Patent Publication Number: US-2006006890-A1

Title: Interconnect structure that controls spacing between a probe card and a contact substrate

Description:
This is a divisional of U.S. patent application Ser. No. 10/418,512, filed Apr. 16, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/387,216, filed on Mar. 12, 2003. This patent document is also related to U.S. patent application Ser. No. 10/386,875, which was filed on Mar. 12, 2003. All of these prior applications are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD OF THE INVENTION  
      One or more embodiments of the present invention pertain to: (a) one or more structures useful, for example and without limitation, for testing circuits, for example and without limitation, integrated circuits (“ICs”) at a wafer level; and (b) one or more methods for fabricating such structures.  
     BACKGROUND OF THE INVENTION  
      As is known, a substrate (sometimes also referred to in the art as an interposer) is a device that provides a fan-out between I/O (i.e., electrical inputs and outs) of a circuit, for example and without limitation, an integrated circuit (“IC”) and a Probe Card to enable testing of the IC, for example, at a wafer level. Such a substrate may be a rigid substrate, a semi-flex substrate, a flex substrate, and so forth, and such substrates often have a relatively low cost when compared to that of the Probe Card.  
      As IC geometries have decreased in size dramatically since such devices were first introduced several decades ago, so too have geometries associated with wiring connections to their I/O. For example, present designs include the use of bumped wafer pad pitches of 200 μm or less. In order to test such ICs, one is required to utilize high density interconnect (“HDI”) substrates having matching fine connector pitches.  
      Substrates available today, and the manner in which they are used, are problematic for two basic reasons. First, manufacturing techniques used to fabricate such substrates and to connect them to Probe Cards typically require multiple expensive steps. Second, if one of the connectors on the substrate gets damaged, it cannot be replaced, for the most part, or is difficult or expensive to rework. In addition, whenever the substrate wears out, or gets damaged, one typically has to throw away the Probe Card together with the substrate. In particular, this is because, due to manufacturing techniques used to fabricate such substrates and to connect them to Probe Cards, it is a prohibitively lengthy and costly process to separate the substrate from the Probe Card.  
      In light of the above, there is a need in the art for: (a) one or more structures useful, for example and without limitation, for testing circuits, for example and without limitation, ICs at a wafer level that solve one or more of the above-identified problems; and (b) one or more methods for fabricating such structures.  
     SUMMARY OF THE INVENTION  
      One or more embodiments of the present invention satisfy one or more of the above-identified needs in the art. In particular, one embodiment of the present invention is a structure useful for testing circuits that comprises: (a) a substrate having contactors on a first side and pads on a second side; (b) a card having pads on a first side; and (c) interconnectors that electrically connect the pads on the second side of the substrate with the pads on the card; wherein at least one of the interconnectors includes at least a portion that does not melt at temperatures in a range from about 183° C. to about 230° C., and the distance between the substrate and the card is determined by a dimension of the at least a portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  is a cross sectional view that shows a pinalignment fixture used to connect a substrate to a Probe Card in accordance with one or more embodiments of the present invention prior to re-flow;  
       FIG. 1A  is a cross sectional view that shows a stiffening mechanism connected to a Probe Card in accordance with one or more embodiments of the present invention;  
       FIG. 1B  is a bottom view that shows the stiffening mechanism shown in  FIG. 1A ;  
       FIG. 2  is a top view that shows a portion of a flex substrate that is fabricated in accordance with one or more embodiments of the present invention;  
       FIGS. 3-5  are cross sectional views that show substrates which have bevels formed on the edges of the substrates that have been fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 6  shows a clamp mechanism that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 7  is a cross sectional view that shows a chip substrate that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 8  shows a Pogo pin used to fabricate one or more embodiments of the present invention;  
       FIG. 9  is a top perspective view that shows a connector-holder bottom plate that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 10  is a bottom perspective view that shows a connector-holder top plate that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 11  is a cross sectional view that shows a hole in the connector-holder bottom plate shown in  FIG. 9 ;  
       FIG. 12  is a cross sectional view that shows a hole in the connector-holder top plate shown in  FIG. 10 ;  
       FIG. 13  is an exploded view that shows a portion of a structure used to test circuits that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 14  is a cross sectional view that shows a groove cut into a side of a substrate that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 15  is a top view of a clamp that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 16  is a cross sectional view that shows a structure for testing circuits that is fabricated in accordance with one or more embodiments of the present invention;  
       FIG. 17  is a top view that shows a substrate and an RF interface board that are used in the structure shown in  FIG. 16 ; and  
       FIG. 18  is a cross sectional view of a structure that is fabricated in accordance with one or more embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION  
      As is known, circuits such as, for example and without limitation, integrated circuits (“ICs”), are fabricated on wafers, and the circuits are tested by applying electrical signals to circuit inputs and analyzing electrical signals produced at circuit outputs (such circuit inputs and outputs may be bumped or not). As is also known, a Probe Card that provides an interface between the circuit inputs and outputs (“I/O”) on the wafer and a Tester is used to perform such testing.  
      As the density of I/O of ICs has increased, it has become common to connect the Probe Card to a substrate (sometimes referred to in the art as an interposer) having an array of contactors (for example and without limitation, 12-50 μm high structures that are sometimes also referred to in the art as posts) on a top or testing side (i.e., a side that contacts the IC on the wafer) and having a ball grid array (“BGA”) of pads on a bottom side (i.e., a side that contacts the Probe Card). The contactors are wired through the substrate, and each wire ends at a pad in the BGA on the bottom side of the substrate. The array of contactors has a pitch and density (sometimes referred to as a footprint) that matches that of the IC, and the BGA has a pitch and density that matches that of the Probe Card. Substrates used to test present and future ICs, may be high density interconnect (“HDI”) substrates where the pitch of the array of contactors could be as small as 125 μm or less. Thus, one or more embodiments of the present invention relate to methods for assembling a structure used to test circuits, for example and without limitation, ICs, whether bumped or not, on a wafer, and one or more further embodiments relate to the assembled structure itself.  
      In particular, one or more embodiments of the present invention are methods for connecting a substrate, for example and without limitation, a rigid substrate, a flex substrate, a semi-flex substrate, a silicon/glass substrate (for example and without limitation, a silicon/glass structure that includes MEMS-type spring contactors), and so forth, to a Probe Card to provide structures that are used, for example and without limitation, to test circuits, for example and without limitation, integrated circuits (“ICs”), whether bumped or not, on a wafer. Advantageously, in accordance with one or more embodiments of the present invention, structures are produced that may be used cost effectively for testing because, among other reasons, such substrates may be replaced easily and rapidly with a new ones whenever the substrates are damaged or worn. In addition, advantageously, in accordance with one or more embodiments of the present invention, structures are produced having a relatively short distance between the substrate and the Probe Card, whereby electrical connections between the substrate and the Probe Card have better electrical properties than those of structures produced using prior art methods.  
      The following describes a method (“Method I”) for connecting a substrate to a Probe Card (i.e., for connecting BGA pads of a substrate to BGA pads of a Probe Card) in accordance with one or more embodiments of the present invention, which substrate can be, for example and without limitation, a rigid substrate, a flex substrate, or a semi-flex substrate.  FIG. 1  is a cross sectional view that shows a pinalignment fixture used to carry out Method I prior to re-flow.  
      As shown in  FIG. 1 , the pinalignment fixture includes base plate  100 . Base plate  100  is, for example and without limitation, an aluminum base plate, a Durostone® composite material base plate, or a base plate that is fabricated using any one of a number of other materials that are well known to those of ordinary skill in the art, which materials are relatively stable at processing temperatures of subsequent steps of Method I. In accordance with one or more embodiments of the present invention, base plate  100  has an area of about the same size as that of Probe Card  130 , and base plate  100  has a thickness in a range, for example and without limitation, from about 5.0 mm to about 7.0 mm. As further shown in  FIG. 1 , the pinalignment fixture includes alignment pins that are affixed to base plate  110  such as alignment pins  120  and  121 . In accordance with one or more embodiments of the present invention, the alignment pins have a diameter in a range, for example and without limitation, from about 0.7 mm to about 1.1 mm diameter. As one can readily appreciate, the pinalignment fixture may include, for example and without limitation, three (3) or four (4) such alignment pins.  
      In a first, optional step of Method I, release film  110  such as, for example and without limitation, a Mylar film or a Teflon film, is aligned with, and placed over, base plate  100  of the pinalignment fixture (holes in release film  110  match the positions of the alignment pins such as pins  120  and  121 ). Next, Probe Card  130  is aligned with, and placed over, release film  110  on the pinalignment fixture (holes in Probe Card  130  match the positions of the alignment pins such as pins  120  and  121 ). Vias  141  and  142  are formed in a commercially available “interconnector alignment” film such as, for example and without limitation, polyimide film  150  having adhesive (not shown) (for example and without limitation, epoxy, acrylic, epoxy-acrylic, and so forth) on one, or both, side(s), and a release film (not shown) (for example and without limitation, a Mylar film or Teflon film) disposed on the adhesive side. Vias  141  and  142  may be formed in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by drilling, punching, lasing, and so forth. The locations of vias  141  and  142  in polyimide film  150  match the locations of BGA pads  131  and  132 , respectively, on the top side of Probe Card  130 . Although not shown as such in  FIG. 1 , the cross sectional area of vias  141  and  142  is typically larger that the cross sectional areas of pads  131  and  132 , respectively. As one can readily appreciate, the step of fabricating the interconnector alignment film (i.e., polyimide film  150 ) may take place at any time before it is needed to be placed in use. Next, polyimide film  150  is aligned with, and placed over, Probe Card  130  on the pinalignment fixture (holes in polyimide film  150  match the positions of the alignment pins such as pins  120  and  121 ). Next, weight  210 , for example, an aluminum or stainless steel plate having a thickness in a range, for example and without limitation, from about 10 mm to about 12.7 mm, and having an area of about the same size as that of Probe Card  130  is aligned with, and placed over polyimide film  150  on the pinalignment fixture to apply pressure to polyimide film  150  (holes in plate  210  match the positions of the alignment pins such as pins  120  and  121 ). Next, polyimide film  150  is laminated to Probe Card  130  by, for example and without limitation, baking in an oven. The oven temperature is in a range, for example and without limitation, from about 150° C. to about 200° C., the pressure exerted by the weight of plate  210  is in a range, for example and without limitation, from about 14 kg/cm 2  to about 28 kg/cm 2 , and the time spent in the oven is in a range, for example and without limitation, from about 1 hour to about 2 hours. Next, weight  210  is removed.  
