Method of filling through-holes

Abstract

The methods inhibit or reduce dimpling and voids during copper electroplating of through-holes with flash copper layers in substrates such as printed circuit boards. An acid solution containing disulfide compounds is applied to the through-holes of the substrate followed by filling the through-holes with copper using an acid copper electroplating bath which includes additives such as brighteners and levelers.

What is claimed is: 
     
         1 . A method comprising:
 a) providing a substrate with a plurality of through-holes and a layer of copper flash on a surface of the substrate and walls of the plurality of through-holes;   b) applying an aqueous acid solution to at least the plurality of through-holes, the aqueous acid solution comprising one or more disulfide compounds having a formula:   
       
         
           
           
               
               
           
         
         
           wherein X is sodium, potassium or hydrogen, R is independently hydrogen or an alkyl, n and m are integers of 1 or greater, the one or more disulfide compounds are in amounts of 50 ppb to 10 ppm; and 
         
         c) electroplating at least the through-holes with copper using an acid copper electroplating bath comprising one or more brighteners and one or more levelers. 
       
     
     
         2 . The method of  claim 1 , wherein the disulfide compounds are in amounts of 50 ppb to 500 ppb. 
     
     
         3 . The method of  claim 1 , wherein X is sodium or hydrogen. 
     
     
         4 . The method of  claim 1 , wherein R is independently hydrogen or (C 1 -C 6 )alkyl. 
     
     
         5 . The method of  claim 1 , wherein m and n are independently integers of 1-6. 
     
     
         6 . The method of  claim 1 , wherein the disulfide compound is bis(3-sulfopropyl)disulfide. 
     
     
         7 . The method of  claim 1 , wherein the one or more levelers of the copper electroplating bath are reaction products of one or more imidazole compounds and one or more epoxy compounds.