Method of Pretreatment for Electroless Plating

Abstract

A method of electrolessly metal plating exposed copper or copper alloy on an article while preventing plating on areas other than the copper or copper alloy of the article to be plated. The method comprises the steps, in order, of a) immersing the article in a ruthenium based activator solution; b) immersing the article in a solution comprising one or more divalent sulfur compounds; and c) electrolessly plating the exposed copper or copper alloy on the article. The article may optionally be cleaned and/or microetched prior to being immersed in the ruthenium based activator solution. This pre treatment method eliminates extraneous plating on the article and reduces the initiation time for plating to begin on the copper or copper alloy during subsequent electroless plating.

What is claimed is: 
     
         1 . A method of electrolessly plating a metal on exposed copper or copper alloy on an article comprising the steps:
 a) optionally cleaning and/or microetching the article;   b) immersing the article in an activation solution comprising ruthenium metal ions;
 wherein there are no palladium compounds in solution, 
   c) immersing the article in a pre treatment solution comprising a divalent sulfur compound or combination of divalent sulfur compounds; and then   d) immersing the article in an electroless metal plating bath;
 wherein the divalent sulfur compound aids in reducing the time in which plating commences on the copper or copper alloy of said article by further activating the copper or copper alloy. 
   
     
     
         2 . The method according to  claim 1 , wherein the divalent sulfur compound or combination of divalent sulfur compound in the pre treatment solution is selected from β-thio-dipropionic acid, (methylene-dithio)-diacetic acid, 3-hydroxy-thionaphthene-2-carboxylic acid, 2-(α-hydroxy-ethyl-thio)-4-ethylbenzoic acid, dilauryl sulfide, distearyl dithiodipropionate, thiobenzoic acid, 1-octadecanethiol, S-(2-carboxyphenyl)-thioglycolic acid, thiourea, thiodiglycolic acid, dithiodiglyoclic acid, 3-(amidinothio)-1-propanesulfonic acid, thiophene, 2,2′-thiodiethanol, 4,4′-dinitro-diphenyl-sulfide-6,6′ -disulfonic acid, 2-(m-aminophenyl)-7-hydroxy-naptho-(2,3-d) thiazole-5-sulfonic acid, 2-hydroxy thionaphthene, 2-thiophene carboxylic acid, thiosalicylic acid, thiolactic acid, L-cysteine, cysteamine, thiodiacetic acid, potassium tetrathionate, 2,2′-thio-di(5-amino-benzene sulfonic acid), 3-carboxymethyl-thio-2-anthraquinone carboxylic acid, 4-hydroxy thiophenol, (2-nitro-4-acetamidophenyl-thio)-acetic acid, S(8-chloro-1-naphthyl)-thioglycolic acid, (p-chlorophenyl-thio)-acetic acid, 4-amino thiophenol, and 2-amino thiophenol. 
     
     
         3 . The method according to  claim 1 , wherein the concentration of the divalent sulfur compound or combination of divalent sulfur compounds is from 0.1 mg/L to 10,000 mg/L. 
     
     
         4 . The method according to  claim 3 , wherein the concentration of the divalent sulfur compound or combination of divalent sulfur compounds is from 0.5 mg/L to 5,000 mg/L. 
     
     
         5 . The method according to  claim 4 , wherein the concentration of the divalent sulfur compound or combination of divalent sulfur compounds is from 1.0 mg/L to 1,000 mg/L. 
     
     
         6 . The method according to  claim 1 , wherein the pre treatment solution further comprises a mineral acid. 
     
     
         7 . The method according to  claim 6 , wherein the mineral acid is sulfuric acid. 
     
     
         8 . The method according to  claim 6 , wherein the mineral acid concentration is 1% to 20% by volume. 
     
     
         9 . The method according to  claim 1 , wherein the initiation time in an electroless plating bath is less than two minutes. 
     
     
         10 . The method according to  claim 9 , wherein the initiation time in an electroless plating bath is less than one minute. 
     
     
         11 . The method according to  claim 10 , wherein the initiation time in an electroless plating bath is less than 30 seconds. 
     
     
         12 . The method according to  claim 1 , wherein there is no extraneous plating or bridging on the article. 
     
     
         13 . The method according to  claim 1 , wherein the pre treatment solution further comprises a pH adjuster. 
     
     
         14 . The method according to  claim 1 , wherein the pre treatment solution further comprises a surfactant. 
     
     
         15 . The method according to  claim 1 , wherein the pre treatment solution further comprises a complexor. 
     
     
         16 . A pre treatment method for a copper or copper alloy to be electrolessly metal plated comprising the steps of:
 a) activating the copper or copper alloy in a solution comprising ruthenium metal ions;   b) immersing the copper or copper alloy in a solution comprising one or more divalent sulfur compounds;   c) immersing the copper or copper alloy in an electroless metal plating bath.