      Next, vias  141  and  142  are filled with paste  171  and  172 , respectively, using, for example and without limitation, the release film of polyimide film  150  as a mask. Paste  171  and  172  may be any one of a number of conductive pastes that are well known to those of ordinary skill in the art such as, for example, and without limitation, a Ag conductive paste, a Au conductive paste, a Cu conductive paste, and so forth, or it may be any one of a number of solder pastes that are well known to those of ordinary skill in the art. Paste  171  and  172  may be applied utilizing any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, methods utilizing a dispensing machine, methods utilizing screen-printing, methods utilizing a squeegee, and so forth. Also, in accordance with one or more further embodiments of the present invention, paste  171  and  172  can be a compliant, conductive paste. Such a compliant conductive paste may be any one of a number of such products that are well known to those of ordinary skill in the art such as, for example and without limitation, an elastomer such as a silicone elastomer having conductive particles embedded therein. The use of a compliant conductive paste may be advantageous in that the resulting structure (sometimes referred to as a “lay-up”) may be able to take up vertical movements or movements in a Z-direction caused during testing by non-planarity of contactors on the substrate, pads on the substrate, pads on the Probe Card, and/or I/O contacts on the wafer. Next, the release film is removed.  
      Next, a stencil (sometimes referred to in the art as a solder ball stencil—not shown) that is fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art is aligned with, and placed, over polyimide film  150  on the pinalignment fixture (holes in the stencil match the positions of the alignment pins such as pins  120  and  121 ); the edges of the stencil could have a corral formed thereon, for example, a corral of tape, to trap balls within the confines of the stencil. The holes in the stencil are slightly larger than the largest cross section of interconnectors, for example and without limitation, balls (described below), so the interconnectors, for example and without limitation, balls, will fall through the holes in the stencil when the stencil is removed. In accordance with one or more embodiments of the present invention, balls  181  and  182  shown in  FIG. 1  are comprised of a rigid core, for example and without limitation, a solid copper (Cu) core, and a coating, for example and without limitation, a solder coating such as, for example and without limitation, a eutectic solder coating. Next, balls  181  and  182  are placed over the stencil, and the stencil is removed. The diameter of the core of balls  181  and  182  is in a range, for example and without limitation, from about 5 mils to about 10 mils, and the coating has a thickness in a range, for example and without limitation, from about 20 μm to about 25 μm. The diameter of the core of balls  181  and  182  ought to be larger than the thickness of polyimide film  150  so that the core of balls  181  and  182  can contact pads  191  and  192 , respectively, on substrate  190  and pads  131  and  132 , respectively, on Probe Card  130 .  
      Next, substrate  190  (for example and without limitation, a rigid substrate, a flex substrate, a semi-flex substrate, and so forth) is aligned with, and placed over balls  181  and  182  on the pinalignment fixture (holes in substrate  190  match the positions of the alignment pins such as pins  120  and  121 ). Next, optional release film  200 , for example and without limitation, a Mylar or Teflon film, is aligned with, and placed over, structure  190  (and contactors  195  and  196 ) on the pinalignment fixture  1000  (holes in release film  200  match the positions of the alignment pins such as pins  120  and  121 , for example and without limitation, release film  200  may have a cut-out region where the cut-out region includes an area in which the contactors are disposed so that they are not damaged during re-flow). Next, weight  210  is aligned with, and placed over, release film  200  on the pinalignment fixture  1000  to apply pressure. Next, the solder coating on balls  181  and  182  is re-flowed, for example and without limitation, by baking in an oven at a temperature in a range, for example and without limitation, from about 200° C. to about 230° C. Advantageously, polyimide film  150  holds balls  181  and  182  in place during the re-flow, and it helps support each ball during testing. During the re-flow process, weight  210  provides a force that causes the solder to flow so that the distance between substrate  190  and Probe Card  130  is determined by a dimension of the core of balls  181  and  182 , for example and without limitation, the diameter of a Cu core of balls  181  and  182  (it should be understood that other mechanisms for applying such a force may be used to fabricate one or more further embodiments of the present invention such as, for example and without limitation, by the use of springs that are adapted to urge substrate  190  and Probe Card  130  towards each other). Thus, the rigid core of balls  181  and  182  acts as a stopper to vertical displacement of substrate  190  relative to Probe Card  130 . Since three (3) points determined a plane, the plane of substrate  190  will be determined substantially by the diameter of the three largest cores (where the core diameters are expected to vary due to manufacturing tolerances). Advantageously, Method I provides a structure wherein a plane of substrate  190  is substantially parallel to a plane of Probe Card  130 . Finally, the structure or lay-up comprised of connected substrate  190  and Probe Card  130  is removed from the pinalignment fixture, and release films  110  and  200  are removed.  
      In accordance with one or more further embodiments of the present invention, a stiffening mechanism is connected to a side of the Probe Card opposite from the side to which the substrate is connected.  FIG. 1A  is a cross sectional view that shows how stiffening mechanism  447  is connected to Probe Card  457  in accordance with one or more embodiments of the present invention, and  FIG. 1B  is a bottom view that shows stiffening mechanism  447 . As shown in  FIG. 1A , stiffening mechanism  447  is connected to Probe Card  457  so that substrate  467  is encompassed within an area delineated by the perimeter of stiffening mechanism  447 . As further shown in  FIG. 1A , the area delineated by the perimeter of stiffening mechanism  447  does not include electrical contacts  477  disposed on Probe Card  457 , which electrical contacts  477  provide electrical connections between Probe Card  457  and a test interface system.  
      As shown in  FIG. 1A , stiffening mechanism  447  includes leg structure  451  that is used to connect ring structure  448  (shown in  FIG. 1B ) to Probe Card  457  at a multiplicity of locations about the periphery of stiffening mechanism  447 . Leg structure  451  may comprise, for example and without limitation, a number of legs, leg structure  451  may be a ring, and so forth. Stiffening mechanism  447  is connected to Probe Card  557  using a connection mechanism such as, for example and without limitation, screws and nuts. Also, in accordance with one or more alternative such embodiments, ring structure  448  shown in  FIG. 1B  may further include supports such as radial arms, struts, ribs, and the like. In accordance with one or more further embodiments of the present invention, stiffening mechanism  447  may be comprised of a solid plate, with or without a leg structure like leg structure  451  described above. Lastly, stiffening mechanism  447  may be fabricated from any one of a number of materials such as, for example and without limitation, as a metal, a plastic, a ceramic, and so forth. Advantageously, in accordance with such embodiments of the present invention, stiffening mechanism  447  provides support for substrate  467  during testing.  
      It should be understood by those of ordinary skill in the art that balls  181  and  182  utilized in the above-described embodiment of the present invention are interconnectors that provide electrical continuity between pads on the bottom or non-testing side of the substrate and pads on the top side of the Probe Card. In general, the interconnectors may be any type of electrical conductor (for example and without limitation, it is comprised of an electrical conducting material): (a) whose electrical conductivity is sufficient to satisfy design electrical requirements of a resulting structure or lay-up; and (b) that has at least a core that does not melt as a result of applying heat during the fabrication process. For example and without limitation, the core does not melt at temperatures used to re-flow eutectic solder (for example, temperatures in a range from about 183° C. (the melting point of eutectic solder) to about 230° C.). Thus, for this case, for example, and without limitation, the core may be a material that melts at a temperature that is higher than 230° C. since such a material would not melt in the specified range. In light of this, when the interconnectors are embodied as balls, such balls may be: (a) solid Cu balls; (b) solid Cu balls that are coated with eutectic solder; (c) solid Indium alloy balls; (d) solid Indium alloy balls that are coated with solder; (e) solid high lead solder (for example and without limitation, 97/3 or 95/5) balls; (f) solid high lead solder (for example and without limitation, 97/3 or 95/5) balls that are coated with solder; and (g) so forth. In addition, further embodiments can be fabricated wherein the core of the interconnectors (for example and without limitation, balls) is not solid, and further embodiments can be fabricated wherein the core of the interconnectors (for example and without limitation, balls) comprises a ceramic material that is embedded with a conducting material such as, for example, and without limitation, gold, Cu, silver, Indium, Ni, and so forth. Embodiment of such balls may be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, and one or more embodiments of such balls are commercially available.  
      In accordance with one or more further embodiments of the present invention, the interconnectors may be compliant conductive balls, for example and without limitation, compliant conductive plastic balls. For example, suitable conductive, compliant balls are commercially available that have a plastic core (for example and without limitation, a plastic core having a hollow center), which plastic core is surrounded or coated with: (a) a layer of Cu; (b) a layer of Cu and a layer of Ni; (c) a layer of Cu, a layer of Ni, and a layer of Au; (d) one or more of a layer of Cu; a layer of Ni; and a layer of Au; and (e) so forth. In addition, in accordance with one or more still further embodiments of the present invention, the interconnectors may be springs (suitable springs may be obtained commercially). Advantageously, in accordance with one or more such embodiments of the present invention, such compliant, conductive balls may compress when the structure is used in a Tester and, thereby, the compliant, conductive balls may be able make up for any non-planarity of the structure as a whole.  
