Topography compensating land grid array interposer

Abstract

LGA connectors are fabricated with buttons or spring contacts preformed to different heights to accommodate the initial topography of a typical module or PCB of a particular product type. This is accomplished during fabrication by measuring topographies of mating surfaces of a first electronic device and of a second electronic device; fabricating interposer contacts to form opposing non-planar sides having respective inverse topographies for contacting the mating surfaces; and sandwiching the interposer between the first and second electronic devices with the opposing sides in contact with respective mating serfaces. For those LGA types made by molding techniques such as the metal-in-polymer type (eg. Tyco Electronics MPI, or Shin Etsu RP) or the Metal-on-Elastomer type (IBM), using molds with the desired topography provides the desired LGA topography. For those LGAs made of metal springs, cantilevers, armatures and the like, the desired topography is imposed by shaping of the buttons during or after fabrication using a sizing die with the desired topography.

1 . An array of electrical contacts for connecting to an electronic device, said array comprising a contact having a height substantially equal to a z-dimension at a corresponding xy position on said electronic device to which it will be mating, said z-dimension being substantially equal to a deviation from planarity at that position determined with respect to a plurality of said electronic devices.  
   
   
       2 . The array of  claim 1 , further comprising a 2-dimensional array of a plurality of said contacts.  
   
   
       3 . The array of  claim 2 , further comprising an LGA interposer comprising a plurality of individual contacts, a geometric feature of individual contacts differing for obtaining substantially equal load disktribution of said array.  
   
   
       4 . The array of  claim 3 , said geometric feature including diameter, with contacts in one region where it is desirable to have a large compliance made with a small diameter and contacts in another region where it is desirable to have a smaller compliance made with a larger diameter.  
   
   
       5 . A land grid array interposer (LGA) for interconnecting mating parts of two electronic devices, 
 a first side of said interposer having an array of contacts of varying heights substantially equal to a dimensions corresponding to deviations from planarity of a first mating part of one type;    a second, opposing side of said interposer having has an array of contacts of varying heights substantially equal to a dimension corresponding to deviations from planarity a second mating part of a second type.    
   
   
       6 . The land grid array interposer (LGA) of  claim 5 , comprising: 
 said first side consisting of compliant contacts pre-formed into a topography matching that of a first electronic part to which it will be mated, and    said second side consisting of an array a solderable connections for connecting to a second electronic part.    
   
   
       7 . The LGA interposer of  claim 5  for mating parts of two electronic devices having equivalent topologies on mating parts, the topographies of opposing sides of said interposer having a same topography.  
   
   
       8 . The land grid array (LGA) interposer of  claim 6 , said interposer further comprising 
 a first array of solderable connections including larger solder balls to be soldered to a low spot on a mating surface of said second electronic part, and a second array of solderable connections including smaller solder balls to be soldered to a high spot on said mating surface, thereby providing for filling in nonuniformities in topography of said second electronic part, said solder balls before reflow substantially conforming to topography of said second electronic part.    
   
   
       9 . The LGA interposer of  claim 5 , further comprising compliant contact geometries modified to tune compression curves to even out force distribution.  
   
   
       10 . The LGA interposer of  claim 9 , further comprising tall elastomeric contacts of a first diameter different from a second diameter of short contacts to achieve asame dimensional change upon application of a same compressive force.  
   
   
       11 . A method for making an LGA interposer, comprising: 
 measuring topographies of mating surfaces of a first electronic device and of a second electronic device;    fabricating interposer contacts to form opposing non-planar sides having respective inverse topographies for contacting said mating surfaces; and    sandwiching said interposer between said first and second electronic devices with said opposing sides in contact with respective mating serfaces.    
   
   
       12 . The method of  claim 11 , said interposer contacts being formed by a molding operation, each contact having an individually specified height within an overall non-planar topography.  
   
   
       13 . The method of  claim 11 , said contacts being made to have a desired topography by a mechanical sizing operation after said contacts have been placed into position on a carrier plane, each contact having an individually specified height to form an overall non-planar topography.  
   
   
       14 . The method of  claim 13 , said contacts being made to have a desired topography by a mechanical sizing operation that is carried out with one of simultaneous and subsequent application of ultraviolet light and at an elevated temperature.  
   
   
       15 . The method of  claim 11 , further comprising: 
 manufacturing molds for arrays of compliant contacts where topographic information from a fabricated part is converted to a height value for contacts centered on a given pitch.    
   
   
       16 . The method of  claim 15 , further comprising: 
 scanning a mating surface of a chip module by a topographic measurement method;    dividing a resulting data into a discrete number of individual height values equaling a number of contacts and taken at a position where said contacts will positioned.    
   
   
       17 . The method of  claim 15 , further comprising manufacturing molds by selectively drilling and etching individual heights of contacts into said mold.  
   
   
       18 . The method of  claim 11 , comprising 
 determining an average and standard deviation of each contact position for a sampling of parts;    from said average and standard deviation, determining a best fit inverse topography for accommodating variation at each said contact position.    
   
   
       19 . A method for manufacturing a topographically sculptured LGA interposer for use with multichip modules, comprising: 
 measuring an average topography of a module I/O surface;    building and applying to said module an LGA interposer having a topography that is the inverse of said average topography;    actuating to mate said module I/O surface and said LGA interposer.    
   
   
       20 . The topographically sculptured LGA of  claim 19 , one side of said LGA interposer having a first array of compliant conducting contacts on a first side to accommodate a topography of a first mating surface and a second array of solder contacts selectively of uniform and varying amounts of solder to accommodate a topography of a second mating surface.