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
  • C25D3/38—Electroplating: Baths therefor from solutions of copper
  • C25D3/40—Electroplating: Baths therefor from solutions of copper from cyanide baths, e.g. with Cu+

Definitions

• This invention relates to copper cyanide electroplating electrolytes containing lithium as an addition agent, and to the process for electroplating copper therefrom.
• aqueous copper cyanide electroplating electrolytes may be greatly improved by adding thereto small critical amounts of lithium, whereby the electrodeposition of copper therefrom, without sacrifice of quality, may be very substantially increased. In some instances, there is an improvement in quality attended with a higher rate of plating.
• the object of this invention is to provide for the electrodeposition of copper from aqueous copper cyanide electrolytes containing small critical amounts of lithium.
• a further object of this invention is to provide an aqueous cyanide electroplating electrolyte containing small critical amounts of lithium therein as an addition agent to enable satisfactory plating at a higher rate than would be possible in the absence of the lithium.
• Another object of the invention is to provide for electroplating copper by means of periodic reverse current from an aqueous cyanide copper electroplating electrolyte containing lithium a an addition agent.
• electrodeposition of copper from an aqueous copper cyanide electroplating electrolyte may be greatly benefitted by adding to the electrolyte from 0.01 to 0.4 ounce of lithium per gallon.
• the presence of lithium in these proportions enables the electrodeposition of copper from the electrolyte at a rate of about from 20% to 25% greater than would be otherwise possible from the same electrolyte, with the copper deposits being of substantia ly equal quality.
• the lithium additions may be added to copper cyanide electrolytes containing either zinc in the proportions from 0.004 to 0.57 ounce per gallon, or from 0.1 to 10 ounces per gallon of thiocyanate (CNS-) in the electrolyte, or both.
• thiocyanate CNS-
• the combination of lithium, zinc and thiocyanate in an aqueous copper cyanide electrolyte has enabled the plating of copper in commercial installations at the highest rate known heretofore for given members.
• the electrolytes from which copper is to be electroplated may be potassium cyanide electrolytes, sodium cyanide electrolytes, mixed potassium and sodium cyanide electrolytes, and Rochelle copper cyanide electrolytes; and when the lithium, zinc and thiocyanate are introduced therein in the proportions herein set forth, the electrodeposition of copper by periodic reverse current is markedly benefitted.
• a copper cyanide electroplating electrolyte may be prepared with from 2 to 15 ounces per gallon of dissolved copper, an alkali metal cyanide in an amount to complex the copper in solution, that is, to produce the more soluble alkali metal-copper cyanide double salt, and in addition to provide for 0.5 to 5 ounces per gallon of free alkali metal cyanide, from 2 to 12 ounces per gallon of alkali metal hydroxide, and up to 20 ounces per gallon of alkali metal carbonate.
• the cyanide solutions are usually maintained at a pH of from 12 to 13.5 and slightly higher.
• the electrolyte may contain other components commonly present in cyanide copper electroplating electrolytes such, for example, as 3 to 8 ounces per gallon of Rochelle salts (potassium sodium tartrate).
• the lithium may be introduced into the electrolyte in the form of any one of a number of lithium salts that are soluble in the plating solution.
• the lithium may be introduced as lithium hydroxide, lithium nitrate, lithium carbonate, lithium citrate and lithium thiocyanate.
• the lithium thiocyanate both lithium and thiocyanate are added simultaneously to the electrolyte. The optimum benefits are obtained when lithium is present in the proportions of from 0.04 ounce to 0.1 ounce per gallon of the cyanide electrolyte.
• zinc In the case that zinc is also to be added to the electrolyte, it may be added as zinc oxide, zinc cyanide, or zinc thiocyanate, or other water soluble salts. In some cases, the zinc may be added by introducing a zinc anode into the copper cyanide plating bath and passing a deplating current to the zinc anode, whereby to dissolve zinc in the electro yte.
• a composite mixture may be prepared for introducing lithium, zinc and thiocyanate into the electrolyte.
• the following examples are typical of such composite addition agent mixture in which all parts are by weight:
• Aqueous copper cyanide electroplating electrolytes containing lithium as an addition agent, can be employed with most satisfactory results with periodic reverse current.
• I am a co-inventor Serial No.
• periodic reverse current plating involves a cycle of plating followed by deplating and comprises the passing of a plating electrical current through the member being plated while it is in contact With an electroplating electrolyte for a period of time of the order of from /5 second to 300 seconds and then reversing the fiow of electrical current, usually for a shorter period of time and at a current density so that the coulombs of deplating current comprise from 10% to 90% of the coulombs applied during the plating period.
• the plating portion of the periodic reverse current cycle deposits an increment of copper on the member being plated, while the succeeding deplating portion of each cycle deplates a portion of the previously plated copper proportional to the coulombs of the deplating current.
• Example I An aqueous electrolyte having the following composition was prepared:
• wire of a diameter of approximately 0.06 inch was passed while mounted on a revolving reel.
• the reel revolved at 50 revolutions per minute.
• a periodic reverse current having a cycle having a 15 second plating period and a 3 second deplating period, the current density being equal in both plating and deplating periods.
• Tests showed that to product good copper plating on the wire, the maximum allowable plating current density was amperes per square foot. Any increase in plating current density above 100 square feet resulted in building up of nodules and the burning of the copper on the wire.
• the electrolyte of this example was modified by adding thereto lithium hydroxide monohydrate to provide a total of 0.08 ounce of lithium per gallon.
• a plating current of amperes per square foot could be applied to the wire with the quality of copper being equal to that obtained at a plating current of only 100 amperes per square foot Without any lithium.