      It should be understood that further embodiments of the present invention exist wherein the interconnectors may be affixed to the substrate and to the Probe Card utilizing any one of a number of methods that are well known to those of ordinary skill in the art. For example and without limitation, if an interconnector is embodied as a solder coated Cu ball, such a solder coated ball may be affixed: (a) by re-flow; (b) by re-flow after applying flux to the substrate and/or the Probe Card; (c) by re-flow after applying conductive paste to the substrate and/or the Probe Card; (d) by re-flow after applying conductive paste to the substrate or the Probe Card and applying flux to the Probe Card or the substrate, respectively; (e) and so forth. As a further example, if an interconnector is embodied as a Cu ball or as a conductive, compliant ball such as that described above, such a ball may be affixed: (a) by re-flow after applying solder paste to the substrate and the Probe Card; (b) by curing after applying conductive paste to the substrate and the Probe Card; (c) by re-flow after applying conductive paste to the substrate or the Probe Card and applying solder paste to the Probe Card or the substrate, respectively; (d) and so forth. As a still further example, if the interconnector is embodied as a spring, such a spring may be affixed: (a) by re-flow after applying solder paste to the substrate and the Probe Card; (b) by curing after applying conductive paste to the substrate and the Probe Card; (c) by re-flow after applying conductive paste to the substrate or the Probe Card and applying solder paste to the Probe Card or the substrate, respectively; (d) and so forth.  
      In accordance with one or more still further embodiments of the present invention, the interconnectors may be eutectic solder balls that are affixed by curing after applying conductive paste to the substrate and the Probe Card. For example, such a curing step will occur at temperatures in a range, for example and without limitation, from about 120° C. to about 160° C., which range of temperatures is below the melting temperature (˜183° C.) of eutectic solder. Thus, in accordance with such still further embodiments of the present invention, the eutectic solder ball will not melt as a result of applying heat during the fabrication process. Further, as was explained above, because the eutectic solder ball will not melt as a result of applying heat during the fabrication process, the distance between the substrate and the Probe Card may be determined by the size of the eutectic solder balls.  
      It should also be understood that further embodiments of the present invention exist wherein: (a) no interconnector alignment film is used; (b) an interconnector alignment film is applied to the Probe Card (see the above-described embodiment where the interconnector alignment film is embodied as polyimide film  150 ); (c) an interconnector alignment film may be applied to the substrate in a manner that will be readily understood by one of ordinary skill in the art in light of the specification; (d) and so forth.  
      In accordance with one or more embodiments of the present invention, when the interconnectors are short, structures fabricated utilizing such interconnectors have short interconnection distances from IC bumps under test to the Probe Card. For example, when interconnectors are embodied as balls such as balls  181  and  182  described above having a solid Cu core with a diameter in a range, for example and without limitation, from about 5 mils to about 10 mils, structures fabricated utilizing such balls have interconnection distances from IC bumps under test to the Probe Card that are short. Advantageously, the resulting structures have electrical properties, such as, for example and without limitation, line resistance, inductance, and so forth, that are improvements over similar electrical properties for structures having longer interconnection distances.  
      An advantage provided by one or more of the above-described embodiments of the present invention is that the substrate may be removed from the Probe Card when the substrate becomes worn or is damaged. For example, to do this, one would remove the Probe Card from a Tester, de-solder the worn or damaged substrate utilizing any one of a number of de-soldering methods that are well known to those of ordinary skill in the art, and connect a new substrate to the Probe Card in its place. For example and without limitation, such a de-soldering method may include the use of forced hot air (the temperature being above the melting point of solder), and a suction to retrieve the substrate when the solder has melted to a sufficient degree. The new structure may then be replaced in the Tester.  
      The following describes another method (“Method II”) for connecting a substrate to a Probe Card (i.e., for connecting BGA pads of a substrate to BGA pads of a Probe Card) in accordance with one or more embodiments of the present invention wherein, in accordance with Part I of Method II, interconnectors are connected to the substrate before the substrate is connected to the Probe Card, which substrate can be, for example and without limitation, a rigid substrate, a flex substrate, or a semi-flex substrate.  
      In a first, optional step of Part I of Method II, a release film (such as, for example and without limitation, a release film like that described above in conjunction with Method I) is aligned with, and placed over, a base plate of a pinalignment fixture (such as, for example and without limitation, a base plate and a pinalignment fixture like those described above in conjunction with Method I). Next, a substrate is aligned with, and placed over, the release film on the pinalignment fixture with its BGA pad side up. Next, a paste stencil mask that is fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art is aligned with, and placed over, the substrate on the pinalignment fixture. Next, a paste such as, for example and without limitation, a flux or a no-clean solder paste is applied onto the BGA pads of the substrate utilizing any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, methods utilizing a dispensing machine, methods utilizing screen-printing, methods utilizing a squeegee, and so forth. Also, in accordance with one or more further embodiments of the present invention, the paste may be any one of a number of conductive pastes that are well known to those of ordinary skill in the art such as, for example, and without limitation, a Ag conductive paste, a Au conductive paste, a Cu conductive paste, and so forth, or it may be any one of a number of solder pastes that are well known to those of ordinary skill in the art. Further, the paste can be a compliant, conductive paste where such compliant conductive paste may be any one of a number of such products that are well known to those of ordinary skill in the art such as, for example and without limitation, an elastomer such as a silicone elastomer having conductive particles embedded therein. The use of a compliant conductive paste may be advantageous in that the resulting structure may be able to take up vertical movements or movements in a Z-direction caused during testing by non-planarity of contactors on the substrate, pads on the substrate, pads on the Probe Card, and/or I/O contacts on the wafer. Next, the paste stencil mask is removed.  
      Next, a stencil (such as, for example and without limitation, a stencil like that described above in conjunction with Method I to position balls) is aligned with, and placed over, the substrate on the pinalignment fixture; the edges of the stencil could have a corral formed thereon (such as, for example and without limitation, a corral like that described above in conjunction with Method I). Next, balls having a rigid core and a solder coating (such as, for example and without limitation, balls like those described above in conjunction with Method I) are placed over the stencil, and the stencil is removed. Next, the solder coating on the balls is re-flowed (in a re-flow step such as, for example and without limitation, a re-flow step like that described above in conjunction with Method I). The resulting piece may be inspected, and re-work may take place if necessary. As one can readily appreciate from the above, Part I of Method II may be utilized, among other things, to prepare a replacement substrate for connection to a Probe Card by affixing balls to the BGA pads thereof.  
      It should be understood by those of ordinary skill in the art that the balls utilized in the above-described embodiment of the present invention are interconnectors that provide electrical continuity between pads on the bottom or non-testing side of the substrate and pads on the top side of the Probe Card. In general, the interconnectors may be any type of electrical conductor (for example and without limitation, it is comprised of an electrical conducting material): (a) whose electrical conductivity is sufficient to satisfy design electrical requirements of a resulting structure or lay-up; and (b) that has at least a core that does not melt as a result of applying heat during the fabrication process. For example and without limitation, the core does not melt at temperatures used to re-flow eutectic solder (for example, temperatures in a range from about 183° C. (the melting point of eutectic solder) to about 230° C.). Thus, for this case, for example, and without limitation, the core may be a material that melts at a temperature that is higher than 230° C. since such a material would not melt in the specified range. In light of this, when the interconnectors are embodied as balls, such balls may be: (a) solid Cu balls; (b) solid Cu balls that are coated with eutectic solder; (c) solid Indium alloy balls; (d) solid Indium alloy balls that are coated with solder; (e) solid high lead solder (for example and without limitation, 97/3 or 95/5) balls; (f) solid high lead solder (for example and without limitation, 97/3 or 95/5) balls that are coated with solder; and (g) so forth. In addition, further embodiments can be fabricated wherein the core of the interconnectors (for example and without limitation, balls) is not solid, and further embodiments can be fabricated wherein the core of the interconnectors (for example and without limitation, balls) comprises a ceramic material that is embedded with a conducting material such as, for example, and without limitation, gold, Cu, silver, Indium, Ni, and so forth. Embodiment of such balls may be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, and one or more embodiments of such balls are commercially available.  
      In accordance with one or more further embodiments of the present invention, the interconnectors may be compliant conductive balls, for example and without limitation, compliant conductive plastic balls. For example, suitable conductive, compliant balls are commercially available that have a plastic core (for example and without limitation, a plastic core having a hollow center), which plastic core is surrounded or coated with: (a) a layer of Cu; (b) a layer of Cu and a layer of Ni; (c) a layer of Cu, a layer of Ni, and a layer of Au; (d) one or more of a layer of Cu; a layer of Ni; and a layer of Au; and (e) so forth. In addition, in accordance with one or more still further embodiments of the present invention, the interconnectors may be springs (suitable springs may be obtained commercially).  
      It should be understood that further embodiments of the present invention exist wherein the interconnectors may be affixed to the substrate utilizing any one of a number of methods that are well known to those of ordinary skill in the art. For example and without limitation, if an interconnector is embodied as a solder coated Cu ball, such a solder coated ball may be affixed to the substrate: (a) by re-flow; (b) by re-flow after applying flux to the substrate; (c) by re-flow after applying conductive paste to the substrate; and (d) so forth. As a further example, if an interconnector is embodied as a Cu ball or as a conductive, compliant ball such as that described above, such a ball may be affixed to the substrate: (a) by re-flow after applying solder paste to the substrate; (b) by curing after applying conductive paste to the substrate; and (c) so forth. As a still further example, if the interconnector is embodied as a spring, such a spring may be affixed to the substrate: (a) by re-flow after applying solder paste to the substrate; (b) by curing after applying conductive paste to the substrate; and (c) so forth.  
      It should also be understood that further embodiments of the present invention exist wherein: (a) no interconnector alignment film is used; or (b) an interconnector alignment film is applied to the substrate in a manner that will be readily understood by one of ordinary skill in the art in light of the specification.  
