Classifications

• • 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
  • C25D3/64—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of silver

Definitions

• the Invention concerns conductive coatings for use In the .manufacture', of, for example, electrical connectors, LED arrays, and lead frames used in the computer industry.
• Electrical connectors are composed of a. first body, typically metal, that is mechanically inserted into or otherwise contacted with a second bodyy also typically metal,
• the electrical connection is enabled by the contact of an interface of the first body with an interface of the second, body,
• the materia! properties of these interfaces are crucial for the performance of the connection and the connector.
• the connectors must exhibit good electric contact, .e., low contact resistance, generally less than 10 rn-ohm, and stability. Ideally, the low contact res.ista.nce should not change with aging.
• the connectors roust also exhibit good wear resistance. What is good wear resistance depends on: the purpose for which the cornice tor is used. Some connectors have to sustain only a fe Cycles durin their lifetime; with cycles being defined a the number of times the connectors are contacted (or mated) and released. A light bulb and its socket is an example of this type of connection and connectors. Some connectors have to withstand up to hundreds and thousands of cycles, for sample, in the case of appliance plugs and sockets. Wear resistance i measured by the co-efficient of friction (COP) of the connectors.
• COP co-efficient of friction
• the coefficient of friction should be less than 0.8 after 50 mating cycles, in micro-electronic applications, with lower voltages and lower currents, the requirements are specially demanding: typically contact resistance of less then 10 mi!iioh ns with load forces from 10 -700 grams,
• the connectors also must exhibit good corrosio resistance. As the connector's properties should stay constant during the lifetime of the connector, Tl-A0.Q0.6P corrosion would have negative effects on contact resista.n.ee :1 wear resistance and. appearance. Preferably, minimal to no corrosion, should be observed, upon, subjecting the connector to the Mixed Flowing Gas (MFC) test, in. aoeordariee with industry standards (for example, standard EiA-364-65B i Class IIA; Temperature; 30°C +/ ⁇ ⁇ ;; Relative Humidity: 70% +/- 2%; Cb .: 10 + / ⁇ 3 ppb: 3 ⁇ 4 S: 10 +/- ⁇ * *? ppb )s: 200 +/- 50 ⁇ ppb: SO3: 100 -f /- 0 ppb).
• MFC Mixed Flowing Gas
• a typical, interface may be composed of a bronze body as a substrate layer onto which a barrier layer of nickel is electroplated. Onto the barrier layer a contact layer i then electroplated. Alternatively, the contact, layer may be applied using a molten bath method. See for ex mple United States Patent No. 5,075,176, which discloses tin allo electrical connector contact layers containing 0.
• Gold ha been, the metal of choice for the contact layer of electrical connectors because of its superior wear resistance and excellent corrosion resistance, especially for connectors that must be inserted and removed, multiple times over their useful life.
• the high cost of gold however has caused the Industry to try to substitute other conductive .finishes to replace gold, especially on connectors.
• Antimony is a silvery, lustrous gray metal that has Mo s scale hardness of 3, It has been used for over 2,000 years.
• United. States Patent No, 5,6.10,347 discloses materials for electric contacts composed: of a silver matrix and a metal oxide: component present in the ' form of oxide particles of tin oxide and zinc oxide and one of another metal oxide/carbide particles selected from antimony and other elements. Including the preferred molybdenum.
• the tin oxide is composed of 0,01- 10 weight percent of the othe metal oxide/carbide and i present in the contact In the amount of 5-20 weight percent *
• the silver matrix includes areas of tin oxide and is free of other oxide/ carbide particles, which are confined in a boundary area between the tin -oxide particles and the sliver matrix.
