Nickel-gold plateable thick film silver paste
View Patent ↗Described are LTCC devices, with external silver containing electrical contacts, that are sequentially plated with a nickel containing metal and a gold containing metal, with a defined silver paste composition for manufacture.
1. A printed silver paste composition on a green LTCC substrate, for eliminating silver pad lift off upon electro-less nickel and gold plating onto a silver pad of a LTCC device, consisting essentially of, based on weight percent, 75-90% silver powder of different sizes and shapes appropriate for screen printing, 0.5-4% glass composition and the balance organic medium, wherein the glass composition is an alumino-borosilicate glass as “network formers” with Zn, Ba, Mg, Sr, Sn, Ti, and Na ions as “net-work modifying cations”; wherein the silver paste is printed on a green LTCC substrate at a thickness of 10 to 30 microns, so as to be capable of forming a silver pad after firing at a heating profile of 3.5 hours or greater appropriate for the LTCC substrate; wherein the green LTCC substrate is formed by casting a thin layer of a slurry dispersion of glass, ceramic filler, polymeric binder, and solvent, followed by heating in order to remove said solvent; wherein the percent weight loss due to leaching of the LTCC substrate after firing at said heating profile, as measured by dipping the fired LTCC substrate into separate 10% acid strength of HCl and H 2 SO 4 at a constant temperature of 40° C. for a constant period of time of 30 minutes, is less than about 0.42 for HCl and less that about 0.23 for H 2 SO 4 ; and wherein said glass composition comprises by weight percentage 20.2% SiO 2 ; 2.8% Al 2 O 3 ; 20.4% B 2 0 3 ; 10.1% ZnO; 19.0% BaO; 3.1% MgO; 3.3% Na 2 0; 13.7% SrO; 5.5% TiO 2 ; and 1.9% SnO 2 .