Co-fired capacitor and method for forming ceramic capacitors for use in printed wiring boards

Abstract

A capacitor structure is fabricated by forming a pattern of first dielectrics over a foil, forming first electrodes over the first dielectrics, and co-firing the first dielectrics and the first electrodes. Co-firing of the dielectrics and the electrodes alleviates cracking caused by differences in thermal coefficient of expansion (TCE) between the electrodes and the dielectrics. Co-firing also ensures a strong bond between the dielectrics and the electrodes. In addition, co-firing allows multi-layer capacitor structures to be constructed, and allows the capacitor electrodes to be formed from copper.

What is claimed is:  
     
         1 . A method for making a fired-on-foil capacitor structure, comprising: 
 providing a metallic foil;    forming at least one first dielectric over the foil;    forming at least one first electrode over the first dielectric; and    co-firing the first dielectric and the first electrode.    
     
     
         2 . The method of  claim 1 , wherein forming the first electrode comprises: 
 forming the first electrode comprising a metal, wherein the metallic foil also comprises the metal.    
     
     
         3 . The method of  claim 2 , wherein the metal is copper.  
     
     
         4 . The method of  claim 1 , comprising: 
 forming at least one second dielectric over the first electrode; and    forming at least one second electrode over the second dielectric.    
     
     
         5 . The method of  claim 4 , comprising: 
 co-firing the second dielectric and the second electrode.    
     
     
         6 . The method of  claim 4 , wherein co-firing comprises: 
 co-firing the second dielectric and the second electrode along with the first dielectric and the first electrode.    
     
     
         7 . The method of  claim 4 , comprising: 
 forming a trench in the foil to electrically isolate the first and second electrodes.    
     
     
         8 . The method of  claim 4 , comprising: 
 laminating a side of the foil containing the first dielectric and the first electrode.    
     
     
         9 . The method of  claim 4 , comprising: 
 forming at least one third dielectric over the second electrode; and    forming at least one third electrode over the third dielectric.    
     
     
         10 . The method of  claim 9 , comprising: 
 co-firing the third dielectric and the third electrode.    
     
     
         11 . The method of  claim 9 , wherein co-firing comprises: 
 co-firing the third dielectric and the third electrode along with the first and second dielectrics and the first and second electrodes.    
     
     
         12 . The method of  claim 9 , comprising: 
 forming a trench in the foil to electrically isolate the first and third electrodes from the second electrode.    
     
     
         13 . The method of  claim 1 , wherein providing a foil comprises: 
 treating the foil with an underprint; and    firing at a temperature below the softening point of the foil.    
     
     
         14 . The method of  claim 1 , wherein forming the first dielectric comprises: 
 screen-printing a layer of dielectric ink over the foil; and    drying the dielectric ink.    
     
     
         15 . The method of  claim 14 , wherein forming the first electrode comprises: 
 screen-printing a layer of metallic ink over the first dielectric; and    drying the metallic ink.    
     
     
         16 . The method of  claim 1 , wherein: 
 forming at least one first dielectric comprises forming a pattern of a plurality of first dielectrics over the foil; and    forming at least one first electrode comprises forming a pattern of a plurality of first electrodes over the first dielectrics.    
     
     
         17 . A capacitor structure, comprising: 
 a metallic foil;    at least one dielectric disposed over the foil;    at least one first electrode disposed over a portion of the dielectric; and    at least one second electrode disposed over a portion of the dielectric and over a portion of the first electrode, wherein a portion of the dielectric is disposed between the first and second electrodes.    
     
     
         18 . The capacitor structure of  claim 17 , wherein the foil comprises: 
 a trench that electrically isolates the first electrode from the second electrode.    
     
     
         19 . The capacitor structure of  claim 17 , wherein: 
 the at least one dielectric comprises a plurality of dielectrics;    the at least one first electrode comprises a plurality of first electrodes;    the at least one second electrode comprises a plurality of second electrodes; and    the dielectrics, the first electrodes, and the second electrodes are arranged as a plurality of stacks on the metallic foil, each stack comprising a first electrode, a second electrode, and a dielectric.    
     
     
         20 . The capacitor structure of  claim 19 , comprising: 
 a plurality of third electrodes, one in each stack, wherein each third electrode is disposed over a portion of a corresponding dielectric and over a portion of a corresponding first electrode and is electrically connected to the corresponding first electrode.    
     
     
         21 . The capacitor structure of  claim 19 , wherein the metallic foil and the first and second electrodes comprise copper.