      The following describes Part II of Method II, i.e., a method for connecting a structure having balls affixed to the BGA pads thereto to the Probe Card. In a first, optional step of Part II of Method II, a release film (such as, for example and without limitation, a release film like that described above in conjunction with Method I) is aligned with, and placed over, a base plate of a pinalignment fixture (such as, for example and without limitation, a base plate and a pinalignment fixture like those described above in conjunction with Method I). Next, the Probe Card is aligned with, and placed over, the release film on the pinalignment fixture. Next, a paste stencil mask (such as, for example and without limitation, a paste stencil mask like that described above in conjunction with Part I of Method II) is aligned with, and placed over the Probe Card on the pinalignment fixture. Next, a paste (such as, for example and without limitation, a paste like that described above in conjunction with Part I of Method II) is applied onto the pads of the Probe Card (in a paste application step such as, for example and without limitation, a paste application step like that described above in conjunction with Part I of Method II). Next, the paste stencil is removed.  
      Next, the substrate, with the balls facing down, is aligned with, and placed over the Probe Card on the pinalignment fixture. Next, in an optional step, a release film (such as, for example and without limitation, a release film like that described above in conjunction with Part I of Method II) is aligned with, and placed over, the structure on the pinalignment fixture. Next, a weight (such as, for example and without limitation, a weight like that described above in conjunction with Method I) is aligned with, and placed over, the release film on the pinalignment fixture. Next, the solder coating on the balls is re-flowed (in a re-flow step such as, for example and without limitation, a re-flow step like that described above in conjunction with Part I of Method II). During the re-flow process, the weight provides a force that causes the solder to flow so that the distance between the substrate and the Probe Card is determined by a dimension of the core of the balls (for example and without limitation, the diameter of the core). It should be understood that other mechanisms for applying a force (i.e., other than the weight) that causes the solder to flow so that the distance between the substrate and the Probe Card is determined by the diameter of the core of the balls may be used to fabricate one or more further embodiments of the present invention such as, for example and without limitation, by the use of springs that are adapted to urge the substrate and the Probe Card towards each other. Finally, the structure or lay-up comprised of the connected substrate and Probe Card is removed from the pinalignment fixture, and the release films are removed. In an alternative embodiment of Part II of Method II, a support film such as, for example and without limitation, a polyimide film, may be placed over the Probe Card before the paste is applied to help support the balls during testing. In addition, a stiffening mechanism like that described above may be (optionally) connected to a side of the Probe Card opposite from the side to which the substrate is connected.  
      It should be understood that further embodiments of the present invention exist wherein the interconnectors may be affixed to the Probe Card utilizing any one of a number of methods that are well known to those of ordinary skill in the art. For example and without limitation, if an interconnector is embodied as a solder coated Cu ball, such a solder coated ball may be affixed to the Probe Card: (a) by re-flow; (b) by re-flow after applying flux to the Probe Card; (c) by re-flow after applying conductive paste to the Probe Card; and (d) so forth. As a further example, if an interconnector is embodied as a Cu ball or as a conductive, compliant ball such as that described above, such a ball may be affixed to the Probe Card: (a) by re-flow after applying solder paste to the Probe Card; (b) by curing after applying conductive paste to the Probe Card; and (c) so forth. As a still further example, if the interconnector is embodied as a spring, such a spring may be affixed to the Probe Card: (a) by re-flow after applying solder paste to the Probe Card; (b) by curing after applying conductive paste to the Probe Card; and (c) so forth.  
      In accordance with one or more still further embodiments of the present invention, the interconnectors may be eutectic solder balls that are affixed by curing after applying conductive paste to the substrate and the Probe Card. For example, relevant curing steps will occur at temperatures in a range, for example and without limitation, from about 120° C. to about 160° C., which range of temperatures is below the melting temperature (˜183° C.) of eutectic solder. Thus, in accordance with such still further embodiments of the present invention, the eutectic solder ball will not melt as a result of applying heat during the fabrication process. Further, as was explained above, because the eutectic solder ball will not melt as a result of applying heat during the fabrication process, the distance between the substrate and the Probe Card may be determined by the size of the eutectic solder balls.  
      The following describes another method (“Method III”) for connecting a structure comprised of at least two substrates to a Probe Card (i.e., for connecting BGA pads of the structure comprised of at least two substrates to BGA pads of the Probe Card) in accordance with one or more embodiments of the present invention. Due to limitations in wiring density for substrates presently available in the market, for high I/O chip applications (for example and without limitation, chip applications involving over 3,000 I/O connections) the wiring density may be insufficient to wire all contactors from the top or testing surface of a substrate through to the other side to pads that are to be connected to a Probe Card. Thus, for example and without limitation, in such high I/O chip applications, a substrate having contactors that face a wafer might be fanned-out to another substrate that is sometimes referred to as a second level substrate. Then, in accordance with one or more embodiments of the present invention, a first substrate having contactors for use in testing a circuit is connected to a second substrate using interconnectors such as, for example and without limitation, any of the interconnectors described above in conjunction with Methods I or II; and the two substrates are connected utilizing any of the embodiments described above in conjunction with Method I or Method II. Next, the structure comprised of the two substrates may be connected to the Probe Card utilizing any of the embodiments described above in conjunction with Method I or Method II. In addition, a stiffening mechanism like that described above may be (optionally) connected to a side of the Probe Card opposite from the side to which the substrate is connected.  
      The following describes another method (“Method IV”) for connecting a flexible substrate (sometimes referred to as a “flex substrate”) to a Probe Card (i.e., for connecting BGA pads of the flex substrate to BGA pads of the Probe Card) in accordance with one or more embodiments of the present invention. A suitable flex substrate may be fabricated from polyimide or from any other suitable materials that are well known to those of ordinary skill in the art. In accordance with one or more such embodiments, the flex substrate has a thickness in a range from, for example and without limitation, about 1 mil to about 3 mils to provide a predetermined degree of flexibility. The degree of flexibility that may be utilized in a particular application may be determined, for example and without limitation, readily by one of ordinary skill in the art without undue experimentation by testing.  
       FIG. 2  is a top view that shows a portion of flex substrate  175  that is fabricated in accordance with one or more embodiments of the present invention. As shown in  FIG. 2 , and in accordance with one or more such embodiments of the present invention, the BGA pads on the bottom or non-testing side of flex substrate  175  (i.e., the side opposite contactors  177   1 - 177   6 ) is laid out in accordance with any one of a number of methods that are well known to those of ordinary skill in the art so that the following is true for a predetermined fraction of the BGA pads for a particular grid, for example and without, a 0.8 mm grid or a 0.65 mm grid. An area surrounded by pads  179   1 - 179   4  (shown in phantom in  FIG. 2 ) encompasses contactors  177   1 - 177   6 . Next, in accordance with one or more such embodiments of the present invention, the substrate is connected to the Probe Card using interconnectors such as, for example and without limitation, any of the interconnectors described above in conjunction with Methods I or II; and the substrate and the Probe Card are connected utilizing any of the embodiments described above in conjunction with Method I or Method II. Advantageously, in accordance with one or more such embodiments of the present invention, during use in a Tester or Test System, the flex substrate acts like a drum membrane. As a result, whenever a structure fabricated in accordance with this embodiment of the present invention is used in a Tester, the contactors are able to move distances that make up for at least some non-planarity in the structure itself, and/or for any non-uniformity in bump height on the wafer.  
      The following describes another method (“Method V”) for connecting a substrate to a Probe Card (i.e., for connecting BGA pads of a substrate to BGA pads of a Probe Card) in accordance with one or more embodiments of the present invention, which substrate can be, for example and without limitation, a rigid substrate, a flex substrate, or a semi-flex substrate.  
      In a first step of Method V, a thickness of at least two edges of a substrate such as, for example and without limitation, a rigid substrate, is reduced by use of any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, using a router, a laser, and so forth to form bevels.  FIGS. 3-5  are cross sectional views that show substrates  186 ,  187 , and  188 , respectively, that have bevels formed on the edges of thereof in accordance with one or more embodiments of the present invention. In accordance with one such embodiment, the thickness of the edge of the substrate is reduced to a thickness in a range, for example and without limitation, from about 0.2 mm to about 0.3 mm.  
      Next, compliant interconnectors such as, for example and without limitation, compliant, conductive balls or springs (such as, for example and without limitation, compliant, conductive balls or springs like those described above in conjunction with Methods I or II) are connected to the substrate utilizing any of the embodiments described above in conjunction with Part I of Method II.  
      Next, an optional interconnector alignment film (for example and without limitation, a polyimide film like that described above having holes in it that align to the Probe Card pads), may be affixed to the Probe Card utilizing methods described above in conjunction with, for example, Method I. Such an interconnector alignment film would act as a guide for the balls or springs.  
      Next, electrical connection between pads on the substrate and pads on the Probe Card is provided by a clamp mechanism shown in  FIG. 6 . As shown in  FIG. 6 , the clamp mechanism includes: (a) substrate cover  310 ; (b) a connection mechanism shown, for example and without limitation, as a releasable connection mechanism comprised of screws  305   1 - 305   4  and nuts  307   1 - 307   4 ; and (c) guide pins  320   1 - 320   4 . As shown in  FIG. 6 , guide pins  320   1 - 320   4  are used to align the substrate to holes  325   1 - 325   4  in Probe Card  330 , and to align substrate cover  310  over the substrate so that the balls or springs connected to the substrate are aligned with pads on Probe Card  330 . As further shown in  FIG. 6 , substrate cover  310  includes a recess that is formed by lip  327 . As further shown in  FIG. 6 , area  329  of the recess in substrate cover  310  is open to enable access to contactors disposed on a top side of the substrate during testing. In addition, lip  327  of substrate cover  310  is formed so that it fits over the beveled edges of the substrate to hold the substrate in place when the structure is assembled. Guide pins  320   1 - 320   4  are removed after substrate cover  310  is connected to Probe Card  330  using, for example and without limitation, a connection mechanism, for example and without limitation, a releasable connection mechanism comprised of screws  305   1 - 305   4  and nuts  307   1 - 307   4 . In accordance with one or more such embodiments, electrical contact is ensured by pressure applied by the wafer during testing. In addition, a stiffening mechanism like that described above may be (optionally) connected to a side of the Probe Card opposite from the side to which the substrate is connected. It should be understood that in one or more alternatives of the above-described embodiment, the substrate may not have bevels formed in the sides, and lip  327  of substrate cover  310  is formed so that it fits over the edges of the substrate to hold the substrate in place when the structure is assembled.  
