Patent Publication Number: US-8120373-B2

Title: Stiffener assembly for use with testing devices

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 11/860,406, filed Sep. 24, 2007, entitled “Stiffener Assembly For Use With Testing Devices,” which is a continuation-in-part of U.S. patent application Ser. No. 11/617,929, filed Dec. 29, 2006, entitled “Stiffener Assembly for use with Testing Devices.” The foregoing applications Ser. No. 11/860,406 and Ser. No. 11/617,929 are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to testing of partially or fully completed semiconductor devices and, more particularly, to stiffener assemblies for use in connection with apparatus for testing such devices. 
     2. Description of the Related Art 
     When testing partially or fully completed semiconductor devices formed on a semiconductor substrate, such as integrated circuits and the like, a plurality of contact elements are typically brought into contact with the device to be tested—sometimes referred to as a device under test (or DUT). The contact elements are typically part of a probe card assembly or other similar device coupled to a test mechanism that provides electrical signals to terminals on the DUT in accordance with a predetermined testing protocol. 
     In order to sufficiently and accurately contact all desired terminals of the DUT during a particular testing protocol, the contact elements disposed on the probe card assembly must be brought into contact with the desired terminals of the DUT and must maintain alignment therewith. However, various forces applied to the probe card assembly may cause the assembly to deflect in a manner that may cause misalignment of the contact elements. Accordingly, the probe card assembly generally includes stiffening members and/or assemblies designed to minimize such deflection of the probe card assembly. 
     Generally, such stiffening members or assemblies are disposed above the contact elements in order to minimize deflection of the probe card assembly in regions where the contact elements will be directly affected. However, the probe card assembly may be subject to greater forces than a particular stiffening assembly can compensate for. In addition, restrictions on the space available to design and implement a suitable stiffening assembly may be limited. Moreover, forces applied outboard of the region where the contact elements are disposed may still affect the alignment thereof. 
     Therefore, there is a need for an improved stiffening element for use in the probe card assembly. 
     SUMMARY OF THE INVENTION 
     A stiffener assembly for use with testing devices is provided herein. In some embodiments, a stiffener assembly for use with testing devices can part of a probe card assembly that can include a stiffener assembly comprising an upper stiffener coupled to a plurality of lower stiffeners; and a substrate constrained between the upper stiffener and the plurality of lower stiffeners, the stiffener assembly can restrict non-planar flex of the substrate while facilitating radial movement of the substrate with respect to the stiffener assembly. 
     In some embodiments, a stiffener for use with testing devices can part of a probe card assembly that can include a stiffener assembly comprising an upper stiffener coupled to a lower stiffener and having a plurality of flexures that provide a rigid coupling in a z direction and that facilitate relative movement between the upper stiffener and the lower stiffener in an xy plane; and a substrate constrained between the upper and the lower stiffener, wherein the stiffener assembly can restrict non-planar flex of the substrate while facilitating radial movement of the substrate with respect to the stiffener assembly. 
     In another aspect of the invention, a method of using a probe card assembly is provided. In some embodiments, a method of using a probe card assembly can include providing a probe card assembly having a stiffener assembly comprising an upper stiffener coupled to a plurality of lower stiffeners, a substrate constrained between the upper stiffener and the plurality lower stiffeners, and a probe substrate coupled to the substrate, the probe substrate having a plurality of resilient contact elements extending therefrom; and heating the probe card assembly, wherein the stiffener assembly can restrict non-planar flex of the substrate while facilitating radial movement of the substrate with respect to the stiffener assembly due to differences in thermal expansion between the stiffener assembly and the substrate. 
     In some embodiments, a method of using a probe card assembly can include providing a probe card assembly having a stiffener assembly comprising an upper stiffener coupled to a lower stiffener, and having a plurality of flexures that can provide a rigid coupling between the upper stiffener and the lower stiffener in a z direction and that can facilitate relative movement between the upper stiffener and the lower stiffener in an xy plane, a substrate constrained between the upper and the lower stiffener, and a probe substrate coupled to the substrate, the probe substrate having a plurality of resilient contact elements extending therefrom; and heating the probe card assembly, wherein the stiffener assembly can restrict non-planar flex of the substrate while facilitating radial movement of the substrate with respect to the stiffener assembly due to differences in thermal expansion between the stiffener assembly and the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention and others described below can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  depicts a schematic top view of a stiffener assembly according to some embodiments of the present invention. 
         FIG. 2A  depicts a schematic side view of a probe card assembly according to some embodiments of the present invention, shown in cutaway corresponding to section lines  2 A of the stiffener assembly shown in  FIG. 1 . 
         FIG. 2B  depicts a schematic side view of a probe card assembly according to some embodiments of the present invention, shown in cutaway corresponding to section lines  2 B of the stiffener assembly shown in  FIG. 1 . 
         FIG. 3  depicts an exploded front and side view of a portion of the stiffener assembly of  FIG. 1  in accordance with some embodiments of the present invention. 
         FIG. 4  depicts a probe card assembly having stiffening elements in accordance with some embodiments of the present invention. 
