Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/562—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of iron or nickel or cobalt
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/615—Microstructure of the layers, e.g. mixed structure
  • C25D5/619—Amorphous layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
  • H01H1/021—Composite material

Definitions

• the invention relates to an electrical contact surface (such as an electrical switch contact) having low contact resistance, relatively low cost, acceptable solderability, and high corrosion resistance.
• the electrical contact surface, and method of formation thereof, according to the present invention are particularly designed to replace conventional electrical contact surfaces wherein a gold layer of at least about 30 microinches thickness is applied over a crystalline substrate..
• gold is currently used to insure low contact resistance, and thus effective conduction.
• the gold is applied over a crystalline base metal such as copper, brass, or silver, with or without an intermediate strike of nickel, and the thickness of the gold layer is normally at least about 30 microinches (e.g. 50-100 microinches). At a thickness of 50 microinches the cost of the gold layer is on the order of 5 cents/cm 2 .
• gold has less than ideal solderability since it dissolves in and embrittles some solder alloys.
• an electrical contact surface is provided which overcomes the drawbacks associated with the conventional electrical contact surfaces described above, so that in low and intermediate voltage and/or current signal situations effective conduction can be obtained at less cost and over longer periods of time.
• an electrical contact surface is provided comprising an electrically conductive substrate (preferably a metal such as copper, bronze, brass, aluminum, or silver) with an amorphous (as opposed to crystalline) transition metal alloy electrolytically deposited thereon.
• An "amorphous" alloy is one that has a geometric or topological configuration of the atoms forming the alloy that is different from crystalline (i.e. non-crystalline). Typically, metal alloys are crystalline. When X-ray diffraction tests are done on crystalline materials, it can be seen that the materials exhibit sharp peaks for the d-spacings between planes in the ordered crystal structure, the narrowness or width of these peaks relative to thick height gives an indication of the size of the crystals. For amorphous materials, there are no particularly sharp peaks, the amorphous material being characterized by lack of order in the atomic structure.
• the amorphous transition metal alloy according to the invention preferably is a nickel-phosphorus alloy, such as one having about 15-25 atomic percent phosphorus (preferably about 20 percent), with cobalt, or some other transition metals, utilizable in addition to, or in place of, the nickel.
• Various materials may be added to the plating bath to enhance the corrosion protection of the electrical contact surface being formed, particularly advantageous materials being hexafluosilicate (SiF 6 --), hexafluotitanate (TiF 6 --), or hexafluozir- conate (ZrF 6 --) ions.
• the amorphous nickel alloy is preferably coated with a layer of gold.
• the contactor that results exhibits superior properties compared to conventional contactors wherein the same thickness of gold is coated on a crystalline metal alloy.
• a gold thickness of less than 30 microinches over the amorphous nickel alloy produces an electrical contact structure according to the invention that is equal to, or superior to, conventional contactors wherein a coating of 50-100 microinches of gold is provided.
• a method of producing an electrical contact surface comprises the steps of providing a plating bath for electrolytically depositing an amorphous transition metal alloy on a conductive substrate, immersing the substrate in the bath, and then subsequently coating the amorphous electrolytically deposited alloy with a flash of gold.
• Nickel chloride, cobalt carbonate, and phosphorous acid are preferred bath constituents.
• a number of bath additives can be provided to influence contact resistance and corrosion protection in a positive way.
• Typical bath additives include boric acid, hydroxyacetic acid, acetic acid, B -alanine, succinic acid, surfactants of the alkoxylated linear alcoholic class, SiF 6 -- ions, TiF 6 -- ions and ZrF 6 -- ions.
• the bath temperature conditions, and the current density at the cathode, are maintained so that effective electrolytic deposition takes place.
• a deposition of an amorphous transition metal alloy can be provided on a substrate by immersing the substrate (or a portion thereof) in a plating bath.
• Amorphous transition metal alloys have been found to have better corrosion resistance than crystalline materials, and a thinner coating of gold over an amorphous transition metal alloy produces a contactor having the same, or better, properties than a contactor formed by a thicker coating of gold over a crystalline material. Further, acceptable contacts can be obtained, according to the invention, with only a very thin coating of gold.
