Nickel-gold plateable thick film silver paste, and plating process for low temperature co fired ceramic devices and ltcc devices made therefrom

Abstract

Described are LTCC devices, with external silver containing electrical contacts, that are sequentially plated with a nickel containing metal and a gold containing metal.

What is claimed is: 
     
         1 . A method for nickel-gold plating on a fired LTCC structure having a printed silver composition to reduce pad lift of the printed silver composition from the LTCC structure comprising the sequential steps of:
 a. activation of the printed silver composition;   b. electroless plating nickel onto the activated printed silver composition;   c. providing a catalyst layer of immersion gold; and   d. electroless plating of a gold layer onto the immersion gold layer, wherein the plating conditions of (i) pH, (ii) temperature and (iii) thickness of the nickel and immersion gold layer are complimentary to the LTCC structure and printed silver composition.   
     
     
         2 . The method of  claim 1 , wherein the plating bath conditions of pH are in the range of 4-12. 
     
     
         3 . The method of  claim 2  wherein the plating thickness of nickel of 100-300 micro-inches, preferably 100-150 micro-inches and a plating thickness of electro-less gold over nickel of thickness of 20-100 micro-inches preferably 20-60 micro-inches. 
     
     
         4 . The method of  claim 3 , wherein the temperature of the electroless plating is 77-90° C. 
     
     
         5 . The method of  claim 4 , wherein the silver paste composition consisting essentially of, based on weight percent, 75-90% silver powder of different sizes and shapes, optionally 0.5-4% high refractory glasses and the balance organic medium. 
     
     
         6 . The method of  claim 5 , wherein the glass is a alumino-borosilicate glass as “network formers” with Zn, Ba, Mg, Sr, Sn, Ti. Na ions are as “net-work modifying cations”. 
     
     
         7 . The method of  claim 6 , wherein the glass comprises 20.2% SiO 2 ; 2.8% Al 2 O 3 ; 20.4 B 2 O 3 ; 10.1 ZnO; 19.0% BaO; 3.1% MgO; 3.3% Na 2 O; 13.7% SrO; 5.5% TiO 2 ; and 1.9% SnO 2 .