         FIG. 5  depicts a flow chart for testing a substrate in accordance with some embodiments of the present invention. 
         FIG. 6A  depicts a bottom view of a probe card assembly having a stiffening element in accordance with some embodiments of the present invention. 
         FIG. 6B  depicts a partial, cutaway side view of the probe card assembly of  FIG. 6A . 
         FIG. 7  depicts a partial side view, partially in cross-section, of a stiffener assembly in accordance with some embodiments of the present invention. 
     
    
    
     Where possible, identical reference numerals are used herein to designate identical elements that are common to the figures. The images used in the drawings are simplified for illustrative purposes and are not necessarily depicted to scale. 
     DETAILED DESCRIPTION 
     The present invention provides embodiments of stiffener assemblies and probe card assemblies incorporating the same. Methods of use of the stiffener assembly and the probe card assembly are further provided. The stiffener assembly can advantageously provide stiffening of a substrate used with a probe card assembly while significantly reducing the heat transfer between stiffener assembly components, thereby minimizing the thermal mass of the stiffener assembly that must be heated during testing and reducing heating times to bring the stiffener assembly up to temperature. In some embodiments, an inner portion may also be moved relative to an outer portion to assist in orienting a probing plane with a surface to be probed. 
     The Figures and following description provided herein illustratively refer to an exemplary Cartesian coordinate system where the x and y axes are substantially parallel to a plane defined by a stiffener assembly and/or probe card assembly incorporating same, and wherein the z axis is substantially normal, or perpendicular, to such a plane. For example,  FIG. 1  illustratively depicts a top view of a stiffener assembly in an x-y plane, where the z axis would extend perpendicularly into and out of the page.  FIGS. 2A-B  illustratively depict side views in an x-z plane. 
       FIG. 1  depicts a top view of a stiffener assembly  100  according to some embodiments of the present invention. The stiffener assembly  100  is illustratively shown coupled to a substrate  102  to demonstrate an illustrative use of the stiffener assembly  100 . The stiffener assembly  100  is further explained with reference to  FIGS. 2A-B , respectively depicting schematic side views of the stiffener assembly  100  as illustratively used in a probe card assembly according to some embodiments of the present invention.  FIGS. 2A-B  are shown in cutaways corresponding to section lines  2 A and  2 B of the stiffener assembly  100  shown in  FIG. 1 . 
     The stiffener assembly may include an upper stiffener (or multiple upper stiffeners) and a lower stiffener (or multiple lower stiffeners). The upper and lower stiffeners may be utilized to constrain a substrate therebetween to restrict z-direction, or non-planar, movement of the substrate (such as bending, warping, deflection, or the like) while facilitating a radial degree of freedom between the substrate and the stiffener assembly to facilitate relative radial movement therebetween (e.g., expansion and/or contraction of the substrate relative to the stiffener assembly, for example, in the x-y plane). The upper stiffener and the lower stiffener may be coupled together in any suitable manner such as by use of fasteners, bolts, screws, pins, or the like. In some embodiments, the upper stiffener and the lower stiffener may be configured to move laterally with respect to each other via flexures, hinges, or the like. In some embodiments, the upper stiffener may be coupled to the substrate proximate a center of the substrate where there is little or no relative radial movement while remaining uncoupled to the substrate at other locations, thereby providing a radial degree of freedom for the substrate to expand and/or contract relative to the stiffener assembly. 
     For example, in some embodiments, and as shown in  FIG. 1 , the stiffener assembly  100  may include an upper stiffener  101  and a lower stiffener  160 . The upper stiffener  101  and the lower stiffener  160  may be integral (e.g., one piece) or may be separate components. The upper stiffener  101  may be a single element (not shown) or may be made from multiple elements, such as, in a non-limiting example, an inner member  104  and an outer member  106 . The inner member  104  comprises a body  150  that, in some embodiments, can generally have a size and shape corresponding to one or more probe substrates (such as probe substrates  202  shown in  FIGS. 2A-B ) disposed beneath the substrate  102 . The inner member  104  in some instances may rest directly against the substrate  102 . Alternatively, additional layers (not shown) may be disposed between the inner member  104  and the substrate  102 . In some embodiments, one or more locating pins (not shown) may be provided to facilitate alignment of the inner member  104  and the substrate  102 . 
     In some embodiments, the upper stiffener may be coupled to the substrate. The upper stiffener may be coupled to the substrate in any suitable manner, such as bolts, screws, clamps, and the like, and may be coupled to the substrate in any location. In some embodiments, the upper stiffener may be coupled to the substrate in a manner that retains the radial degree of freedom of movement of the substrate relative to the upper stiffener. In some embodiments, the upper stiffener may be coupled to the substrate in a central location. The central location may be a geometric center or the substrate, a thermal center of the substrate, or both. For example, in the embodiment depicted in  FIGS. 1 ,  2 A and  2 B, the inner member  104  may be coupled to the substrate  102  in a central location of the substrate  102  by a screw  105 . The central location of the substrate  102  may be the geometric center and/or the thermal center of the substrate  102 . 
