Formaldehyde-free electroless copper plating solution

Abstract

The invention relates to an electroless aqueous copper plating solution, comprising a source of copper ions, a source of glyoxylic acid as reducing agent, and at least one polyamino disuccinic acid or at least one polyamino monosuccinic acid, or a mixture of at least one polyamino disuccinic acid and at least one polyamino monosuccinic acid as complexing agent, as well as to a method for electroless copper plating utilizing said solution and the use of the solution for the plating of substrates.

1 . An electroless aqueous copper plating solution, comprising
 a source of copper ions,   a source of glyoxylic acid, as reducing agent, and   at least one polyamino disuccinic acid, or at least one polyamino monosuccinic acid, or a mixture of at least one polyamino disuccinic acid and at least one polyamino monosuccinic acid, as complexing agent,   
       wherein the molar ratio of the complexing agent to copper ions is in the range of 1.1:1 to 5:1. 
     
     
         2 . The electroless aqueous copper plating solution according to  claim 1 , wherein the molar ratio of glyoxylic acid to complexing agent is <4.6:1. 
     
     
         3 . The electroless aqueous copper plating solution according to one of the preceding claims, wherein the molar ratio of the complexing agent to copper ions is in the range of 1.5:1 to 5:1. 
     
     
         4 . The electroless aqueous copper plating solution according to one of the preceding claims, which does contain less than 0.01 ppm of a thiocarboxylic acid. 
     
     
         5 . The electroless aqueous copper plating solution according to one of the preceding claims, wherein the complexing agent is at least one polyamino disuccinic acid. 
     
     
         6 . The electroless aqueous copper plating solution according to one of the preceding claims, wherein the complexing agent is ethylenediamine-N,N′-disuccinic acid (EDDS). 
     
     
         7 . The electroless aqueous copper plating solution according to one of the preceding claims, wherein the solution further comprises one or more of a stabilizing agent. 
     
     
         8 . The electroless aqueous copper plating solution according to  claim 7 , wherein the stabilizing agent is selected from dipyridyls, phenanthroline, mercapto-benzothiazole, thio-urea or its derivatives, cyanides, thiocyanates, iodides, ethanolamines, mercapto-benzotriazole, Na 2 S 2 O 3 , polymers, like polyacrylamides, polyacrylates, polyethylene glycols or polypropylene glycols or their co-polymers. 
     
     
         9 . The electroless aqueous copper plating solution according to one of the preceding claims, wherein the solution further comprises a source of hydroxide ions. 
     
     
         10 . The electroless aqueous copper plating solution according to one of the preceding claims, wherein the solution comprises, besides glyoxylic acid, a second reducing agent. 
     
     
         11 . The electroless aqueous copper plating solution according to  claim 10 , wherein the second reducing agent is selected from the group of hypophosphoric acid, glycolic acid, formic acid, and a salt of these acids. 
     
     
         12 . A method for electroless copper plating, the process comprising contacting a substrate with an electroless aqueous copper plating solution according to one of  claims 1 - 11 . 
     
     
         13 . The method according to  claim 12 , which is carried out at a temperature in the range of 20-60° C. 
     
     
         14 . The use of an electroless aqueous copper plating solution according to one of  claims 1 - 11  for the plating of printed circuit boards, integrated circuit substrates, wafers, molded interconnect devices, displays or plastic parts. 
     
     
         15 . The use of an electroless aqueous copper plating solution according to one of  claims 1 - 11  for the plating of glass substrates, particularly glass substrates for displays.