Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper
  • C23C18/40—Coating with copper using reducing agents
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/42—Coating with noble metals
  • C23C18/44—Coating with noble metals using reducing agents

Definitions

• the electroless plating bath disclosed includes an aqueous solution of an imide complex of the Group lB metal to be plated, an alkali metal cyanide, and a reducing agent, and is maintained at a pH of from about 1 1 to 14 by the addition of alkali metal hydroxides.
• an electroless gold plating bath is disclosed, including an aqueous solution of an alkali metal gold imide complex.
• non-metallic substrates are to be plated
• the surfaces are rendered catalytically active prior to immersion in the electroless plating baths
• metallic substrates are plated, they are preferably pre-coated with a thin plate by immersion in an aqueous plating bath including a soluble gold salt, an ammonium buffering agent, and an organic chelating agent, prior to immersion in the electroless plating baths of the present invention.
• the present invention relates to improved electroless plating baths for the autocatalytic deposition of Group [B metals upon substrates.
• the present invention relates to improved electroless silver, copper and gold plating baths for autocatalytic deposition upon catalytic surfaces, which baths provide improved palting characteristics, including improved plating rates.
• the present invention relates to improved methods of plating various substrates utilizing electroless plating baths of the Group IB metal to be plated thereon.
• electroless plating baths for the autocatalytic deposition of gold and other Group [B metals upon various substrates has become widely known.
• Such baths as compared to conventional electroplating baths, are characterized by an ability to deposit these metals on a wide variety of metallic and nonmetalic substrates without requiring the use of electricity.
• Dr. Okinaka has described the electroless deposition of gold using as reducing agents borohydride and dimethylamine borane, and alkali metal cyanides as the source of gold, with a demonstrable deterioration in the baths with increased cyanide concentrations, particularly upon replenishment with additional alkali metal gold cyanide.
• borohydride and dimethylamine borane as the source of gold
• alkali metal cyanides as the source of gold
• an electroless gold plating bath including a water-soluble gold salt and a complexing agent for the gold, in addition to the water-soluble borohydride or amine borane reducing agent, and a stabi lizing amount of a cyanide compound, all maintained at a pH of between 10 and 14.
• This disclosure thus teaches the use of a complexing agent of form a gold complex in an attempt to prevent gold precipitation during plating.
• This disclosure also teaches that the amount of water-soluble cyanide compound, between 5 micrograms and 500 milligrams per liter, is critical.
• electroless plating baths for autocatalytic deposition upon various substrates are provided, resulting in the deposition of thick silver, copper and gold plates.
• the electroless plating baths of this invention comprise an aqueous so lution of an imide complex of the Group IB metal to be plated, an alkali metal cyanide in an amount sufficient to stabilize the bath, and a reducing agent selected from the group consisting of water soluble alkali metal borohydrides, water soluble amine boranes and formaldehyde.
• the pH of the bath is maintained from about 1 l to 14. It has thus been found that these electroless plating baths exhibit superior plating rates, without concomitant bath decomposition. Specifically, plating rates of greater than 2.5 microns per hour, and preferably greater than 2.7 microns per hour are obtainable therewith.
• the required pH level is maintained by the addition of alkali metal hydroxides to the bath, and preferably alkali metal buffering salts are added thereto in addition to the alkali metal hydroxides, in order to obtain a superior degree of pH control.
• organic chelating agents may be added to these electroless plating baths, particularly when metallic substrates are to be plated therewith, in order to form complexes with the replaced metals, and prevent the precipitation thereof.
• improved methods for plating various substrates are provided, in which the metallic or non-metallic substrates are rendered catalytically active prior to immersion to the improved electroless plating baths hereof.
• Ductile silver, copper and gold plates are thus provided, having strong adherence to the substrates employed, and of relatively uniform thicknesses as compared to the plates obtainable by the prior art plating baths.
• the imides of the present invention which are capable of forming particularly strong complexes with the Group ID metals to be plated, such as gold, have a general formula as follows:
• R is a radical selected from the group consisting of alkylene, substituted alkylene, arylene, and substituted arylene.
• R will be a substituted arylene, such as sulfonyl-o-phenylene (SO C H in which case the imide formed will be sulphobenzoic imide, (i.e., saccharin, or o-benzosulfimide) C H (S0 (C .))--Nl-l.