• 4, 859,238 discloses electrical contacts formed from a. silver-fron material which contains 3-30% by weight of Iron and one or more of the components manganese., copper, zinc, antimony, bismuth oxide., molybdenum. Tl-A0.Q0.6P oxide:, tungsten oxide or Chromium nitride in an amount totalin 0.05-5 weight percent, the balance being silver, P €T International Patent Publication No, WO 92 / 14282 discloses electrical contacts having superior wear characteristics comprising a member formed of copper, a copper alloy, or brass having a thick plating layer on it composed of silver and antimony, This plating layer has a thickness of at least 30 microns, preferably 40 microns, ith an amount of antimony about 1%, particularly between 0,3 and 0.7%,
• United State Patent " o. 3,425,917 discloses adding antimony to a. silver cyanide electrolyte In the amo nt of between 0,01-10 g/t, preferably between 0.2-3 g/l to improve brightness and hardness.
• United States Patent No. 3,219,558 discloses adding up to 3 g/l antimony in combination with an alkal metal sal of methylene bis n ph alene sulfonic -acid to a conventional silver plating solution t obtain, fully bright deposits and United States Patent No. 2,777,010 discloses Improved, results by adding 0.1 - 1 .0 g/l antimon to a silver cyanide electroplating: bath to improve ' brightness results.
• the invention is n aqueous electrolyte solutio for use in electrodepositing a. silver— antimony alloy.
• the solution contains the following srihstances in substantially the proportions indicated:
• the electrolyte solution may also contain between 0.10 and 2.00 ppm Selenium, preferably as potassium or sodium selenoeyarude,
• the Invention in another aspect, includes a method of preparing a hard silver alloy deposit on a. conductive article- in the method * the article is used as. the cathode in. an electroplating process employing one of the foregoing ao-ueous electrolyte solutions, and: electroplating the article at a current density of between 50 and 150 asf in a preferred embodiment, the method further includes the steps of drying the electroplated article, and then immersing the article in a protective substance lor a sufficient amount of time to coat the article with the substance.
• the protective substance or coating is composed of either a polyphenol ether or a perlluropoiylether. Once suftlciently immersed., the article is allowed to redry so that the coaling sets and forms the protective layer a top the silver allo deposit.
• the invention includes electrical connectors comprising silver - antimony alloy containin between 2 and 8 percent antimony made in accordance with these methods, and electrical connectors comprising a. body composed of bronze or copper, a barrier layer composed of nickel, and a contact layer covering the nickel layer in which the contact layer is composed of a. silver - antimony alloy containing between 2 and 8 percent antimony.
• Sneh electrical connectors may also he composed of an additional, protective layer composed of a polyphenol ether or a perfluropolylether covering, the contact layer ⁇
• Figure 1 is a graphic representation of the percentage of antimony plated as a function of current density (CD) as described in Example 5.
• Figure 2 is a. graphic representation of the results of the wear resis ance test described in Example 8 for the 5% antimony deposit samples described in Examples 3 and 5,
• Figure 3 is a graphic representation of the coefficient of friction (COP) results ibr 5% antimony deposit samples coated: with polyphenol ether or perf uropolylether as described in.
• COP coefficient of friction
• Figures 4 . 5., ⁇ and 6 axe graphic representations, of th results of the Mixed. Flowing Gas teste conducted o samples as described in Example 10.
• Si er-antimony alloys have been used to produce harder silve deposits than pur silver hut the still do not wear well because of silver's unique fretting, characteristics, (cold welding). Alloys of silver containing 0-1% antimony have been, used in decorative applications to produce mirror bright silver finishes. A. by product of alloying silver with this amount of antimony has been, better corrosion resistance on storage at. ambien conditions, but such alloys still do not approach the corrosion, resistance of gold deposits.
• the bath was heated to 13CFF, and the deposit was plated at 40as.f.
• the deposit was white in appearance and did not crack on bending at 2.5 microns thickness.
