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
  • C25D3/12—Electroplating: Baths therefor from solutions of 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
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
  • C25D21/14—Controlled addition of electrolyte components

Definitions

• the field of the invention relates to a bath for electroplating low-stress nickel to conductive substrates and processes utilizing such baths.
• Nickel sulfamate baths are generally used when a low stress nickel coating is required, such as in electroforming applications, or where the nickel deposit will be subjected to external stress.
• Nickel sulfamate solutions are preferred over nickel sulfate solutions because (a) the mechanical properties of the sulfamate produced coating are superior to those formed from sulfate solutions, (b) high rates of deposition are possible from the sulfamate solution, and (c) the deposit quality is less affected by variations in pH and current density.
• several issues need to be addressed when a nickel sulfamate bath is used.
• a typical nickel sulfamate solution contains nickel sulfamate (400 - 650 g/l), nickel chloride (5 - 20 g/l) and boric acid (30 - 40 g/l).
• the operating pH is between 3.5 - 4.5 and the temperature may vary from 35 - 50°C.
• Soluble nickel anodes are used to replenish the nickel which is plated on the cathode during electrolysis. Current density varies from 0.5 - 30 A/dm 2 .
• the sulfamate ion is stable in neutral or slightly alkaline solution even at elevated temperature. However, because of nickel hydroxide precipitation, these solutions are not used at a pH greater than 5.
• Hydrolysis of the sulfamate ion may be a problem.
• the hydrolysis of sulfamate is generally characterized by the formation of ammonium ions and a bisulfate or sulfate anion: H 2 NSO 3 - +H 3 O + ⁇ NH 4 + + HSO 4 -
• the sulfamate hydrolysis reaction has been investigated and has been found to be at an increased rate at greater hydrogen ion concentrations (e.g., lower pHs). These investigators also found the sulfamate hydrolysis reaction increases with an increase in temperature of the electrolyte; thus nickel sulfamate solutions are commonly operated at lower temperatures than Watts type nickel plating solution.
• the sulfamate ion also decomposes at the anode, for example, at insoluble anodes such as platinum and at passive nickel oxide electrodes.
• the decomposition of sulfamate appears to produce several intermediates such as sulfite, dithionate, azodisulfonate and another unknown species which may effect the quality of the electrodeposited coating.
• Nickel solution When choosing a nickel solution from which to deposit a layer of nickel it is important to consider the resultant internal stress of the nickel coating. Stresses in nickel deposits range from -15,000 PSI (compressive) to about +100,000 PSI (tensile). A high tensile stress may lead to cracking of the nickel deposit particularly if the nickel is subjected to mechanical deformation (stresses and strains) or elevated temperatures. Nickel electroforms such as those produced from nickel sulfamate solutions may have warpage or change dimensions when the substrate is removed if the nickel is in a state of tensile stress. High tensile stresses may also lead to lower fatigue life of steels and aluminum alloys.
• Organic additives are commonly added to nickel solutions to reduce the tensile stress of the deposits.
• the composition and concentration of the stress reducers is dependent upon the nature of the nickel electrolyte (e.g., nickel sulfate or nickel sulfamate).
• the effects of organic stress reducers on the internal stress of nickel deposits from a nickel sulfate solution has been examined.
• Additives which contain sulfur such as saccharin, naphthalene-1,5-disulfonic acid and naphthalene trisulfonic acid are effective stress reducers. Sulfur containing compounds and their influence on the internal stress in nickel coatings has also been studied.
• Benzene sulfonate, benzene sulfonamide and sulfanilic acid reduce the internal stress but only benzene sulfonamide imparts a compressive stress.
• p-amino benzene sulfonamide causes the stress to become very tensile in nickel deposits plated from sulfate solutions.
• Kudryavtsev ct al. disclose that disadvantages of the sulfamate bath include (1) the sulfamate bath being chemically unstable (2) sulfamate starting to decompose at 60°C but the baths run at 45 to 60°C, and (3) the bath being very sensitive to impurities of other metal ions, thus to prevent deterioration in coating quality, reduction in ductility and cathode current efficiency, the maximum Fe which can be present in the bath is 20 mg/L, maximum Cu is 10 mg/L, maximum Zn is 10 mg/L, maximum Pb is 2 mg/L and maximum Cr is 2 mg/L.
