GB1602041A - Gold plating process - Google Patents

Gold plating process Download PDF

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Publication number
GB1602041A
GB1602041A GB523378A GB523378A GB1602041A GB 1602041 A GB1602041 A GB 1602041A GB 523378 A GB523378 A GB 523378A GB 523378 A GB523378 A GB 523378A GB 1602041 A GB1602041 A GB 1602041A
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Prior art keywords
nickel
gold
workpiece
plating
finish
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Expired
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GB523378A
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Burr Brown Research Corp
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Burr Brown Research Corp
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Priority to GB523378A priority Critical patent/GB1602041A/en
Publication of GB1602041A publication Critical patent/GB1602041A/en
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    • 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

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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)
  • Electroplating And Plating Baths Therefor (AREA)
  • Electroplating Methods And Accessories (AREA)

Description

(54) GOLD PLATING PROCESS (71) We, BURR-BROWN RESEARCH CORPORATION, a corporation organised under the laws of the state of Arizona, United States of America, of International Airport Industrial Park, Tucson, Arizona, 85734, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a metal plating process for producing a gold alloy finish.
Gold plating is currently accomplished by several techniques, including electrolytic plating, immersion plating, and autocatalytic plating (reduction of gold from gold solutions). Because of the rapid rise in gold prices, the plating industry is concentrating considerable effort in finding ways to produce metal finishes that exhibit the desirable properties of gold plating, including environmental aging, temperature and humidity cycling, handling, solderability, TC and ultrasonic weldability, cosmetic appearance and abrasion resistance. Among the substitute metal finishes which have been used are tin, nickel/boron, tin/nickel and tin/lead films. None of the foregoing have been found to approximate substantially the qualities of gold.Gold/nickel electroplating has also been employed, but-such a process suffers from the disadvantage that control of the chemistry is difficult and electrical connection to the workpiece is required. Electroless gold alloy finishes have been prepared in an attempt to extend the amount of gold without sacrificing performance. For example, Japanese Patent No. 33-7514, reports a gold/nickel alloy having 1.5 times the anti-abrasion properties of gold. However, the nickel to gold ratio is relatively low, at best only 1520%, and thus the goal of significant costs savings is not achieved.
According to the invention there is provided a metal plating process for plating a workpiece independent of application of electrical power to the workpiece, comprising the steps of providing a workpiece having a nickel based finish, the finish being at least 85% by weight nickel; and treating the workpiece with a bath comprising a plating source component and a buffering component, the plating source component comprising one or more gold containing compounds wherein said gold is capable of alloying with the nickel based finish, the buffering component forming a nickel complex soluble in the bath, and comprising a mixture of sodium bicarbonate and ammonium hydroxide, or ammonium bifluoride, or ammonium citrate, the treating being conducted for a time and at a temperature sufficient to provide a layer on the workpiece, the layer comprising an alloy of nickel and gold, the layer having a molecular ratio of nickel to gold of from 1:1 to 6:1, and wherein the source of the nickel in said layer is the nickel from the nickel based finish.
The plating bath preferably contains as a plating source component a monovalent gold compound.
The nickel based finish occurring on the substrate or workpiece may be produced by conventional plating techniques for nickel and nickel alloys. The nickel based finish may be pure nickel (99.99% pure) or nickel alloyed or combined with other elements such as cobalt, boron, and phosphorus. The nickel is present to the extent of at least 85% by weight. Phosphorus has been found to inhibit the plating of gold and reduce the temperature stability of the gold based finish. For certain uses, however, the presence of phosphorus can be tolerated, but should preferably not exceed 6% by weight of the nickel based finish.Typical nicked based finishes include nickel (99.99%), nickeUcobalt/phosphorus (85/10/5 by weight, respectively), nickeUphosphorus (95/5 by weight, respectively) and nickel/boron (99/1 by weight, respectively). Typically the nickel based finish is relatively uniform in thickness, being between 100 and 150 microinches (25000--3750 microns) thick.
