Alloy composition and plating method

Abstract

Disclosed are electrolyte compositions for depositing tin-copper alloys that are substantially free of lead. Also disclosed are methods of plating tin-copper alloys that are substantially free of lead on substrates and uses for such plated substrates.

1 - 20 . (canceled)  
   
   
       21 . An electrolyte composition for depositing a tin-copper alloy on a substrate, consisting essentially of 5 to 100 g/L tin, 0.01 to 10 g/L copper, one or more acidic electrolytes, one or more wetting agents selected from ethylene oxide derivatives of aliphatic alcohols containing an alkyl group of up to 7 carbons and aromatic alcohols having up to 2 aromatic rings substituted with an alkyl group having up to 6 carbons and one or more additives selected from alloying materials, reducing agents, acetaldehyde, glutaraldehyde and brightening agents, wherein the composition is substantially free of lead and substantially free of added conductivity compounds selected from citric acid, sodium gluconate, ammonium sulfate, ammonium citrate, sodium acetate, sodium carbonate or potassium pyrophosphate; and provided that when sulfuric acid is the acidic electrolyte it is used as the only acidic electrolyte.  
   
   
       22 . A method for high speed electroplating of tin-copper alloys comprising the steps of: a) utilizing high speed electroplating equipment comprising an electroplating cell; an overflow reservoir adjacent the cell; means for returning solution from the reservoir to the electroplating cell; means for directing a substrate to be plated from an entry point at one end of the cell to an exit at a second end of the cell; b) introducing an electrolyte composition consisting essentially of a basis solution of 5 to 100 g/L tin, 0.01 to 10 g/L copper, one or more acidic electrolytes, one or more wetting agents selected from ethylene oxide derivatives of aliphatic alcohols containing an alkyl group of up to 7 carbons and aromatic alcohols having up to 2 aromatic rings substituted with an alkyl group having up to 6 carbons and one or more additives selected from alloying materials, reducing agents, acetaldehyde, glutaraldehyde and brightening agents, wherein the composition is substantially free of lead and substantially free of added conductivity compounds selected from citric acid, sodium gluconate, ammonium sulfate, ammonium citrate, sodium acetate, sodium carbonate or potassium pyrophosphate; and provided that when sulfuric acid is the acidic electrolyte it is used as the only acidic electrolyte; and c) continuously electroplating the substrate with tin-copper alloy at a sufficient current density and at a sufficient temperature for high speed electroplating as the substrate passes through the electrolyte composition within the cell.  
   
   
       23 . A method for depositing a tin-copper alloy including the steps of a) contacting a printed wiring board with an electrolyte composition consisting essentially of 5 to 100 g/L tin, 0.01 to 10 g/L copper, one or more acidic electrolytes, one or more wetting agents selected from ethylene oxide derivatives of aliphatic alcohols containing an alkyl group of up to 7 carbons and aromatic alcohols having up to 2 aromatic rings substituted with an alkyl group having up to 6 carbons, and one or more additives selected from reducing agents, acetaldehyde, glutaraldehyde and brightening agents, wherein the composition is substantially free of lead and substantially free of added conductivity compounds selected from citric acid, sodium gluconate, ammonium sulfate, ammonium citrate, sodium acetate, sodium carbonate or potassium pyrophosphate; and provided that when sulfuric acid is the acidic electrolyte it is used as the only acidic electrolyte; and b) passing a current through the electrolyte to deposit the tin-copper alloy on the printed wiring board.