Abstract:
A composite spring contact structure includes a structural component and a conduction component distinct from each other and having differing mechanical and electrical characteristics. The structural component can include a group of carbon nanotubes. A mechanical characteristic of the composite spring contact structure can be dominated by a mechanical characteristic of the structural component, and an electrical characteristic of the composite spring contact structure can be dominated by an electrical characteristic of the conduction component. Composite spring contact structures can be used in probe cards and other electronic devices. Various ways of making contact structures are also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The application is a Continuation in Part of co-pending U.S. patent application Ser. No. 11/872,008, filed Oct. 13, 2007, entitled “Making and Using Carbon Nanotube Probes.” 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/093,677, filed Sep. 2, 2008, entitled “Carbon Nanotube Spring Contact Structures with Mechanical and Electrical Components.” 
    
    
     BACKGROUND 
     Electrically conductive spring contact structures on an electronic device can make temporary, pressure based electrical connections with terminals or other such input and/or outputs of a second electronic device. For example, the spring contact structures on the electronic device can be pressed against the terminals of the second electronic device to make temporary electrical connections between the spring contact structures and the terminals and thus between the electronic device and the second electronic device. Embodiments of the present invention are directed to improvements in such spring contact structures, processes of making such spring contact structures, and applications of such spring contact structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of a spring contact structure comprising a mechanical component and an electrical component according to some embodiments of the invention. 
         FIGS. 2A and 2B  illustrate an example of a spring contact structure comprising a carbon nanotube structure and an electrical wire according to some embodiments of the invention. 
         FIGS. 3-5  illustrate an example of a process of making a spring contact structure like the spring contact structure of  FIGS. 2A and 2B  according to some embodiments of the invention. 
         FIGS. 6-8  illustrate another example of a process of making a spring contact structure like the spring contact structure of  FIGS. 2A and 2B  according to some embodiments of the invention. 
         FIGS. 9A and 9B  illustrate an example of a spring contact structure comprising carbon nanotube columns and electrical wires according to some embodiments of the invention. 
         FIGS. 10-12  illustrate an example of a process of making a spring contact structure like the spring contact structure of  FIGS. 9A and 9B  according to some embodiments of the invention. 
         FIG. 13  illustrate an example of a spring contact structure comprising a carbon nanotube structure and an electrical connection according to some embodiments of the invention. 
         FIGS. 14-17  illustrate an example of a process of making a spring contact structure like the spring contact structure of  FIG. 13  according to some embodiments of the invention. 
         FIGS. 18A and 18B  illustrate an example of a spring contact structure comprising an electrically conductive material in a hollow portion of a carbon nanotube structure according to some embodiments of the invention. 
         FIG. 19  illustrates a test system with a probe card assembly that can include spring contact structures comprising a mechanical component and an electrical component according to some embodiments of the invention. 
         FIG. 20  illustrates a test socket that can include spring contact structures comprising a mechanical component and an electrical component according to some embodiments of the invention. 
         FIG. 21  illustrates an example of a spring contact structure comprising a carbon nanotube structure and serpentine electrical conductor disposed in a hollow portion of the carbon nanotube structure according to some embodiments of the invention. 
         FIG. 22  illustrates an example of a spring contact structure comprising a carbon nanotube structure and coiled electrical conductor disposed in a hollow portion of the carbon nanotube structure according to some embodiments of the invention. 
         FIG. 23  illustrates an example of a spring contact structure comprising a carbon nanotube structure and an electrical connection separated from the carbon nanotube structure by a gap according to some embodiments of the invention. 
         FIGS. 24A-24C  illustrate an example of a spring contact structure comprising a carbon nanotube structure with an open portion and an electrical connection disposed in the open portion according to some embodiments of the invention. 
         FIG. 25  illustrates another example of a spring contact structure comprising a carbon nanotube structure with an open portion and an electrical connection disposed in the open portion according to some embodiments of the invention. 
         FIGS. 26A-26B  illustrate an example of a process of making a spring contact structure according to some embodiments of the invention. 
         FIGS. 27A-27B  illustrate another example of a process of making a spring contact structure according to some embodiments of the invention. 
         FIGS. 28A-34B  illustrate another example of a process of making a spring contact structure according to some embodiments of the invention. 
         FIGS. 28A-36B  illustrate another example of a process of making a spring contact structure according to some embodiments of the invention. 
