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
  • C23C18/42—Coating with noble metals
  • C23C18/44—Coating with noble metals using reducing agents

Definitions

• the invention relates to an aqueous bath for the electroless deposition of gold layers which, in addition to a reducing agent and a stabilizer made of 2-mercaptobenxothiazole or a derivative thereof, contains a gold complex obtained from an anionic gold (III) compound and a complexing agent in aqueous solution.
• gold layers to be used for electronic purposes include, among other things, the lowest possible porosity, layer thicknesses of about 0.5 to 10 micrometers, firm adhesion to the base and good solderability and bondability.
• US Pat. No. 3,032,436 describes a method for depositing gold from a bath containing potassium gold cyanide and having a pH between 3 and 12.
• the preferred reducing agent is hydrazine hydrate; however, the use of other reducing agents, for example alkali metal hydridoborates, sugars, hydroquinones and alkali metal hypophosphites, is also possible.
• an aqueous alkaline bath for electroless deposition of gold coatings is known, which is characterized by the use of gold in Ford of a gold (III) compound, for example alkali metal cyanoaurate (III).
• the bath is more stable and has a higher deposition rate than baths containing gold (I) compounds.
• a buffer substance and optionally an organic complexing agent (chelating agent) for example ethylenediaminetetraacetic acid, and / or free cyanide, it contains an alkylaminoborane, alkali metal boranate or cyanoboranate as reducing agent.
• a gold as gold (III) complex with borate, carbonate, phosphate, pyrophosphate or silicate ligands containing aqueous alkaline bath for electroless gold plating is described in DE-PS 32 47 144.
• Suitable stabilizers that can be added to the bath also include mercaptans, for example 2-mercaptobenzothiazole.
• a soluble tert-amine borane or the diisopropylamine borane is used as the reducing agent.
• the bath is prepared by heating an aqueous solution containing the gold (III) compound, e.g. potassium tetrachloroaurate (III) and the ligand, and adding the reducing agent and stabilizer to the solution after it has cooled.
• alkaline bath containing gold both as gold (I) component and as gold (III) component for example alkali metal cyanoaurate (III), for the electroless plating of gold, which is stable, enables better deposition rates and can be supplemented known from DE-PS 33 20 308.
• Alkylamine boranes, alkali metal borohydrides, alkali metal cyanoborohydrides, hydrazine or hyposulfite are used here as reducing agents. If greater stability is required, alkali metal cyanides can be added to the bath in an amount of 1 to 20 g / l.
• an aqueous alkaline bath for the electroless deposition of gold layers is known, the gold as alkali metal cyanoaurate (III), an organic complexing agent such as ethylenediaminetetramethylenephosphonic acid or 1-hydroxyethane-1,1-diphosphonic acid, Contains 2-mercaptobenzothiazole or a derivative thereof as a stabilizer and a mixture of at least two reducing agents - one of which can be a hypophosphite - and has a pH between 8 and 14.
• alkali metal cyanoaurate (III) an organic complexing agent such as ethylenediaminetetramethylenephosphonic acid or 1-hydroxyethane-1,1-diphosphonic acid
• 2-mercaptobenzothiazole or a derivative thereof as a stabilizer and a mixture of at least two reducing agents - one of which can be a hypophosphite - and has a pH between 8 and 14.
• the stability of the bath should - when supplemented in accordance with the consumption of gold and the other bath components - be such that three times the amount of gold contained in the batch electrolyte can be deposited.
• the bath representing the solution to the problem is characterized according to the invention in that it contains the gold complex obtained by leaving the aqueous solution of an alkali metal cyanoaurate (III) and ethylenediaminetetramethylenephosphonic acid or 1-hydroxyethane-1,1-diphosphonic acid as a complexing agent at room temperature for at least 24 hours contains and has a working pH between 0.2 and 1.8.
• an alkali metal cyanoaurate (III) and ethylenediaminetetramethylenephosphonic acid or 1-hydroxyethane-1,1-diphosphonic acid as a complexing agent at room temperature for at least 24 hours contains and has a working pH between 0.2 and 1.8.
• the aqueous solution is heated to about 80 ° C. at room temperature before being left to stand, and the bath has a working temperature between 85 and 100 ° C.
• the aqueous solution 0.5 - 15 g / l, preferably 1- 10 g / l gold as alkali metal cyanoaurate (III) and 2.5 - 45 g / l, preferably 7.5 - 20 g / l l contains the complexing agent.
