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
  • C25D3/50—Electroplating: Baths therefor from solutions of platinum group metals

Definitions

• the present invention relates to the electroplating of bright, crack-free, relatively thick deposits of low-stress ruthenium from specially prepared ruthenium electrolytes.
• Electrodeposits of ruthenium are valuable as coatings for electrical contacts, e.g., those in reed switches, and for other surfaces requiring good resistance to wear. They have also been found useful for decorative coatings. At present, however, ruthenium deposits obtained from baths of known composition have limited utility.
• Y is chlorine or bromine.
• Y is chlorine or bromine.
• the anions are preferably introduced as their ammonium salts and that the method of electrodepositing ruthenium is from an aqueous acidic bath having a pH not exceeding 4.
• the complex anions are believed to be nitrogen-bridged compounds of ruthenium, the anion of which has the following structure:
• L represents the aquo, chloro or bromo ligands.
• the deposits are bright only up to a thickness of about 2 to 3 millimicrons (pm). At greater thicknesses, surface-cracking becomes apparent and the deposits are matte and gray.
• Another object of the invention is to provide a novel ruthenium electroplating bath composition.
• novel ruthenium electroplating baths of this invention are prepared by dissolving the compound Ru N(0H) -nH O in either aqueous sulfuric or sulfamic acid and refluxing, for example, at about 100C. or higher, for between about one and hours.
• the sulfate ion concentration must exceed about 15 grams per liter (gpl) in order to obtain crackfree deposits, but does not normally exceed about gpl as no further benefit is obtained and current efficiency is reduced.
• the resulting solution obtained after refluxing may be used directly as the plating bath; however, if the sulfate ion concentration is not sufficiently high, it may be increased by adding a sulfate salt, for example, ammonium, sodium or potassium sulfate.
• a sulfate salt for example, ammonium, sodium or potassium sulfate.
• the term sulfate ion includes both sulfate and bisulfate ion and any mixture thereof. Any concentration of sulfate ion mentioned herein is to be deemed to be the result of complete ionization of any sulfate salts or acid added to the baths of the present invention. It is also essential that the pH of the bath solution does not exceed about 4.
• the plating bath be prepared by dissolving a quantity of the compound in water and adding sufficient alkali, for example, potassium hydroxide, to precipitate the compound Ru N- (OH) -nH O. This compound is then filtered off and thoroughly washed to remove chloride and other impurities.
• an aqueous solution of K [Ru(- NO)Cl is basified with alkali, e.g., potassium hydrox ide, and then treated with a reducing agent such as formaldehyde.
• a precipitate of Ru N(OH) 'nH O is formed on warming the solution, for example, on a steam bath, which is then filtered off and thoroughly washed with water.
• the compound Ru N(OH) 'nH O is then used to prepare the plating bath in accordance with the procedures described hereinabove.
• the pH of the bath solution should not exceed about 4. In practice, the pH should be from about 0.5 to about 4 and is preferably from about 1 to 3. If the pH of the bath solution is too low, the deposition of ruthenium takes place at a low cathode current efficiency. If the pH is too high, the resulting ruthenium deposit is black. Increasing the pH still further leads to the formation of a brownish deposit on the cathode that is not metallic ruthenium.
• the pH may be modified by the addition of suitable pH modifying agents such as potassium, sodium or ammonium hydroxides and sulfuric or sulfamic acids. If necessary, the pH of the bath can be similiarly adjusted during operation so as to maintain the pH within the proper-operating ranges.
• the ruthenium concentration in the plating bath is advantageously from about one to about 20 gpl. Higher concentrations of ruthenium may be used although there is nopractical advantage in doing so. Moreover, losses of ruthenium from the bath by drag-out are increased and the capital cost of the bath becomes unnecessarily high. Agitation of the bath is desirable at ruthenium contents exceeding about 20 gpl.
• the plating bath should be stabilized by the presence of sulfamate ions at a level of at least about 2 gpl and, preferably, about 20 gpl. This level should be maintained throughout the plating operation and additions to the bath may be made by using such sulfamate salts as ammonium, potassium or sodium. Loss of sulfamate ions occurs through anodic oxidation and it is therefore necessary to periodically check the concentration during the plating operation and to add further sulfamate ions if required.
• the temperature of the bath is not critical,
• the solution was cooled aha its pH found to be 1
• the pH was increased to 1.5 by the addition of potassium hydroxide and this solution was then employed as the electrolyte from which ruthenium electrodeposits it is advantageous that the operating temperature of the bath be maintained between about 50C. and 70C. since plating proceeds more slowly at lower temperatures, while at higher temperatures excessive losses, due to evaporation, mayoccur.
• the bath can only be operated within a limited range of current densities, since the cathode efficiency is found to rapidly decrease as the cathode current density is increased to about 1 ampere per square decimeter (A/dm).
• Temperature of electrolyte 70 l.5 Cathode current density (Aldm l Anode current density (A/dm) 0.] Time (minutes) Thickness of deposit (p.111) 5 Current efficiency 33 Internal stress after 1 [IJII deposited (kg/mm) 20 The deposit was bright and crack-free.
• Baths of this invention compare quite favorably with baths of known composition such as US. Pat. No. 3,576,724, noted hereinabove.
• These baths containing [Ru N(H O) Cl when measured under similar testing conditions, have internal stresses on the order of 40 to 60 kg lmm which is significantly higher than the internal stress of baths of this invention, as shown hereinabove.
• a process for producing a ruthenium electroplating bath having a pH of about 4 or less which comprises:
• a process in accordance with claim 1 further comprising adjusting the sulfate ion concentration of said bath to a level of at least about gpl by the addition of sulfate salt.
• sulfate salt is selected from the group consisting of ammonium sulfate, sodium sulfate and potassium sulfate.
• a process in accordance with claim 1 further comprising adjusting the sulfamate ion concentration to a level of at least about 2 gpl by the addition of a sulfamate salt.
• sulfamate salt is selected from the group consisting of ammonium sulfamate, sodium sulfamate and potassium sulfamate.
• X is at least one member selected from the group consisting of chlorine and bromine and adjusting the pH of said solution to precipitate 7.
• said complex anion is a part of the ammonium salt.
• au mom -nn o is produced by a. providing an aqueous solution of a compound having, in the ionic state, a complex anion of the formula [Ru(NO)Cl b. adjusting the pH of said solution to an alkaline pH;
• a ruthenium electroplating bath producible by a process in accordance with claim 1.
• a process in accordance with claim 12 further comprising maintaining a concentration of sulfamate ions in the bath of at least about 2 gpl.

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• Chemical & Material Sciences (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)
• Inorganic Compounds Of Heavy Metals (AREA)

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Publications (1)

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Family Applications (1)

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Cited By (8)

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Citations (4)

• 1971
  • 1971-12-17 GB GB5878071A patent/GB1407592A/en not_active Expired
• 1972
  • 1972-12-12 US US00314390A patent/US3793162A/en not_active Expired - Lifetime
  • 1972-12-15 FR FR7244916A patent/FR2163734B1/fr not_active Expired
  • 1972-12-18 JP JP47127597A patent/JPS4868432A/ja active Pending
  • 1972-12-18 IT IT54799/72A patent/IT974137B/it active
  • 1972-12-18 DE DE19722261944 patent/DE2261944A1/de active Pending

Patent Citations (4)

Non-Patent Citations (1)

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