     The inner member  104  may comprise any materials suitable to maintain acceptable rigidity of a probe card assembly (as discussed further below with respect to  FIG. 4 ) when subjected to forces utilized in testing (such as forces used to pre-load the stiffener assembly and/or probe card assembly, applied due to varying energy flows through the stiffener assembly and/or probe card assembly, applied to make sufficient electrical contact with the terminals of a DUT, or the like) and to closely match the thermal strain between the stiffener assembly  100  and the substrate  102  to mitigate shear coupling therebetween. Non-limiting examples of suitable materials include metals and metal alloys such as Kovar®, Invar®, steel, stainless steels, or the like. The materials comprising the inner member  104  may further be selected to facilitate a desired rate of heat transfer, or a desired heat capacity for the inner member  104 . 
     In some embodiments, as shown in  FIG. 2A , a probe substrate alignment mechanism  206  may be provided to locally adjust both the lateral and the planar alignment of probe substrates  202  disposed beneath the inner member  104 . Accordingly, a plurality of openings  124  may be formed through the body  150  of the inner member  104  to facilitate such planar alignment of probe substrates  202 . In some embodiments, the probe substrate alignment mechanism  206  may comprise one or more adjuster plates  208  disposed above the inner member  104 . Each adjuster plate  208  may be coupled to respective pluralities of planar alignment mechanisms  204  that interface with the probe substrates  202 . In some embodiments, the alignment mechanism  204  may be a screw. However, the alignment mechanism  204  may comprise other devices suitable for selectively adjusting planarity of the probe substrates  202 . Each planar alignment mechanism  204  passes through a respective opening  124  in the inner member  104  and a corresponding opening  125  in the substrate  102 . The openings  124 ,  125  may have a larger diameter than the planar alignment mechanisms  204  to facilitate lateral movement thereof with respect to the inner member  104  and the substrate  102 . 
     In operation, the adjuster plates  208  may be laterally positioned to control the respective lateral positions of contact elements formed on respective probe surfaces  210  of the probe substrates  202  with respect to the inner member  104  and the substrate  102 . Once in a desired position, the adjuster plates  208  may be locked into position, for example, by clamping, bolting, or otherwise securing the adjuster plates  208  to the inner member  104 . The planar alignment mechanisms  204  may be individually adjusted to selectively control the planarity of the probe substrates  202  before or after lateral alignment of the probe substrates  202 , or both. 
     Returning to  FIG. 1 , the outer member  106  generally comprises a body  107  having a central opening  140 . The size and shape of the opening  140  can generally correspond to the size and shape of the inner member  104 , such that the outer member  106  substantially circumscribes, or surrounds, the inner member  104 . 
     In some embodiments, a plurality of arms  126  may extend outwardly from the body  107  of the outer member  106  to facilitate stiffening regions  128  of the substrate  102  that are disposed radially outwards of the body  107 . The outwardly extending arms  126  may be formed integrally with the body  107  or may be affixed thereto in any suitable manner able to withstand the forces generated during use. In the embodiment depicted in  FIG. 1 , four such outwardly extending arms  126  are depicted. It is contemplated that greater or fewer arms  126  may be provided. In some embodiments, the outer member  106  can be mechanically coupled to a tester (not shown), e.g., via a plurality of the arms  126 . 
     The outwardly extending arms  126  may further facilitate constraining the substrate  102  to restrict non-planar deflection or movement thereof (for example, from downward pressure along the upper surface of the substrate—as viewed in FIG.  2 A—as might be present from connectors disposed on the upper surface), while at the same time facilitating a radial degree of freedom between the stiffener assembly  100  and the substrate  102 . In some embodiments, the substrate  102  may be movably coupled to the outer member  106 , such that the substrate  102  is free to expand and contract (e.g., radially) with respect to the stiffener assembly  100 . 
     In some embodiments, and as depicted in  FIG. 1 , the lower stiffener  160  may be coupled to the upper stiffener  101  in a manner that facilitates disposing the substrate  102  therebetween, thereby restricting non-planar deflection of the substrate  102  (e.g., constraining the substrate  102 ). The substrate  102 , while constrained between the upper stiffener  101  and the lower stiffener  160  to restrict non-planar deflection or movement of the substrate  102 , retains a degree of radial freedom to facilitate expansion and contraction of the substrate  102  independent of the stiffener assembly  100 . In the embodiment depicted in  FIG. 1 , a plurality of lower stiffeners  160  are provided, each lower stiffener  160  being arranged about the substrate  102  such that together, the plurality of lower stiffeners  160  retain and constrain the substrate  102  between the lower stiffeners  160  and the upper stiffener  101 , as discussed above. 
