Method of selectively treating copper in the presence of further metal

Abstract

The present invention relates to a method of selectively treating the surface of copper or copper alloys without affecting other metals, particularly tin. The methods are suited for treating surfaces of copper or copper alloys in order to facilitate subsequent deposition of metal layers and enhance solderability of the surfaces of copper, copper alloys and said subsequently deposited metal layers. The methods are applied to printed circuit boards (PCBs) and lead frames or integrated circuit substrates (IC substrates).

1 . A method of selectively treating the surface of copper or copper alloys, comprising the steps of
 (i) contacting said surface with an alkaline treatment solution, and   (ii) contacting the surface obtained by step (i) with an acidic treatment solution, and   wherein the alkaline treatment solution comprises:
 at least one source of copper (II) ions, 
 at least one source of halide ions, and 
 ammonia. 
   
     
     
         2 . The method according to  claim 1  wherein the alkaline treatment solution has a pH value ranging from 7.0 to 9.0. 
     
     
         3 . The method according to  claim 1  wherein the acidic treatment solution comprises at least one acid wherein the at least one acid is selected from the group consisting of carboxylic acids, aromatic sulfonic acids and mineral acids. 
     
     
         4 . The method according to  claim 1  wherein the acidic treatment solution comprises at least one acid in a concentration ranging from 50 g/l to 200 g/l. 
     
     
         5 . The method according to  claim 1  wherein the copper alloy comprises one or more alloying metal and the one or more alloying metal is selected from the group consisting of iron, chromium, silicon, zinc, tin, nickel, zirconium and phosphorous. 
     
     
         6 . The method according to  claim 1  wherein the source of copper (II) ions is selected from the group consisting of copper(II) chloride, copper(II) bromide and copper(II) nitrate. 
     
     
         7 . The method according to  claim 1  wherein the source of halide ions is selected from the group consisting of ammonium chloride, copper(II) chloride, lithium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, aluminum chloride, copper(II) bromide, ammonium bromide, lithium bromide, sodium bromide, potassium bromide, magnesium bromide, copper(II) fluoride, ammonium fluoride, sodium fluoride, potassium fluoride, ammonium iodide, sodium iodide and potassium iodide. 
     
     
         8 . The method according to  claim 1  wherein the acidic treatment solution further comprises an oxidising agent. 
     
     
         9 . The method according to  claim 8  wherein the oxidising agent is selected from the group consisting of hydrogen peroxide and disodium peroxodisulfate. 
     
     
         10 . The method according to  claim 1  wherein the alkaline treatment solution has a temperature ranging from 15° C. to 90° C. and wherein the acidic treatment solution has a temperature ranging from 15° C. to 30° C. 
     
     
         11 . The method according to  claim 1  wherein the step (i) is performed for 1 second to 10 minutes and wherein the step (ii) is performed for 3 seconds to 30 minutes. 
     
     
         12 . The method according to  claim 1  comprising the further step (iii):
 (iii) metal plating the surface obtained by step (ii) by a wet chemical plating method. 
 
     
     
         13 . The method according to  claim 12 , wherein the wet chemical plating method is selected from the group consisting of an electroless and an immersion plating method. 
     
     
         14 . The method according to  claim 1  wherein the surfaces of copper or copper alloys are part of workpieces and the workpieces are selected from the group consisting of printed circuit boards, lead frames and integrated circuit substrates.