• Kudryavtsev et al. disclose that the compositions they tested were comprised of Ni(CH 3 SO 3 ) 2, 100 to 400 g/l; H 3 BO 3, 17 to 40 g/l; saccharin, .01 to 1.8 g/l; and sodium lauryl sulfate, .02 to 0.5 g; and that the electroplating process was at a pH of 0.8 to 2.0; temperature of 30 to 60°C; and a current density (CD) of 0.5 to 39 A/dm 2 .
• CD current density
• the general aim herein is to provide new and useful compositions and methods for electrodepositing nickel coatings; preferred aims include the reduction or elimination of one or more of the limitations and disadvantages of the known processes as discussed above. In particular a preferred aim is to avoid tensile stress in the coating.
• the invention comprises a composition of matter which allows the use of nickel alkane sulfonic acid in an electrodepositing process to produce low-stress nickel coatings having compressive stress.
• One embodiment of the invention is a composition of matter for producing low stress electrodepositing nickel coatings.
• the composition is an acidic aqueous electroplating bath comprising a nickel alkane sulfonic acid and a stress-reducing additive that imparts compressive stress to the coating.
• Another embodiment of the present invention is a process for producing electrodeposited coatings by electroplating a cathodic conductive substrate in a coating bath having an anode inserted therein, the bath consists essentially of a nickel alkane sulfonic acid and a stress-reducing additive that imparts a compressive stress to the coating, maintaining the coating bath at a pH from about 0 to about 5; and maintaining the current density on the substrate at from about 1 to about 100 A/dm 2 .
• Another embodiment of the invention is a composition of matter for replenishing a spent electroplating bath for producing low stress electrodeposited nickel coatings, the spent bath initially containing Ni(CH 3 SO 3 ) 2 (or other nickel alkane sulfonate) and a stress-reducing additive that imparts a compressive stress to the coating, the composition being a slurry comprising nickel carbonate and further said stress-reducing additive, e.g. an aromatic sulfonic acid.
• the nickel alkane sulfonic acids include sulfonic acids of the formula (R) (SO 3 ) x , where R and x are defined hereinafter.
• the nickel alkane sulfonate comprises a water soluble compound by which it is meant that the compound is soluble in water at about room temperature (about 20°C) or lower (about 10°C to about 20°C), and preferably from these temperatures up to or slightly below the operating temperature of the bath, and preferably has the formula: Ni[(R)(SO 3 ) x ] y where
• R is an alkyl group having from 1 to about 15 carbon atoms and especially 1 to about 7 carbon atoms including the straight chain and branch chain isomers thereof such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, isobutyl, pentyl, isopentyl, and the like. Hydroxy substituted alkyls, as alkyl is defined herein, are also included.
• nickel salts in this regard comprise nickel methane sulfonates, nickel ethane sulfonates, nickel propane sulfonates, nickel isopropane sulfonates, nickel butane sulfonates, nickel isobutane sulfonates, nickel t-butane sulfonates, nickel pentane sulfonates, nickel isopentane sulfonates, and the like, as well as the hydroxy substituted compounds thereof.
• R also includes cyclic, and heterocyclic hydrocarbon substituents such as cycloaliphatic, unsaturated cycloaliphatic, and aromatic groups having from 4 to about 16 carbon atoms and especially from about 6 to about 14 carbon atoms including cyclobutyl, cyclobutenyl, cyclohexyl, cyclohexenyl, cyclohexadienyl, cyclooctanyl, cyclooctadienyl.
• substituents such as cycloaliphatic, unsaturated cycloaliphatic, and aromatic groups having from 4 to about 16 carbon atoms and especially from about 6 to about 14 carbon atoms including cyclobutyl, cyclobutenyl, cyclohexyl, cyclohexenyl, cyclohexadienyl, cyclooctanyl, cyclooctadienyl.
• the compound is present in sufficient quantity so that the concentration of Ni ++ is preferably 25 to 135 g/l, more preferably 50 to 100 g/l, most preferably about 80 g/l.
• Preferred for use in the bath of the present invention is nickel methane sulfonic acid - Ni(CH 3 SO 3 ) 2 .
• the invention also includes depositing alloys of nickel as the nickel coating of the present invention, e.g. by employing alkane sulfonate salts of the alloying metals and nickel alkanesulfonates, where in formula (A), the alloying metal will be substituted for "Ni", “y” has a value of 1 up to the valence of the alloying metal, and "x" has the values given above.