     In some embodiments, and as depicted in  FIG. 1 , the upper stiffener  101  may comprise the inner member  104 , the outer member  106 , and the arm  126 . The upper stiffener  101  may be coupled to the lower stiffener  160  in any suitable manner, such as by fasteners, bolts, screws, pins, or the like. For example, in some embodiments, each arm  126  may further include an extension  130  having a flange  132  extending therefrom (shown through illustrative cutaway  138  in the substrate  102 ). The flange  132  (and, optionally, the extension  130 ) may form at least part of the lower stiffener  160 . For example, the flange  132  may interface with a slot  134  and corresponding shelf  136  formed in the substrate  102  (revealed via illustrative cutaway  142 ). Interference between the flange  132  and the shelf  136  restricts deflection of the substrate  102 , thereby providing added stability and/or rigidity to the substrate  102  in the regions  128  disposed radially outwards of the body  107  of the outer member  106 . However, co-planar, lateral (e.g., radial) movement of the stiffener assembly  100  with respect to the substrate  102  may still occur due to slippage between the flange  132  and the shelf  136 . 
     In some embodiments—for example, to facilitate construction of the stiffener assembly  100  with a substrate as used in a probe card assembly—the outwardly extending arms  126  and the extensions  130  may be separate components that may be suitably coupled together. Accordingly, one or more mechanisms, such as a screw, may be utilized to couple the outwardly extending arms  126  to the respective extensions  130 . For example, in the embodiment depicted in  FIG. 3 , two holes  302  are provided in the outwardly extending arms  126 . Corresponding holes  304  are provided in the extension  130  to facilitate using screws (not shown) to couple the outwardly extending arms  126  to the extensions  130 . In some embodiments, the dimensions of the extension  130  and flange  132  relative to the slot  134  and shelf  136  formed in the substrate  102  may be selected to facilitate slideable coupling therebetween, thereby allowing lateral movement between the outwardly extending arms  126  and the substrate  102 . 
     It is contemplated that other configurations of the outwardly extending arms  126 , the extensions  130 , and the flanges  132  may also suitably be utilized. For example, the outwardly extending arms  126  and the extensions  130  may be integrally formed and have the flanges  132  coupled thereto. Alternatively, the outwardly extending arms  126 , the extensions  130 , and the flanges  132  may be integrally formed and may be laterally inserted into position with respect to the substrate  102 . In such embodiments, the outwardly extending arms  126  may be coupled to the upper stiffener  101  (such as to the outer member  106 ) after being positioned about the substrate  102 . 
     For example,  FIG. 7  depicts a partial side view, partially in cross-section, of a stiffener assembly having an arm  726 , an extension  730 , and a flange  732  that are integrally formed. The arm  726  is shown removed from the substrate  102  with dashed lines indicating the assembly of the arm  726  with the stiffener  102  and an upper stiffener  701  disposed thereupon. As shown in  FIG. 7 , the extension  730  and the flange  732  may be aligned with the slot  134  and the shelf  136  of the substrate  102  and laterally inserted into position to interface therewith. The arm  726  may be coupled to the upper stiffener  701  in any suitable manner such as by clamps, bolts, screws, pins, or the like. In some embodiments, the arm  726  may have a feature configured to interface with the upper stiffener to facilitate robust coupling therewith. For example, in embodiments represented by  FIG. 7 , the arm  726  may have a protrusion  702  configured to fit in a corresponding recess  704  formed in the upper stiffener  701 . The arm  726 , extension  730 , and flange  732  may otherwise be similar to the arm  126 , extension  130 , and flange  132  described above with respect to  FIG. 1 . 
     Returning to  FIG. 1 , although illustratively shown in  FIG. 1  as part of a stiffener assembly  100  having a multi-piece upper stiffener  101 , it is contemplated that the lower stiffener  160  may be utilized in combination with other stiffening elements or assemblies having other configurations, including one-piece upper stiffening assemblies. In addition, although the lower stiffener  160  is depicted in  FIG. 1  as being disposed on, coupled to, or part of an extending arm, or four extending arms, it is contemplated that the lower stiffener  160  may be coupled to the upper stiffener in other geometries and forms and in greater or fewer numbers. 
     Alternatively or in combination, other embodiments of the lower stiffener  160  may be utilized in combination with embodiments of the upper stiffener  101 . For example,  FIGS. 6A-B  respectively depict a bottom view and a partial sectional side view of a lower stiffener  660  coupled to an upper stiffener  101  and having the substrate  102  disposed therebetween. As shown in  FIG. 6A , the lower stiffener  660  can generally comprise a member  602  that provides continuous support about the substrate  102  proximate a perimeter thereof. The member  602  may generally be larger, the same size as, or smaller than the substrate  102 . The member  602  may have sufficient material thickness such that the lower stiffener  660  may constrain the substrate  102  in a planar or substantially planar orientation while providing a radial degree of freedom to facilitate radial expansion and/or contraction of the substrate  102  relative to the upper stiffener  101  and the lower stiffener  660 . 
     The member  602  of the lower stiffener  660  may be a single element, or may be fabricated from multiple components, such as segments, concentric shapes, or the like, or combinations thereof. The member  602  may have an inner opening  614  that is large enough to accommodate the one or more probe substrates  202 . In some embodiments, the inner opening  614  may have a form that substantially corresponds to the shape of an outer perimeter of the probe substrates  202 . 
