Plating method

Abstract

The present invention discloses compositions for increasing the adhesion of a layer of silver deposited from an immersion plating bath as well as methods of increasing the adhesion of silver layers obtained using these compositions. Such compositions and methods are particularly useful in the manufacture of electronic devices.

What is claimed is:  
     
         1 . A method of improving the adhesion of a layer of silver deposited from an immersion plating bath comprising the step of: contacting a metal that is less electropositive than silver with an azole compound prior to contacting the metal with an immersion silver plating bath.  
     
     
         2 . The method of  claim 2  wherein the azole compound is selected from the group consisting of triazoles, benzotriazoles, tetrazoles, imidazoles, benzimidazoles, indazoles and mixtures thereof.  
     
     
         3 . The method of  claim 2  wherein the azole compound is benzotriazole, substituted benzotriazole, imidazole or substituted imidazole.  
     
     
         4 . The method of  claim 3  wherein the substituted imidazole is selected from the group consisting of (C 1 -C 16 )alkylimidazole and arylimidazole.  
     
     
         5 . The method of  claim 1  wherein the azole compound is selected from the group consisting of methylimidazole, ethylimidazole, propylimidazole, hexylimidazole, decylimidazole, undecylimidazole, 1-phenylimidazole, 4-phenylimidazole, hydroxybenzotriazole, aminobenzotriazole, 2-imidazolecarboxaldehyde, benzotriazolecarboxylic acid, 2-guanidinobenzimidazole, 2-aminoindazole, chlorobenzotriazole, hydroxyethylbenzotriazole, hydroxyethylimidazole, hydroxybenzimidazole and 1,2,4-triazole.  
     
     
         6 . The method of  claim 1  wherein the azole compound is present in a pretreatment composition in an amount from 0.005 to 50 g/L.  
     
     
         7 . The method of  claim 6  wherein the pretreatment composition is a microetching composition.  
     
     
         8 . The method of  claim 1  wherein the immersion silver plating bath comprises a source of silver ions, water and a complexing agent.  
     
     
         9 . The method of  claim 8  wherein the complexing agent is a multidentate ligand.  
     
     
         10 . The method of  claim 1  wherein the metal that is less electropositive than silver is selected from the group consisting of zinc, iron, tin, nickel, lead, copper and alloys thereof.  
     
     
         11 . A method of depositing a layer of silver on a substrate comprising the steps of: contacting a metal that is less electropositive than silver with an azole compound; and then contacting the metal with an immersion silver plating bath.  
     
     
         12 . A bath for promoting the adhesion of a layer of silver deposited from an immersion plating bath comprising an azole compound, water and an acid.  
     
     
         13 . The bath of  claim 12  further comprising a source of copper ions.  
     
     
         14 . A method of manufacturing a printed wiring board comprising the steps of: contacting a metal that is less electropositive than silver with an azole compound; and then contacting the metal with an immersion silver plating bath.  
     
     
         15 . A method of manufacturing a printed wiring board comprising the steps of: contacting a metal that is less electropositive than silver with an etchant composition; contacting the metal with an azole compound; and then contacting the metal with an immersion silver plating bath to provide a layer of silver.  
     
     
         16 . The method of  claim 15  wherein the azole compound is selected from the group consisting of triazoles, benzotriazoles, tetrazoles, imidazoles, benzimidazoles, indazoles and mixtures thereof.  
     
     
         17 . The method of  claim 15  wherein the metal that is less electropositive than silver is selected from the group consisting of zinc, iron, tin, nickel, lead, copper and alloys thereof.  
     
     
         18 . A method of improving the adhesion of a layer of silver deposited from an immersion bath comprising the step of: contacting a metal that is less electropositive than silver with a microetching composition including water, an azole compound, and a microetchant selected from sulfuric acid/hydrogen peroxide or an alkali metal persulfate, prior to contacting the metal with an immersion silver plating bath to provide the layer of silver.  
     
     
         19 . A method of reducing tarnish of a layer of silver deposited from an immersion bath comprising the step of: contacting a metal that is less electropositive than silver with an imidazole compound prior to contacting the metal with an immersion silver plating bath to provide the layer of silver.  
     
     
         20 . A method for manufacturing a printed wiring board comprising the steps of: a) contacting a printed wiring board substrate having pads, through holes, soldermask and a layer of a metal that is less electropositive than tin with an immersion plating bath including a source of tin ions, water and a complexing agent, to form a tin deposit on the metal; b) then contacting the tin plated printed wiring board substrate with an azole compound; c) then contacting the tin with an immersion silver plating bath including a source of silver ions, water and a complexing agent, to form an immersion silver deposit on the tin deposit; and d) heating the silver-tin deposit to form a tin-silver alloy.