• Typical transition metal alloys that are useful in forming electrical contact surfaces (such as electrical switch contacts) according to the invention are nickel and cobalt.
• Nickel is the preferred transition metal since it has the least cost for the most corrosion resistance, of suitable transition metals.
• cobalt for all or part of the nickel, in the plating bath.
• An amorphous deposition of the nickel on the conductive substrate (which preferably comprises a metal such as copper, bronze, brass, aluminum, or silver, or alloys thereof) is formed when phosphorous acid is included in the plating bath, and a relatively high percentage of phosphorus is provided in the alloy that is formed.
• a phosphorus concentration of at least about 12%, and preferably of about 15-25 atomic percent is desired in order to achieve good corrosion resistance and low contact resistance.
• the amorphous deposited alloy has about 20 atomic percent phosphorus.
• the bath temperature conditions, and the current density at the cathode, are controlled in order to maximize the corrosion resistance and minimize the contact resistance.
• current density is about 50 amp./ft. 2 - 2500 amp./ft. 2 , with a range of about 100-900 amp./ft. 2 preferred.
• Typical temperatures are 70-85°C with 75-80°C preferred. Temperature is not critical, but lower temperature will have a tendency to increase the preference of cobalt for nickel in the plating where both are present in the bath.
• Various additives may be provided in the bath in order to positively affect the contact resistance and corrosion resistance.
• the bath contains hexafluosilicate ions at a concentration of about 0.1 molar to the solubility limit (with the addition of small amounts of HF to maintain solubility if necessary) the overall corrosion resistance of the amorphous nickel alloy may be enhanced.
• a generally comparable enhancement of corrosion resistance may also be obtained by substituting TiF 6 -- or ZrF 6 -- ions for part or all of the SiF 6 -- ions.
• any suitable anode and cathode materials may be utilized.
• the anode can either be inert (platinized titanium, platinum, or graphite), or can be of nickel (or like transition metal to be deposited). If TiF 6 --, SiF 6 -- or ZrF 6 -- ions are included in the bath a nickel or cobalt anode must be used. With an inert anode additions of nickel or cobalt must be made from time to time (preferably in the form of NiC0 3 or C O C0 3 ) to maintain the nickel content.
• nickel anode With the nickel anode the content of nickel ion in the bath tends to rise since each two electrons at the anode cause the dissolution of about one nickel ion, while at the cathode both nickel and phosphorus are being reduced.
• a nickel and an inert anode can be used together such that each carries only a portion of the current, and thus maintain a balanced bath with regard to nickel.
• Phosphorous, in the form of phosphorous or hypophosphorous acid, and preferably in the form of phosphorous acid, must be added from time to time -- irrespective of the anode construction -- to maintain the proper bath balance, although the proportion of phosphorous acid is not critical and the bath balance can be maintained rather easily.
• a coating of gold is applied over the amorphous alloy. Preferably this is accomplished by providing an electrodeposit that is applied for a controlled time at a controlled current density.
• the thickness of the gold coating is determined by the desired end properties of the contactor produced. Within wide ranges, whatever the thickness of the gold coating on the amorphous alloy, the contactor that results can be expected to have enhanced properties compared to contactors formed by the same thickness of gold coating over a crystalline material. In fact, acceptable electric contacts can be produced even when the thickness of the gold coating is about 1 microinch.
• the gold coating is in the range of 5-30 microinches, and more preferably 5-15 microinches.
• the gold used for the coating preferably is hard gold, although soft gold is also practical although usually with somewhat less desirable results.
• the thickness of the amorphous transition metal alloy on the substrate is not particularly critical. It merely need be thick enough to achieve the desired results according to the invention. A preferred thickness is in the range of about 50 microinches - 150 microinches. Ranges of 25 microinches - 1000 microinches are practical.
• the electrically conductive substrate is formed into the desired final contact shape. It is then immersed in a cleaner, and then deionized water, and then a dilute hydrochloric acid solution. Then it is placed in the Ni-Co-P plating bath and after plating it is rinsed is deionized water. Then the gold plating is provided thereon in any conventional way, such as in a gold plating bath maintained at about 30-35°C with a current density of about 10 amp./ft. 2. After the gold plating is applied it is again immersed in deionized water.