         FIGS. 37A-39B  illustrate additional operations that can be included in a process of making a spring contact structure according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     This specification describes exemplary embodiments and applications of the invention. The invention, however, is not limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. Moreover, the Figures may show simplified or partial views, and the dimensions of elements in the Figures may be exaggerated or otherwise not in proportion for clarity. In addition, as the terms “on” and “attached to” are used herein, one object (e.g., a material, a layer, a substrate, etc.) can be “on” or “attached to” another object regardless of whether the one object is directly on or attached to the other object or there are one or more intervening objects between the one object and the other object. Also, directions (e.g., above, below, top, bottom, side, up, down, under, over, upper, lower, horizontal, vertical, “x,” “y,” “z,” etc.), if provided, are relative and provided solely by way of example and for ease of illustration and discussion and not by way of limitation. In addition, where reference is made to a list of elements (e.g., elements a, b, c), such reference is intended to include any one of the listed elements by itself, any combination of less than all of the listed elements, and/or a combination of all of the listed elements. 
       FIG. 1  illustrates a schematic depiction of a spring contact structure  104  on a substrate  102  according to some embodiments of the invention. Spring contact structure  104  can be for making pressure based temporary electrical connections with a terminal  112  of an electrical device  110 . For example, spring contact structure  104  can be pressed against terminal  112 . Spring characteristics of contact structure  104  can create a force against terminal  112  that creates an electrical connection between spring contact structure  104  and terminal  112  while spring contact structure  104  is pressed against terminal  112 . Spring contact structure  104  can be electrically connected to a terminal  114  (which can be connected to external or internal wiring (not shown) on or in substrate  102 ), and spring contact structure  104  can thus create a temporary electrical connection between terminal  112  of electrical device  110  and terminal  114  of substrate  102 . These temporary electrical connections can be used, for example, to test electrical functionality, and/or otherwise interact with the electrical device  110 . 
     As shown in  FIG. 1 , spring contact structure  104  can comprise a mechanical component  106  (a non-limiting example of a structural component) that provides dominant mechanical characteristics of the spring contact structure  104  and an electrical component  108  (a non-limiting example of a conduction component) that provides dominant electrical characteristics of the spring contact structure  104 . For example, one or more mechanical characteristics (e.g., spring constant, elastic range, etc.) of spring contact structure  104  can be substantially the same as corresponding mechanical characteristics of the mechanical component  106 . In some embodiments, this can mean that mechanical characteristics of the electrical component  108  make a negligible contribution to the mechanical characteristics of the spring contact structure  104 . Similarly, one or more electrical characteristics (e.g., electrical resistance or conductivity) of the spring contact structure  104  can be substantially the same as corresponding electrical characteristics of the electrical component  108 , which can mean in some embodiments that electrical characteristics of the mechanical component  106  make a negligible contribution to the electrical characteristics of the spring contact structure  104 . Alternatively, in some embodiments, the mechanical component  106  can have electrical characteristics that contribute somewhat or significantly to the overall electrical characteristics of the spring contact structure  104 . For example, in some embodiments, the electrical characteristics of the mechanical component  106  can be approximately the same as the electrical characteristics of the electrical component  108 . 
     Moreover, in some embodiments, the mechanical component  106  can be mechanically decoupled from the electrical component  108 . Mechanically decoupled means: (1) the electrical conductivity (or resistance) of the electrical component  108  is not appreciably changed by elastic deformation of the mechanical component  106 , and (2) the electrical component  108  does not appreciably affect the mechanical characteristics of the mechanical component  106 . Alternatively or in addition, the electrical component  108  can be electrically decoupled from the mechanical component  106 . Electrically decoupled means: (1) the mechanical properties of the mechanical component  106  are not appreciably changed by electrical conduction through electrical component  108 , and (2) the mechanical component  106  does not appreciably affect the electrical characteristics of electrical component  108 . 
     Mechanical component  106  can be resilient. In other words, the mechanical component can be capable of springing back to its original form or position after being bent or compressed by an applied force. In other words, mechanical component  106  can be elastically deformable over a predefined elastic range of forces. This means that a force within the predefined elastic range applied to mechanical component  106  can deform mechanical component  106 , but when the force is removed, mechanical component  106  will return substantially to its original position and shape. For example, the mechanical component  106  can behave elastically over a range of about 0.1-50 grams (g) of applied force, although operation above or below this range can also be provided. As particular (though non-limiting) examples, the elastic range can be between 0.1 g-1 g or between 1 g-3 g. The electrical component  108  can be designed to move with the mechanical component  106  or otherwise constrained so that the electrical component  108  and mechanical component  106  move together. Mechanical component  106  can be configured to have predefined mechanical characteristics including but not limited to an elastic range, a spring constant, etc. In some cases, mechanical component  106  can experience plastic deformation (e.g., after many deformations of the mechanical component  106 ). Electrical component  108  need not have such mechanical characteristics. For example, electrical component  108  can be plastically deformable. For example, application of a force in the elastic range of mechanical component  106  can deform electrical component  108 , which will not, by itself, return to its original position or shape upon removal of the force. Alternatively, electrical component  108  can be elastically deformable. In such a case, however, the counter force generated by the mechanical component  106  can dominate and be substantially equal to the counter force generated by the spring contact structure  104  in response to a deforming force applied to the contact structure  104 . 