      In accordance with one or more further alternatives of the above-described embodiment, instead of connecting the conductive, compliant balls or springs to the substrate (as described above), they are connected to Probe Card  330  using the same steps set forth above for connecting the conductive, compliant balls or springs to the substrate. In accordance with such further alternative embodiments, a polyimide film may be applied to the Probe Card to support the balls or springs as was done in Method I, however, this is not necessary. Next, electrical connection between pads on the substrate and pads on the Probe Card is provided by using the clamp mechanism shown in  FIG. 6 . In either case, if the substrate wears out or is damaged, it is easily replaced by releasing the connection mechanism, for example and without limitation, by removing screws  305   1 - 305   4 , thereby causing minimum equipment downtime. Advantageously, compliant balls or springs may make up for at least some non-planarity in the structure itself, and/or for any non-uniformity in bump height on the wafer.  
      The following describes another method (“Method VI”) for connecting a substrate to a Probe Card (i.e., for connecting BGA pads of a substrate to BGA pads of a Probe Card) in accordance with one or more embodiments of the present invention. In accordance with one or more embodiments of the present invention, the substrate is a chip having spring-type contactors on a testing side, which chip is fabricated, for example and without limitation, using standard MEMS technology. In accordance with one or more such embodiments, each contactor is wired through vias on the chip to make contact with pads on the bottom side of the chip in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Advantageously, the spring type contactors on the top of the chip make up for at least some non-planarity in the structure itself, and/or for any non-uniformity in bump height on the wafer. The chip may be connected to the Probe Card using any one of the above-described embodiments. For example,  FIG. 7  is a cross sectional view that shows chip substrate  360  that is fabricated in accordance with one or more embodiments of the present invention. As shown in  FIG. 7 , chip substrate  360  includes bevels  361   1 - 361   2 ; alignment vias  367   1 - 367   2 ; spring-type contactors  363   1 - 363   2 ; wiring  369   1 - 369   2 ; and pads  367   1 - 367   2  to enable use of one or more embodiments of Method V above.  
      The following describes another method (“Method VII”) for connecting a substrate to a Probe Card (i.e., for connecting BGA pads of a substrate to BGA pads of a Probe Card) to provide an inventive structure in accordance with one or more embodiments of the present invention. In accordance with one or more such embodiments, the inventive structure comprises a substrate, a Probe Card, and an interconnector in the form of a connector-holder that is aligned to the substrate and the Probe Card, wherein electrical connections between pads on the substrate and pads on the Probe Cards are made through the connector-holder utilizing electrical connectors such as, for example and without limitation, electrical connectors having first and second retractable ends (for example, Pogo pins). Advantageously, in accordance with one or more such embodiments of the present invention, inventive structures are produced that may be used cost effectively for testing because, among other reasons, the substrate may be replaced easily and rapidly with a new one when the substrate is damaged or worn.  
      In accordance with one or more embodiments of the present invention, a flexible, HDI substrate is fabricated utilizing, for example and without limitation, polyimide, Teflon, and so forth in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. In accordance with one or more such embodiments of the present invention, the substrate has a thickness in a range, for example and without limitation, from about 2 mils to about 3 mils, and the substrate has contactors disposed on a top side of the substrate in an array that has the same pitch as that of bumps on a chip on a wafer to be tested. The contactors are wired through vias in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, and the wires contact BGA pads disposed on a bottom side of the substrate, which BGA pads are disposed in a grid array that has a predetermined grid array spacing, for example and without limitation, a spacing in a range from about 0.65 mm to about 1.27 mm. Although it is not required to utilize a flex substrate to carry out Method VII, one advantage of using a flex substrate is that the resulting structure may make up for at least some non-planarity in the structure itself, and/or for any non-uniformity in bump height on the wafer. This is because movement in a Z-axis (i.e., an axis perpendicular to a plane of the substrate) is provided by the flex substrate, with or without the need for compliant connectors disposed between it and the Probe Card.  
      In accordance with Part I of Method VII, a connector-holder is fabricated. In accordance with one or more such embodiments, the connectors are electrical connectors having first and second retractable ends (for example, Pogo pins), and the connector-holder for these Pogo pins is fabricated from plastic such as, for example and without limitation, ULTEM™, Torlon, and so forth.  FIG. 8  shows Pogo pin  800  that is commercially available from any one of a number of sources. As shown in  FIG. 8 , Pogo pin  800  includes plungers  810  and  811  and barrel  820 . Pogo pin  800  provides an electrical conduit between the tips of plungers  810  and  811 , and as such, it is preferable that the tips of plungers  810  and  811  of Pogo pin  800  be narrow to enable better electrical contact with the pads. As such, plungers  810  and  811  may be fabricated, for example and without limitation, of gold-plated hardened steel; barrel  820  may be fabricated, for example and without limitation, of a gold-plated copper alloy; and internal springs (not shown) may be fabricated, for example and without limitation, of gold-plated piano wire.  
      The connector-holder comprises a connector-holder bottom plate and a connector-holder top plate that are both fabricated, for example and without limitation, from plastic.  FIG. 9  is a top perspective view that shows connector-holder bottom plate  600  that is fabricated in accordance with one embodiment of the present invention, and  FIG. 10  is a bottom perspective view that shows connector-holder top plate  700  that is fabricated in accordance with one embodiment of the present invention. Connector-holder bottom plate  600  and connector-holder top plate  700  may be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by injection molding, and holes may be fabricated therein in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by drilling. Referring to  FIG. 9 , the locations of the holes in array  610  of connector-holder bottom plate  600  match the locations of BGA pads on the Probe Card. Further, referring to  FIG. 10 , the locations of the holes in array  710  of connector-holder top plate  700  match the locations of BGA pads on the substrate. Still further, in accordance with one or more embodiments of the present invention, the holes in array  610  of connector-holder bottom plate  600  (such as hole  615  shown in  FIG. 11 ) comprise hole  616  within hole  617  for retaining Pogo pins in place when connector-holder bottom plate  600  and connector-holder top plate  700  are connected. For example, (a) the diameter of hole  616  is larger—preferably by a small amount—(for example and without limitation, the diameter of hole  616  is in a range from about 1 mil to about 3 mils) than the diameter of plunger  810  of Pogo pin  800  shown in  FIG. 8 ; and (b) the diameter of hole  617  larger—preferably by a small amount—than the diameter of barrel  820  of Pogo pin  800 . Yet still further, in accordance with one or more embodiments of the present invention, the holes in array  710  of connector-holder top plate  700  (such as hole  715  shown in  FIG. 12 ) comprise hole  716  within hole  717  for retaining Pogo pins in place when connector-holder bottom plate  600  and connector-holder top plate  700  are connected. For example, the (a) the diameter of hole  716  is larger—preferably by a small amount—than the diameter of plunger  811  of Pogo pin  800 ; and (b) the diameter of hole  717  is larger—preferably by a small amount—than the diameter of barrel  820  of Pogo pin  800 .  
      As shown in  FIG. 9 , connector-holder bottom plate  600  includes posts  611   1 - 611   4 . Posts  611   1 - 611   4  include holes for connection mechanisms (for example and without limitation, releasable connection mechanisms) comprised, for example and without limitation, of screws  937   1 - 937   4  (shown in  FIG. 13 ) that are used to hold connector-holder bottom plate  600  and connector-holder top plate  700  together (as will be described below). As further shown in  FIG. 10 , connector-holder top plate  700  includes receptacles  711   1 - 711   4 . Receptacles  711   1 - 711   4  include holes for the connection mechanisms (for example and without limitation, releasable connection mechanisms) comprised, for example and without limitation, of screws  937   1 - 937   4  (shown in  FIG. 13 ) that are used to hold connector-holder bottom plate  600  and connector-holder top plate  700  together (as will be described below). The shape of receptacles  711   1 - 711   4  is such that posts  611   1 - 611   4 , mate with receptacles  711   1 - 711   4  when connector-holder bottom plate  600  and connector-holder top plate  700  are connected to each other. As still further shown in  FIG. 10 , connector-holder top plate  700  further includes: (a) vias  712   1 - 712   4  that are used for guide pins  910   1 - 910   4  (shown in  FIG. 13 ); and (b) holes  713   1 - 713   4  that are used for connection mechanisms (for example and without limitation, releasable connection mechanisms) comprised, for example and without limitation, of screws  940   1 - 940   4  (shown in  FIG. 13 ) to hold the connector-holder in place after final assembly (as will be described below).  
      To assemble the connector-holder in accordance with one or more embodiments of the present invention: (a) Pogo pins are placed into the holes of array  710  of connector-holder top plate  700 ; (b) connector-holder bottom plate  600  is then placed over connector-holder top plate  700 ; and (c) as indicated in  FIG. 13 , connector-holder bottom plate  600  is connected to connector-holder top plate  700  by screwing connector-holder bottom plate  600  into connector-holder top plate  700  at four (4) corners using screws  937   1 - 937   4 .  
      In accordance with Method VII, vias are formed for guide pins  910   1 - 910   4  (shown in  FIG. 13 ) in the substrate and the Probe Card in accordance with any one of a number of methods that are well known to those of ordinary skill in the art.  
       FIG. 13  is an exploded view that shows a portion of a structure used to test circuits that is fabricated in accordance with one or more embodiments of the present invention. Clamp  930  (a bottom perspective view of clamp  930  is shown in  FIG. 13 ) includes: (a) vias  965   1 - 965   4  that are used for guide pins  910   1 - 910   4  (shown in  FIG. 13 ); and (b) holes  961   1 - 961   4  that are used for screws  940   1 - 940   4  (shown in  FIG. 13 ) to hold the connector-holder and the substrate in place on Probe Card  920  (as will be described below). As shown in  FIG. 13 , clamp  930  includes a recess that is formed by lip  978 . As further shown in  FIG. 13 , area  987  of the recess in clamp  930  is open to enable access to contactors disposed on a top side of the substrate during testing. In addition, lip  978  is formed so that it fits over, and may make contact with the edges or any bevels in the edges, of the substrate when the structure is assembled. Clamp  930  is fabricated, for example and without limitation, from plastic in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by injection molding, and holes may be fabricated therein in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by drilling.  
