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
  • C25D3/48—Electroplating: Baths therefor from solutions of gold

Definitions

• a gold plating electrolyte for providing gold deposits with controlled hardness below 130 Knoop, which contains gold as the sulfite complex, an alkali metal sulfite, a buffering and conducting salt and the combination of a polycarboxylic acid together with a semi-metal brightener.
• the addition of a controlled amount of the polycarboxylic acid and the semi-metal brightener provide for bright, ductile pure gold deposits having a hardness below 130 Knoop, and by altering the quantities of the aforesaid acid and semi-metal, deposits having a hardness below 90 Knoop are obtained.
• the gold electrolyte according to the invention contains:
• the gold sulfite complex is selected from the group consisting of potassium gold sulfite, sodium gold sulfite and ammonium gold sulfite.
• alkali metal or ammonium buffering salts examples include alkali metal or ammonium citrates, borates, phosphates, sulfamates and pyrophosphates.
• the alkali metal sulfites employed are sodium or potassium sulfites.
• polycarboxylic acids which are often used as bulfering or conducting media in gold electrolytes.
• soluble salts of the semi-metal employed are the soluble salts of antimony, arsenic, selenium and tellurium such as potassium antimony tartrate, arsenic trioxide, selenium as selenic acid neutralized with an alkali such as potassium or sodium hydroxide, and tellurium as a soluble salt such as tellurium dioxide dissolvedin potassium or sodium hydroxide.
• the preferred combination of a polycarboxylic acid and semi-metal is oxalic acid and arsenic trioxide.
• the brightening hardness control solution is prepared by warming to dissolve the arsenic trioxide in an aqueous solution of oxalic acid. It has been determined that by increasing or decreasing the concentration of oxalic acid in the brightener or electrolyte, with, for example, the same concentration of arsenic, electrodeposits of varying hardness are obtained. It is preferred that the oxalic acid be added together with the brightening semi-metal.
• EXAMPLE 1 Solution A. Into an amount of water suflicient to form one liter of solution is dissolved: 50 grams oxalic acid crystals and 10 grams arsenic as arsenic trioxide.
• EXAMPLE 2 Solution B. Into an amount of water sufiicient to form one liter of solution is dissolved: grams oxalic acid crystals and 10 grams arsenic as arsenic trioxide.
• the polycarboxylic acid and semi-metal brightener combination is added to the solution in the range of 4:1 to 20:1 ratio of polycarboxylic acid to semi-metal.
• the ratio may be 5:1 which gives the deposit a hardness of 90 to 130 Knoop and, preferably, the ratio may be :1 which gives the deposit a hardness of below 90 Knoop.
• the quantity of such additive in the electrolyte is dependent upon the speed at which the electrolyte is operated.
• the following example illustrates the use of the additive in an electrolyte which is formulated to operate at substantially high current density where the current density is higher than given in Examples 1-4.
• the increase in the concentration of gold and potassium citrate is necessary to operate the electrolyte at such higher current density.
• EXAMPLE 6 Gold as potassium gold cyanide-10 grams/liter Potassium citrate-70 grams/liter Potassium dihydrogen phosphate grams/liter Solution A (from Example 1)3 mls./liter pH adjusted to 6.5 with H PO or KOH The hardness of the deposit plated at 5 ASP was 140 Knoop.
• Example 6 the same hardness of Example 6 is obtained without the use of the combination additive of the invention, i.e. where the polycarboxylic acid (oxalic acid) is eliminated.
• EXAMPLE 7 Gold as potassium gold cyanide10 grams/liter Potassium citrate-70 grams/liter Potassium dihydrogen phosphate-30 grams/liter Arsenic as arsenic trioxide30 mg./liter pH adjusted to 6.5 with H PO or KOH The hardness of the deposit plated at 5 ASP was 140 Knoop.
• Example 6 indicate that the efiect of the hardness control additive is eifective. only in the noncyanide gold electrolytes.
• An aqueous alkaline goldplating electrolyte comprising:
• a bulfering salt selected from the group consisting of alkali metal or ammonium citrates, borates', phosphates, sulfamates and pyrophosphates,
• a semi-metal brightener as metal, selected from the group consisting'of arsenic, antimony, selenium and tellurium, the combination of the non-hydroxy polycarboxylic acid and the semi-metal brightener being in the range of a 4:1 to 20:1 ratio of non-hydroxy polycarboxylic acid to semi-metal brightener, and sufficient alkali metal hydroxide to adjust the pH of the electrolyte to 8-11.

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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)

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Publications (1)

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ID=22898643

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Cited By (6)

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• 1972
  • 1972-03-27 US US00238615A patent/US3776822A/en not_active Expired - Lifetime
• 1973
  • 1973-03-23 JP JP48033421A patent/JPS497129A/ja active Pending
  • 1973-03-23 IT IT48989/73A patent/IT979980B/it active
  • 1973-03-26 GB GB1440073A patent/GB1430799A/en not_active Expired
  • 1973-03-26 FR FR7310728A patent/FR2177969B1/fr not_active Expired
  • 1973-03-27 DE DE2315309A patent/DE2315309A1/de active Pending

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