     Regardless of whether the electrical component  108  is elastically or plastically deformable, electrical component  108  can be configured to have predefined electrical characteristics such as, without limitation, a desired electrical resistance (or conductivity). Mechanical component  106  need not have such electrical characteristics. For example, mechanical component  106  can have a significantly higher electrical resistance than electrical component  108 . 
     Note that the depiction in  FIG. 1  is conceptual only and is intended to show only that spring contact structure  104  can have two functional components. The depiction in  FIG. 1  is not intended to convey any particular spatial, structural, or other such relationship of the mechanical component  106  to the electrical component  108 . For example, although shown side-by-side in  FIG. 1 , the mechanical component  106  and the electrical component  108  need not be side-by-side. As another non-limiting example, the mechanical component  106  need not be a single entity, nor does the electrical component  108  need to be a single entity. 
     As mentioned, the mechanical component  106  can provide dominant mechanical characteristics of the spring contact structure  104 , and as such, the mechanical component  106  can be selected and/or optimized to provide desired mechanical characteristics of spring contact structure  104 . In some embodiments, the mechanical component  106  can be a carbon nanotube structure (e.g., a structure comprising vertically aligned carbon nanotubes). Carbon nanotube structures can have mechanical properties (e.g., elastic range, spring constant, etc.) that are desirable in spring contact structure  104 . Untreated carbon nanotube structures, however, do not typically have sufficiently low electrical resistance desired for spring contact structure  104 , and treating such a carbon nanotube structure and/or individual carbon nanotubes to decrease electrical resistance typically also changes the mechanical properties of the carbon nanotube structure. The carbon nanotube structure that constitutes mechanical component  106  in  FIG. 1  need not be treated to decrease its electrical resistance because spring contact structure  104  includes electrical component  108 . Electrical component  108  can be any structure with the desired electrical characteristics (e.g., low electrical resistance) of spring contact structure  104 . It is noted that electrical component  108  need not be selected for or treated to enhance its mechanical properties because mechanical component  106  provides the dominant mechanical properties of spring contact structure  104 . 
     The carbon nanotube structure that constitutes mechanical component  106  in  FIG. 1  can comprise, without limitation, one or more columns made of vertically aligned carbon nanotubes, which can be formed using any suitable process for forming columns of vertically aligned carbon nanotubes. For example and not by way of limitation, mechanical component  106  can comprise a column of vertically aligned carbon nanotubes grown on substrate  102  (e.g., on a terminal  114  of substrate  102 ). Alternatively, mechanical component  106  can comprise a column of vertically aligned carbon nanotubes grown on another substrate (not shown) and transferred to substrate  102  (e.g., to a terminal  114  of substrate  102 ). Moreover, whether grown on substrate  102  or on another substrate (not shown), the column of vertically aligned carbon nanotubes can be grown using any suitable process. For example and not by way of limitation, the column of vertically aligned carbon nanotubes can be grown using a floating catalyst process or a fixed catalyst process. In a floating catalyst process, a column of carbon nanotubes can be grown on a surface of a growth material (e.g., a seed layer, an oxide film on any material) by exposing the growth material to a material (e.g., a gas) comprising a catalyst (e.g., ferrocene) and a source of carbon (e.g., xylene). In a fixed catalyst process, a column of carbon nanotubes can be grown on a surface of a catalyst layer (e.g., iron) by exposing the catalyst layer to a material (e.g., a gas) comprising a source of carbon (e.g., hydrocarbon gas). 
     For example and not by way of limitation, a floating catalyst process will now be described. Carbon nanotubes are grown on substrate  102  by providing materials (e.g., a gas) comprising a catalyst and a source of carbon in the presence of proper ambient conditions. For example, substrate  102  can be placed in an interior of an enclosure such as a furnace (not shown), and the interior of the enclosure can be heated and a gas comprising a catalyst and a source of carbon can be introduced (e.g., pumped) into the interior of the enclosure. The specific catalyst material, carbon source material, and any other materials and the concentrations and mixtures of those materials as well as the specific ambient conditions (e.g., temperature) can be referred to as a “recipe,” and any recipe suitable for growing carbon nanotubes on growth surfaces can be used. 
