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
  • C23C18/18—Pretreatment of the material to be coated
  • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
  • C23C18/28—Sensitising or activating
• • 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

• This invention relates to a bath for the electroless deposition of palladium.
• Electroless deposition is the process by which metal is reduced from a solution of suitable composition and deposited on a catalytic surface through oxidation of a reducing agent at that surface.
• Platinum Group metals, gold and some other metals are catalytic to the reaction and surfaces which are not catalytic to the reaction can be rendered so by well known procedures.
• Deposition is accomplished by immersing the catalytic surface in the electroless deposition bath for a predetermined time in accordance with the thickness of deposit desired. Since no electric current is employed, no electrical contact to the surface to be plated is required. For a given substrate material, the chemical reduction or the deposition rate can, within limits, be controlled by the composition and temperature of the plating bath.
• Patent No. 2,915,406 the only technique for electroless deposition of palladium that is known to have been reported is disclosed in Patent No. 2,915,406.
• the electroless plating bath that is described in that patent is chemically unstable and decomposes rapidly. Such a bath is not suitable for many types of plating operations.
• the present invention provides an improved bath for the electroless deposition of palladium that not only permits palladium to be readily deposited on metallic and non-metallic substrates but which bath possesses a high degree of chemical stability.
• the baths of the present invention are not only stable during plating operations but are also sutficiently stable to be stored and reused.
• the electroless palladium plating solution of the pres ent invention comprises an aqueous solution containing divalent palladium which is chelated with ethylenediaminetetraacetic acid, C H N O or with a salt of that acid and ammonium, lithium, sodium, potassium or calcium or combinations thereof and ethylenediamine, NH CH CH NH hypophosphite ion, H PO as hypophosphorous acid or as the ammonium, lithium, sodium, potassium or calcium salt of that acid.
• a solution incorporating these ingredents has demonstrated a high order of chemical stability over a wide range of temperatures and when maintained at a suitable temperature and pH performs very well as a bath for the electroless deposition of palladium.
• the present invention teaches that the divalent palladium may be introduced into a new bath in the chelated form or that the chelate may be formed in solution by adding a suitable salt of divalent palladium to a solution containing a suitable concentration of ethylenediaminetetraacetic acid or of a salt of that acid and ammonium, lithium, sodium, potassium or calcium or combinations thereof.
• the chemical stabilities of the bath are such that the palladium and hypophosphite contents of the solutions may be depleted through use and must be replenished.
• the palladium content may be replenished by addition of a suitable salt of divalent palladium and formation of the chelate in the solution.
• the hypophosphite content is replenished by addition of hypophosphorous acid or of an ammonium, lithium, sodium, potassium or calcium salt of that acid to the bath after the palladium has been chelated.
• the electroless palladium plating bath of the present invention is an aqueous solution, generally containing the following constituents:
• the pH of the solution may be adjusted upwardly by the addition of ethylenediamine in the range of 9-75 grams per liter or downwardly by the addition of nitric, sulfuric or hydrochloric acid to a desired pH in the range of 8.0l1.0, electrometric.
• a bath for electroless deposition of palladium may have as constituents:
• An electroless plating bath must be so composed that the reducing agent present in the bath will reduce the plating metal from the solution only at a surface which is catalytic to the oxidation of the reducing agent. Otherwise, the metal is quickly precipitated on the Walls and bottom of the container and the bath is said to have decomposed.
• the stability constants of the compounds of the plating metal in solution must be such that decomposition does not occur but also such that reduction of the plating metal at a suitably catalytic surface will proceed at a controlled rate.
• Complexing, sequestering or chelating agents added to the bath to prevent decomposition but permitting metal deposition are called stabilizing agents.
• the stabilizing agents are ethylenediamine and ethylenediaminetetraacetic acid or a salt of that acid with ammonium, lithium, sodium, potassium or calcium or with combinations thereof.
• Ethylenediamine performs the additional function of increasing the pH of the solution.
• chelates of many metals with ethylenediamine have lower stability constants than do chelates of the same metals with ethylenediaminetetraacetic acid or with salts of that acid and ammonium, lithium, sodium, potassium or calcium or with combinations thereof.
• the stability constants of chelates of palladium with ethylenediaminetetraacetic acid or with the aforementioned salts are to great to permit deposition except at a very low rate, and then, only when the temperature of the solution is very high.
• the stabilizing agents in the baths of the present invention form stable, soluble compounds which minimize codeposition of these impurities with palladium.
• Hypophosphite ion H PO is the reducing agent in the bath of the present invention which when oxidized at the catalytic surface provides the electrons necessary to reduce the palladium from the solution and to deposit it on the catalytic surface.
• Hypophosphite ion is supplied in the bath as hypophosphorous acid or as an ammonium, lithium, sodium, potassium or calcium salt of that acid.