      In accordance with one embodiment of Part II of Method VII, the substrate is connected to the connector-holder fabricated in accordance with Part I of Method VII. In a first optional step of this embodiment of Part II of Method VII, a thickness of at least two edges of a substrate is reduced by use of any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, using a router, a laser, and so forth to form bevels like those fabricated in accordance with Method V. The thickness of the routed edges is a function of the Z-movement of the Pogo pins used to fabricate the connector-holder described above.  
      Next, in another optional step of this embodiment of Part II of Method VII, a release film such as, for example and without limitation, a release film like that described above in conjunction with Method I) is aligned with, and placed over, a base plate of a pinalignment fixture (such as, for example and without limitation, a base plate and a pinalignment fixture like those described above in conjunction with Method I). Next, a substrate is aligned with, and placed over, the release film on the pinalignment fixture with its BGA pads side up. Next, a paste stencil mask that is fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art is aligned with, and placed over, the substrate on the pinalignment fixture. Next, a paste such as, for example and without limitation, a no-clean solder paste is applied onto the BGA pads of the substrate utilizing any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, methods utilizing a dispensing machine, methods utilizing screen-printing, methods utilizing a squeegee, and so forth. Also, in accordance with one or more further embodiments of the present invention, the paste may be any one of a number of conductive pastes that are well known to those of ordinary skill in the art such as, for example, and without limitation, a Ag conductive paste, a Au conductive paste, a Cu conductive paste, and so forth, or it may be any one of a number of solder pastes that are well known to those of ordinary skill in the art. Further, the paste can be a compliant, conductive paste where such compliant conductive paste may be any one of a number of such products that are well known to those of ordinary skill in the art such as, for example and without limitation, an elastomer such as a silicone elastomer having conductive particles embedded therein. Next, the paste stencil mask is removed.  
      Next, in accordance with this embodiment of Part II of Method VII, a connector-holder fabricated in accordance with Part I of Method VII is pinaligned (using two or more of guide pins  910   1 - 910   4  shown in  FIG. 13 ) to the substrate fabricated in accordance with Part II of Method VII. Next, the resulting substrate structure is re-flowed or cured, depending on the type of paste used, to connect the Pogo pins to the BGA pads on the substrate.  
      Next, two or more of guide or dowel pins  910   1 - 910   4  are used to align the resulting substrate structure with, and place the resulting substrate structure over, Probe Card  920  so that the tips of the Pogo pins align with the pads on Probe Card  920 . Finally, clamp  930  is aligned with, and placed over, Probe Card  920  utilizing two or more of guide or dowel pins  910   1 - 910   4 , and clamp  930  is connected to Probe Card  920  utilizing screws  940   1 - 940   4  (screws  940   1 - 940   4  also pass through the connector-holder) and nuts  950   1 - 950   4 , thereby holding the final assembly in place. Alternatively, clamp  930  and the connector-holder may be connected to Probe Card separately. Next, the guide pins are removed. In addition, a stiffening mechanism like that described above may be (optionally) connected to a side of the Probe Card opposite from the side to which the substrate is connected.  
      Advantageously, using a flex substrate and Pogo pins in accordance with the above-described embodiments enables bump height non-uniformity or non-planarity of the structure to be made up by movement in a Z-axis during testing. Further, a short interconnection distance between the substrate and the Probe Card obtained from the use of small Pogo pins can create better electrical properties than those of structures produced using prior art methods. Still further, in accordance with the above-described embodiments, whenever the flex substrate wears out or becomes damaged, the Pogo pins can be removed from it by de-soldering in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. Then a new substrate may be incorporated into the assembly, and the Probe Card may be reused.  
      In accordance with one or more alternative embodiments of Method VII described above, the substrate is laid out in accordance with any one of a number of methods that are well known to those of ordinary skill in the art so that all the wiring to the bottom side of the substrate (i.e., the side opposite from the contactors) is routed to a periphery of the substrate. As a result, in accordance with this embodiment of the present invention, there are no pads underneath contactors disposed in a region of the substrate, for example and without limitation, a center of the substrate. Next, a compliant substance such as, for example and without limitation, a compliant elastomer, is applied to the bottom side of the substrate, in the central area, in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by screen printing or stenciling methods. The compliant substance would be thick enough so that it contacts connector-holder top plate  700  when the substrate is connected to the connector-holder as described above. Since the pads on the bottom side of the substrate are on the periphery of the substrate, so too are the Pogo pins held by the connector-holder disposed about the periphery of the substrate. As a result, whenever the contactors on the substrate move up and down during testing, the substrate can flex sufficiently to make up for at least some non-planarity in the structure itself, and/or for any non-uniformity in bump height on the wafer. In addition, in accordance with one or more further such alternative embodiments, the connector-holder has a hole in the middle, and the compliant substance applied to the bottom side of the substrate is made so thick that it extends through to the Probe Card, which Probe Card may also be milled to provide a recessed area into which the substance is seated.  
      The following describes another method (“Method VIII”) for connecting a substrate to a Probe Card (i.e., for connecting BGA pads of a substrate to BGA pads of a Probe Card) in accordance with one or more embodiments of the present invention, which substrate can be, for example and without limitation, a rigid substrate, a semi-rigid substrate, a silicon/glass substrate having MEMS-type springs, and so forth.  
      In accordance with Part I of Method VIII, an interconnector in the form of a connector-holder is fabricated in accordance with Part I of Method VII. Next, vias are formed for guide pins in the substrate and the Probe Card in accordance with any one of a number of methods that are well known to those of ordinary skill in the art.  
      Next, clamp  960  is fabricated, for example and without limitation, from plastic in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by injection molding. Holes may be fabricated in clamp  960  in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by drilling.  FIG. 15  is a top view that shows clamp  960 . As shown in  FIG. 15 , clamp  960  includes: (a) vias  975   1 - 975   4  that are used for to guide pins (to be described below); and (b) holes  971   1 - 971   4  that are used for connection mechanisms, for example and without limitation, releasable connection mechanisms comprised of screws, (to be described below) to connect clamp  960  to the connector-holder. As further shown in  FIG. 15 , clamp  960  includes stationary structures  981   1  and  981   2  which have lips (shown in phantom) that are disposed to cover a portion of the edges or any bevels in the edges (see below) of the substrate and to engage (optional) grooves in the beveled edges of the substrate. As further shown in  FIG. 15 , clamp  960  includes a substrate alignment mechanism. In particular, as further shown in  FIG. 15 , clamp  960  includes laterally movable structures  981   3  and  981   4  which have lips (shown in phantom) that are disposed to cover at least a portion of the beveled edges (see below) of the substrate and to engage (optional) grooves in the beveled edges of the substrate. As further shown in  FIG. 15 , clamp  960  includes springs  991   1  and  991   2  and springs  991   3  and  991   4 . Springs  991   1  and  991   2  urge movable structure  981   3  toward the center of clamp  960 , and springs  991   3  and  991   4  urge movable structure  981   4  toward the center of clamp  960 . In use, when clamp  960  is placed over the substrate (see below), stationary structures  981   1  and  981   2  and movable structures  981   3  and  981   4  engage the edges of the substrate (for example and without limitation, in grooves disposed therein), and springs  991   1 ,  991   2 ,  991   3 , and  991   4  provide lateral forces that help align the substrate. Those of ordinary skill in the art should understand that (although the embodiment described above in conjunction with  FIG. 15  indicated that structures  981   1  and  981   2  were stationary and that structures  981   3  and  981   4  were laterally movable) further embodiments exist where all of some of structures  981   1 - 981   4  are movable. For example and without limitation, in accordance with one or more further embodiments, structures  981   1  and  981   4  are movable and structures  981   2  and  981   3  are stationary, or vice versa.  
      In accordance with Part II of Method VIII, first, (optionally) a thickness of at least two edges of the substrate is reduced by use of any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, using a router, a laser, and so forth to form bevels like those fabricated in accordance with Method V. The thickness of the routed edges is a function of the Z-movement of the Pogo pins used to fabricate the connector-holder. Next, optional grooves, for example and without limitation, V-shape grooves are cut into two or more sides of the substrate in accordance with any one of a number of methods that are well known to those of ordinary skill in the art.  FIG. 14  is a cross sectional view that shows an edge of the substrate with groove  657 .  
      Next, guide or dowel pins are used to align the connector-holder with the Probe Card (as a result, Pogo pins in the connector-holder are connected to pads on the Probe Card). Once the connector-holder is aligned with respect to the Probe Card, the connector-holder is connected to the Probe Card using a connection mechanism, for example and without limitation, a releasable connection mechanism comprised of screws and nuts. For example, four (4) screws are inserted through the connector-holder and the Probe Card, and four (4) nuts are secured to the screws to connect the connector-holder and the Probe Card. Next, the guide or dowel pins are removed. Next, the substrate is aligned with, and placed over, the connector-holder (two or more guide or dowel pins are used to align the Pogo pins of the connector-holder with the BGA pads of the substrate). Next, clamp  960  is aligned with, and placed over, the substrate (two or more guide or dowel pins are use to align the clamp and the substrate), and clamp  960  is connected to the connector-holder using a connection mechanism, for example and without limitation, a releasable connection mechanism comprised of screws. For example, four (4) screws are screwed into the connector-holder. As described above, clamp  960  confines vertical movement of the substrate as well as providing lateral alignment by spring action. In addition, a stiffening mechanism like that described above may be (optionally) connected to a side of the Probe Card opposite from the side to which the substrate is connected. The Probe Card/substrate assembly is now ready for use in testing circuits.  