     The following is a non-limiting, exemplary recipe that can be used to grow carbon nanotubes. Substrate  102  can be placed in a furnace (not shown), which can be heated to about 750° Celsius. A gas comprising xylene (C8H10) as a carbon source and ferrocene (Fe(C5H5)2) as a catalyst can be mixed with a carrier gas (e.g., argon or another generally inert gas) and introduced (e.g., pumped) into the furnace (not shown). In some embodiments, the ratio of ferrocene to xylene mixed with the carrier gas can be about one gram of ferrocene per one hundred milliliters of xylene, and the ferrocene/xylene mixture can be mixed with the carrier gas at a temperature of about 150° Celsius at a rate of about 6 milliliters per hour. The foregoing recipe can produce carbon nanotubes that are vertically aligned. As mentioned, the foregoing recipe is exemplary only, and other materials comprising a catalyst and a source of carbon can be utilized. Moreover, the growth surface can be exposed to the foregoing catalyst and source of carbon at temperatures other than 750° Celsius. 
     As another example, and not by way of limitation, a fixed catalyst process will now be described. A buffer layer can be provided on substrate  102  and a catalyst layer formed on the buffer layer. The catalyst layer can comprise catalyst material that, as generally discussed above, can cause growth of carbon nanotubes (which can be vertically aligned) in the presence of a source of carbon. The buffer layer can provide a buffer between the substrate  102  and the catalyst layer. The buffer layer can be any material that does not appreciably react with the catalyst material and/or the material that is the source of carbon. Aluminum oxide (Al2O3) is a non-limiting example of a suitable buffer layer. Catalyst layer can comprise a material that, in the presence of a source of carbon, causes growth of carbon nanotubes. Catalyst layer can be formed by depositing catalyst material only on selected areas of buffer layer. Alternatively, catalyst layer can formed by depositing catalyst material as a blanket layer of material on buffer layer and then removing selected portions of the deposited catalyst material, leaving the catalyst material in a pattern and shapes that correspond to desired locations and cross-sectional shapes of the carbon nanotube columns to be grown on the catalyst layer. 
     Carbon nanotubes can be grown by providing a material (e.g., a gas) comprising a source of carbon in the presence of proper ambient conditions. For example, substrate  102  with buffer layer and catalyst layer can be placed in an interior of an enclosure such as a furnace (not shown), and the interior of the enclosure can be heated and a gas comprising a source of carbon can be introduced (e.g., pumped) into the interior of the enclosure. The specific material that composes the catalyst layer, the specific material that composes the source of carbon, and any other materials and the concentrations and mixtures of those materials as well as the specific ambient conditions (e.g., temperature) can be referred to as a “recipe.” Any recipe suitable for growing carbon nanotubes on catalyst layer can be used to grow carbon nanotubes. 
     The following is an exemplary, non-limiting recipe that can be used to grow carbon nanotubes. The catalyst layer can comprise any transition metal. For example, the catalyst layer can comprise iron (Fe). For example, the catalyst layer can comprise a layer of iron (Fe), and buffer layer can comprise aluminum oxide (Al2O3). In some embodiments, the thickness of an iron (Fe) film and an aluminum oxide (Al2O3) film can be about 1.2 nm of iron (Fe) and about 10 nm of aluminum oxide (Al2O3). Substrate  102  can be placed in a furnace (not shown), which can be heated to about 750° Celsius, and a hydrocarbon gas can be introduced into the furnace. Under such conditions, the catalyst layer can catalyze the growth of carbon nanotubes on the patterned catalyst layer from carbon in the hydrocarbon gas. In some embodiments, after the substrate  102  is placed in the furnace (not shown), the furnace can be operated as follows. For about 10 minutes, while the furnace is at a temperature of about 0° Celsius, an inert gas (e.g., argon) can be pumped through the furnace at a flow rate of about 400 standard cubic centimeters per minute (sccm). Then, for about 15 minutes, while the temperature in the furnace (not shown) is changed from 0° Celsius to 750° Celsius, and thereafter for about 10 minutes while the temperature is maintained at 750° Celsius, the inert gas can continue to be pumped through the furnace at a flow rate of about 400 sccm. Thereafter, for about 5 minutes, while the temperature is maintained at about 750° Celsius, a gas containing hydrogen H2 can be mixed with the inert gas flowing through the furnace (not shown) at about 400 sccm. For example, the gas containing hydrogen can be H2/Ar in a ratio of about 40 parts of H2 to about 15 parts of Ar. Thereafter, a source of carbon can be added to the inert gas flowing through the furnace while maintaining the furnace at 750° Celsius. For example, the source of carbon can be a gas comprising C2H4/H2/Ar in a ratio of about 10 parts of C2H4, 40 parts of H2, and 10 parts of Ar, which can result in the growth of carbon nanotubes on the catalyst layer from carbon in the gas. The carbon nanotubes can grow from the catalyst layer as vertically aligned carbon nanotube columns. As mentioned, the foregoing recipe is exemplary only, and other materials can comprise the catalyst layer, and a different source of carbon can be utilized. Moreover, the catalyst layer can be exposed to the foregoing source of carbon at temperatures other than 750° Celsius. Moreover, different gas mixtures, flow rates, and time periods can be used. 
