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.

What is claimed is:  
     
         1 . An electrolyte composition for depositing a tin—copper alloy on a substrate, comprising 5 to 100 g/L tin, 0.01 to 10 g/L copper, and one or more acidic electrolytes, 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 than when sulfuric acid is the acidic electrolyte it is used as the only acidic electrolyte.  
     
     
         2 . The composition of  claim 1  wherein the tin is in the form of a tin compound selected from tin halides, tin sulfates, tin alkanesulfonate, tin alkanolsulfonate or mixtures thereof.  
     
     
         3 . The composition of  claim 1  wherein the copper is in the form of a copper compound selected from copper halides, copper sulfate, copper alkanesulfonate, copper alkanolsulfonate or mixtures thereof.  
     
     
         4 . The composition of  claim 1  wherein the acidic electrolyte is selected from alkanesulfonic acids, arylsulfonic acids, sulfuric acid, sulfamic acid, hydrochloric acid, hydrobromic acid or fluoroboric acid.  
     
     
         5 . The composition of  claim 1  wherein the acidic electrolyte is present in an amount of 10 to 400 mL/L.  
     
     
         6 . The composition of  claim 1  further comprising water.  
     
     
         7 . The composition of  claim 1  further comprising one or more additives selected from alloying materials, reducing agents, wetting agents, brightening agents or mixtures thereof.  
     
     
         8 . A method for depositing a tin—copper alloy on a substrate comprising the steps of contacting the substrate with the electrolyte composition of  claim 1  and passing a current through the electrolyte to deposit the tin—copper alloy on the substrate, wherein the alloy is substantially free of lead.  
     
     
         9 . The method of  claim 8  wherein the current used has a current density in the range of 1 to 2000 ASF.  
     
     
         10 . The method of  claim 8  wherein the substrate is selected from copper, copper alloys, nickel, nickel alloys, nickel—iron containing materials, electronic components, or plastics.  
     
     
         11 . The method of  claim 10  wherein the electronic components are selected from lead frames, semiconductor packages, components, connectors, contacts, chip capacitors, chip resistors, or printed wiring boards.  
     
     
         12 . A substrate having a tin—copper alloy deposited thereon according to the method of  claim 8 .  
     
     
         13 . A substrate comprising a tin—copper alloy comprising 80 to 99.99 wt % tin and 0.01 to 20 wt % copper, wherein the alloy is substantially free of lead.  
     
     
         14 . 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 comprising a basis solution of 5 to 100 g/L tin, 0.01 to 10 g/L copper, and one or more acidic electrolytes, wherein the composition is substantially free of lead and substantially free of added conductivity compounds selected from citric acid, sulfuric acid, sodium gluconate, ammonium sulfate, ammonium citrate, sodium acetate, sodium carbonate or potassium pyrophosphate; and provided than when sulfuric acid is the acidic electrolyte it is used as the only acidic electrolyte; and c) continuously electroplating substrates with tin—copper alloy at a sufficient current density and at a sufficient temperature for high speed electroplating as the substrates pass through the electroplating solution within the cell.  
     
     
         15 . A method for depositing a tin—copper alloy including the steps of a) contacting a printed wiring board with an electrolyte composition comprising 5 to 100 g/L tin, 0.01 to 10 g/L copper, and one or more acidic electrolytes, wherein the composition is substantially free of lead and substantially free of added conductivity compounds selected from citric acid, sulfuric acid, sodium gluconate, ammonium sulfate, ammonium citrate, sodium acetate, sodium carbonate or potassium pyrophosphate; and provided than 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.  
     
     
         16 . The method of  claim 15  wherein the tin is in the form of a tin compound selected from tin halides, tin sulfates, tin alkanesulfonate, tin alkanolsulfonate or mixtures thereof.  
     
     
         17 . The method of  claim 15  wherein the copper is in the form of a copper compound selected from copper halides, copper sulfate, copper alkane sulfonate, copper alkanol sulfonate or mixtures thereof.  
     
     
         18 . The method of  claim 15  wherein the acidic electrolyte is selected from alkanesulfonic acids, arylsulfonic acids sulfuric acid, hydrochloric acid, hydrobromic acid or fluoroboric acid.  
     
     
         19 . The method of  claim 15  wherein the acidic electrolyte is present in an amount of 10 to 400 mL/L.  
     
     
         20 . The method of  claim 15  wherein the electrolyte composition further comprises one or more additives selected from alloying materials, reducing agents, wetting agents, brightening agents or mixtures thereof.