• SO C H sulfonyl-o-phenylene
• S0 (C .) o-benzosulfimide
• the imides with which the Group 18 metals to be plated are complexed will have a general formula as follows:
• R is a radical selected from the group consisting of alkylene, substituted alkylene, arylene, and substituted arylene.
• R will be alkylene.
• the imide will be succinimide
• R is an arylene radical such as C l-i (o-phenylene)
• the imide will be phthalimide.
• these two compounds, succinimide and phthalimide will be particularly preferred, thus forming complexes with the gold in the form of alkali metal gold succinimide, particularly potassium gold succinimide, and alkali metal gold phthalimide, particularly potassium gold phthalimide.
• the electroless plating baths of this invention include soluble cyanide compounds in critical amounts in order to maintain the stability of the bath.
• water soluble cyanide compounds are the alkali metal cyanides, such as sodium, potassium and lithium cyanide. Among these, sodium and potassium cyanide are particularly preferred. Other such compounds may, however, be employed, such as nitriles, including alpha-hydroxynitriles, etc. as described in U.S. Pat. No. 3,589,916 which compounds are thus incorporated herein by reference. It is critical, however, that the water-soluble cyanide compounds be used in specific amounts, generally from between about 2 and 20 grams per liter, and preferably from about 5 to grams per liter.
• the reducing agents employed in connection with the present electroless plating baths include any of the borohydrides or amine boranes which are soluble and stable in aqueous solution.
• alkali metal borohydrides preferably sodium and potassium borohydrides
• substituted borohydrodes such as sodium or potassium trimethoxyborohydride, Na[K]B(OCH I-l
• amine boranes such as monoand dilower alkyl, e.g., up to C alkyl-amine boranes, preferably isopropyl amine borane and dimethylamine borane.
• formaldehyde is also an excellent reducing agent for use in these baths, particularly for the deposition of copper and silver.
• the electroless plating baths of the present invention be maintained at a pH of between about 11 and 14, principally to prevent spontaneous decomposition thereof. It is thus preferred that an alkali metal hydroxide, such as sodium or potassium hydroxide, be employed to maintain the pH at this level. It has, however, been discovered that pH control is considerably easier when alkali metal buffering salts are employed in addition to the alkali metal hydroxide. Thus, while the alkali metal hydroxide is necessary in order to maintain the present electroless baths at the required pH level during plating, as the pH tends to drop, the ease of pH control is considerably facilitated by the addition of such alkali metal buffering salts.
• an alkali metal hydroxide such as sodium or potassium hydroxide
• alkali metal buffering salts thus include the alkali metal phosphates, citrates, tartrates, borates, metaborates, etc.
• the alkali metal buffering salts may this include sodium or potassium phosphate potassium pyrophosphate, sodium or potassium citrate, sodium potassium tartrate, sodium or potassium borate, sodium or potassium metaborate, etc.
• the preferred alkali metal buffering salts are sodium or potassium citrate and sodium or potassium tartrate. in order to further improve the electroless plating baths of this invention, it is preferred to add an organic chelating agent thereto.
• Such chelating agents combine with the replaced surface metal ions, thus preventing their interference with the plating process, and the consequent deterioration of the color characteristics of the deposited plates, as well as other plate properties such as adherence and thickness.
• These organic chelating agents thus include ethylenediamine tetraacetic acid, and the di-sodium, tri-sodium and tetra-sodium and potassium salts of ethylenediamine tetraacetic acid, di-ethylene triamine pentacetic acid, nitrilotriacetic acid.
• the ethylenediamine tetraacetic acid and its di-, tri-, and tetrasodium salts are the preferred chelating agents, with the triand tetra-sodium salts being particularly preferred.
• non-metallic substrates With the use of non-metallic substrates, however, these surfaces must be rendered catalytically active by producing a film of particles of catalytic material thereon. This may be done in the method described in U.S. Pat. No. 3,589,916, upon such surfaces as glass, ceramics, various plastics. etc.
• a plastic substrate is to be plated according to the present invention, it is initially etched, preferably in a solution of chromic and sulfuric acid. After rinsing, the substrate is immersed in an acidic solution of stannous chloride, such as stannous chloride and hydrochloric acid, rinsed with water and then contacted with an acid solution of a precious metal, such as paladium chloride in hydrochloric acid. Subsequently, the now catalytically acitve non-metallic substrate may be contacted with the electroless plating solutions of this invention in order to autocatalytically deposite Group 18 metal plates thereon.
• stannous chloride such as stannous chlor
• a preplating step is employed.
