Microelectronic contacts with asperities and methods of making same

Abstract

Microelectronic contacts, such as flexible, tab-like, cantilever contacts, are provided with asperities disposed in a regular pattern. Each asperity has a sharp feature at its tip remote from the surface of the contact. As mating microelectronic elements are engaged with the contacts, a wiping action causes the sharp features of the asperities to scrape the mating element, so as to provide effective electrical interconnection and, optionally, effective metallurgical bonding between the contact and the mating element upon activation of a bonding material.

What is claimed is:  
     
         1 . A contact for a microelectronic device comprising a base portion defining a base surface and one or more asperities integral with said base portion protruding upwardly from said base surface to a height of less than about 40 microns, each said asperity defining a tip surface and a substantially sharp edge bounding said tip surface.  
     
     
         2 . A contact as claimed in  claim 1  wherein said base portion includes a first metal at said base surface, each said asperity including a column of said first metal extending from said base surface and a cap of a second metal on such column defining said sharp edge.  
     
     
         3 . A contact as claimed in  claim 2  wherein said second metal consists essentially of one or more metals selected from the group consisting of gold, osmium, rhenium, platinum and palladium and alloys and combinations thereof.  
     
     
         4 . A contact as claimed in  claim 3  wherein said first metal consists essentially of a metal selected from the group consisting of copper and copper-bearing alloys.  
     
     
         5 . A contact as claimed in  claim 1  wherein each said top surface is substantially flat.  
     
     
         6 . A contact as claimed in  claim 1  wherein each said asperity is substantially cylindrical and each said edge is substantially circular.  
     
     
         7 . A contact as claimed in  claim 1  wherein each said asperity is substantially in the form of a elongated slab, each such slab defining at least one generally vertical major surface intersecting said tip surface so that the intersection of such major surface and the tip surface defines at least a part of said sharp edge as an elongated, generally straight edge.  
     
     
         8 . A contact as claimed in  claim 1  wherein said base portion includes an anchor region and at least one flexible projection, at least one said asperity being disposed on each said projection remote from said anchor portion.  
     
     
         9 . A contact as claimed in  claim 8  wherein said anchor region is substantially ring-like and defines a center, and said at least one flexible projection includes a plurality of flexible projections extending inwardly from the ring-like anchor region towards said center.  
     
     
         10 . A contact as claimed in  claim 1  wherein each said asperity protrudes upwardly from said base surface between about 10 μm and about 40 μm.  
     
     
         11 . A connector comprising a body having a top surface and a hole extending into the body from said top surface, and a contact as claimed in  claim 9  mounted to said top surface so that said ring-like anchor region encircles the hole at said top surface and said projections extend inwardly over said hole.  
     
     
         12 . A connector comprising a body and a contact as claimed in  claim 8  mounted to the body so that the anchor region of the contact is secured to the body and said projection is free to flex.  
     
     
         13 . A contact assembly including a plurality of contact portions, said contact portions being disposed in a regular contact pattern, each said contact portion defining a base surface, and a plurality of asperities on said contact portions each said asperity protruding upwardly from the base surface of one said contact portion and having a tip remote from the base surface, each said asperity having a substantially sharp feature at its tip, said asperities being disposed in a regular asperity pattern, said asperity pattern being in registration with said contact pattern so that at least one said asperity is disposed on each said contact portion.  
     
     
         14 . A contact assembly as claimed in  claim 13  wherein said contact portions are substantially identical to one another and said asperities are disposed in substantially the same location on each said contact portion.  
     
     
         15 . A contact assembly as claimed in  claim 13  wherein said contact portions include a plurality of flexible projections connected to at least one anchor region, each such projection having a distal end remote from the associated anchor region, and wherein said asperities are located on each said projection adjacent the distal end thereof.  
     
     
         16 . A contact assembly as claimed in  claim 13  wherein each said asperity protrudes upwardly from the associated base surface less than about 50 μm.  
     