A typical bath for obtaining a nickel/phosphorus metal finish contains nickel chloride, sodium citrate, ammonium bifluoride, and sodium hypophosphite.
Substituting dimethyl amine borane for sodium hypophosphite yields a nickel/boron metal finish. The addition of nickel cobalt will introduce cobalt into the nickel based finish. The workpiece on which the nickel based finish is applied may be nickel, copper, nickel/steel, or any other substrate capable of being nickel plated.
After providing the workpiece with the nickel based finish, the workpiece is prepared for the gold plating bath. A typical preparation involves degreasing the surface by washing with a suitable solvent such as methylene chloride, rinsing with an acid solution followed by extensive water rinsing, and treatment with a solution of potassium cyanide containing hydrogen peroxide, followed by rinsing in deionized water. The prepared workpiece is then ready for the plating bath, which has been previously prepared. The plating component of the bath is one or more water soluble monovalent gold compounds, exemplary of which are potassium gold cyanide, gold chloride, and gold citrate. A buffering component is also part of the bath, and comprises a mixture of sodium bicarbonate and ammonium hydroxide, or ammonium bifluoride or ammonium citrate.The buffering component is added to the solution of the plating component, care being taken to avoid inhalation of hydrogen cyanide which may be produced with certain mixtures. The precise role assumed by the buffering component is not fully understood. In addition to serving as a buffer the agent also combines with the nickel in the nickel based layer to form a complex soluble in the gold plating bath.
The workpiece to be plated is immersed in the bath maintained at a constant temperature, preferably about 90" to 95"C. Agitation is initially vigorous, and then reduced for the plating period. After completion of the plating process, the plated workpiece is rinsed. The process produces gold based metal finishes 100 or more microinches (2500 microns) thick. The gold based metal finish is an alloy containing nickel and gold in which the molecular ratio of nickel to gold is from 1:1 to 6:1.
The gold based finish exhibits the physical characteristics of pure gold plating with the exception of resistance to salt spray and nitric acid according to standard test procedures. The finish is slightly yellowish with high brightness of nickel platetone and is of high corrosion and antiabrasion qualities.
The plating component of the bath should be present in an amount sufficient to achieve the desired thickness of plating. Generally, the plating component is present in an amount of at least three grams per litre of bath. The buffering component is present in an amount of at least 75 grams per litre and generally 100 grams per litre or more. The plating may take place in any suitable container. A preferred container has an inner tank lined with an inert material surrounded by a jacket through which circulates fluid to heat the bath. In terms of the surface to be plated, it is desirable that the gold plating compound be present in an amount of from 1 to 10, preferably 2 to 8 times 10-5 moles per litre per square inch to be plated. The buffering component may be present in an amount of from 3x10-4 to 4x1Q-3 moles per litre per squre inch to be plated.
The following examples are provided to illustrate the invention further.
Example 1 A bath is prepared consisting of the following: Ingredient Concentration (grams/litre) Plating Component Potassium gold cyanide 3 Buffering Component Sodium bicarbonate 100 Ammonium hydroxide 15 Water, balance to make 1.0 litre The plating component is prepared by dissolving the potassium gold cyanide in deionized water. The buffering component is prepared by adding the sodium bicarbonate and ammonium hydroxide to the plating component solution.
Sufficient deionized water is then added to make one litre of bath solution.
The workpiece, which has a pure nickel surface 150 microinches (3750 microns) thick, is subjected to a cleaning and activation process prior to plating.
The nickel based finish is washed with methylene chloride to degrease the nickel.
