Micro-bumps to enhance lga interconnections

Abstract

An improved Land Grid Array interconnect structure is provided with the use of small metal bumps on the substrate electrical contact pad. The bumps interlock with segments of the fuzz button connection and increase the physical contact surface area between the contact pad and fuzz button. The improved contact reduces displacement of electrical contact points due to thermo-mechanical stress and lowers the required actuation force during assembly.

1 . A Land Grid Array (LGA) structure comprising: 
 a chip carrier,    at least one bottom surface contact pad on a bottom surface of said chip carrier,    at least one micro-bump on said at least one bottom surface contact pad;    a circuit board having at least one circuit board contact pad, and    at least one fuzz button disposed between and in contact with said at least one said bottom surface contact pad and said at least one circuit board contact pad, wherein said at least one micro-bump contacts and increases the contact area between said at least one fuzz button and said at least one bottom surface contact pad.    
   
   
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       3 . The Land Grid Array (LGA) structure of  claim 1  wherein said at least one bottom surface contact pad and micro-bump are comprised of copper, nickel and gold.  
   
   
       4 . The Land Grid Array (LGA) structure of  claim 1  wherein said at least one bottom surface contact pad and micro-bump are comprised of molybdenum, nickel and gold.  
   
   
       5 . The Land Grid Array (LGA) structure of  claim 1  wherein said at least one micro-bump is circular with a base diameter ranging from approximately 100 μm to 250 μm with height ranging from approximately 30  82  m to 50 μm.  
   
   
       6 . The Land Grid Array (LGA) structure of  claim 1  wherein said at least one bottom surface contact pad has a plurality of said micro-bumps uniformly and symmetrically distributed.  
   
   
       7 . The Land Grid Array (LGA) structure of  claim 6  wherein the diameter and height of said plurality micro-bumps have a variation of less than approximately 10 μm.  
   
   
       8 . The Land Grid Array (LGA) structure of  claim 1  further comprising: 
 an interposer holding said at least one fuzz button and configured to the geometry and pitch of said at least one bottom surface contact pad and said at least one circuit board contact pad.    
   
   
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