     
         17 . A contact assembly as claimed in  claim 13  wherein each said asperity includes a tip surface at its tip and said sharp feature of each said asperity includes a substantially sharp edge bounding the tip surface of the asperity.  
     
     
         18 . A contact assembly as claimed in  claim 13  wherein each said sharp feature of each said asperity includes a point at the tip of the asperity.  
     
     
         19 . A method of making an electronic contact comprising the steps of: 
 (a) depositing an etch-resistant material in a plurality of spots on a top surface of a sheet including a first metal at said top surface;    (b) etching said first metal in a first etching process so that at least a portion of the first metal is removed in areas other than said spots, whereby the etched areas will define a base surface and the areas covered by said spots will form asperities projecting upwardly from said base surface, said etching step forming tips on said asperities remote from said base surface and substantially sharp edges bounding said tips.    
     
     
         20 . A method as claimed in  claim 19  wherein said etch-resistant material is a second metal and wherein said second metal at least partially defines said sharp edges.  
     
     
         21 . A method as claimed in  claim 20  wherein said second metal consists essentially of one or more metals selected from the group consisting of gold, osmium, rhenium, platinum and palladium and alloys and combinations thereof.  
     
     
         22 . A method as claimed in  claim 20  wherein said first metal consists essentially of one or more metals selected from the group consisting of copper and copper-bearing alloys.  
     
     
         23 . A method as claimed in  claim 19  wherein said sheet includes a layer of an etch-resistant stop metal beneath said first metal.  
     
     
         24 . A method as claimed in  claim 23  wherein said etching step is continued until said stop metal is exposed in said etched areas, whereby said stop metal layer will define said base surface.  
     
     
         25 . A method as claimed in  claim 19  further comprising the step of subdividing said sheet into a plurality of contact portions, said subdividing and etching steps being conducted so that at least one asperity is disposed on each said contact portion.  
     
     
         26 . A method as claimed in  claim 25  wherein said subdividing step includes the step of etching said sheet in a second etching process.  
     
     
         27 . A method as claimed in  claim 26  wherein said second etching process includes the step of etching said sheet from a bottom surface to form grooves in said bottom surface before said first etching step, and wherein said first etching step is performed so that said base surface is disposed adjacent said grooves.  
     
     
         28 . A method as claimed in  claim 19  wherein said step of depositing said etch-resistant material in said spots includes the step of applying a resist to said top surface of said sheet and exposing said resist to radiant energy in a pattern constituting a positive or negative image of said spots.  
     
     
         29 . A method as claimed in  claim 19  wherein said step wherein said step of depositing said etch-resistant material in said spots includes the step of applying a resist to said top surface of said sheet and exposing said resist to energetic charged particles in a pattern corresponding to a positive or negative image of said spots.  
     
     
         30 . A method as claimed in  claim 29  wherein said top surface of said sheet is non-planar at the time of said exposing step.  
     
     
         31 . A method of making an electronic contact comprising the steps of: 
 (a) in a surface-forming step, etching a top surface of a sheet including a first metal at said top surface so that at least a portion of the first metal is removed except at locations in a predetermined asperity pattern and so that the etched areas define a base surface and asperities will projecting upwardly from said base surface at said locations, said surface-forming etching step forming tips on said asperities remote from said base surface and sharp features at each said tip; and    (b) severing said sheet to form a plurality of contact portions according to a predetermined severing pattern, said severing pattern and said asperity pattern being in registration with one another so that at least one asperity is disposed on each said contact portion.    
     
     
         32 . A method as claimed in  claim 31  wherein said severing step includes the step of forming grooves in a bottom surface of said sheet.  
     
     
         33 . A method as claimed in  claim 32  wherein said step of forming said grooves is performed before said surface forming step and wherein said surface forming step is performed so as to cut through the sheet at said grooves.  
     
     
         34 . A method of engaging a microelectronic device having electrical elements thereon with a connector comprising the step of moving said device and said connector relative to one another so that said electrical elements of the device engage and deform resilient contacts carried on a body of the connector, so that each electrical element moves relative to the contact engaged therewith, and so that sharp edges at tips of asperities protruding from the contacts scrape the engaged electrical elements.  
     
