Bonding arrangement and method for LTCC circuitry

Abstract

An LTCC (low temperature cofired ceramic) structure which has conductors to which leads are to be bonded for connection to external circuitry. The conductors include additives to promote adhesion to the ceramic layer. The presence of these additives degrade bonding performance. For better bondability of the leads, a pure conductor metal layer, devoid of the additives is placed on the conductors in areas where leads are to be bonded. This pure conductor metal layer may be cofired with the stack of ceramic layers or may be post fired after stack firing.

1 . An LTCC structure comprising: 
 a plurality of stacked layers of ceramic material including metallization in predetermined patterns on and through said layers;    said stacked layers including a plurality of exposed electrical conductors to which leads are to be bonded;    said conductors being of a metal which includes one or more additives to promote adhesion to said ceramic layer on which said conductors are deposited;    a bonding metal layer on top of said conductors at predetermined locations and being of said same metal as said conductors, however devoid of said one or more additives;    said leads being bonded to said bonding metal layer.    
   
   
       2 . Apparatus according to  claim 1  wherein: 
 said bonding metal layer is deposited on a limited area of a said conductor only where said lead is to be bonded.    
   
   
       3 . Apparatus according to  claim 1  wherein: 
 said conductors are of a gold paste with said additives;    said bonding metal layer is of a pure gold paste devoid of said additives.    
   
   
       4 . Apparatus according to  claim 1  wherein: 
 predetermined ones of said layers include respective cavities;    predetermined ones of said conductors being located on at least one said layer below the top layer of said stacked layers;    said predetermined ones of said conductors being accessible through said cavities for bonding of said leads.    
   
   
       5 . A method of making an LTCC structure, comprising the steps of: 
 providing a plurality of ceramic layers to be stacked together to form a module;    applying to said layers, prior to said stacking, conductor patterns of a metal containing one or more additives to promote adhesion of said conductor patterns to said layers;    applying to areas of exposed conductors to which leads will be bonded said same metal, however devoid of said additives, to form a bonding layer at said areas;    stacking and firing said layers to form said module;    bonding said leads to said bonding layers on said exposed conductors.    
   
   
       6 . A method according to  claim 5  which includes: 
 providing predetermined ones of said layers with cavities such that some of said exposed conductors are on a layer other than a surface layer, and are accessible through said cavities for lead bonding.    
   
   
       7 . A method of making an LTCC structure, comprising the steps of: 
 providing a plurality of ceramic layers to be stacked together to form a module;    applying to said layers, prior to said stacking, conductor patterns of a metal containing one or more additives to promote adhesion of said conductor patterns to said layers;    stacking and firing said layers to form said module;    applying to areas of conductors, on a surface layer, to which leads will be bonded, said same metal, however devoid of said additives, to form a bonding layer at said areas;    firing said stack a second time;    bonding said leads to said bonding layers.