     The lower stiffener  660  may be coupled to the upper stiffener  101  in any suitable manner, such as by fasteners, screws, bolts, pins, or the like. In the embodiment depicted in  FIGS. 6A-B , a plurality of screws  608  can be utilized to couple the lower stiffener  660  to the upper stiffener  101  through openings  612  formed in the substrate  102 . In some embodiments, coupling of the lower stiffener  660  to the upper stiffener  101  may be rigid in all directions. In some embodiments, the coupling of the lower stiffener  660  to the upper stiffener  101  may be rigid in a z direction (e.g., up and down as depicted in  FIG. 6B ) In some embodiments, the coupling of the lower stiffener  660  to the upper stiffener  101  may be flexible to facilitate differences in the amount of expansion and/or contraction of the lower stiffener  660  with respect to the upper stiffener  101  and vice-versa (e.g., the coupling may facilitate movement in the xy plane—left, right, up, or down as depicted in  FIG. 6A ). 
     For example, the upper stiffener  101  and/or the lower stiffener  660  may comprise a plurality of flexures to facilitate relative motion between the upper and lower stiffeners  101 ,  660 , respectively. A plurality of flexures  604  in the lower stiffener  660  are illustratively depicted in  FIGS. 6A-B . The embodiments and variations described herein with respect to flexures  604  apply to any flexures that may be disposed in the upper stiffener  101 . In some embodiments, the flexures  604  may be disposed proximate the coupling points between the lower stiffener  660  and the upper stiffener  101 . In some embodiments, the flexures  604  may be formed within or proximate openings  610  disposed in the lower stiffener  660 . Flexible members  606  may extend from the lower stiffener  660  into the openings  610  to a central portion  607  that is suitably sized to allow a robust connection to the upper stiffener  101 . For example, in the embodiment depicted in  FIGS. 6A-B , the central portion  607  can accommodate the screws  608  (or other attachment mechanism) that extend into the upper stiffener  101 . The flexible members  606  may be aligned within the opening  610  to facilitate radial movement of the lower stiffener  660  with respect to the upper stiffener  101 . The number and geometry of the flexures  604  shown in  FIGS. 6A-B  are illustrative only and other numbers of flexures and/or other geometries of the flexures are contemplated. With reference to  FIG. 6A , such a flexure provides rigidity in the connection at screw  608  in a direction perpendicular to the page, yet permits movement in a direction parallel to the page. 
     In some embodiments, the upper and lower stiffeners  101 ,  660  may facilitate radial expansion and/or contraction of the substrate  102  with respect to either or both of the upper and lower stiffeners  101 ,  660  while restricting non-planar deflection of the substrate  102 . For example, the upper and lower stiffeners  101 ,  660  may be coupled together on opposing sides of the substrate  102  (e.g., the substrate  102  may be trapped, or sandwiched, between the upper and lower stiffeners  101 ,  660 , but allowed to slide or float between the upper and lower stiffeners  101 ,  660 ). For example, as illustratively shown in  FIG. 6B , the substrate  102  may have a plurality of oversized slots, holes, passages, or the like (e.g., openings  612 ) through which the coupling mechanism (e.g., screws  608 ) may pass. Similarly, as shown in  FIG. 1 , the upper and lower stiffeners  101 ,  160  are coupled together without being coupled to the substrate  102 . 
     The upper and lowers stiffeners  101 ,  160  and/or  660  (or any components thereof) may comprise any materials suitable to maintain acceptable rigidity of a probe card assembly (as discussed further below with respect to  FIG. 4 ) when subjected to forces utilized in testing (such as forces used to pre-load the stiffener assembly and/or probe card assembly, applied due to varying energy flows through the stiffener assembly and/or probe card assembly, applied to make sufficient electrical contact with the terminals of a DUT, or the like). The materials comprising these components may also be selected to closely match the thermal strain between the stiffener assembly  100  and the substrate  102  to mitigate shear coupling therebetween. Non-limiting examples of suitable materials include metals and metal alloys such as Kovar®, Invar®, steel, stainless steels, metal matrix composites, ceramics, cermets, or the like. In any specific embodiment, the lower stiffener (or any components thereof) may be made from the same or different materials as the upper stiffener (or any components thereof). 
     In embodiments where the upper stiffener  101  includes and inner member  104  and an outer member  106 , the materials comprising the outer member  106  may be selected to facilitate a desired rate of heat transfer, or a desired heat capacity for the inner member  104 . The inner and outer members  104 ,  106  may comprise the same or different materials. Moreover, the materials comprising the inner and outer members  104 ,  106  may advantageously be selected to provide similar or different thermal characteristics to the inner and outer members  104 ,  106 . For example, in some embodiments, the inner member  104  may have a low heat capacity and/or a high heat transfer rate to facilitate rapid heating of the inner member  104  to process temperatures during testing. In some embodiments, the outer member  106  may have a high heat capacity and/or a low heat transfer rate to facilitate preventing heat from flowing out of the inner member  104  through the outer member  106 . It is contemplated that the thermal characteristics of the inner and outer members  104 ,  106  may be reversed from the above description depending upon the specific application. 