The degreased workpiece is then rinsed in a 120"F. solution of 50% HCI for 1 to 5 seconds after gassing starts followed by cold water rinsing for several minutes. The nickel coated workpiece is then plated in a solution of 10 grams/litre KCN and 50 ml./litre H202 and the solution agitated for ten minutes. The workpiece is removed from the solution, rinsed with deionized water, and placed in the plating bath.
The plating bath is preheated to 900 to 950C. After placing the cleaned nickel coated workpiece in the bath, the solution is agitated for one minute, and then occasionally for several minutes. The workpiece is removed and rinsed with tap water for several minutes followed by a rinse with deionized water. A gold plated finish is produced 60 microinches (1500 microns) thick having a nickel/gold molecular ratio of 6:1.
Examples 11 and 111 The procedure of Example 1 except that baths of the following formulations are employed. In each case, a nickel/gold alloy metal finish is produced.
Example 11 Ingredient Concentration (grams/litres) Plating Component KAu (CN)2 6 Buffer Component Ammonium bifluoride 100 Example 111 Ingredient Concentration (grams/litres) Plating Component KAu (CN)2 Buffer Component Ammonium citrate 100 Water, balance to make 1 litre The gold plated finish is an alloy of nickel and gold and such other elements as may be present in the nickel based finish, e.g., cobalt, boron, and phosphorus. The gold/nickel alloy wherein the nickel based finish is substantially pure nickel (99i99 Ó) provides a high temperature stable (at least 4500 C.) gold alloy. The presence of phosphorus in the nickel based finish results in a gold based finish which deteriorates at a temperature of 300"C. and above.
The mechanism by which the gold based finish is produced is not completely understood. The deep penetration of the gold appears to rule out the conventional immersion mechanism. It appears rather that the nickel based finish is removed to a substantial depth, and passes into the gold plating bath, where it is alloyed with gold and redeposited on the workpiece. The gold based finish is uniform, strongly adherent to the base, and preferably at least 15 microinches (375 microns) thick.
Thicknesses of from 60 to 100 microinches or more have been achieved.
WHAT WE CLAIM IS: 1. A metal plating process for plating a workpiece independent of application of electrical power to the workpiece, comprising the steps of providing a workpiece having a nickel based finish, the finish being at least 85% by weight nickel; and treating the workpiece with a bath comprising a plating source component and a buffering component, the plating source component comprising one or more gold containing compounds wherein said gold is capable of alloying with the nickel of the nickel based finish, the buffering component forming a nickel complex soluble in the bath, and comprising a mixture of sodium bicarbonate and ammonium hydroxide, or ammonium bifluoride, or ammonium citrate, the treating being conducted for a time and a temperature sufficient to provide a layer on the workpiece, the layer comprising an alloy of nickel and gold, the layer having a molecular ratio of nickel to gold of from 1:1 to 6: 1, and wherein the source of the nickel in said layer is the nickel from the nickel based finish.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. bicarbonate and ammonium hydroxide to the plating component solution. Sufficient deionized water is then added to make one litre of bath solution. The workpiece, which has a pure nickel surface 150 microinches (3750 microns) thick, is subjected to a cleaning and activation process prior to plating. The nickel based finish is washed with methylene chloride to degrease the nickel. The degreased workpiece is then rinsed in a 120"F. solution of 50% HCI for 1 to 5 seconds after gassing starts followed by cold water rinsing for several minutes. The nickel coated workpiece is then plated in a solution of 10 grams/litre KCN and 50 ml./litre H202 and the solution agitated for ten minutes. The workpiece is removed from the solution, rinsed with deionized water, and placed in the plating bath. The plating bath is preheated to 900 to 950C. After placing the cleaned nickel coated workpiece in the bath, the solution is agitated for one minute, and then occasionally for several minutes. The workpiece is removed and rinsed with tap water for several minutes followed by a rinse with deionized water. A gold plated finish is produced 60 microinches (1500 microns) thick having a nickel/gold molecular ratio of 6:1. Examples 11 and 111 The procedure of Example 1 except that baths of the following formulations are employed. In each case, a nickel/gold alloy