Tin plating method

Abstract

Methods of electrodepositing layers of tin or tin-alloys on a substrate are provided. The methods involve electrolytically treating a substrate with a solution comprising a phosphoric acid and a carboxylic acid, and electrodepositing a layer of tin or tin-alloy on a surface of the treated substrate. The methods can provide tin or tin-alloy layers having a reduced tendency to form whiskers.

What is claimed is:  
     
         1 . A method of electrodepositing a layer of tin or tin-alloy on a substrate, comprising: 
 electrolytically treating a substrate with a solution comprising a phosphoric acid and a carboxylic acid; and    electrodepositing a layer of tin or tin-alloy on a surface of the treated substrate.    
     
     
         2 . The method according to  claim 1 , wherein the substrate is constructed of a copper-containing metal or metal-alloy.  
     
     
         3 . The method according to  claim 2 , wherein the substrate is constructed of copper.  
     
     
         4 . The method according to  claim 1 , wherein the electronic device substrate is a printed wiring board substrate, a lead frame, a semiconductor package, a chip capacitor, a chip resistor, a connector, or a contact.  
     
     
         5 . The method according to  claim 5 , wherein the electronic device substrate is a lead frame.  
     
     
         6 . The method according to  claim 1 , wherein the phosphoric acid is orthophosphoric acid present in the solution an amount of from 20 to 80% by volume.  
     
     
         7 . The method according to  claim 1 , wherein the carboxylic acid is malic acid, tartaric acid, citric acid, lactic acid, or a combination thereof.  
     
     
         8 . The method according to  claim 1 , wherein the carboxylic acid is a hydroxycarboxylic acid.  
     
     
         9 . The method according to  claim 1 , wherein the solution further comprises an alkali metal hydroxide.  
     
     
         10 . The method according to  claim 1 , wherein the solution further comprises an organic solvent.  
     
     
         11 . The method according to  claim 10 , wherein the organic solvent is ethylene glycol, propylene glycol, glycerin, ethanol, isopropyl alcohol, or a combination thereof.  
     
     
         12 . The method according to  claim 1 , wherein the step of electrolytically treating is conducted at a voltage effective to polish the surface of the substrate.  
     
     
         13 . A method of electrodepositing a layer of tin or tin-alloy on a substrate, comprising: 
 electrolytically treating a substrate with a solution comprising from 50 to 80% by volume of a carboxylic acid; and    electrodepositing a layer of tin or tin-alloy on a surface of the treated substrate.    
     
     
         14 . The method according to  claim 13 , wherein the solution further comprises a phosphoric acid.  
     
     
         15 . The method according to  claim 13 , wherein the carboxylic acid is malic acid, tartaric acid, citric acid, lactic acid, or a combination thereof.  
     
     
         16 . The method according to  claim 13 , wherein the carboxylic acid is a hydroxycarboxylic acid.  
     
     
         17 . The method according to  claim 1 , wherein the step of electrolytically treating is conducted at a voltage effective to polish the surface of the substrate.