Electrolytic stripping method

Abstract

The present invention provides an electrolytic stripping method comprising electrolytically stripping: a copper plating film exposed from a silver plating film that partially covers a copper plating film formed on the entire surface of a member; and leaking silver formed on an exposed portion of the copper plating film and having a smaller thickness than the silver plating film, using the copper plating film as an anode, wherein the electrolytic stripping is carried out using a cyan compound-free electrolytic copper-stripping liquid, and the electrolytic stripping liquid comprises a compound capable of forming, with silver, a complex ion that is more easily dissociated than a complex ion of silver and cyan; and wherein silver and copper are deposited on a cathode which is used as a counter electrode to the anode and which is made of a metal that is chemically stable against the electrolytic stripping liquid.

1 . An electrolytic stripping method comprising electrolytically stripping: 
 a copper plating film exposed from a silver plating film that partially covers a copper plating film formed on the entire surface of a member; and    leaking silver formed on an exposed portion of the copper plating film and having a smaller thickness than the silver plating film, using the copper plating film as an anode,    wherein the electrolytic stripping is carried out using a cyan compound-free electrolytic copper-stripping liquid, and the electrolytic stripping liquid comprises a compound capable of forming, with silver, a complex ion that is more easily dissociated than a complex ion of silver and cyan; and    wherein silver and copper are deposited on a cathode which is used as a counter electrode to the anode and which is made of a metal that is chemically stable against the electrolytic stripping liquid.    
     
     
         2 . The electrolytic stripping method according to  claim 1 , wherein the compound capable of forming, with silver, a complex ion that is more easily dissociated than a complex ion of silver and cyan is a compound capable of forming, with silver, a complex ion having a lower complex stability constant than the complex ion of silver and cyan.  
     
     
         3 . The electrolytic stripping method according to  claim 1 , wherein the compound capable of forming, with silver, a complex ion that is more easily dissociated than the complex ion of silver and cyan comprises at least one compound selected from the group consisting of ammonia water, an ammonium salt, a tartaric acid salt, phosphoric acid, and a citric acid salt.  
     
     
         4 . The electrolytic stripping method according to  claim 1 , wherein the electrolytic stripping liquid further comprises a copper compound or an aromatic nitro compound as a copper-oxidizing agent and has a pH of from 9 to 12.  
     
     
         5 . The electrolytic stripping method according to  claim 4 , wherein the copper compound is a copper ammonium complex derived from an ammonium source and a copper source.  
     
     
         6 . The electrolytic stripping method according to  claim 1 , wherein the cathode is surrounded by a cathode bag for collecting silver particles comprising the deposited silver.  
     
     
         7 . The electrolytic stripping method according to  claim 1 , wherein the member is a lead frame made of an iron based alloy.  
     
     
         8 . The electrolytic stripping method according to  claim 1 , further comprising 
 circulating the electrolytic stripping liquid in the vicinity of the cathode through a circulation line equipped with a filter, thereby collecting silver particles comprising the deposited silver.