• a rapid contamination of the plating bath with the base metals replaced by the Group lB metals plated thereon occurs, thus affecting the purity of the deposit obtained, and the stability of the electroless plating solution.
• a pre-plating step for the provision of a thin plate of gold be carried out. This may be accomplished by using the Atomex process as described in US. Pat. No.
• the plated substrate may be immersed in the electroless plating baths of the present invention in order to provide a thick, ductile plate of the Group 18 metal having the improved properties obtainable in accordance with the present invention.
• a gold solution is obtained by dissolving potassium gold succinimade in water, and heating to between about 70 and 95C. Potassium cyanide, tripotassium citrate, potassium hydroxide, and ethylene diamine tetraacetic acid are added thereto, the pH being maintained at about 13 and the temperature at about 80C. Dimethylamine borane is then dissolved in water, and added to this solution. In order to continue the gold plating, gold is replenished from an aqueous solution containing gold, as potassium gold succinimide. Additional amounts of dimethylamine borane may be required, as well as potassium hydroxide in order to maintain the proper pH.
• the initial plating bath thus prepared has the following composition:
• the silver plating bath thus prepared has the following composition:
• the copper bath thus prepared has the following composition:
• An electroless plating bath for autocatalytic deposition of Group IB metals upon a substrate comprising an aqueous solution of an imide complex of the Group 13 metal to be plated, said imide complex of the Group IB metal to be plated including an imide selected from the group consisting of imides having the formula H O, and cyclic imides having the formula R NH 0, wherein R is selected from the group consisting of alkylene, substituted alkylene, arylene, and substituted arylene, an alkali metal cyanide in an amount ranging from about 2 to 20 grams per liter, suf ficient to stabilize said bath, and a reducing agent selected from the group consisting of water soluble alkali metal borohydrides, water soluble amine boranes and formaldehyde, said bath maintained at a pH of from about 11 to 14.
• the electroless plating bath of claim 3 including an alkali metal buffering salt selected from the group consisting of alkali metal phosphates, citrates, tartrates, borates, metaborates, and mixtures thereof.
• An electroless gold plating bath for the autocatalytic deposition of gold upon a substrate comprising an aqueous solution of an alkali metal gold imide complex, said alkali metal gold imide complex including an imide selected from the group consisting of imides having the formula RNHQO, and cyclic imides having the formula lECONHCO, wherein R is selected from the group consisting of alkylene, substituted alkylene, arylene, and substituted arylene, an alkali metal cyanide in an amount sufficient to stabilize said bath, a reducing agent selected from the group consisting of water soluble alkali metal borohydrides, water soluble amine boranes, and formaldehyde, said bath maintained at a pH of from about 11 to 14.
• the electroless gold plating bath of claim 6 including an organic chelating agent capable of forming a chelate with the metal of said substrate.
• the electroless gold platng bath of claim 10 including an alkali metal buffering salt selected from the group consisting of an alkali metal phosphates, citrates, tartrates, borates, metaborates, and mixtures thereof.
• a method of plating a metallic substrate with a Group [B metal comprising:
• aqueous gold plating bath comprising a soluble gold salt selected from the group consisting of the alkali metal gold cyanides, an ammonium buffering agent capable of maintaining the pH of said bath between about 5.5 and 14, an organic chelating agent capable of chelating the metal ions of said substrate, for sufficient time to place said substrate with a thin layer of gold; and
• step (a) is from about 2 to 10 microinches.
• said electroless plating bath includes an alkali metal buffering salt.
• said electroless plating bath includes an organic chelating agent capable of forming a chelate with the metal of said substrate.
• said imide comprises an imide selected from the group consisting of succinimide and phthalimide.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)

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Cited By (24)

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Citations (8)

• 1974
  • 1974-04-26 US US464666A patent/US3917885A/en not_active Expired - Lifetime
• 1975
  • 1975-04-09 MX MX157698A patent/MX146110A/es unknown
  • 1975-04-23 CA CA225,269A patent/CA1038559A/en not_active Expired
  • 1975-04-24 GB GB1712775A patent/GB1448659A/en not_active Expired
  • 1975-04-24 JP JP50050163A patent/JPS5818430B2/ja not_active Expired
  • 1975-04-24 FR FR7512789A patent/FR2268595B1/fr not_active Expired
  • 1975-04-24 IT IT49280/75A patent/IT1035454B/it active
  • 1975-04-25 BR BR3224/75A patent/BR7502540A/pt unknown
  • 1975-04-25 DD DD185707A patent/DD117488A5/xx unknown
  • 1975-04-25 DE DE19752518559 patent/DE2518559A1/de not_active Ceased

Patent Citations (8)

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