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

Definitions

• This invention relates to the deposition of copper by chemical reduction. More particularly, this invention relates to metallizing, namely to the deposition of copper from aqueous solutions of its salts by chemical reduction.
• Copper is deposited by chemical reduction on such nonconductors as plastics or ceramics to provide a conductive primer coating on which heavier metallic deposits may then be formed by electrodeposition.
• the solutions employed generally contain an inorganic copper salt as a source of copper, a complexing agent, normally the salt of an organic acid or an organic base to form complex ions with copper, and a reducing agent.
• the known copper deposition solutions heretofore used are relatively unstable and decompose within one or two days. Their copper content is precipitated spontaneously, either as metallic copper or as a copper oxide.
• Stabilizers have been proposed heretofore, but have been found to be of limited value.
• the known stabilizers only moderately extend the useful life of the copper depositing solutions, and the relatively more effective known stabilizers tend to cause discoloration and other deterioration of the copper deposits formed. Yet, even the best known stabilizers do not permit uniform conditions to be maintained for continuous operation of the copper deposition process.
• X is S or NH; R is hydrogen, lower alkyl, phenyl, carboxy-lower alkyl, or amino; and R is hydrogen, lower alkyl, or nitro.
• the copper deposition solutions of the invention are stable not only at room temperature, but also even at elevated temperatures which are known to be deleterious to the conventional copper deposition solutions, thus permitting operation at temperatures at which the deposition rate is faster than at room temperature.
• the copper coatings formed from the solutions of the invention are bright red and consist of pure metal.
• the stabilizing agents of the invention are known chemical compounds, and are prepared by known methods, rhodanine, for example, is readily obtained by reacting salts of dithiocarbamic acid with a halocetic acid in aqueout solution and subsequent heating in the presence of hydrochloric acid.
• Thiohydantoin is formed at elevated temperature from glycine and isothiocyanates.
• Rhodanine N-methylrhodanine N-phenylrhodanine Rhodanine-N-acetic acid N-aminorhodanine 3-phenyl-5-nitrorhodanine S-ethylrhodanine Thiohydantoin Rhodanine and N-methylrhodanine have been found to stabilize copper deposition solutions over the longest periods, and are capable of preventing decomposition of such solutions over practically unlimited periods.
• the stabilizing agents of the invention may be employed in concentration between one milligram and 0.5 gram per liter, but they are so effective in small amounts that nothing is gained by using more than about 0.05 gram per liter.
• concentration of the conventional constituents of the solutions may be varied within the usual limits without affecting thestabilizing effect of the aforedefined compounds, and the specific nature and concentration of the copper salts, complexing agents, reducing agents, buffers, wetting and brightening agents employed is not critical.
• the presence of the stabilizing agents does not aifect the mode of operation of the deposition solution, and the deposits formed have the expected electrical conductivity so that heavier metal deposits can be formed thereon by electro-deposition.
• Metals as well as non-conductors may be metallized in copper deposition solutions of the invention.
• the coatings produced by chemical reduction in the presence of the aforedescribed stabilizing agents are distinguished by their clear, bright red, metallic appearance from the relatively dark and grainy deposits containing significant amounts of copper oxides which are characteristic of solutions containing the known 2-mercaptobenzthiazole as a stabilizing agent.
• Suitable tan-ks for storage are therefore such which consists of non-metallic vinyl chloride, polyethylene, polypropylene, or similar plastics which are nonconductors and are resistant to chemical attack by the copper solutions of the invention.
• the solutions of the invention When brought into contact with metals or non-metals suitably prepared in a known manner, the solutions of the invention promptly cause the deposition of copper coatings.
• the solutions are preferably used having a specific gravity of about 1.04, a pH value of 12.0 to 12.5, and at a temperature of 20 40 C.
• the containers employed are either plastic tanks or steel tanks coated with suitable plastics. Mechanical agitation is preferred to obtain or effect greater uniformity of the copper coatings. Furthermore, air agitation is not advisable so as to avoid oxidation.
• the usual time of immersion for steel objects is preferably about to 20 minutes, and a deposition time of more than 20 minutes is not usually needed.
• the deposition rate in the typical solutions of Examples I and II is 0.3 micron in 10 minutes at 20 C., and 0.6 micron in 20 minutes. At 40 C., the deposition rate rises to 0.8 micron in 10 minutes, and 1.3 microns in 20 minutes.
• the rate of deposition decreases with the use of the solution, and can be increased by raising the temperature if the time needed for adequate coverage becomes excessive.
• the solution composition is best controlled by determining the copper content by analysis, and making additions of a concentrated stock solution to restore the original copper content.
• the copper coatings produced by immersion in the solutions of the invention may be covered by electrolytically produced metal layers in a conventional manner.
• Plastics may be prepared for accepting 4 copper coatings by chemical etching and surface activation, and the following procedure, illustrate a typical process.
• Molded objects of acrylonitrile-butadiene-styrene copolymer were etched by immersion in concentrated sulfuric acid at 50-65 C. for about 15 to 30 minutes. The objects were then rinsed and immersed in a solution prepared by dissolving 2.5 to 5 kg. of stannous chloride in 5 liters of hydrochloric acid of density 1.19, and diluting to liters with water. The temperature of the stannous chloride solution was kept between 15 and 25 C., and the immersion time was about 1 to 3 minutes. The plastic objects were then transferred to a solution containing 0.1 to 0.3 kg. silver nitrate and 1.0 liter ammonium hydroxide, d. 0.9, in 100 liter water at 15 to 25 C. in which they were kept immersed for one to three minutes. They were then ready for copper deposition in any one of the copper deposition baths indicated in the invention hereinabove.
• An aqueous solution for the deposition of copper by chemical reduction containing a source of copper ions, a complexing agent for said ions, a reducing agent for reducing the complex copper ions and as a stabilizing agent 0.001 to 0.5 gram per liter of a compound of the formula wherein X is S or NH; R is hydrogen, lower alkyl, phenyl, carboxy-lower alkyl, or amino; and R is hydrogen, lower alkyl, or nitro.
• the stabilizing agent is selected from the group consisting of rhodanine, N-methylrhodanine, N-phenylrhodanine, rhodanine- N-acetic acid, N-aminorhodanine, 3-phenyl-5-nitrorhodanine, S-ethylrhodanine, thiohydantoin.
• a method of depositing copper on a receptive base from a solution set forth in claim 4 comprising etching such base, rinsing, and immersing said base in a solution as set forth in claim 4.

Landscapes

• 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)
• Electroplating And Plating Baths Therefor (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=7433913

Family Applications (1)

Country Status (6)

Cited By (6)

Families Citing this family (1)

Citations (2)

Family Cites Families (1)

• 1965
  • 1965-02-20 DE DESCH36568A patent/DE1266099B/de active Pending
  • 1965-12-22 US US515753A patent/US3454416A/en not_active Expired - Lifetime
• 1966
  • 1966-02-10 CH CH189366A patent/CH464643A/de unknown
  • 1966-02-15 GB GB6561/66A patent/GB1128306A/en not_active Expired
  • 1966-02-18 BE BE676720D patent/BE676720A/xx unknown
  • 1966-02-18 NL NL666602102A patent/NL149857B/xx not_active IP Right Cessation

Patent Citations (2)

Also Published As

Similar Documents