     Returning to  FIG. 1 , a gap  108  may be maintained between the inner and outer members  104 ,  106 , such that the members are disposed in a predominantly spaced apart relation with respect to each other. The gap  108  can restrict conductive heat transfer between the inner and outer members  104 ,  106 , thereby facilitating greater control over the desired thermal characteristics of the stiffener assembly  100 . 
     A plurality of alignment mechanisms  110  may be provided for orienting the inner and outer members  104 ,  106  with respect to each other. In the embodiment depicted in  FIG. 1 , three such alignment mechanisms  110  are shown. It is contemplated that greater or fewer alignment mechanisms may be provided. Each alignment mechanism  110  may be additionally utilized to transfer forces applied to a lower surface of the inner member  104  to the outer member  106  (for example, when contacting a DUT with contact elements of the probe substrate  202 ). Furthermore, the plurality of alignment mechanisms  110  may provide the predominant conductive heat transfer passageway between the inner and outer members  104 ,  106  due to the maintenance of the gap  108  therebetween. By utilizing such alignment mechanisms  110  to position the inner and outer members  104 ,  106  with respect to each other while providing the gap  108  therebetween, the stiffener assembly  100  is advantageously strongly mechanically coupled (thereby facilitating stiffening of a substrate or probe card assembly in which the stiffener assembly  100  is being used), and at the same time loosely thermally coupled (thereby facilitating reduced heat ramp-up, or soak, times required to reach steady state prior to testing). 
     In some embodiments, the alignment mechanism  110  may comprise a protrusion extending from one of the inner or outer members  104 ,  106  that interfaces with a recess formed in the other of the inner or outer members  104 ,  106 , and an actuator for controlling the relative distance between the inner and outer members  104 ,  106  at the location of the alignment mechanism  110 . For example, in the illustrative embodiments shown in  FIGS. 1 and 2B , a protrusion  112  extends from the inner member  104  into a recess  212  provided in the outer member  106 . The protrusion  112  and the recess  212  are sized to maintain the gap  108  between the inner and outer members  104 ,  106 . An actuator  114  extends between the inner and outer members  104 ,  106  and may be used to selectively control the distance therebetween, thereby selectively controlling the relative positions of the inner and outer members  104 ,  106 . In combination with other alignment mechanisms  110  disposed about the stiffener assembly  110 , the alignment mechanisms  110  may control the planar alignment between the inner and outer members  104 ,  106 , thereby advantageously controlling the planar alignment of the probe substrates  202  while maintaining rigid support of the substrate  102 . In some embodiments, the actuator  114  may be a screw, such as a set screw. Alternatively, other actuatable mechanisms may be utilized. 
     In some embodiments, a plurality of lateral alignment mechanisms  116  may be provided to facilitate lateral alignment of the inner and outer members  104 ,  106  and/or provide additional transfer of forces from the inner member  104  to the outer member  106 . In the embodiment depicted in  FIG. 1 , six such lateral alignment mechanisms  116  are provided. It is contemplated that greater or fewer lateral alignment mechanisms  116  may be provided. In some embodiments, the lateral alignment mechanism  116  may comprise a protrusion  118  extending into a recess similarly described above with respect to alignment mechanism  110 . Optionally, an actuatable mechanism  120 , such as a set screw, may further be provided to assist in restricting lateral movement and/or deflection of the inner member  104  with respect to the outer member  106 . The actuatable mechanism  120  provides minimal additional points of conductive thermal transfer between the inner and outer members  104 ,  106 , thereby maintaining the low rate of conductive thermal transfer therebetween. 
     Optionally, one or more flexures  122  may be provided for upwardly biasing the inner member  104  with respect to the outer member  106 . The flexures  122  may additionally provide additional x-y rigidity to the stiffener assembly  100  as well as z-compliance. The flexures  122  provide low conductive thermal transfer rates between the inner and outer members  104 ,  106 , due to the small cross sectional area of the flexure, thereby maintaining the low rate of conductive thermal transfer between the inner and outer members  104 ,  106 . The heat transfer between the stiffener members may be further controlled by selection of the material properties of the flexures  122 . Although three flexures  122  are shown in  FIG. 1 , greater or fewer flexures may be provided. Furthermore, although the flexures  122  are illustrated generally as rectangular (as viewed looking toward  FIG. 1 ), they could be other shapes as well. 
       FIG. 4  depicts a schematic side view of a probe card assembly  400  utilizing a stiffener assembly  100  according to some embodiments of the present invention. The stiffener assembly  100  shown in  FIG. 4  illustratively comprises an upper stiffener  101 , a lower stiffener  160 , and a lower stiffener  660 . It is contemplated that the stiffener assembly  100  may comprise either of lower stiffeners  160 ,  660  alone or in combination. The exemplary probe card assembly  400  illustrated in  FIG. 4  can be used to test one or more electronic devices (represented by DUT  428 ). The DUT  428  can be any electronic device or devices to be tested. Non-limiting examples of a suitable DUT include one or more dies of an unsingulated semiconductor wafer, one or more semiconductor dies singulated from a wafer (packaged or unpackaged), an array of singulated semiconductor dies disposed in a carrier or other holding device, one or more multi-die electronics modules, one or more printed circuit boards, or any other type of electronic device or devices. The term DUT, as used herein, refers to one or a plurality of such electronic devices. 