       FIGS. 2A and 2B  illustrate a non-limiting example embodiment of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  204  comprising a carbon nanotube structure  208 , electrically conductive wire  212 , and electrically conductive cap  214  according to some embodiments of the invention. Spring contact structure  204  can be a non-limiting example of spring contact structure  104  in  FIG. 1 ; carbon nanotube structure  208  can be a non-limiting example of mechanical component  106  in  FIG. 1 ; and wire  212  and cap  214  can be a non-limiting example of electrical component  108  of  FIG. 1 . 
     As shown in  FIGS. 2A and 2B , carbon nanotube structure  208  can be disposed on terminal  114  of substrate  102  and can include a hollow portion  210 . An electrically conductive wire  212  can be disposed in the hollow portion  210 , and an electrically conductive cap  214  can be disposed on an end of the carbon nanotube structure  208 . The wire  212  can contact both the terminal  114  and the cap  214 . In some embodiments, wire  212  can be attached to one or both of terminal  114  and cap  214 . The wire  212  can be made of a material that has a desired low level of electrical resistance. The wire  212  can be resilient and therefore under compression between the cap  214  and terminal  114  so that the wire  212  remains in electrical contact with the terminal  114  and the cap  214  over the operating range of the spring contact structure  204  (e.g., the elastic range of the carbon nanotube structure  208 ). Alternatively, the wire  212  can be attached to the terminal  114  and the cap  214  so that the wire remains in electrical contact with the terminal  114  and the cap  214  over the operating range of the spring contact structure  204 . The wire  212  can also be of low mechanical stiffness relative to carbon nanotube structure  208 . Wire  212  can be, for example, a wire comprising a conductive material such as copper, gold, or other such material including alloys of the foregoing. As another non-limiting example, wire  212  can comprise a bundle of conductive nanowires. Cap  214  can also comprise a conductive material such as the materials mentioned above for wire  212 . Alternatively, cap  214  can comprise a material or materials that are both conductive and wear resistant. Non-limiting examples of such materials include without limitation, nickel, palladium, rhodium, and alloys of the foregoing including without limitation palladium-cobalt and rhodium-cobalt. 
     Carbon nanotube structure  208  in  FIGS. 2A and 2B  can be, for example and not by way of limitation, a column of vertically aligned carbon nanotubes as generally discussed above with respect to  FIG. 1 . As such, carbon nanotube structure  208  can provide desired mechanical characteristics of spring contact structure  204 , such as desired elastic range, spring constant, etc. Carbon nanotube structure  208  can, but need not be, highly electrically conductive. This is because wire  212  and cap  214  can provide a highly conductive (i.e., a low resistance) electrical path through spring contact structure  204 . Similarly, wire  212  and cap  214  need not provide desired mechanical characteristics because, as discussed above, carbon nanotube structure  208  can provide desired mechanical characteristics of spring contact structure  204 . In some embodiments, carbon nanotube structure  208  can be mechanically decoupled (as defined above) from wire  212  and cap  214 , and/or wire  212  and cap  214  can be electrically decoupled (as defined above) from carbon nanotube structure  208 . In some embodiments, carbon nanotube structure  208  can be elastically deformable in a particular elastic range while wire  212  and/or cap  214  are not elastically deformable, by themselves, over all or part of the elastic range of the carbon nanotube structure  208 . Wire  212  and/or cap  214  can, however, be plastically deformable. As another non-limiting example, wire  212  can be elastically deformable but may have a lower stiffness than carbon nanotube structure  208 . In some embodiments, wire  212  and cap  214  can have a significantly lower electrical resistance than carbon nanotube structure  208 . 
