Plating method

Abstract

The present invention provides compositions and methods for immersion depositing highly adherent silver layers. The compositions contain silver ions, water and a carboxylic acid-substituted nitrogen-containing heterocyclic compound. Such compositions and methods are particularly useful in the manufacture of electronic devices.

What is claimed is:  
     
         1 . A method of depositing a layer of silver on a substrate comprising the step of contacting a substrate having a layer of a metal that is less electropositive than silver with an immersion silver plating bath comprising one or more sources of silver ions, water and one or more carboxylic acid-substituted nitrogen-containing heterocyclic compounds, wherein the bath has a pH of less than or equal to 4.  
     
     
         2 . The method of  claim 1  wherein the substrate is a printed wiring board substrate.  
     
     
         3 . The method of  claim 1  wherein the metal that is less electropositive than silver is chosen from zinc, iron, tin, nickel, lead, copper or alloys of zinc, iron, tin, nickel, lead and copper.  
     
     
         4 . The method of  claim 1  wherein the carboxylic acid-substituted nitrogen-containing heterocyclic compounds is chosen from picolinic acid, quinolinic acid, nicotinic acid, isonicotinic acid, fusaric acid, isonipecotic acid, nipecotic acid, 2,6-pyridine dicarboxylic acid, piperazine-2-carboxylic acid, pyrrole-2-carboxylic acid and piperolinic acid.  
     
     
         5 . The method of  claim 1  wherein the carboxylic acid-substituted nitrogen-containing heterocyclic compound comprises a nitrogen-containing heterocyclic moiety chosen from pyridine, piperidine, piperazine, pyrrole, morpholine, pyrrolidine, triazole, and imidazole.  
     
     
         6 . A method of manufacturing a printed wiring board comprising the step of contacting a printed wiring board substrate having a layer of a metal that is less electropositive than silver with an immersion silver plating bath comprising one or more sources of silver ions, water and one or more carboxylic acid-substituted nitrogen-containing heterocyclic compounds, wherein the silver plating bath has a pH of less than or equal to 4.  
     
     
         7 . An immersion silver plating bath comprising one or more sources of silver ions, water and one or more carboxylic acid-substituted nitrogen-containing heterocyclic compounds, wherein the silver plating bath has a pH of less than or equal to 4.  
     
     
         8 . The immersion silver plating bath of  claim 7  wherein the bath is free of cyanide ions, ammonia and ammonium ions.  
     
     
         9 . The immersion silver plating bath of  claim 7  wherein the carboxylic acid-substituted nitrogen-containing heterocyclic compound is chosen from picolinic acid, quinolinic acid, nicotinic acid, isonicotinic acid, fusaric acid, isonipecotic acid, nipecotic acid, 2,6-pyridine dicarboxylic acid, piperazine-2-carboxylic acid, pyrrole-2-carboxylic acid and piperolinic acid.  
     
     
         10 . The immersion silver plating bath of  claim 7  wherein the carboxylic acid-substituted nitrogen-containing heterocyclic compound comprises a nitrogen-containing heterocyclic moiety selected chosen from pyridine, piperidine, piperazine, pyrrole, morpholine, pyrrolidine, triazole, and imidazole  
     
     
         11 . The immersion silver plating bath of  claim 7  further comprising one or more thickness control agents.  
     
     
         12 . The immersion silver plating bath of  claim 11  wherein the thickness control agent is chosen from azoles, amino acids, hydroxy-substituted aromatic compounds, sulfur-containing compounds and hydantoins.