     The probe card assembly  400  generally acts as an interface between a tester (not shown) and the DUT  428 . The tester, which can be a computer or a computer system, typically controls testing of the DUT  428 , for example, by generating test data to be input into the DUT  428 , and receiving and evaluating response data generated by the DUT  428  in response to the test data. The probe card assembly  400  includes electrical connectors  404  configured to make electrical connections with a plurality of communications channels (not shown) from the tester. In some embodiments, the connectors  404  may be configured to interface with removable connectors (such as zero insertion force, or ZIF, connectors) configured to be removably coupled to the probe card assembly  400 . In some embodiments, the coupling of the connectors  404  to the probe card assembly  400  causes the application of a force to the upper surface of the probe card assembly  400 . This force may be sufficient to cause deformation of the probe card assembly or components thereof (such as the various substrates that may be part of the probe card assembly as described herein). The embodiments of the stiffener assembly  100  described herein may facilitate restricting the deformation, or flexing, of the probe card assembly  400 , or any substrates therein, due to the forces arising from coupling of the connectors  404  to the probe card assembly  400  (as well as due to any other forces arising in operation of the probe card assembly). 
     The probe card assembly  400  also includes one or more resilient contact elements  426  configured to be pressed against, and thus make temporary electrical connections with, one or more input and/or output terminals  420  of DUT  428 . The resilient contact elements  426  are typically configured to correspond to the terminals  420  of the DUT  428  and may be arranged in one or more arrays having a desired geometry. 
     The probe card assembly  400  may include one or more substrates configured to support the connectors  404  and the resilient contact elements  426  and to provide electrical connections therebetween. The exemplary probe card assembly  400  shown in  FIG. 4  has three such substrates, although in other implementations, the probe card assembly  400  can have more or fewer substrates. In the embodiment depicted in  FIG. 4 , the probe card assembly  400  includes a wiring substrate  402 , an interposer substrate  408 , and a probe substrate  424 . The wiring substrate  402 , the interposer substrate  408 , and the probe substrate  424  can generally be made of any type of suitable material or materials, such as, without limitation, printed circuit boards, ceramics, organic or inorganic materials, and the like, or combinations thereof. As shown in  FIG. 4 , the stiffener assembly  100  may be coupled to the wiring substrate  402 . The stiffener assembly  100  may be utilized, as described above, to maintain the respective tips of the resilient contact elements in a configuration, or topography, within a pre-defined tolerance of a corresponding topography of the respective top surfaces of the terminals  420  of the DUT  428 . In some embodiments the tolerance is within  30  microns. In some embodiments, the topography is substantially planar. In some embodiments, the topography may be non-planar. 
     Electrically conductive paths (not shown) are typically provided from the connectors  404  through the various substrates to the resilient contact elements  426  and components  430 . For example, in the embodiment depicted in  FIG. 4 , electrically conductive paths (not shown) may be provided from the connectors  404  through the wiring substrate  402  to a plurality of electrically conductive spring interconnect structures  406 . Other electrically conductive paths (not shown) may be provided from the spring interconnect structures  406  through the interposer substrate  408  to a plurality of electrically conductive spring interconnect structures  419 . Still other electrically conductive paths (not shown) may further be provided from the spring interconnect structures  419  through the probe substrate  424  to the resilient contact elements  426 . The electrically conductive paths through the wiring substrate  402 , the interposer substrate  408 , and the probe substrate  424  can comprise electrically conductive vias, traces, or the like, that may be disposed on, within, and/or through the wiring substrate  402 , the interposer substrate  408 , and the probe substrate  424 . 
     The wiring substrate  402 , the interposer substrate  408 , and the probe substrate  424  may be held together by one or more brackets  422  and/or other suitable means (such as by bolts, screws, or other suitable fasteners). The configuration of the probe card assembly  400  shown in  FIG. 4  is exemplary only and is simplified for ease of illustration and discussion and many variations, modifications, and additions are contemplated. For example, a probe card assembly may have fewer or more substrates (e.g.,  402 ,  408 ,  424 ) than the probe card assembly  400  shown in  FIG. 4 . As another example, a probe card assembly may have more than one probe substrate (e.g.,  424 ), and each such probe substrate may be independently adjustable (as described above with respect to  FIGS. 1-2 ). Other non-limiting examples of probe card assemblies with multiple probe substrates are disclosed in U.S. patent application Ser. No. 11/165,833, filed Jun. 24, 2005. Additional non-limiting examples of probe card assemblies are illustrated in U.S. Pat. No. 5,974,662, issued Nov. 2, 1999 and U.S. Pat. No. 6,509,751, issued Jan. 21, 2003, as well as in the aforementioned U.S. patent application Ser. No. 11/165,833. It is contemplated that various features of the probe card assemblies described in those patents and application may be implemented in the probe card assembly  400  shown in  FIG. 4  and that the probe card assemblies described in the aforementioned patents and application may benefit from the use of the inventive stiffener assembly disclosed herein. 