     Spring contact structure  204  is exemplary only and many variations are possible. For example, although one wire  212  is shown in  FIGS. 2A and 2B , a plurality of wires  212  can be in hollow portion  210 . As another non-limiting example, carbon nanotube structure  208  need not be rectangular but can be other shapes including without limitation cylindrical. Hollow portion  210  also need not be rectangular but can but other shapes including without limitation cylindrical. Moreover, the shape of the carbon nanotube structure  208  can be different from the shape of the hollow portion  210 . As still another non-limiting example, cap  214  need not be flat. By way of example and not limitation, cap  214  can comprise one or more shapes configured to facilitate contact with terminal  112  of electronic component  110  (see  FIG. 1 ). For example, an outer surface (in  FIGS. 2A and 2B  a top surface) of cap  214  can comprise structures (e.g., a sharp tip or sharp corners or tips) configured to penetrate terminal  112 . Non-limiting examples of shapes of such structures include a pyramid, truncated pyramid, or blade shape. 
       FIGS. 3-5  illustrate a non-limiting example of a process for making a spring contact structure like the spring contact structure  204  of  FIGS. 2A and 2B . As shown in  FIG. 3 , carbon nanotube structure  208  with hollow portion  210  can be formed on or otherwise attached to terminal  114  of substrate  102 . As mentioned, carbon nanotube structure  208  can comprise one or more columns of vertically aligned carbon nanotubes, and as such, carbon nanotube structure  208  can be formed in any of the ways discussed above with respect to  FIG. 1 . For example, carbon nanotube structure  208  can be grown on terminal  114  or grown on another substrate (not shown) and transferred to terminal  114 . Also, whether grown on terminal  114  or on another substrate (not shown), carbon nanotube structure  208  can be grown using a floating catalyst method or a fixed catalyst method. Hollow portion  210  can be formed in any suitable manner. For example, carbon nanotube structure  208  can be grown around a plug (not shown), which can be removed, leaving hollow portion  210 . As another non-limiting example, carbon nanotube structure  208  can be grown on a seed material (not shown) patterned such that the carbon nanotube structure  208  does not grow on a center portion (or other portion) of the seed material. As yet another non-limiting example, an interior (or other) portion (not shown but corresponding to hollow portion  210 ) can be removed (e.g., by cutting, ablating, etching, etc.) from carbon nanotube structure  208 . 
     As shown in  FIG. 4 , wire  212  can be inserted into hollow portion  210 . As mentioned above, more than one wire  212  can be inserted into hollow portion  210 . As shown in  FIG. 5 , cap  214  can be attached (e.g., soldered, welded, adhered with an adhesive, etc.) to an end of carbon nanotube structure  208 . Wire  212  can be longer than the length of hollow portion  210  so that wire  212  is compressed between terminal  114  and cap  214 . Alternatively or in addition, wire  212  can be attached (e.g., soldered, bonded, adhered, etc.) to terminal  114  and/or cap  214 . 
     The method illustrated in  FIGS. 3-5  is exemplary only and other methods can be used to make a spring contact structure like  204 .  FIGS. 6-8  illustrate a non-limiting example of such other methods. 
       FIGS. 6-8  illustrate another non-limiting example of a process for making a spring contact structure like the spring contact structure  204  of  FIGS. 2A and 2B . As shown in  FIG. 6 , wire  212  can be attached (e.g., bonded, soldered, welded, adhered with an electrically conductive adhesive, etc.) to or otherwise held in place on terminal  114  of substrate  102 . Although one wire  212  is shown, multiple such wires can be attached or held in place on terminal  114 . As shown in  FIG. 7 , carbon nanotube structure  208  can be formed (e.g., grown, attached to, etc.) on terminal  114  around wire  212 . For example, carbon nanotube structure  208  can be, as discussed above, one or more columns of vertically aligned carbon nanotubes, and such column or columns can be grown on terminal  114  around wire  212 . Alternatively, carbon nanotube structure  208  can be formed on another substrate (not shown) with hollow portion  210  generally as shown in  FIG. 3  and then transferred from the other substrate (not shown) to terminal  114  such that wire  212  is inside hollow portion  210 . As shown in  FIG. 8 , cap  214  can be attached (e.g., soldered, welded, adhered with an adhesive, etc.) to an end of carbon nanotube structure  208 . Wire  212  can extend the length of carbon nanotube structure  208  such that wire  212  contacts both terminal  114  and cap  214 . 