• a plating bath was formed with the following composition:
• An electrically conductive substrate was immersed in the bath, which was maintained at a temperature of about 80°C, and with a current density at the cathode of about 150 ma/cm 2 .
• the substrate When removed from the bath, the substrate had an amorphous nickel-phosphorus alloy thereon. A one (1) microinch strike of gold was provided on the amorphous alloy.
• the electrical contact surface that resulted had a contact resistance that was substantially as low as a similar substrate with a 50 microinch or greater coating of gold, the contact resistance was stable over time, and as stable in corrosive environments (such as when subjected to the S0 2 test -- 100 percent relative humidity and 1 percent concentration of sulfur dioxide, room temperature, over forty hours --, and the mixed gas test -- the same conditions as the S0 2 test only adding 1 percent nitrogen dioxide and 1 percent chlorine).
• the electrical contact surface formed was much less expensive than the conventional one, and had better solderability characteristics.
• the bath composition, temperature, and current density characteristics were substantially the same as in example 1.
• an approximately 10 microinch strike of gold was provided on the amorphous alloy.
• the electrical contact surface that resulted had contact resistance, and other properties, equal, or superior to, an electrical contact surface formed utilizing similar materials in crystalline form, and with a 50 microinch coating of gold.
• the bath composition in this example was as follows:
• the bath temperature conditions, current density, and like parameters, were substantially the same as for example 1, and after deposition of the amorphous nickel-phosphorus alloy on the substrate a 1 microinch flash of gold was applied.
• the electrical contact surface formed was found to have acceptable contact resistance (i.e. less than 4 milliohms when tested according to ASTM B667-80) and corrosion resistance, although it was not as good as the electrical contact surface produced in example 1.
• the bath composition for this example was as follows:
• the bath temperature was maintained at about 75°C, with a current density at the cathode of about 200 ma/cm 2 .
• An anal sis of the plating resulting from immersion of the substrate in this bath showed bulk values (in atomic percent) of 6.8 ⁇ 4%.cobalt, 0.6 oxygen, 73.3 percent nickel, and 19.3 percent phosphorus.
• a 1 microinch strike of gold was provided on the amorphous alloy.
• the electrical contact surface formed had low contact resistance and high corrosion resistance, and was an excellent substitute for conventional electrical contact surfaces of gold about 50 microinches thick (or thicker) applied over a crystalline base metal.
• a member of platings were produced on electrically conductive substrates to produce platings having about 20% phosphorous, X% cobalt, and 80-X% nickel, utilizing the constituents indicated in the following table:
• Plating was accomplished at 75-78°C using a hard anode (e.g. platinum or platinized titanium) and a current density of about 100 amp./ft. 2 .
• a hard anode e.g. platinum or platinized titanium
• the sum of the nickel plus cobalt is one mole/liter in each formulation, and CoCO 3 is the source of all the cobalt in each of the formulations. Therefore, the Co +2 /Ni +2 ratio in the bath is M/1 CoCO 3 /(1-M/1 CoC0 3 ).
• the Co/Ni ratio in the plating is %Co(80-%Co).
• the relationship between Co +2 /Ni +2 in the bath and Co/Ni in the plate is:
• the plating formed as actual electrical connectors, having 10% Co were coated with 5, 10, or 15 microinches of hard gold, or 5 microinches soft gold, and subjected to durability cycling utilizing conventional techniques, and exposure in a BCL Class III environment, and utilizing the same material on both the PC boards and the connector openings.
• the following results were achieved, wherein

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• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Engineering & Computer Science (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Composite Materials (AREA)
• Contacts (AREA)
• Electroplating Methods And Accessories (AREA)
• Manufacture Of Switches (AREA)
• Coupling Device And Connection With Printed Circuit (AREA)
• Conductive Materials (AREA)

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Cited By (14)

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Citations (3)

• 1984
  • 1984-05-30 DE DE8484303633T patent/DE3476684D1/de not_active Expired
  • 1984-05-30 AT AT84303633T patent/ATE40721T1/de not_active IP Right Cessation
  • 1984-05-30 EP EP84303633A patent/EP0160761B1/fr not_active Expired
  • 1984-05-31 JP JP11217484A patent/JPS6129021A/ja active Pending
  • 1984-06-11 ES ES533300A patent/ES8601557A1/es not_active Expired

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