• Alloys of nickel may also be deposited employing alloying additives to the coating bath in lieu of or in addition to the sulfonate alloying compounds described herein. Any of the other Group IB, IIB, IIIA, IVA, IVB, VA, VB, VIB, VIIB or VIIIB metals may be used as alloying metals. Mixtures of alloying metals from Group VIII and/or Group IIB or Cr or Mn may also be prepared, especially the two component or three component alloys where the alloying metal is present in the coating in an amount anywhere from about 0.1 to about 20 percent by weight and especially from about 5 to about 15 percent by weight. Examples include NiZn, NiCr, NiFe, NiP, NiMn, NiSn and NiW.
• the alloys are prepared by inserting the alloy metal into the coating baths either as an anode in a manner well known in the art or by adding a salt of the alloying metal to the coating bath.
• a stress reducing additive that imparts a compressive stress to the electrodeposited coating is in the bath, usually at a concentration of 0.5 to 15 g/l, preferably 2 to 15 g/l, more preferably 5 to 10 g/l, and most preferably about 8 g/l.
• concentration of the additive will range from 5 to 20 % of the concentration of the nickel ion present in the bath .
• Useful additives include those known as being useful in Watts and Sulfamate baths. Included are aromatic sulfonic acids e.g. in which the aromatic group of compound may be any six membered ring or polynuclear ring having from about 10 to about 14 carbon atoms, all of which are well known in the art. Anywhere from one to about three sulfonate groups can be substituted on the aromatic ring.
• Examples include aminobenzene sulfonic acid, benzene sulfonic acid, benzene disulfonic acid, napththylamine disulfonic acid, naphthalene monosulfonic acid, naphthalene disulfonic acid, naphthalene trisulfonic acid, naphthol monosulfonic acid and p-toluene sulfonic acid.
• Benzene sulfamide cysteine hydrochloride
• saccharin useful when the bath will be maintained at a pH > 2
• p-toluene sulfonamide thioacetamide
• thiosemicarbazide thiourea
• naphthalene trisulfonic acid especially 1,3,6-naphthalene trisulfonic acid.
• the bath preferably contains a nickel halogen, such as, for example, NiCl 2 or NiBr 2 .
• the nickel halogen aids in the dissolution of the soluble anode.
• the amount of nickel halogen is usually up to about 100 g/l, preferably 20 to 40 g/l.
• Such other additives include, for example, 0 to about 60 g/l, preferably 35 to 45 g/l of buffers, such as boric acid and/or 0 to about 2 ml/l, preferably about 1 ml/l of a surfactant, for example, sodium lauryl sulfate, to reduce surface tension and prevent bubbling of hydrogen gas.
• buffers such as boric acid
• surfactant for example, sodium lauryl sulfate
• Electrodeposition according to the process takes place at a pH from about 0 to about 5, preferably about 0.5 to about 4.5, and most preferably about pH 1 to 4.
• composition and process typically operate at current densities from about 1 Amps/dm 2 to about 200 Amps/dm 2 and preferably from about 2 Amps/dm 2 to about 30 Amps/dm 2 .
• the preferred current density is about 50 Amps/dm 2 to about 100 Amps/dm 2 .
• the process usually proceeds at temperatures from about room temperature (20°C) to about 80°C, and preferably from about 30°C to about 70°C, and most preferably from about 40°C to about 60°C.
• solution agitation may be employed. Air agitation, mechanical stirring, pumping, cathode rod and other means of solution agitation are all satisfactory. Additionally, the solutions may be operated without agitation.
• the agitation of the bath preferably produces a flow rate of about 0.5 to 5 meters/sec.
• a suitable composition for the replenishing the spent nickel alkane sulfonic acid and stress-reducing additive containing electroplating bath is a slurry comprising (a) nickel carbonate which replenishes the nickel and increases the pH of the bath, and (b) the stress reducing additive of the initial bath used to impart compressive stress to the electrodeposit.
• the slurry usually will contain 0.5 to 10 g/l, preferably 1.5 to 5 g/l, of the stress reducing additive for every 1000 g/l of the nickel carbonate present in the slurry.
• the amount of the stress reducing additive will be dependent on the particular stress-reducing additive used in the slurry. For example, if 1,3,6-naphthalene trisulfonic acid is the stress reducing agent the amount will preferably be about 1 to 6 g/l, most preferably about 3 g/l per 1000 g/l of nickel carbonate.
• the amount of slurry added to the bath will be based on the Amp hours to which the spend bath has been exposed and will be sufficient to maintain the amount of nickel in the bath at the concentration desired by the electroplater.
