of from 15 to 20 milliohms. Example 2. An experiment was carried out, analogous to Example 1, on a layer consisting essentially of 95 atomic percent nickel and 5 atomic percent phosphorus. Contact resistance was 1.8 milliohm before the test and 4.4 to 5 milliohms after the test. Example 3. An experiment was carried out, analogous to Example 1, on a layer consisting essentially of 95 atomic percent nickel and 5 atomic percent boron. Contact resistance was in the range of from 2.9 to 3.5 milliohms before the test and in the range of from 10 to 14 milliohms after the test. Example 4. An experiment was carried out, analogous to Example 1, on a layer consisting essentially of 95 atomic percent nickel and 5 atomic percent silicon. Contact resistance was in the range of from 1.6 to 2.1 milliohms before the test and in the range of from 4.5 to 6 milliohms after the test. Example 5. An experiment was carried out, analogous to Example 1, on a layer consisting essentially of 95 atomic percent nickel and 5 atomic percent germanium. Contact resistance was in the range of from 1.5 to 1.85 milliohms before the test and 10 to 14 milliohms after the test. Example 6. An aqueous solution was prepared containing 208 gum/1 NiC12.6H20, 49 gum/1 H3PO4 85 percent, and 5 gum/1 H3PO3. The solution was used to electroplate onto a copper electrode; plating bath temperature was 75 degrees C, current density was 150 mA/cm2, and plating rate was approximately 3 micrometers per minute. The deposited layer had a thickness of approximately 4.5 micrometers. Contact resistance of the deposited layer was less than 10 milliohms after exposure to the testing ambient. Example 7. An aqueous solution of 0.087 molar of As205 and 0.5 molar of NiCl2.6H2O was prepared. A copper electrode was plated with nickel arsenide by pulse-plating from the solution at a temperature of 75 degrees C; current pulses of 200 mA/cm2 were on for 1.5 seconds and off for 0.5 seconds. Deposited layer thickness was approximately 4.5 micrometers. Contact resistance of the deposited layer was less than 10 milliohms after exposure to the testing ambient. Example 8. To a solution of 5 gm GeO2 in 50 cc water plus 4 cc ammonium hydroxide and 0.5 molar of NiCl2.6H20, 150 gum/1 ammonium citrate were added. The solution was filtered, and ammonium hydroxide was added until pH was 8.5. A layer of nickel-germanium was plated from the solution at a temperature of 75 degrees C onto a copper electrode; current density was 150 mA/cm2 and plating rate was approximately 2.5 micrometers per minute. Deposited layer thickness was approximately 4.5 micrometers. Contact resistance of the deposited layer was less than 10 milliohms after exposure to the testing ambient. Example 9. A layer of nickel having a thickness of approximately 350 nm was deposited on a polished copper foil. A portion of the nickel layer was covered with an aluminum foil, and alpha-particles were implanted in the uncovered portion of the nickel layer. Alpha-particles had an energy of approximately 1.8 MeV, and a dose of approximately 1.6x1016 particles per cm2 was found to be optimal or near-optimal for minimized contact resistance (less than 10 milliohms) after exposure to humid air at elevated temperature as described in Example 1 above. (This test is considered to be an approximate equivalent of exposure to ordinary atmospheric conditions for a duration of 5 years.) Also, visual inspection of the implanted portion after the test as compared with the portion which had been covered with aluminum foil, showed the latter to be dull and brownish while the former appeared bright and shiny.

Claims: Claims 1. Apparatus comprising an electrical contact, said contact comprising a surface of a body of contact material, CHARACTERIZED IN THAT said contact material is crystallographically disordered and comprises a substantial amount of nickel. 2. Apparatus according to claim 1, CHARACTERIZED IN THAT said contact material is crystallographically disordered by ion bombardment. 3. Apparatus according to claim 1 or 2, CHARACTERIZED IN THAT said contact material comprises nickel and at least one additional element selected from boron, silicon, germanium, phosphorus, arsenic, antimony, and bismuth, said at least one additional element being present in said contact material in an amount in the range of from 1 to 40 atom percent of the combined amount of nickel and said at least one additional element, said combined amount being greater than or equal to 70 atom percent of said contact material. 4. Apparatus according to claim 3, CHARACTERIZED IN THAT said disordered structure is produced upon exposure of said contact material to an oxidizing ambient. 5. Apparatus according to claim 3, CHARACTERIZED IN THAT the presence of sulfur, selenium, and tellurium in combination begin limited in said contact material to less than 0.5 atomic percent. 6. Apparatus according to claim 1 or 3, CHARACTERIZED IN THAT surface having a contact resistance which is less than 100 milliohms. 7. Apparatus of claim 1 or 3, CHARACTERIZED IN THAT said body of contact material being in the form of a layer deposited on a substrate. 8. Apparatus according to claim 1, CHARACTERIZED IN THAT said contact material further comprising cobalt. 9. Apparatus of claim 3, said at least one additional element being boron or phosphorus or arsenic. 10. Apparatus of claim 3, said at least one additional element being silicon or germanium. 11. Apparatus of claim 3, said at least one additional element being antimony or bismuth.

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: 1985
Main classification: H01H1
IPC codes: H01H1