• Finely crystalline gold layers can be deposited on metals, for example nickel and copper, from the bath according to the invention and on non-metals, for example ceramic and plastic, provided with a catalytically activated surface by suitable pretreatment belonging to the prior art of the Tecknick.
• the deposition rate is practically constant in the range of 1 - 1 ⁇ m / h.
• the gold layers have high adhesive strength, a regular layer structure and excellent solderability and bondability.
• They are particularly suitable for electronic purposes, for example for gold-plating lead frames, chip carriers, printed circuit boards, the interconnects of hybrid circuits and the inner walls of hollow bodies, for example hollow tubes.
• the bath can be easily supplemented during operation by the continuous addition of aqueous solutions which contain the substances forming the bath, but in a lower concentration than there.
• the substances used to complement the bath are added in the appropriate amounts in the amount of gold deposited. With an appropriate addition, three times the amount of gold contained in a newly prepared bath can be separated.
• Alkali metal cyanoaurate (III) means the cyanoaurate (III) of a suitable alkali metal or the ammonium cyanoaurate (III);
• the reaction product of ethylenediaminetetramethylenephosphonic acid or 1-hydroxyethane-1,1-diphosphonic acid with potassium cyanoaurate (III) has proven particularly useful.
• hypophospites especially the alkali metal hypophospites, have proven themselves as reducing agents; the sodium compound is preferred.
• the amount of reducing agent depends on the gold content of the bath and is selected so that the gold layer is continuously built up in a defined layer thickness.
• 2-mercaptobenzothiazole-S-propanesulfonic acid in the form of its alkali metal salts, preferably the sodium salt has proven to be a particularly effective stabilizer for the bath according to the invention.
• the effective amount of the stabilizer is 0.01 - 150 mg / l.
• Hydrochloric acid is preferably used to adjust the pH of the aqueous solution to about 0.5-0.8 and the working pH of the bath.
• the bath contains a wetting agent, preferably in an amount of 0.1 to 5 g / l.
• a suitable wetting agent is, for example, sodium dodecyl ether phosphate, commercially available as forlanon (registered trademark of Henkel, Düsseldorf).
• baths according to the invention their preparation and the deposition of gold layers therefrom are described in the following examples.
• 5 ml / l stabilizer are extracted from a 1 l solution with 200 mg / l 2-mercaptobenzothiazole-S-propanesulfonic acid sodium using a pipette and 5 ml / l forlanon (registered trademark of Henkel, Dusseldorf, for the wetting agent sodium dodecyl ether phosphate) and then 0.5 ml / l reducing agent from a 1 l solution with 100 g / l sodium hypophosphite with the aid of a pipette.
• the finished bath with a pH of about 0.5 contains 15 g / l ethylenediaminetetramethylenephosphonic acid, 2 g / l gold as potassium cyanoaurate (III), 50 ml / l HC1, 32%, 1 mg / l 2-mercaptobenzothiazole-S-propanesulfonic acid sodium, 3 g / l forlanon and 50 mg / l sodium hypophosphite.
• the deposition is very uniform in the observed period and only takes place on the surfaces intended for the gilding. Game separation, for example on the walls of the container containing the bath, does not occur.
• the finished bath contains a pH of about 0.6 30 g / l 1-hydroxyethane-1,1-diphosphonic acid, 4 g / l gold as potassium cyanoaurate (III), 10 ml / l HCl, 32%, 0.2 mg / l 2-mercaptobenzothiazole and 50 mg / l sodium hypophosphite.
• the bath is now brought to a working temperature of 92 - 97 ° C for the deposition of gold layers.
• Gold layers produced in an electroless manner produce 0.4 ⁇ m thick gold layers in 15 minutes and 1.4-1.5 ⁇ m thick gold layers in 60 minutes.
• the deposition is very uniform in the observed period and only takes place on the surfaces intended for the gilding. Game separation, for example on the walls of the container containing the bath, does not occur.

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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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• 1986
  • 1986-11-24 DE DE3640028A patent/DE3640028C1/de not_active Expired
• 1987
  • 1987-05-23 EP EP87107525A patent/EP0268732A3/fr not_active Withdrawn
  • 1987-07-02 JP JP62164128A patent/JPS63137178A/ja active Granted
  • 1987-12-08 US US07/130,082 patent/US4830668A/en not_active Expired - Fee Related

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