       FIGS. 9A and 9B  illustrate another non-limiting example of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  904  according to some embodiments of the invention. As shown in  FIGS. 9A and 9B , spring contact structure  904  can comprise a plurality of carbon nanotube columns  908  and a plurality of wires  912  attached at one end to terminal  114  of substrate  102 . As shown, the wires  912  can be interspersed between the carbon nanotube columns  908 . Spring contact structure  904  can also include a cap  914  attached to opposite ends of the carbon nanotube columns  908  and the wires  912 . 
     The carbon nanotube columns  908  can each be a column of vertically aligned carbon nanotubes. In some non-limiting examples, carbon nanotube columns  908  can be the same as or generally similar to carbon nanotube structure  208  of  FIGS. 2A and 2B  except thinner so that a plurality of such carbon nanotube columns  908  along with a plurality of wires  912  can be disposed on terminal  114 . Also, carbon nanotube columns  908  need not have a hollow portion like hollow portion  210  of  FIGS. 2A and 2B . Wires  912  can be the same as or generally similar to wire  212  of  FIGS. 2A and 2B , and conductive cap  914  can be the same as or similar to cap  214  of  FIGS. 2A and 2B . 
     The carbon nanotube structure columns  908  can provide dominant mechanical characteristics of spring contact structure  904  and can thus be a non-limiting example of mechanical component  106  in  FIG. 1 . The wires  912  and cap  914  can provide dominant electrical characteristics of spring contact structure  904  and thus be a non-limiting example of electrical component  108  of  FIG. 1 . In some embodiments, carbon nanotube columns  908  can be mechanically decoupled (as defined above) from wires  912  and cap  914 , and/or wire  912  and cap  914  can be electrically decoupled (as defined above) from carbon nanotube columns  908 . In some embodiments, carbon nanotube columns  908  can be elastically deformable in a particular elastic range while wires  912  are not elastically deformable, by themselves, over all or part of the elastic range of the carbon nanotube columns  908 . Alternatively, wires  912  can be elastically deformable over all of the elastic range of the carbon nanotube columns  908 . In some embodiments, wires  912  and cap  914  can have a significantly lower electrical resistance than carbon nanotube columns  908 . Alternatively, nanotube columns  908  can be electrically conductive. Cap  914  can be generally inelastic (rigid) over the elastic range of the carbon nanotube columns  908 . 
     Spring contact structure  904  is exemplary only and many variations are possible. For example, a different number and/or pattern of carbon nanotube columns  908  and/or wires  912  than shown in  FIGS. 9A and 9B  can be used. As another non-limiting example, carbon nanotube columns  908  need not be rectangular but can be other shapes including without limitation cylindrical. As still another non-limiting example, cap  914  need not be flat but can have other shapes including without limitation any of the shapes and variations thereof discussed above for cap  214 . 
       FIGS. 10-12  illustrate a non-limiting example of a process for making a spring contact structure like the spring contact structure  904  of  FIGS. 9A and 9B . As shown in  FIG. 10 , wires  912  can be attached (e.g., bonded, soldered, welded, adhered with an electrically conductive adhesive, etc.) to terminal  114  of substrate  102 . Although two wires  912  are shown, only one wire  912  or more than two wires  912  can be attached to terminal  114  in  FIG. 10 . As shown in  FIG. 11 , carbon nanotube columns  908  can be formed on terminal  114 . For example, carbon nanotube columns  908  can be, as discussed above, one or more columns of vertically aligned carbon nanotubes, and such columns can be grown on terminal  114 . Terminal  114  can be masked so that carbon nanotube columns  908  only grow on portions of terminal  114  defined by the masking (not shown). As another non-limiting example, carbon nanotube columns  908  can be grown on a seed material (not shown) on terminal  114 , and the seed material can be pattern such that carbon nanotube columns  908  grow only on portions of terminal  114 . Alternatively, carbon nanotube columns  908  can be formed on another substrate (not shown) and then transferred from the other substrate (not shown) to terminal  114 . As shown in  FIG. 12 , cap  914  can be attached (e.g., soldered, welded, adhered with an adhesive, etc.) to ends of carbon nanotube structures  908  and ends of wires  912 . Wires  912  can extend from terminal  114  to cap  914 . 
       FIG. 13  illustrates another non-limiting example embodiment of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  1304  according to some embodiments of the invention. As shown in  FIG. 13 , spring contact structure  1304  can comprise a carbon nanotube structure  1308  to which a conductive cap  1314  can be attached. The carbon nanotube structure  1308  can be attached to a surface of substrate  102 , and a conductive post  1316  can be attached to terminal  114 . An electrically conductive wire  1312  or other connector can electrically connect cap  1314  to post  1316 . 
