Acidic aqueous binary silver-bismuth alloy electroplating compositions and methods

Abstract

Aqueous acid binary silver-bismuth alloy electroplating compositions and methods enable electroplating silver rich binary silver-bismuth deposits. The aqueous acid binary silver-bismuth alloy electroplating compositions include 5-membered heterocyclic nitrogen compounds with a thiol functionality which enable deposition of the silver rich binary silver-bismuth alloys. The silver rich silver-bismuth deposits are matte to semi-bright, uniform and have a low coefficient of friction.

1 - 6 . (canceled) 
     
     
         7 . A method of electroplating a binary silver-bismuth alloy on a substrate comprising:
 a) providing the substrate;   b) contacting the substrate with a binary silver-bismuth alloy electroplating composition comprising a source of silver ions, a source of bismuth ions, wherein the binary silver-bismuth alloy electroplating composition is free of additional alloying metals and a 5-membered aromatic heterocyclic nitrogen compounds having general formula:   
       
         
           
           
               
               
           
         
         wherein Q 1 -Q 4  can be a substituted or unsubstituted nitrogen or a substituted or unsubstituted carbon with the proviso that at least two of Q 1 -Q 4  are nitrogen, wherein substituent groups include, but are not limited to, (C 1 -C 4 )alkyl, amino group, aminoalkyl group, carboxyl, carboxy(C 1 -C 4 )alkyl or alkylsulfonate, an aliphatic thiol terminal compound selected from the group consisting of thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, cysteine, mercaptosuccinic acid, 3-mercapto-l-propanesulfonic acid, 2-mercaptoethanesulfonic acid, salts of the thiol terminal compounds, and mixtures thereof, and a pH of less than 7; and 
         c) applying an electric current to the binary silver-bismuth alloy electroplating composition and substrate to electroplate a binary silver-bismuth deposit on the substrate. 
       
     
     
         8 . The method of  claim 7 , wherein the 5-membered aromatic heterocyclic nitrogen compound is selected from the group consisting of 3-mercapto-1,2,4-triazole, 3-amino-1,2,4-triazole-5-thiol, 3-amino-5-mercapto-1,2,4-triazole, 3-mercapto-4-methyl-4H-1,2,4-triazole, 1H-imidazole-2-thiol, salts of the 5-membered aromatic heterocyclic nitrogen compounds, and mixtures thereof. 
     
     
         9 . The method of  claim 7 , wherein the binary silver-bismuth alloy electroplating composition further comprises a thioether or mixtures thereof. 
     
     
         10 . (canceled) 
     
     
         11 . An article comprising a binary silver-bismuth alloy layer adjacent a surface of a substrate made according to the method of  claim 7 , wherein the binary silver-bismuth alloy layer comprises 90% to 99.8% silver and 0.2% to 10% bismuth, and has a coefficient of friction of 1 or less.