     Typically, the inner and outer members of the stiffener assembly  100  may be aligned relative to each other, as described above, to provide an initial planar and/or lateral orientation of the probe substrates  424  and/or resilient contact elements  426  disposed thereon during an initial assembly of the probe card assembly  400 . In addition, the inner and outer members of the stiffener assembly  100  may further be moved relative to each other for further planar and/or lateral adjustment, for example, after the probe card assembly  400  is installed in a particular testing apparatus to compensate for planarity and/or lateral positional variations in particular probers/testers being utilized and/or particular DUTs being tested. 
     In operation, the resilient contact elements  426  are brought into contact with the terminals  420  of the DUT  428  by moving at least one of the DUT  428  or the probe card assembly  400 . Typically, the DUT  428  can be disposed on a movable support disposed in the test system (not shown) that moves the DUT  428  into sufficient contact with the resilient contact elements  426  to provide reliable electrical contact with the terminals  420 . The DUT  428  can then tested per a pre-determined protocol as contained in the memory of the tester. For example, the tester may generate power and test signals that are provided through the probe card assembly  400  to the DUT  428 . Response signals generated by the DUT  428  in response to the test signals are similarly carried through the probe card assembly  400  to the tester, which may then analyze the response signals and determine whether the DUT  428  responded correctly to the test signals. Typically, the DUT  428  is tested at an elevated temperature (for example, up to 250 degrees Celsius for wafer level burn in). Accordingly, the probe card assembly  450  is typically preheated to a temperature equal to or within a given tolerance of the testing temperature. The stiffener assembly  100  embodiments having inner and outer members  104 ,  106  may facilitate rapid heating times due to the reduced thermal mass of the stiffener assembly that is required to be heated (e.g., the inner member  104 ). In some embodiments, the stiffener assembly  100  may also facilitate independent radial expansion and/or contraction of the substrate with respect to both of the upper and lower stiffeners  101 ,  160 , and/or  660 , as described above, due to the heating and/or cooling of components. 
     When moving the DUT  428  to contact the resilient contact elements  426  of the probe card assembly  400 , the DUT  428  typically continues to move towards the probe card assembly  400  until all of the resilient contact elements  426  come into sufficient contact with the terminals  420 . Due to one or both of the non-planarity of the respective tips of the resilient contact elements  426  disposed on the probe card assembly  400  and the variations of the heights of the terminals  420 , the DUT  428  may continue to move towards the probe card assembly  400  for an additional non-limiting exemplary range of about 1-4 mils (about 25.4-102 μm) after the initial contact of the first resilient contact element  426  to contact the DUT  428  (sometimes referred to as overtravel). The actual amount of overtravel depends on the characteristics of the non-planarity of the respective tips of the resilient contact elements  426  and/or the variations in height of the terminals  420 . Accordingly, some of the resilient contact elements  426  may undergo more deflection than others. However, the overtravel requirement imparts forces to the probe substrate  424  that are transferred to the wiring substrate  402 . The stiffener assembly  100  facilitates restricting any bending, or deflection of the wiring substrate  402  that may undesirably cause the positions of the tips of the contact elements  426  to move and possibly lose contact with the terminals  420  of the DUT  428 . The stiffener assembly  100  may restrict flex of the substrate either through use of the upper stiffener  101  alone, or through use of the upper stiffener  101  in combination with the lower stiffeners  160  and/or  660 , as described above. In some embodiments, the stiffener assembly  100  may additionally provide a radial degree of freedom of movement of the substrate to facilitate independent radial movement (e.g., expansion and/or contraction) of the substrate relative to the stiffener assembly  100  (or components thereof). 
     For example,  FIG. 5  depicts a process  500  for testing a semiconductor device, or DUT, utilizing a probe card assembly  400  as described above with respect to  FIG. 4  according to some embodiments of the invention. The exemplary process  500  begins at  502 , where a probe card assembly  400  is provided having a stiffener assembly  100  coupled thereto. Typically, a plane of the inner member  104  of the stiffener assembly  100  may be adjusted relative to a plane of the outer member  106  via alignment mechanisms  110 . In addition, the inner member  104  may be laterally adjusted relative to the outer member  106  and/or the probe substrates  424  may be laterally adjusted, as discussed above. Optionally, at  504 , the probe card assembly  400  may be heated. Next, at  506 , a device to be tested may be brought into contact with respective tips of the resilient contact elements  426  of the probe card assembly  400 . 
     Thus, stiffener assemblies and probe card assemblies incorporating the same have been provided herein. The stiffener assembly may comprise components that are strongly mechanically and loosely thermally coupled, thereby advantageously providing stiffening of a substrate in use with a probe card assembly while minimizing heat transfer between stiffener assembly components. The minimized heat transfer between stiffener assembly components facilitates minimizing the thermal mass of the stiffener assembly that must be heated during testing, thereby reducing heating times to bring the stiffener assembly up to temperature. The stiffener assembly may further restrict flexing of a substrate with which the stiffener assembly is used, and, may further facilitate independent radial expansion and/or contraction of the substrate with respect to the stiffener assembly components. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.