      In accordance with one or more further such embodiments of the present invention, a connector-holder is not fixedly connected to the Probe Card, and a clamp is connected directly to the Probe Card, which clamp would include a connector-holder alignment mechanism and a substrate alignment mechanism. For example and without limitation, in accordance with such further embodiments, the connector-holder alignment mechanism and the substrate alignment mechanism may be fabricated utilizing movable structures and springs like those described above in conjunction with clamp  960 .  
      In accordance with one or more such embodiments, advantageously, whenever the substrate wears out or becomes damaged, it is replaced while the Pogo pins stay in place and get reused. If a Pogo pin is damaged, it can easily be pulled out of the connector-holder and be replaced. Advantageously, since neither the connector-holder nor the Pogo pins get replaced (unless a Pogo pin is damaged), there is minimum downtime required for replacing the substrate. In addition, a short interconnection distance between the substrate and the Probe Card obtained from the use of small Pogo pins can create better electrical properties than those of structures produced using prior art methods.  
      Note that if one substrate is not sufficient to handle the wiring density required for a circuit or IC having lots of I/O (for example and without limitation, a circuit having &gt;3000 I/O connections), a composite substrate may be fabricated which comprises a first level substrate and a second level substrate that is connected to the first level substrate. Electrical connection between the first level substrate and the second level substrate can be made using any of the methods described above utilizing interconnectors such as, for example and without limitation, any of the interconnectors described above in conjunction with Methods I or II; and the two substrates are connected utilizing any of the embodiments described above in conjunction with, for example and without limitation, Method I or Method II. The composite substrate may then be connected to the Probe Card utilizing any of the methods described above.  
      One or more further embodiments of the present invention relate to a Probe Card that can function as a universal Probe Card, i.e., a Probe Card that may be useful in a number of different testing applications. In accordance with such one or more further embodiments, the Probe Card has a large number of pads disposed in a grid having, for example and without limitation, at least about four hundred (400) pads and having, for example and without limitation, a 0.8 mm pad pitch. As is well known, for a typical Probe Card, connections to analog I/O on a chip are grouped and connected to one cluster of pins on the outside of the Probe Card, and connections to digital I/O on the chip are grouped and connected to another cluster of pins on the outside of the Probe Card. Thus, in accordance with one such further embodiment of the present invention, the above described universal Probe Card would allocate a one fraction of its pads to analog I/O and another fraction of its pads to digital I/O. The allocation would be such that there would be a sufficient number of connections to analog I/O and to digital I/O to satisfy the required number of connections for a number of different chip designs. This would enable the Probe Card to be used in a number of different testing applications. Then, in accordance with one such further embodiment of the present invention, a substrate specific to the particular chip being tested would be used with the universal Probe Card. Advantageously, the various specific substrates useful for the various specific applications would be connected to the universal Probe Card utilizing one or more of the methods described herein.  
      One or more further embodiments of the present invention relate to a structure for testing circuits that is fabricated in accordance with one or more embodiments of the present invention.  FIG. 16  is a cross sectional view that shows structure  2001  that is fabricated in accordance with one or more embodiments of the present invention. As shown in  FIG. 16 , structure  2001  comprises substrate  2000 , RF interface board  2100 , and Probe Card  2200 . As further shown in  FIG. 16 , substrate  2000  includes array  2010  of contactors on a top or testing side thereof (i.e., a side that contacts an IC on the wafer). As further shown in  FIG. 16 , RF interface board  2100  is connected, on a top side thereof, to BGA pads disposed on a bottom side of substrate  2000  by means of, for example and without limitation, conductive balls  2020 . As further shown in  FIG. 16 , RF interface board  2100  is further connected so that: (a) non-RF I/O BGA pads on a bottom side of RF interface board  2100  are connected to BGA pads on a top side of Probe Card  2200  by means of, for example and without limitation, conductive balls  2030 , and (b) RF coaxial cable connectors (not shown) on a bottom side of RF interface board  2100  are connected to RF test coaxial cables  2110 . As further shown in  FIG. 16 , RF test coaxial cables  2110  are routed through channels  2220  in Probe Card  2200 .  
       FIG. 17  is a top view that shows substrate  2000  and RF interface board  2100  of structure  2001 . As shown in  FIG. 17 , RF interface board  2100  includes wing structures  2110   1 - 2110   4  (i.e., extension structures having perimeters wherein at least a portion of these perimeters extend beyond a perimeter of substrate  2000 ). As further shown in  FIG. 17 , wing structures  2110   1 - 2110   4  include wiring groups  2120   1 - 2120   4  (shown in phantom), respectively. In accordance with one or more embodiments of the present invention, wiring groups  2120   1 - 2120   4  provide electrical connections from RF I/O BGA pads on a top side of RF interface board  2100  to RF coaxial cable connectors (not shown) on a bottom side of RF interface board  2100 . In addition, RF interface board  2100  includes wiring (not shown) that provides electrical connections from non-RF I/O BGA pads on the top side of RF interface board  2100  to non-RF I/O BGA pads on the bottom side of RF interface board  2100 . RF interface board  2100  may be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art using materials utilized to fabricate a rigid substrate, a semi-flex substrate, a flex substrate, a silicon/glass structure, and so forth, and using any one of a number of RF coaxial cable connectors that are well known to those of ordinary skill in the art. Note that although RF interface board  2100  described above includes wing structures  2110   1 - 2110   4  shown in  FIG. 17 , further embodiments of the present invention exist in which structures used to connect to RF I/O may take any one of a number of forms such as, for example and without limitation, a single board whose periphery carries RF connectors, one or more wings, and so forth.  
      In use for testing, structure  2001  might be connected to, for example and without limitation, a Pogo Tower (a Pogo Tower is a type of connector that is well known to those of ordinary skill in the art and which is used in some commercial test systems to provide an interface to a Probe Card). For example, in such an arrangement, a top side of the Pogo Tower would be connected to non-RF test connectors  2210  (shown in  FIG. 16 ) on a bottom side of Probe Card  2200  in a well known manner, and a bottom side of the Pogo Tower would be connected to a test system interface board in a well known manner. Further, RF test coaxial cables  2110  (which are routed through channels  2220  in Probe Card  2200 ) would be further routed through a central aperture in the Pogo Tower (many commercial embodiments of a Pogo Tower are fabricated to have an aperture in the center), and would be connected directly to the test system interface.  
      In accordance with one or more such embodiments of the present invention, substrate  2000  may be any of the substrates that have been described herein such as, for example and without limitation, a rigid substrate, a flex substrate, a semi-flex substrate, a silicon/glass substrate (for example and without limitation, a silicon/glass structure that includes MEMS-type spring contactors), and so forth. In addition, Probe Card  2200  may be any one of a number of Probe Cards that are well known to those of ordinary skill in the art. Channels  2220  in Probe Card  2200  may be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by drilling. Further, channels  2220  are made large enough to enable the desired number of coaxial cables to fit through.  
      In fabricating structure  2001  described above, one may utilize any of the above-described methods to connect substrate  2000  to RF interface board  2100 , and to connect RF interface board  2100  to Probe Card  2200 . Thus, as one can readily appreciate from the above, and in accordance with one or more such embodiments of the present invention, the coaxial cables are connected close to contactors  2010 , and the Pogo Tower is bypassed, thereby decreasing an electrical path between contactors on the substrate and the Test System. As a result, it is expected that better electrical performance will be achieved when using the inventive structures when compared to that of structures fabricated in accordance with the prior art.  
      One or more further embodiments of the present invention relate to a structure for testing circuits that is fabricated in accordance with one or more embodiments of the present invention.  FIG. 18  is a cross sectional view of structure  3000  that is fabricated in accordance with one or more embodiments of the present invention. As shown in  FIG. 18 , structure  3000  includes flex substrate  3010 . Flex substrate  3010  is fabricated from any one of a number of flexible materials that are well known to those of ordinary skill in the art such as, for example and without limitation, polyimide, liquid crystal polymer (“LCP”), Teflon, and so forth. In addition, flex substrate  3010  has circuitry on both sides, or is a multi-layer structure (for example and without limitation, to provide a multi-level fan-out) depending on the amount of I/O circuitry on a chip to be tested, which multilayer structure may be fabricated in accordance with one or more of the methods described herein. As shown in  FIG. 18 , flexible substrate  3010  has an array of contactors (for example, posts or bumps  3005   1 - 3005   2 ) located on a top or testing side (i.e., a side that contacts an IC on a wafer), which contactors make contact with bumped or non-bumped pads of a IC chip on a wafer during testing. Posts or bumps on the top side of flex substrate  3010  (for example, posts or bumps  3005   1 - 3005   2 ) are connected with traces through flex substrate  3010  to pads (for example, pads  3015   1 - 3015   2 ) on the bottom side of flex substrate  3010 . In accordance with one or more embodiments of the present invention, pads  3015   1 - 3015   2  are on the periphery of the array of contactors on the top side of flex substrate  3010 , i.e., pads  3015   1 - 3015   2  are not under posts or bumps  3005   1 - 3005   2 . Posts or bumps  3005   1 - 3005   2  may have a height, for example and without limitation, in a range from about 40 μm to about 60 μm. Further, the posts or bumps on the top side of flex substrate  3010 , the traces, and the pads on the bottom side of flex substrate  3010  may be fabricated using any one of a number of methods that are well known to those of ordinary skill in the art. For example and without limitation, the pads (for example, pads  3015   1 - 3015   2 ) on the bottom side of flex substrate  3010  may be fabricated from alloys such as Cu/Ni/Au, Ni/Au and so forth.  
