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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/62—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of gold

Definitions

• This invention is based on the discovery that silver acts as a brightener, in what are essentially non-cyanide baths providing the silver ion concentration is maintained small by adding complexing or chelating agents to the bath, for example. Under these circumstances, the bath pH may be maintained over relatively wide pH values; 6 to 13 in contrast to the normal bright gold plating baths employing silver as an addition agent where the pH values in practice have been of the order of 12.
• the baths of the present invention may be operated at a pH of 6l3, there is a definite advantage in being able to operate a bright gold bath at a pH of 6.5 to 7.0, with a low content of free cyanide, especially when plating workpieces such as printed circuit boards where the solvent action of the alkaline cyanide bath on the copper-plastic laminate is a problem.
• This invention provides a bath which has relatively low susceptibility to the effect or".
• foreign ions such as nickel, copper and other base metal ions, which ions normally have a deleterious effect on brightness effected by the silver ion by virtue of the presence of the silver complexing agent which in general will complex higher valent cations more effectively.
• the objects of the invention are attained by providing an aqueous bath containing about 4-20 g./l. of potas sium gold cyanide, 25-300 mg./l. of silver ion and 5400 g./l. of one or more alkali metal salts. To this hath no free cyanide is added although a limited amount of free cyanide may be set free as the bath is operated.
• alkali metal gold cyanide provides the necessary gold ions for the orderly disposition of the gold, but does not supply sufiicient ions to provide the conductivity required for good commercial operation of the bath. Consequently, alkali metal such as sodium or, preferably potassium salts of organic acids, inorganic and organo-inorganic acids, (re added to provide the nectill essary conductivity.
• alkali metal sulfates, phosphates, nitrates, sulfamates, and the alkali metal salts of such organic acids as citrate, tartrate, lactate, as well as the organo-inorganic acid such as naphthalene sulfonic, benzene sulfonic acids are useful in this connection.
• the bath contains the following ingredients:
• Alkali hydroxide Suflicient to produce pH of 6.5l3 preferably pH 6.57.5.
• Chelating agent l to 50 g./l.
• the chelating or complexing agent for silver must be such that the silver ion concentration, with 5 to 50 grams per liter of the agent present, will be reduced to no more than that provided by potassium or sodium silver cyanide in the presence of free potassium cyanide. Otherwise, the silver salt must be kept at low concentration and fed frequently. If silver is added as potassium silver cyanide, as silver-sulfate, nitrate or other soluble silver salt, the available silver ions in the cathode film are considerable with the result that rapid deposition of silver along with the gold occurs.
• minor brightening agents such as potassium nickel and cobalt cyanides may be added to the aforedescribed bath to provide a small increase in brilliance, but in general, these materials are unnecessary and contribute to deposit brittleness.
• Example 1 In an amount of water sufficient to provide one liter of solution was dissolved:
• Example 2 in an amount of Water sufiicient to provide one liter of solution was added:
• Example 4 In an amount of water sufficient to provide one liter of solution was added:
• Example 5 In an amount of water sufiicient to provide one liter of solution was added:
• Triglycollamic acid gm Triglycollamic acid gm.
• Example 6 To the bath of Example 5, absent the silver nitrate, was added 145 mg./l. of silver sulfate. Again not all the silver salt dissolved at once, but a bright deposit was obtained.
• Silver salts silver fluoride, silver acetate.
• the above baths were normally operated at room temperature, but they can be operated up to a temperature of 45 C. Above this temperature hazy deposits are apt to be obtained.
• the baths can be operated at temperatures down to about 15 C.
• the normal current density range is 1 to 5 a.s.f. (0.1O.5 amp/43m?) depending upon the gold content, the temperature, and the rate of agitation. At higher temperatures, high gold content and very vigorous agitation, considerably higher current densities can be employed, but the control of commercial baths becomes somewhat more critical.
• agitation either solution volume or mechanical agitation is useful and, actually air agitation is etleetive for this bath in contrast to high free cyanide gold baths where the ethciency drops rapidly when air agitation is used.
• An aqueous electrolyte for the production of bright gold deposits consisting essentially of the following ingredients:
• KAu(CN) (calculated as Au) 4 to 20 g./l.
• KAg(CN) (calculated as Ag) 25 to 500 mg./l.
• Alkali metal conducting salt (other than cyanide) 5 to g./l.
• Alkali hydroxide to pH 6.513.
• Triglycollamic acid 5 to 10 g./l.
• An aqueous electrolyte for the production of bright gold deposits consisting essentially of the following ingredients:

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

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ID=22185447

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Cited By (7)

Families Citing this family (4)

Citations (2)

• 0
  • NL NL273924D patent/NL273924A/xx unknown
• 1957
  • 1957-10-02 CH CH51162A patent/CH399865A/fr unknown
• 1961
  • 1961-01-24 US US84517A patent/US3174918A/en not_active Expired - Lifetime
  • 1961-12-15 GB GB45060/61A patent/GB939007A/en not_active Expired
• 1962
  • 1962-01-18 FR FR885252A patent/FR1311023A/fr not_active Expired

Patent Citations (2)

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