Cyanide-free plating solutions for monovalent metals

Abstract

A solution for use in electroplating which comprises at least one monovalent metal such as copper, silver or gold which is complexed by a thiosulfate ion; and a stabilizer of an organic sulfinate compound such as, for example, one having the formula R-SO2-X wherein R is an alkyl, heterocyclic or aryl moiety and X is a monovalent cation. The stabilizer is present in an amount sufficient to stabilize the thiosulfate ion when the solution is operated at an acidic pH of less than 7. Also, the solution is substantially free of cyanide.

What is claimed is: 
     
       1. A solution for use in electroplating which comprises: at least one monovalent metal which is complexed by an amount of a thiosulfate ion; and   a stabilizer of an organic sulfinate compound in an amount sufficient to stabilize the thiosulfate ion when the solution is operated at an acidic pH of less than 7.   
     
     
       2. The solution of claim 1 wherein the monovalent metal is copper, silver, gold or combinations thereof. 
     
     
       3. The solution of claim 1 wherein the metal is present in an amount of between about 0.5 to 100 g/l. 
     
     
       4. The solution of claim 1 wherein the thiosulfate ion and metal ion or ions are present in a molar ratio of about 1:1 to 3:1. 
     
     
       5. The solution of claim 1 wherein the thiosulfate ion is present in excess of the amount necessary to complex the metal. 
     
     
       6. The solution of claim 1 further comprising an alloying element for deposition with the monovalent metal. 
     
     
       7. The solution of claim 6 wherein the alloying element is palladium, nickel or zinc. 
     
     
       8. The solution of claim 7 wherein the alloying element is complexed with a complexing agent other than a thiosulfate. 
     
     
       9. The solution of claim 1 wherein the stabilizer has the formula R-SO 2  -X wherein R is an alkyl, heterocyclic or aryl moiety and X is a monovalent cation. 
     
     
       10. The solution of claim 9 wherein R is an alkyl group having one to eighteen carbon atoms in a linear or branched configuration; or an aromatic or heterocyclic group having between five and fourteen carbon atoms in a configuration of one, two or three rings, wherein each ring is optionally substituted by an alkyl group having one to six carbon atoms. 
     
     
       11. The solution of claim 9 wherein X is hydrogen, an alkali metal ion, or an ammonium ion. 
     
     
       12. The solution of claim 9 .[.Wherein.]. .Iadd.wherein .Iaddend.R is substituted with a water solubilizing group. 
     
     
       13. The solution of claim 12 wherein the water solubilizing group is a hydroxy group, a carboxyl group, a halide, a sulfate, a sulfonate, a phosphate, a phosphonate or a carboxylate. 
     
     
       14. The solution of claim 1 wherein the stabilizer is benzene, toluene, zylene, naphthalene or bisphenol A sulfinic acid or an alkali or ammonium salt thereof. 
     
     
       15. The solution of claim 1 wherein the stabilizer is present in an amount of at least about 2 to 15 g/l. 
     
     
       16. The solution of claim 15 wherein the stabilizer is present in an amount of about 5 to 15 g/l. 
     
     
       17. The solution of claim 1 further comprising at least one additive to improve or enhance the performance of the solution during electroplating. 
     
     
       18. The solution of claim 17 wherein the additive is an electroplating current density range extender, a surfactant or a brightener. 
     
     
       19. The solution of claim 17 wherein the additive is an amine, an alkylene oxide condensation compound of an organic compound, or a solution soluble derivative thereof. 
     
     
       20. The solution of claim 17 wherein the additive is triethanolamine and is present in an amount of about 10 to 30 g/l. 
     
     
       21. The solution of claim 1 having a pH above about 3.5 and below 7. 
     
     
       22. The solution of claim 21 which further comprises an acid in an amount sufficient to maintain the pH between about 4 and about 6. 
     
     
       23. The solution of claim 1 wherein the temperature of the solution is maintained within about 55° to 120° F. and the solution is substantially free of cyanide. 
     
     
       24. A solution for use in electroplating which comprises: at least one monovalent metal of copper, silver, gold or combinations thereof in an amount of between about 0.5 to 100 g/l which is complexed by a thiosulfate ion and wherein the thiosulfate ion and metal ion or ions are present in a molar ratio of about 1:1 to 3:1; and a stabilizer of an organic sulfinate compound in an amount of at least about 2 to 15 g/l to stabilize the thiosulfate ion when the solution is operated at an acidic pH of between about 4 and 6. 
     
     
       25. The solution of claim 24 further comprising an alloying element for deposition with the monovalent metal and wherein the organic sulfinate compound includes a water solubilizing group. 
     
     
       26. The solution of claim 25 further comprising at least one additive to improve or enhance the performance of the solution during electroplating, and wherein the temperature of the solution is maintained within about 55° to 120° F., and the solution is substantially free of cyanide. 
     
     
       27. The solution of claim 26 wherein the stabilizer has the formula R-SO 2  -X wherein R is an alkyl, heterocyclic or aryl moiety, X is a monovalent cation and the alloying element is complexed with a complexing agent other than a thiosulfate. 
     
     
       28. The solution of claim 27 wherein the thiosulfate ion is present in an amount in excess of that necessary to complex the metal and the solubilizing group is a hydroxy group, a carboxyl group, a halide, a sulfate, a sulfonate, a phosphate, a phosphonate or a carboxylate. .Iadd. 
     
     
       29.  A metal plating bath which comprises: a solution of at least one monovalent metal ion which forms a thiosulfate complex; a solution soluble thiosulfate ion in an amount sufficient to form a complex with the metal ion or ions; and an organic sulfinate ion in an amount sufficient to stabilize the thiosulfate ion in the solution. .Iaddend..Iadd.30. The bath of claim 29 wherein the monovalent metal is copper, silver, gold or combinations thereof and is present in the solution in an amount of up to about 100 g/l. .Iaddend..Iadd.31. The bath of claim 29 wherein the thiosulfate ion and metal ion or ions are present in a molar ratio of greater than 1:1. .Iaddend..Iadd.32. The bath of claim 29 wherein the sulfinate ion is provided by a compound having the formula R-SO 2  -X where R is an alkyl, heterocyclic or aryl moiety and X is a monovalent 
     
     
        cation. .Iaddend..Iadd.33.  The bath of claim 32 wherein R is an alkyl group having one to eighteen carbon atoms in a linear or branched configuration; or an aromatic or heterocyclic group having between five and fourteen carbon atoms in a configuration of one, two or three rings, where each ring is optionally substituted by an alkyl group having one to six carbon atoms, R is optionally substituted with a water solubilizing group, and X is hydrogen, an alkali metal ion or an ammonium ion, said sulfinate compound being present in an amount of at least 2 g/l. .Iaddend..Iadd.34. The bath of claim 29 further comprising an alloying element for deposition with the monovalent metal, where the alloying element is complexed with a complexing agent. .Iaddend..Iadd.35. The bath of claim 29 further comprising at least one additive to improve or enhance the performance of the solution during plating, wherein the temperature of the solution is maintained at about 55° F. to about 120° F. and the solution is substantially free of cyanide. .Iaddend.