      As further shown in  FIG. 18 , substrate  3020  is a rigid substrate. In accordance with one or more embodiments of the present invention, substrate  3020  has no circuitry. Substrate  3020  may be fabricated, for example and without limitation, from FR-4 glass epoxy substrates, BT epoxy materials, and so forth, and may have a thickness in a range, for example and without limitation, from about 0.5 mm to about 1.5 mm. In accordance with one or more embodiments of the present invention, the area of substrate  3020  (in a plane perpendicular to the plane of  FIG. 18 ) is larger than the area of flex substrate  3010  (also in a plane perpendicular to the plane of  FIG. 18 ). As further shown in  FIG. 18 , substrate  3020  includes vias (for example, vias  3027   1 - 3027   2 ) in an array whose locations are aligned with the locations of the pads (for example, pads  3015   1 - 3015   2 ) on the bottom side of flex substrate  3010 . The vias (for example, vias  3027   1 - 3027   2 ) surround at least a portion of a barrel of electrical connectors having first and second retractable ends such as, for example and without limitation, Pogo pins (for example, Pogo pins  3030   1 - 3030   2 ), wherein the diameter of the vias is a function of the diameter of the barrel of the Pogo pins. The Pogo pins shown in  FIG. 18  (for example, Pogo pins  3030   1 - 3030   2 ) are like Pogo pin  800  described above. As further shown in  FIG. 18 , the vias (for example, vias  3027   1 - 3027   2 ) are disposed so that retractable ends of the Pogo pins (for example, Pogo pins  3030   1 - 3030   2 ) contact pads (for example, pads  3015   1 - 3015   2 ) on the bottom side of flex substrate  3010  when structure  3000  is assembled in the manner described herein.  
      As further shown in  FIG. 18 , compliant adhesive layer  3040  includes vias that are aligned with the pads (for example, pads  3015   1 - 3015   2 ) on the bottom side of flex substrate  3010 . Compliant adhesive layer  3040  may be fabricated using any one of a number of materials that are well known to those of ordinary skill in the art such as, for example and without limitation, a silicon elastomer, a flexible epoxy, and so forth.  
      A pinalignment fixture like that described above may be used in a first stage of a method for assembling structure  3000 . In a first, optional step, a release film such as, for example and without limitation, a Mylar film or a Teflon film, is aligned with, and placed over, a base plate of the pinalignment fixture (as was described above, holes in the release film match the positions of alignment pins). Next, flex substrate  3010  is aligned with, and placed over, the release film on the pinalignment fixture (holes in flex substrate  3010  (not shown) match the positions of the alignment pins). Next, compliant adhesive layer  3040  is aligned with, and placed over flex substrate  3010  on the pin alignment structure (holes in compliant adhesive layer  3040  (not shown) match the positions of the alignment pins). Next, rigid substrate  3020  is aligned with, and placed over compliant adhesive layer  3040  (holes in rigid substrate  3020  (not shown) match the positions of the alignment pins). Next, a weight, for example, an aluminum or stainless steel plate having a thickness in a range, for example and without limitation, from about 10 mm to about 12.7 mm, and having an area of about the same size as that of compliant adhesive layer  3040 , is aligned with, and placed over rigid substrate  3020  to apply pressure to compliant adhesive layer  3040  (holes in the weight match the positions of the alignment pins). Next, flex substrate  3010  may be laminated to rigid substrate  3020  by, for example and without limitation, baking in an oven. The oven temperature may be in a range, for example and without limitation, from about 150° C. to about 200° C., the pressure exerted by the weight may be in a range, for example and without limitation, from about 14 kg/cm 2  to about 28 kg/cm 2 , and the time spent in the oven may be in a range, for example and without limitation, from about 1 hour to about 2 hours. Next, the intermediary structure is removed from the pinalignment structure.  
      As further shown in  FIG. 18 , socket interposer  3050  is formed, for example and without limitation, from plastic such as ULTEM™, Torlon, and so forth. Socket interposer  3050  includes holes (for example, holes  3045   1 - 3045   2 ) in an array whose locations are aligned with the locations of the pads (for example, pads  3015   1 - 3015   2 ) on the bottom side of flex substrate  3010 . As further shown in  FIG. 18 , each of the holes in socket interposer  3050  (for example, holes  3045   1 - 3045   2 ) comprises a hole within a hole for seating the Pogo pins (for example, Pogo pins  3030   1 - 3030   2 ) when structure  3000  is assembled in the manner described herein (also refer to the discussion of connector-holder bottom plate  600  above in conjunction with  FIG. 11  to understand the manner in which such holes retain Pogo pins). Note that one or more alternative embodiments may not utilize the hole within a hole seating mechanism.  
      As further shown in  FIG. 18 , socket interposer  3050  also includes: (a) threaded holes (for example, holes  3047   1 - 3047   2 ) that locate connection mechanisms (for example and without limitation, releasable connection mechanisms) comprised, for example and without limitation, of screws  3052   1 - 3052   2 , which connection mechanisms are used to connect socket interposer  3050  and clamp  3060  (as will be described below); and (b) holes (for example, holes  3049   1 - 3049   2 ) that locate connection mechanisms (for example and without limitation, releasable connection mechanisms) comprised, for example and without limitation, of screws  3055   1 - 3055   2  and nuts  3057   1 - 3057   2 , which connection mechanisms are used to connect Probe Card  3070  and socket interposer  3050  (as will be described below). The thickness of socket interposer  3050  is a function of the length of the Pogo pins. Socket interposer  3050  may be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by injection molding, and the holes may be fabricated therein in accordance with any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by drilling.  
      As further shown in  FIG. 18 , clamp  3060  includes: (a) for example and without limitation, four (4) holes (for example, holes  3061   1 - 3061   2 ) that locate connection mechanisms (for example and without limitation, releasable connection mechanisms) comprised, for example and without limitation, of screws  3052   1 - 3052   2 , which connection mechanisms are used to connect socket interposer  3050  and clamp  3060 ; (b) open region  3080  having an area (in a plane perpendicular to the plane of  FIG. 18 ) that is larger than that of flex substrate  3010  and compliant adhesive layer  3040 ; (c) lip  3069  that fits over, and makes contact, when structure  3000  is assembled, with at least a portion of (and preferably most of) a portion of substrate  3020  that extends beyond compliant adhesive layer  3040  (for example and without limitation, at least two or more edges); and (d) wing  3073  that provides a location wherein clamp  3060  may be connected to socket interposer  3050 .  
      In a second stage of the method for assembling structure  3000 , in a first optional step, a release film such as, for example and without limitation, a Mylar film or a Teflon film, is aligned with, and placed over, a base plate of the pinalignment fixture (as was described above, holes in the release film match the positions of alignment pins). Next, Probe Card  3070  is aligned with, and placed over, the release film on the pinalignment fixture (holes in Probe Card  3070  (not shown) match the positions of the alignment pins). Next, socket interposer  3050  is aligned with, and placed over, Probe Card  3070  on the pinalignment fixture (holes in socket interposer  3050  (not shown) match the positions of the alignment pins). Alignment pins are used on opposite corners and placed through socket interposer  3050  and Probe Card  3070  to align the holes in socket interposer  3050  to the pads on Probe Card  3050 . Next, socket interposer  3050  is connected to Probe Card  3070  using connection mechanisms, for example, by inserting screws (for example,  30551 - 30552 ) through socket interposer  3050  and by affixing nuts (for example, nuts  30571 - 30572 ) to the screws. The alignment pins are then removed. Next, Pogo pins (for example, Pogo pins  30301 - 30302 ) are placed inside the holes (for example, holes  30451 - 30452 ) in socket interposer  3050 . Next, the intermediary structure formed during the first stage is aligned with, and placed over, socket interposer  3050  on the pinalignment fixture (holes in substrate  3020  of the intermediary structure (not shown) match the positions of the alignment pins). Next, clamp  3060  is aligned with, and placed over, substrate  3020  and socket interposer  3050  on the pinaligmnent fixture (holes in clamp  3060  (not shown) match the positions of the alignment pins). Next, clamp  3060  is attached to socket interposer  3050  using connection mechanisms (for example, screws  30521 - 30522 ) to form structure  3000 . The alignment pins going through substrate  3010  and socket interposer  3050  are then removed. At this point, structure  3000  is removed from the pinalignment structure.  
      In accordance with one or more alternative embodiments of the present invention, compliant adhesive layer  3040  of structure  3000  is replaced with a layer wherein an area directly under the post and bumps (for example, posts or bumps  30051 - 30052 ) on the top side of flex substrate  3010  is a compliant adhesive material that may be fabricated using any one of a number of materials that are well known to those of ordinary skill in the art such as, for example and without limitation, a silicon elastomer, a flexible epoxy, and so forth. Then, in accordance with one or more such alternative embodiments of the present invention, the remainder of the layer may be a non-compliant adhesive such as, for example and without limitation, polyimide having an adhesive (for example and without limitation, epoxy, acrylic, epoxy-acrylic, and so forth) on both sides, and so forth. In accordance with one or more further alternative embodiment of the present invention, compliant adhesive layer  3040  of structure  3000  is replaced with a layer wherein an area directly under the post and bumps (for example, posts or bumps  30051 - 30052 ) on the top side of flex substrate  3010  is open (i.e., air or even some other gas). Then, in accordance with one or more such further alternative embodiments of the present invention, the remainder of the layer may be any of the compliant adhesives described above or any of the non-compliant adhesives described above.  
      In accordance with one or more still further alternative embodiments of the present invention, substrate  3020  and socket interposer  3050  of structure  3000  may be fabricated as a single layer. In accordance with one or more such still further alternative embodiments, the above-described assembly procedure would be modified so that the Pogo pins are inserted into the vias in compliant adhesive layer  3040  before substrate  3020  is placed over compliant adhesive layer  3040 . In addition, in accordance with one or more still further alternative embodiments, clamp  3060  may be connected directly to Probe Card  3070 . In accordance with such one or more still further alternative embodiments, socket interposer  3050  (or substrate  3020  if substrate  3020  and socket interposer  3050  are fabricated as a single layer) may either be connected separately to Probe Card  3070 , or be held down by clamp  3060 .  
      One or more of the substrates described above have contactors on one side to contact I/O on an IC, for example, an IC on a wafer (bumped or not), which contactors are formed of posts and/or bumps. However, it should be understood that one or more of the above-described embodiments include substrates wherein the contactors are formed of pads. Such pad contactors are useful, for example, for testing ICs on wafers having bumped I/O.  
      Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.