Deposition of copper-tin and copper-tin-zinc alloys from an electrolyte

Abstract

The present invention relates to a cyanide-free electrolyte which contains a phosphate and aliphatic or aromatic thio compounds and also to a process for the electrolytic deposition of an alloy of the elements copper and tin and optionally zinc. The electrolyte and the process are characterized in that stannate ions and copper ions and optionally zinc(II) ions and also aliphatic and/or aromatic thio compounds are present in the electrolyte used. The electrolyte can optionally additionally contain carboxylic acids, wetting agents and/or brighteners. The present invention further provides a process for the electrolytic deposition of alloys of copper, tin and optionally zinc on consumer goods and decorative goods using the electrolyte of the invention.

1 . An aqueous, cyanide-free electrolyte for the electrolytic deposition of an alloy of copper, tin and optionally zinc, which comprises
 at least one salt from the group consisting of phosphates, phosphonates, polyphosphates, diphosphates and mixtures thereof   and   at least one compound selected from the group consisting of aliphatic and aromatic thio compounds,   wherein the metals copper and optionally zinc to be deposited are present in dissolved form and tin is present as dissolved Sn(IV) salt   and wherein the pH of the aqueous, cyanide-free electrolyte is greater than or equal to 9.   
     
     
         2 . The electrolyte as claimed in  claim 1 ,
 characterized in that   it further comprises at least one aliphatic saturated or unsaturated dicarboxylic or tricarboxylic acid, an aromatic carboxylic acid, salts and mixtures thereof.   
     
     
         3 . The electrolyte as claimed in  claim 1 ,
 characterized in that   it additionally contains at least one further salt, wherein the anion is selected from the group consisting of sulfates, fluorides, chlorides, bromides, iodides, carbonates, acetates, formates, propionates, butyrates, valerates, benzoates, nitrates, nitrites, sulfonates, alkylsulfonates, amidosulfonates, sulfamates, anions of amino carboxylic acids and N-heterocyclic carboxylic acids, wherein the cation is selected from among ammonium, lithium, sodium and potassium ions.   
     
     
         4 . The electrolyte as claimed in  claim 1 ,
 characterized in that   it additionally contains at least one brightener selected from the group consisting of bis(3-sulfopropyl) disulfide disodium salt, 3-sulfopropyl O-ethyldithiocarbonate potassium salt, 1-(3-sulfopropyl)pyridinium betaine, 1-(2-hydroxy-3-sulfopropyl)pyridinium betaine, 3-(2-benzothiazole-2-mercapto)propanesulfonic acid sodium salt, S-isothiouronium 3-propanesulfonate, 3-(sulfopropyl) N,N-dimethyldithiocarbamate sodium salt, 1-benzyl-3-sodiocarboxypyridinium chloride, 3-formyl-1-(3-sulfopropyl)pyridinium betaine, N-(3-sulfopropyl)saccharin sodium salt, saccharin sodium salt, carboxethylisothiuronium betaine, cocoamidopropyldimethylammonium 2-hydroxypropanesulfo betaine, N-(3-cocoamidopropyl-N,N-dimethyl)-N-(3-sulfopropyl)ammonium betaine, 6-carboxy-2,4-dihydroxypyrimidine, 2-butenoic acid.   
     
     
         5 . The electrolyte as claimed in  claim 1 ,
 characterized in that   it additionally contains at least one wetting agent selected from among
 a cationic, amine polymer having urea groups, 
 a cationic polymer which is made up of the monomers morpholine, epichlorohydrin and imidazole and has the general formula (C 4 H 9 NO) x *(C 3 H 5 ClO) y *(C 3 H 4 N 2 ) z , 
 a cationic polymer which is made up of the monomers epichlorohydrin and imidazole and has the general formula (C 3 H 5 ClO) x *(C 3 H 4 N 2 ) y , 
 N-alkyl-N-(1-oxoalkyl)amino acids and derivatives and salts thereof and 
 mixtures of these wetting agents. 
   
     
     
         6 . The electrolyte as claimed in  claim 1 ,
 characterized in that   the metals copper and optionally zinc to be deposited are present in ionically dissolved form and the tin is present as Sn(IV) salt, wherein the ion concentration of copper is in the range from 0.05 to 10 g/l of electrolyte, the ion concentration of tin is in the range from 0.5 to 40 g/l of electrolyte and the ion concentration of zinc is in the range from 0.1 to 10 g/l of electrolyte.   
     
     
         7 . The electrolyte as claimed in any of  claim 1 ,
 characterized in that   the compounds of the metals copper and optionally zinc to be deposited which are water-soluble under the given conditions are selected from the group consisting of pyrophosphates, carbonates, hydrogencarbonates, sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxide-hydroxides, oxides and combinations thereof.   
     
     
         8 . The electrolyte as claimed in  claim 1 ,
 characterized in that the dissolved Sn(IV) salt is a stannate.   
     
     
         9 . The electrolyte as claimed in  claim 1 ,
 characterized in that   the thio compound is selected from among 2-mercaptopropionic acid, mercaptosuccinic acid, 2-thiopropanedicarboxylic acid, Na 3-mercapto-1-propanesulfonate, 2-mercaptonicotinic acid, 2-thiouracil, 4,6-dihydroxy-2-mercaptopyrimidine, 2-mercaptopyrimidine, 2-thiocytosine, 6-mercaptopyrimidine-4-carboxylic acid, 2-mercaptopyrimidin-4-ol, 2-thiohydantoin, 5-sulfosalicylic acid.   
     
     
         10 . A process for the electrolytic deposition of an alloy of the elements copper and tin and optionally zinc, wherein the substrate to be coated is dipped as cathode into an electrolyte as claimed in  claim 1  and current flow is established between the anode and the cathode. 
     
     
         11 . The process as claimed in  claim 10 ,
 characterized in that   the proportion of copper in the alloy is in the range from 20 to 80% by weight, the proportion of tin is in the range from 10 to 60% by weight and the proportion of zinc is in the range from 1 to 30% by weight, where the sum of the proportions of all participating metals in the alloy is in each case 100% by weight.   
     
     
         12 . The process as claimed in  claim 10 , characterized in that the proportion of copper in the alloy is from 50 to 60% by weight, the proportion of tin is from 35 to 45% by weight and the proportion of zinc is from 5 to 15% by weight, where the sum of the proportions of all participating metals in the alloy is in each case 100% by weight. 
     
     
         13 . The process as claimed in  claim 10 , characterized in that the proportion of copper in the alloy is in the range from 30 to 90% by weight and the proportion of tin is in the range from 10 to 70% by weight, where the sum of the proportions of all participating metals in the alloy is in each case 100% by weight. 
     
     
         14 . The process as claimed in  claim 10 ,
 characterized in that   the electrolyte is kept in the range from 20 to 90° C.   
     
     
         15 . The process as claimed in  claim 10 ,
 characterized in that   a current density in the range from 0.1 to 100 ampere per square decimeter is set.   
     
     
         16 . The process as claimed in  claim 10 ,
 characterized in that insoluble anodes (e.g. platinated titanium anodes or mixed metal oxide anodes) or soluble anodes composed of a material selected from the group consisting of electrolytic copper, phosphorus-containing copper, tin, tin-copper alloy, zinc-copper alloy and zinc-tin-copper alloy or combinations of these anodes are used.