Claims
- 1. An electroless gold plating composition comprising an aqueous solution of:
- (a) alkali metal gold cyanide sufficient to provide gold (calculated as metal) in the amount of 1.0-16.6 grams per liter;
- (b) alkali metal cyanide in the amount of 3-110 grams per liter;
- (c) a boron compound selected from the group consisting of alkyl amine boranes, alkali metal borohydrides, and mixtures thereof, in the amount of 2-10 grams per liter;
- (d) alkali metal hydroxide in the amount of 10-1100 grams per liter; and
- (e) 0.1-0.3 grams per liter of a stabilizer having the formula ##STR4## wherein R.sub.1 is --COOH, --OH, --CH.sub.2 OH, or --SO.sub.3 OH (or an alkali metal salt thereof)
- R.sub.2 is --COOH, --OH, --Cl, --H, (or an alkali metal salt thereof) and is disposed in the 2, 5, or 6 ring position
- --NO.sub.2 is in the 3 or 4 ring position,
- said composition having a pH of 12.5-14.0, the weight ratio of OH.sup.- /CN.sup.- being 4.0-10.0, the oxidation/reduction potential of the solution being -550 to -700 millivolts.
- 2. The electroless gold plating composition of claim 1 wherein said boron compound is dimethyl amine borane in the amount of 4-7 grams per liter.
- 3. The electroless gold plating composition of claim 1 wherein said stabilizer is nitrobenzene sulfonic acid or an alkali metal salt thereof.
- 4. The electroless gold plating composition of claim 1 wherein said stabilizer is present in the amount of 0.15-0.25 grams per liter.
- 5. The electroless gold plating composition in claim 1 wherein said composition has, at initial makeup, alkali metal cyanide in the amount of 4-6 grams per liter, and alkali metal hydroxide in the amount of 40-50 grams per liter.
- 6. The electroless gold plating composition of claim 1 wherein said composition has gold in the amount of 4-5 grams per liter, calculated as gold metal.
- 7. The electroless gold plating composition of claim 1 wherein said solution has a pH of about 13.4-14.0.
- 8. In a method for electroless plating of gold upon a workpiece, the steps comprising:
- (a) immersion plating upon the surface of a workpiece a thin deposit of immersion gold; and
- (b) immersing said plated workpiece in an electroless gold plating composition comprising an aqueous solution of:
- (i) alkali metal gold cyanide sufficient to provide gold calculated as metal in the amount of 1.0-16.6 grams per liter;
- (ii) alkali metal cyanide in the amount of 3-110 grams per liter;
- (iii) a boron compound selected from the group consisting of alkyl amine boranes, alkali metal borohydrides, and mixtures thereof, in the amount of 2-10 grams per liter;
- (iv) alkali metal hydroxide in the amount of 10-1100 grams per liter; and
- (v) a stabilizer having the formula ##STR5## wherein R.sub.1 is --COOH, --OH, --CH.sub.2 OH, or --SO.sub.3 OH (or an alkali metal salt thereof),
- R.sub.2 is --COOH, --OH, --Cl, --H, (or an alkali metal salt thereof) and is disposed in the 2, 5, or 6 ring position, and
- the --NO.sub.2 group is in the 3 or 4 ring position, said composition having a pH of 12.5-14.0, the weight ratio of OH.sup.- /CN.sup.- being 4.0-10.0, the amount of the stabilizer being in the range of 0.1-0.3 gram per liter to maintain the oxidation/reduction potential of the solution within the range of -550 to -700 millivolts,
- for a period of time sufficient to plate thereon high purity gold in the desired thickness.
- 9. The method of electroless plating of gold upon a workpiece in accordance with claim 8 wherein said solution is maintained at a temperature of about 85.degree.-95.degree. C.
- 10. The method of electroless plating of gold upon a workpiece in accordance with claim 8 wherein said boron compound is dimethyl amine borane in the amount of 4-7 grams per liter.
- 11. The method of electroless plating of gold upon a workpiece in accordance with claim 8 wherein said stabilizer is nitrobenzene sulfonic acid or an alkali metal salt thereof.
- 12. The method of electroless plating of gold upon a workpiece in accordance with claim 8 wherein said stabilizer is present in the amount of 0.15-0.25 gram per liter.
- 13. The method of electroless plating of gold upon a workpiece in accordance with claim 8 wherein said composition has, at initial makeup, alkali metal cyanide in the amount of 4.0-6.0 grams per liter, and alkali metal hydroxide in the amount of 40-50 grams per liter.
- 14. The method of electroless plating of gold upon a workpiece in accordance with claim 8 in which there is included the additional step of replenishing the composition, when the gold content (as metal) has decreased to 1.5-3 grams per liter, with a replenisher formulation comprising:
- (a) alkali metal gold cyanide in the amount of 60-100 grams per liter (as metal);
- (b) alkali metal hydroxide in the amount of 1-10 grams per liter; and
- (c) stabilizer in the amount of 2-6 grams per liter.
- 15. The method of electroless plating of gold upon a workpiece in accordance with claim 8 in which said electroless gold plating composition is prepared by first preparing an aqueous solution of the alkali metal hydroxide, alkali metal cyanide, alkali metal gold cyanide, stabilizer, and the boron compound, then heating the solution to operating temperature while monitoring the heated solution until the oxidation/reduction potential has reached a value of -550 to -700.
- 16. The method of electroless plating of gold upon a workpiece in accordance with claim 8 wherein the oxidation/reduction potential is monitored during the plating step and increments of stabilizer in the amount of 0.05-0.1 gram per liter are added to maintain the potential within the range of -550 to -700 millivolts.
CROSS-REFERENCE TO RELATED APPLICATION
The present invention is a continuation-in-part of Application Ser. No. 07/276,405 filed Nov. 22, 1988, abandoned.
US Referenced Citations (12)
Foreign Referenced Citations (1)
Number |
Date |
Country |
2121444 |
Dec 1983 |
GBX |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
276405 |
Nov 1988 |
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