Composite noble metal wire

Abstract

A method of forming a micron-dimensioned wire having a gold alloy annulus surrounding an electrically-conductive non-noble metal core.

1 . A method of forming a composite wire having a diameter greater than about 15 microns and less than about 100 microns and consisting of a gold alloy annulus surrounding a wire core comprising an electrically-conductive non-noble metal, said method comprising: 
 assembling a composite billet consisting essentially of a core of said non-noble metal, an intermediate layer of said gold alloy and an outer metal layer;    extruding said composite billet with force to form a composite rod comprising corresponding core, intermediate and outer metal layers, wherein the core fraction measured by cross-sectional area of the cylinder defined by the core and intermediate layer of said rod is essentially the same as the corresponding core fraction of said billet;    removing said outer metal layer of said composite rod;    drawing said composite rod to form a first composite wire having a diameter between about 0.5 and about 5 mm and a core fraction essentially the same as said core fraction of said composite rod; and    drawing said first composite wire to form a second composite wire having a diameter between about 15 and about 100 microns and a core fraction essentially the same as said core fraction of said first composite wire.    
     
     
         2 . The method of  claim 1 , wherein said core metal comprises copper.  
     
     
         3 . The method of  claim 2 , wherein said core metal consists essentially of copper.  
     
     
         4 . The method of  claim 1 , wherein said gold alloy is at least 99% gold.  
     
     
         5 . The method of  claim 4 , wherein said gold alloy comprises gold doped with less than 30 ppm calcium, less than 20 ppm beryllium and less than 50 ppm other elements.  
     
     
         6 . The method of  claim 5 , wherein said gold alloy comprises gold doped with less than 10 ppm of beryllium and less than 10 ppm of calcium.  
     
     
         7 . The method of  claim 1 , wherein said core metal and said gold alloy have melting temperatures within a range of 5° C.  
     
     
         8 . The method of  claim 1 , wherein said billet has a core fraction between about 25 and about 95% by cross-sectional area.  
     
     
         9 . The method of  claim 1 , wherein said billet is preheated to a temperature between about 200 and about 700° C. prior to extrusion.  
     
     
         10 . The method of  claim 1 , wherein said billet is extruded with a force between about 50 and about 200 kg/mm 2 .  
     
     
         11 . A composite wire, having a micron-dimensioned diameter, formed by the method of  claim 1.