• the anodes useful in the process of the present invention include soluble anodes, such as, for example, nickel foil, and insoluble anodes, such as, for example, platinum and precious metal oxides.
• the insoluble (inert) anodes used in this invention are insoluble (inert) in the electrolyte solution and consist of either a solid anodic metal or metal compound e.g., oxide, where the metals are of the Group IVB, VB, VIB, VIIB, VIIIB, and IB of the periodic table, or the anodes comprise the above-described metals or their alloys mounted on support materials including, for example, cheaper base metals from the Group IVB, VB, VIB, VIIB, and VIIIB metals and their alloys, e.g., stainless steels.
• a preferred anode metal compound is iridium dioxide (IrO 2 ). Alloy metals of IrO 2 are preferably the metals of Group VIB and VIIB, e.g, chromium, molybdenum, and nickel.
• Insoluble anodes can be used to deposit any galvanic metal, in addition to nickel.
• the metals that can be deposited are known to those skilled in the art and include zinc, copper, lead, chromium, magnesium, tin, molybdenum and alloys thereof.
• Electroplating proceeds in the manner described herein by electrolytically coating a conductive substrate with the composition of the invention, where the substrate (cathode) comprises any electrically conductive substrate or polymer substrate, or insulating substrate (e.g., a polymeric material, such as a synthetic polymeric substrate, or a ceramic substrate) coated with a conductive material such as a metal or any art known conductive substrates such as a carbon substrate.
• the substrate comprises any electrically conductive substrate or polymer substrate, or insulating substrate (e.g., a polymeric material, such as a synthetic polymeric substrate, or a ceramic substrate) coated with a conductive material such as a metal or any art known conductive substrates such as a carbon substrate.
• any conductive substrate may be employed whether a polymer, plastic, pure metal, a metal alloy, and includes other iron-alloy substrates or metals or alloys based on Groups IB, IIB, IIIA, IVA, IVB, VA, VB, VIB, VIIB or VIIIB metals and elements, the alloys comprising combinations of two or more of these metals and elements, especially the two or three or four component combinations of metals and elements.
• Coating proceeds by passing a current between the anode in the electrocoating bath to the cathode substrate in the bath for a period of time sufficient to deposit the desired nickel coating on the cathode.
• a bath was prepared containing Ni(CH 3 SO 3 ) 2 (300 g/l) and 1,3,6-naphthalene trisulfonic acid (7.5 g/l). No nickel halogen or buffer was added.
• the bath was employed to deposit a nickel coating on a steel plate using a 1 liter plating vessel with mild air agitation at 50°C.
• the anode was a piece of nickel foil.
• the average current density was about 4 amp per sq. dm.
• the pH of the bath at the start of plating was 3.5 and at the end of plating 2.1.
• the deposition is carried out for 15 minutes to provide a coating 7 to 10 ⁇ m thick.
• the coating was smooth and semi-bright.
• the stress in the coating was -6000 PSI (compressive).
• a bath was prepared containing Ni(CH 3 SO 3 ) 2 (300 g/l); 1,3,6-naphthalene trisulfonic acid (7.5 g/l), NiCl 2 (40 g/l), and H 3 BO 3 (45 g/l).
• the bath was employed to deposit a nickel coating on a steel plate using a 1 liter plating vessel with mild air agitation at 50°C.
• the anode was a piece of nickel foil.
• the average current density was about 4 amp per sq. dm.
• the pH of the bath at the start of plating was 3.5 and at the end of plating 3.4.
• the deposition was carried out for 15 minutes to provide a coating 9 to 12 ⁇ m thick.
• the coating was smooth and semi-bright.
• the stress was -5200 PSI (compressive).
• a bath was prepared containing Ni(CH 3 SO 3 ) 2 (300 g/l), sodium saccharin (1 g/l), NiCl 2 (40 g/l), and H 3 BO 3 (45 g/l).
• the bath was employed to deposit a nickel coating on a steel plate using a 1 liter plating vessel with mild air agitation at 50°C.
• the anode was a piece of nickel foil.
• the average current density was about 4 amp per sq. dm.
• the pH of the bath at the start of plating was 3.3 and at the end of plating 3.4.
• the deposition was carried out for 30 minutes to provide a coating 19 to 23 ⁇ m thick.
• the coating was smooth and semi-bright.
• the stress was -2000 PSI compressive.
• a bath was prepared containing Ni(CH 3 SO 3 ) 2 (300 g/l) and 1,3,6-naphthalene trisulfonic acid (7.5 g/l)).