• Lithium was added in further amounts up to 0.4 ounce per gallon of the electrolyte, and the maximum plating current density was maintained at substantially 120 amperes per square foot.
• a standard copper cyanide electrolyte containing neither zinc nor thiocyanate was prepared and tested with various periodic reverse current cycles. Lithium was then added, and at a concentration of 0.05 ounce per gallon of lithium, the electrolyte enabled copper to be plated therefrom at a rate 20% higher than could be plated from the same electrolyte without the lithium. Furthermore, the copper plated from the electrolyte with lithium was brighter over a wider range of plating current densities than could be secured without the lithium being present.
• Example III A bath of the following composition was prepared:
• Copper was plated from this bath on zinc die castings using a periodic reverse current having a 20 second plating period and an 8 second deplating period, the current density during the deplating period being 75% of the plating current density.
• the bath was operated at the maximum current density possible to produce good copper without burning. In twenty minutes 0.0008 inch of copper was plated on the die castings.
• Example III To the electrolyte of this Example III, 0.04 ounce per gallon of lithium was added. It was found that the bath could be operated at a 25% increase current density to produce copper plate of the same quality as was produced previously at the lower current density. In twenty minutes 0.001 inch of high quality copper was deposited on the zinc die castings.
• wire has been plated with copper from copper cyanide electrolytes containing lithium as the sole addition agent and found to have a conductivity of well over of the standards for copper conductors.
• the lithium must be replenished fromtime to time inasmuch as it is lost from the electrolyte by being plated out and by drag-out. Also, the zinc and thiocyanate, if they are present, must be similarly replenished.
• the cyanide electrolytes of this invention are preferably agitated or stirred to move the electrolyte past the member being plated at the rate of at least 1 foot per second, and preferably at a rate of the order of 10 feet per second during the plating operation. Filtering of the electrolyte is recommended inasmuch as the electrodeposits produced are so smooth and bright that they will show the presence of any suspended matter in the electrolyte.
• lithium enables the plating of copper at a greater rate than possible without the lithium
• the plated copper is usually smoother and brighter, everything else being equal, than when plated from the same electrolyte without the lithium.
• mirror-bright copper has been obtained over a wide range of current densities from numerous copper cyanide plating electrolytes.
• the presence of lithium enables an increase of leveling to be obtained compared to that possible without the lithium. It should be understood that while with periodic reverse current, substantial leveling is obtained, any increase in leveling is highly desirable.
• Lithium enables an additional reduction in roughness of plated copper.
• a copper cyanide electrolyte with lithium in conjunction with periodic reverse current enables the plater to approach the desired goal of 1 to 2 microinches of final roughness for a thickness of 0.001 inch of copper plated on a surface having from 10 to 15 microinches of roughness before plating.
• the copper cyanide electrolytes with lithium alone or with zinc and thiocyanate may be employed for direct-current plating.
• the benefits of lithium are not as pronounced with direct current as they are with periodic reverse current.
• An aqueous copper cyanide electroplating electrolyte comprising, in combination, from 2 to 15 ounces per gallon of copper, alkali metal cyanide in an amount to complex the copper in solution and to provide from 0.5 to 5 ounces per gallon of free alkali metal cyanide, from 2 to 12 ounces per gallon of alkali metal hydroxide, from 1 to 20 ounces per gallon of alkali metal carbonate, and from 0.01 to 0.4 ounce per gallon of lithium.
• the steps comprising applying to the member as a cathode an aqueous cyanide electrolyte having dissolved therein from 2 to 15 ounces per gallon of copper, alkali metal cyanide in an amount to compex the copper in solution and to provide from 0.5 to 5 ounces per gallon of free alkali metal cyanide, from 2 to 12 ounces per gallon of alkali metal hydroxide, from 1 to 20 ounces per gallon of alkali metal carbonate, and from 0.01 to 0.4 ounce per gallon of lithium, passing a plating electrical current through the electrolyte for a period of time of from 1/5 second to 300 seconds, then passing a deplating electrical current through the electrolyte for a period of time to apply to the member from 10% to 90% of the coulombs applied during the preceding plating period, and continuing the alternate plating and deplating until a desired thickness of copper has been plated on the member.
• the steps comprising immersing the member as a cathode in an aqueous cyanide electrolyte having dissolved therein from 2 to 15 ounces per gallon of copper, alkali metal cyanide in an amount to complex the copper in solution and to provide from 0.5 to 5 ounces per gallon of free alkali metal cyanide, from 2 to 12 ounces per gallon of alkali metal hydroxide, from 1 to 20 ounces per gallon of alkali metal carbonate, and from 0.01 to 0.4 ounce per gallon of lithium, and passing a plating electrical current through the electrolyte to plate copper on the member.
• the steps comprising applying to the member as a cathode a cyanide copper electrolyte having dissolved therein from 0.01 to 0.4 ounce of lithium per gallon of the electrolyte and passing a plating electric current through the electrolyte to plate copper on the member.
• An improved aqueous copper cyanide electroplating electrolyte comprising from 0.01 to 0.4 ounce of lithium per gallon of the electrolyte, the lithium being dissolved in the electrolyte.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electrolytic Production Of Metals (AREA)

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Cited By (3)

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• 1952
  • 1952-10-21 US US316085A patent/US2690997A/en not_active Expired - Lifetime
• 1953
  • 1953-08-29 DE DEW12007A patent/DE925029C/de not_active Expired
  • 1953-10-13 GB GB28120/53A patent/GB753586A/en not_active Expired
  • 1953-10-20 FR FR1090776D patent/FR1090776A/fr not_active Expired

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