• the deposit was tested for corrosion by ' using the Ammonium. Sulfide Vapor Test, Eleetrodeposited Silver Flaring QS&-366D fsee Example 6 below).
• A. pure silver deposit was used, as a comparison,. Both deposits turned dark purple within a.n. hour.
• the hath was heated to 130*F, WfthiaA 30 minutes the bath turned cloudy with precipitate and antimony levels in thn bath fell. Plating felled.
• Sample panels were plated at 100 asf. Using standard, methods, the panels were determined to contain 5% a imony and. a. bright white appearance. The deposits were bent and not cracked at 2.5 microns thickness.
• Sample panels were plated at 100 a h Using standard methods, the panels were determined to contain S% antimony ⁇ and a bright whit appearance. The deposits were bent and no cracked at 2.5 micron thickness.
• the bath was heated to I30 ;> F. No precipitate or cloudiness was observed.
• Sample panels were plated at 100 asf. Using standard methods, the panels were determined to contain 5% antimony and a bright white appearance. Deposits were bent and not. cranked at 2,5 microns thickness.
• the Ammonium. Sulfide Vapor Chamber Test modified from the Federal: Specification for Elecirodeposited Silver Plating QSS ⁇ 36$D f . was used to test the corrosion resistance of the S% antimony silver deposits made in accord with Example 3 and Example 5. Contacts were piated. with 2,5 microns of the deposit. One ml of 20 to 2 percent ammonium sulfide (light),,, reagent grade, was pipetted into a one-liter volumetric flask. The flask was filled to the mark with distilled water and agitated thoroughly. 500 ml of the diluted ammonium sulfide solution was placed at the bottom of a desiccator chamber.
• the plated parts were placed, at least 3 inches above solution in the desiccator on a. ceramic plate, the top of the desiccators w s closed and the parts tested for one hour.
• Other contacts were plated with pure silver deposits and tested a a comparison.
• the pure silver deposits were a deep purple typically, indicative of sliver sulfide formation while the 5% antimony silver deposits were a very light yello color.
• the time in the chamber was increased to over- a few hour's.
• the pure silver deposit continued to darken while the 5% antimony silver deposit remained light yellow in color. This test result was deemed good enough to continue developing the process.
• the ammonium sulfide chamber test was then conducted on 5% antimony-silver deposit sample made as described, in Example 5 coated, with polyphenol ether and perfiuropoiylether coatings. Similar .results to the .5% antimony- ilver samples without, coatings were obtained. Since the coating now seemed to pass both these tests, the wear and ammoniu sulfide tests were repeated after a IDOhr, / 120 '* C hake of the coated 5% antimony silver deposits. The ammonium sulfide tests also produced, little color change in the deposit after the bake for both coatings. How ver, only the perfl.uropolyet.her coating retained stable coefficient of friction values -at 0.3 or below.
• the 5% antimony silver deposits were immersed in separate solutions of (a) a polyphenol ether dissolved in. paraffin oil (TARMBAN CBGi, Technic Inc., Cranston, l3 ⁇ 4l ( ⁇ a perf luropolyether dissolved in a fluroalkane (Nye Lubricants, Fairhaven. MA) and (c) a fluorsxirfacant dissolved In. aqueous solutions.
• the samples were silver-antimony plated, dried, and then Immersed in one of the coat solutions for 5 seconds, after which tile samples were warm air- dried.
• Figure 4 is a graphic representation of the MFC* test result fo the perfluropolyether coated 5% antimony silver sample deposits f l OO b.r/ 120 3 ⁇ 4 C Bake before Test), with Contact esistance plotted as function f Corrosion Resistance. No increase in contact resistance Is seen.
• Figure 5 the wear test results are shown. o Increase in. wear over time is seen.
• Figure 6 shows the ' visual corrosion test results. No visual corrosion can be seen.

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• Chemical Kinetics & Catalysis (AREA)
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• Electroplating And Plating Baths Therefor (AREA)
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Citations (13)

• 2013
  • 2013-03-22 WO PCT/US2013/033445 patent/WO2013142765A1/fr not_active Ceased

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