     
         35 . A method as claimed in  claim 34  wherein each said asperity has an edge portion facing opposite to the direction of motion of the engaged electrical element.  
     
     
         36 . A method as claimed in  claim 35  wherein each said contact bears on the engaged electrical element with a force between about 2 and about 20 grams-force  
     
     
         37 . A method as claimed in  claim 34  wherein said connector body includes a plurality of holes, said contacts include a plurality of contacts extending inwardly over each said hole at a top surface of the connector body, said electrical elements of said microelectronic device include a plurality of bump leads protruding from a lead-bearing surface, and said moving step includes the step of moving said lead-bearing surface of said microelectronic element toward said top surface of said connector body so that said bump leads extend into said holes and said contacts bend downwardly into said holes.  
     
     
         38 . A microelectronic connector comprising a connector body and a plurality of contact units, each contact unit including an anchor region attached to the connector body and at least one resilient tab extending from the anchor region, each such tab including a bottom layer of a polymeric material and a conductive layer thinner than said bottom layer overlying said bottom layer.  
     
     
         39 . A connector as claimed in  claim 38  wherein each said tab includes a metallic asperity protruding upwardly from said conductive layer, each said asperity having a sharp feature at a tip remote from said conductive layer.  
     
     
         40 . A connector as claimed in  claim 39  wherein each said asperity is between about 5 μm and about 25 μm high.  
     
     
         41 . A connector as claimed in  claim 39  wherein each said asperity has a tip surface at its tip remote from said conductive layer and a sharp edge bounding said tip surface.  
     
     
         42 . A connector as claimed in  claim 38  wherein each said conductive layer is metallic an less than about 10 μm thick.  
     
     
         43 . A connector as claimed in  claim 42  wherein each said bottom layer is between about 10 and about 50 μm thick.  
     
     
         44 . A connector as claimed in  claim 42  wherein each said tab is between about 100 and about 300 μm long.  
     
     
         45 . A connector as claimed in  claim 38  wherein said connector body has a plurality of conductors therein, and wherein said bottom layer and conductive layers of each said tab extend into the associated anchor region, the connector further comprising electrically conductive posts extending through the bottom layer in said anchor regions and electrically connecting said conductive layers to said conductors in said connector body.  
     
     
         46 . A method of making a microelectronic connector comprising the steps of: 
 (a) providing a sheet having a polymeric bottom layer, and at least one metallic layer on said bottom layer;    (b) selectively removing metallic material from said at least one metallic layer so as to leave a conductive layer thinner than said bottom layer overlying the bottom layer and a plurality of asperities protruding upwardly from said conductive layer; and    (c) subdividing said conductive layer and said bottom layer to form at least one elongated tab, each such tab having at least one said asperity.    
     
     
         47 . A method as claimed in  claim 46  wherein said at least one metallic layer includes a stop layer adjacent said bottom layer and a first base metal layer overlying said stop layer, said step of selectively removing metallic material including the step of selectively etching said first base metal layer.  
     
     
         48 . A method as claimed in  claim 47  wherein said stop layer resists etching in said step of selectively etching said first base metal layer so that said stop layer remains and forms said conductive layer.  
     
     
         49 . A method as claimed in  claim 46  wherein said subdividing step includes the step of selectively etching said conductive layer so as to expose said bottom layer at channel openings between the tabs and then directing radiant energy through said channel openings so as to ablate the bottom layer in said channel openings, whereby said conductive layer will block radiant energy directed to portions of said bottom layer in said tabs.  
     
     
         50 . A method of making a microelectronic connector comprising the steps of providing a sheet including a metallic layer and a polymeric bottom layer, selectively etching said metallic layer so as to form a plurality of tabs and channel openings between said tabs and thereby expose said bottom layer at the channel openings, and then directing radiant energy through said channel openings so as to ablate the bottom layer in said channel openings, whereby said metallic layer will block radiant energy directed to portions of said bottom layer in said tabs.