• the bath was employed to deposit a nickel coating on a steel plate using a 1 liter plating vessel with mild air agitation at 50°C.
• the anode was a piece of iridium oxide coated titanium.
• the average current density was about 4 amp per sq. dm.
• the pH of the bath at the start of plating was 1.8 and at the end of plating 1.7.
• the deposition was carried out for 60 minutes to provide a coating 40 to 45 ⁇ m thick.
• the coating was smooth and semi-bright.
• the stress was -3200 PSI (compressive).
• a bath was prepared containing Ni(CH 3 SO 3 ) 2 (300 g/l) and 1,3,6-naphthalene trisulfonic acid (7.5 g/l).
• the bath was employed to deposit a nickel coating on a steel plate using a 1 liter plating vessel with mild air agitation at 55°C. Two anodes were used, a soluble nickel foil and a piece of iridium oxide coated titanium. The average current density was about 5 amp per sq. dm.
• the pH of the bath at the start of plating was 2.0 and at the end of plating 1.8.
• the deposition was carried out for 30 minutes to provide a coating 18 to 22 ⁇ m thick.
• the coating was smooth and semi-bright.
• the stress was -1500 PSI (compressive).
• a nickel methanesulfonate solution was prepared by dissolving 150 g/l NiCO3 into 70% MSA. After complete dissolution of the nickel carbonate, this solution was filtered to remove any residual particulate matter. To this was added 30 g/l boric acid, 5 g/l naphthalenetrisulfonic acid. This solution was heated to 60°C to dissolve the boric acid. Upon cooling to room temperature, the pH was adjusted to 2.0 with 70% MSA.
• a steel coupon was anodically cleaned in 50 g/l NaOH followed by water rinses. This was activated in 5% HCL, room temperature for five seconds. The steel was plated at 4 A/dm2 for 15 minutes. The panel was bright and smooth. Cathode current efficiency was 89.3%.
• a nickel methanesulfonate solution was prepared by dissolving 150 g/l NiCO3 into 70% MSA. After complete dissolution of the nickel carbonate, this solution was filtered to remove any residual particulate matter. To this was added 15 g/l nickel chloride, 30 g/l boric acid, 3 g/l napthlene trisulfonic acid. This solution was heated to 60°C to dissolve the boric acid. Upon cooling to room temperature, the pH was adjusted to 3.2 with 70% MSA.
• a 5% aqueous solution of sulfamic acid was prepared and the pH was adjusted to 3.0.
• a three electrode electrochemical setup was used to study the oxidation of the sulfamic acid.
• the counter-electrode was a IrO2 grid.
• the reference electrode was silver/silver chloride.
• the working electrode was iridium-coated titanium. The potential of this system was scanned, starting from -0.2 V, in the anodic direction. A large oxidation peak was seen at +0.3 V.
• insoluble anodes in the nickel methanesulfonate electrolyte and experience no degradation by-products.
• the use of insoluble anodes in the sulfamic acid solution will lead to breakdown products at the anode.
• a bath was prepared containing Ni(CH 3 SO 3 ) 2 (300 g/l) and sodium saccharin (1 g/l). No nickel halogen was used.
• the bath was employed to deposit a nickel coating on a steel plate using a 1 liter plating vessel with mild air agitation at 50°C.
• the anode was a piece of nickel foil.
• the average current density was about 4 amp per sq. dm.
• the pH of the bath at the start of plating was 3.3 and at the end of plating 1.7.
• a white precipitate was seen in the plating solution at the end plating. This is saccharic acid which precipitated due to the drop in pH.
• the deposition was carried out for 30 minutes to provide a coating 17 to 23 ⁇ m thick.
• the coating was slightly rough and semi-bright.
• the stress was +4200 PSI tensile.
• the inventors refer to various materials used in their invention as based on certain components, and intend that they contain substantially these components, or that these components comprise at least the base components in these materials.

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• 1998
  • 1998-06-10 CA CA 2236933 patent/CA2236933A1/fr not_active Abandoned
  • 1998-06-11 EP EP98304642A patent/EP0892087A3/fr not_active Withdrawn
  • 1998-06-12 SG SG1998001409A patent/SG63851A1/en unknown
  • 1998-06-17 JP JP18572298A patent/JPH1171695A/ja not_active Withdrawn
  • 1998-06-18 CN CNB981149332A patent/CN1142327C/zh not_active Expired - Fee Related

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