metal finish is produced. Example 11 Ingredient Concentration (grams/litres) Plating Component KAu (CN)2 6 Buffer Component Ammonium bifluoride 100 Example 111 Ingredient Concentration (grams/litres) Plating Component KAu (CN)2 Buffer Component Ammonium citrate 100 Water, balance to make 1 litre The gold plated finish is an alloy of nickel and gold and such other elements as may be present in the nickel based finish, e.g., cobalt, boron, and phosphorus. The gold/nickel alloy wherein the nickel based finish is substantially pure nickel (99i99 Ó) provides a high temperature stable (at least 4500 C.) gold alloy. The presence of phosphorus in the nickel based finish results in a gold based finish which deteriorates at a temperature of 300"C. and above. The mechanism by which the gold based finish is produced is not completely understood. The deep penetration of the gold appears to rule out the conventional immersion mechanism. It appears rather that the nickel based finish is removed to a substantial depth, and passes into the gold plating bath, where it is alloyed with gold and redeposited on the workpiece. The gold based finish is uniform, strongly adherent to the base, and preferably at least 15 microinches (375 microns) thick. Thicknesses of from 60 to 100 microinches or more have been achieved. WHAT WE CLAIM IS:
1. A metal plating process for plating a workpiece independent of application of electrical power to the workpiece, comprising the steps of providing a workpiece having a nickel based finish, the finish being at least 85% by weight nickel; and treating the workpiece with a bath comprising a plating source component and a buffering component, the plating source component comprising one or more gold containing compounds wherein said gold is capable of alloying with the nickel of the nickel based finish, the buffering component forming a nickel complex soluble in the bath, and comprising a mixture of sodium bicarbonate and ammonium hydroxide, or ammonium bifluoride, or ammonium citrate, the treating being conducted for a time and a temperature sufficient to provide a layer on the workpiece, the layer comprising an alloy of nickel and gold, the layer having a molecular ratio of nickel to gold of from 1:1 to 6: 1, and wherein the source of the nickel in said layer is the nickel from the nickel based finish.
2. A process according to claim I wherein the nickel is at least 99"" by weight
pure.
3. A process according to Claim I or 2 wherein the bath is an aqueous bath.
4. A process according to any preceding claim wherein the gold containing compound is a monovalent gold compound.
5. A process according to Claim 4 wherein the or at least one of the gold containing compounds is potassium gold cyanide.
6. A process according to any preceding claim wherein the gold containing compound is present in an amount of from 1x10-5 to 10x10-5 moles per litre per square inch of surface of the nickel based finish and the buffering compound is present in an amount of from 3x 10-4 to 4x 10-3 moles per litre per square inch of surface of the nickel based finish.
7. A process according to any preceding claim wherein the nickel based finish comprises nickel and at least one member of the group consisting of cobalt, boron, and phosphorus, provided that the phosphorus does not exceed 6 , by weight.
8. A metal plating process substantially as herein described with reference to any one of Examples I to III.
9. A workpiece plated by a process as claimed in any preceding claim.
GB523378A 1978-02-09 1978-02-09 Gold plating process Expired GB1602041A (en)

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Application Number Priority Date Filing Date Title
GB523378A GB1602041A (en) 1978-02-09 1978-02-09 Gold plating process

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Application Number Priority Date Filing Date Title
GB523378A GB1602041A (en) 1978-02-09 1978-02-09 Gold plating process

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3810955A1 (en) * 1987-04-07 1988-10-27 Inco Ltd METHOD FOR PRODUCING AN ARTICLE FROM A CURED BASE BODY PROVIDED WITH A PRECIOUS METAL COVER
DE3810566A1 (en) * 1987-04-01 1988-11-10 Inco Ltd ARTICLE WITH DECORATIVE SURFACE

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3810566A1 (en) * 1987-04-01 1988-11-10 Inco Ltd ARTICLE WITH DECORATIVE SURFACE
DE3810955A1 (en) * 1987-04-07 1988-10-27 Inco Ltd METHOD FOR PRODUCING AN ARTICLE FROM A CURED BASE BODY PROVIDED WITH A PRECIOUS METAL COVER

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Legal Events

Date Code Title Description
PS Patent sealed
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19930209