• the preferred procedure is to add the disodium palladium ethylenediaminetetraacetate, ethylenediamine and sodium hypophosphite to water and dissolve the solids. After adjusting the desired volume, then, adjust the pH of the bath to 8.5, electrometric at 20 C. After heating the bath through a water jacket to a temperature of F. and maintaining the temperature of the bath, begin plating operations.
• Example III To properly prepare the bath of Example III, add the palladium chloride, ethylenediamine and dissodium ethylenediaminetetraacetate to water and dissolve the solids. Permit the solution to stand until chelation is complete. Chelation can be accomplished in approximately 24 hours if the temperature of the solution is maintained at approximately 160 F. After chelation is complete, cool the solution to 20 C. add the sodium hypophosphite and adjust the pH to 8.5, electrometric at 20 C. Heat the bath through a water jacket to a temperature of 160 F. and while maintaining the temperature of the bath, begin plating operations.
• the solutions resulting from the compositions and pro cedures of Examples II and III are essentially identical.
• the electroless plating solution shall contain 6 grams per liter of divalent palladium as disodium palladium ethylenediaminetetraacetate, C H N O Na Pd, 3.0 grams per liter of hypophosphite, H PO as NaH PO and thatthe pH of the bath shall be adjusted to a pH of 8.5, electrometric at 20 C. by addition of hydrochloric acid and that the operating temperature of the bath shall be 160 F.
• disodium palladium ethylenediaminetetraacetate can be obtained in chrystalline form by reacting equimolal' quantities of divalent palladium and disodium dihydrogen ethylenediaminetetraacetate in aqueous solution and then crystalizing the palladium chelate from the solution.
• the palladium may be provided in the form of any suitable salt of divalent palladium.
• io n a sodium hydrogen palladium ethylenediaminetetraacetate
• These baths have also been used for deposition of palladium or non-metallic substrates, such as ceramics, glass and plastics.
• deposition of electric circuits on ceramic substrates deposition of bonding layers between nonmetallic substrates and layers of other electrolessly deposited metals and deposition of conductive films on ceramic substrates to serve as carriers for magnetic alloys which were electrodeposited over the palladium.
• Such magnetic films are employed as recording media in digital computer applications.
• a bath for electroless deposition of palladium comprising an aqueous solution having as constituents:
• hypophosphite ion within a range of from about 1.8 to 10 grams per liter, the solution having a pH value within a range of about 8.0 to 11.0, electrometric.
• hypophosphite ion is provided by hypophosphorous acid, H PO or by an ammonium, lithium, sodium, potassium or calcium salt of that acid, or combined salts thereof.
• a bath for electroless deposition of palladium as defined in claim 1 containing amounts of ethylenediamine, NH CH CH NH in adition to that required for forming chelate compounds with divalent palladium, for upward adjustment of the pH of the solution.
• a bath for electroless deposition of palladium as defined in claim 3 additionally containing hydrochloric acid, HCl, nitric acid, HNO or sulfuric acid, H 50 for proper control of the pH of the solution.
• a bath for electroless deposition of palladium as defined in claim 1 wherein the bath has an operating temperature in the range of to 190 F.
• a bath for electroless deposition of palladium as defined in claim 1 containing dihydrogen palladium ethylenediaminetetraacetate, C H N o Pd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing sodium hydrogen palladium ethylenediaminetetraacetate, C H N O NaPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing potassium hydrogen palladium ethylenediaminetetraacetate, C H N o KPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing ammonium hydrogen palladium ethylenediaminetetraacetate, C H N O Pd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing lithium hydrogen palladium ethylenediaminetetraacetate, C H N o LiPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing disodium palladium ethylenediaminetetraacetate, C H N o Na Pd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing sodium potassium palladium ethylenediaminetetraacetate, C H N o NaKPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in-claim 1 containing sodium ammonium palladium ethylenediaminetetraacetate, C H N O NaPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing sodium lithium palladium e'tliylenediaminetetraacetate, C H N o NaLiPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing dipotassium palladium ethylenediaminetetraacetate, C H N O Pd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing potassium ammonium palladium ethylenediaminetetraacetate, CloHlfiNsOBKPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as defined in claim 1 containing potassium lithium palladium ethylenediaminetetraacetate, C H N O KLiPd, as a chelate of divalent palladium.
• a bath for electroless deposition of palladium as References Cited defined in claim 1 containing dilithium palladium ethyl- UNITED STATES PATENTS enediaminetetraacetate, C H N O Li Pd, as a chelate of 2,8723 46 2/1959 Miner XR divalent Palladium 2,915,406 12/1959 Rhoda et a1.
• 106'1 20.

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• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
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• Metallurgy (AREA)
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• Chemically Coating (AREA)

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Cited By (12)

Citations (3)

• 1967
  • 1967-08-15 US US660588A patent/US3418143A/en not_active Expired - Lifetime
• 1968
  • 1968-08-16 BE BE719589D patent/BE719589A/xx not_active IP Right Cessation

Patent Citations (3)

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