     The carbon nanotube structure  1308  can be a column of vertically aligned carbon nanotubes. In some non-limiting examples, carbon nanotube structure  1308  can be the same as or generally similar to carbon nanotube structure  208  of  FIGS. 2A and 2B  except carbon nanotube structure  1308  can lack a hollow portion like hollow portion  210  of  FIGS. 2A and 2B . Conductive cap  1314  can be the same as or similar to cap  214  of  FIGS. 2A and 2B . As mentioned above, cap  214  can be shaped like a truncated pyramid generally, as cap  1314  is illustrated in  FIG. 13 . Alternatively, cap  1314  (like cap  214 ) can have other shapes such as a pyramid or a blade, or cap  1314  can be flat like  214  is shown in  FIGS. 2A and 2B . Wire  1312  can be any electrically conductive wire or other type of electrical connector, and post  1316  can be any electrically conductive structure. As shown, wire  1312  can be attached (e.g., bonded, soldered, welded, adhered with a conductive adhesive, etc.) at one end to cap  1314  and at the other end to post  1316 . 
     The carbon nanotube structure  1308  can provide dominant mechanical characteristics of spring contact structure  1304  and can thus be a non-limiting example of mechanical component  106  in  FIG. 1 . The cap  1314 , wire  1312 , and post  1316  can provide dominant electrical characteristics of spring contact structure  1304  and thus be a non-limiting example of electrical component  108  of  FIG. 1 . In some embodiments, carbon nanotube column  1308  can be mechanically decoupled (as defined above) from cap  1314 , wire  1312 , and post  1316 ; and/or cap  1314 , wire  1312 , and post  1316  can be electrically decoupled (as defined above) from carbon nanotube column  1308 . In some embodiments, carbon nanotube structure  1308  can be elastically deformable in a particular elastic range while cap  1314 , wire  1312 , and/or post  1316  are not elastically deformable, by themselves, over all or part of the elastic range of carbon nanotube structure  1308 . Cap  1314 , wire  1312 , and/or post  1316 , however, can be plastically deformable. In some embodiments, wire  1312  is compliant, but post  1316  need not be compliant. In some embodiments, cap  1314 , wire  1312 , and post  1316  can have a significantly lower electrical resistance than carbon nanotube structure  1308 . 
     Spring contact structure  1304  is exemplary only and many variations are possible. For example, carbon nanotube structure  1308  need not be rectangular but can be other shapes including without limitation cylindrical. As another non-limiting example, carbon nanotube structure  1308  can comprise a plurality of thinner carbon nanotube columns, for example, like carbon nanotube columns  908  in  FIGS. 9A and 9B . As yet another non-limiting example, post  1316  need not be used. Rather, wire  1312  can be connected from cap  1314  directly to terminal  114 . As still another non-limiting example, carbon nanotube structure  1308  and post  1316  can both be attached to terminal  114 . As yet another non-limiting example, cap  1314  need not have a truncated pyramid shape but can have other shapes including without limitation the alternative shapes discussed. 
       FIGS. 14-17  illustrate a non-limiting example of a process for making a spring contact structure like the spring contact structure  1304  of  FIG. 13 . As shown in  FIG. 14 , carbon nanotube structure  1308  can be formed on or otherwise attached to substrate  102 . As mentioned, carbon nanotube structure  1308  can comprise one or more columns of vertically aligned carbon nanotubes, and as such, carbon nanotube structure  1308  can be formed in any of the ways and variations thereof discussed above with respect to  FIG. 1 . For example, carbon nanotube structure  1308  can be grown on substrate  102  or grown on another substrate (not shown) and transferred to substrate  102 . Also, carbon nanotube structure  1308  can be grown using a floating catalyst method or a fixed catalyst method. 
     As shown in  FIG. 15 , cap  1314  can be attached (e.g., soldered, welded, adhered with an adhesive, etc.) to an end of carbon nanotube structure  1308 . As shown in  FIG. 16 , post  1316  can be formed on or attached (soldered, welded, adhered with a conductive adhesive, etc.) to terminal  114 . Post  1316  can be any electrically conductive structure and can be formed on terminal  114  or formed elsewhere and attached to terminal  114 . As shown in  FIG. 17 , wire  1312  can be attached (e.g., bonded (e.g., by conventional wiring bonding processes), soldered, welded, adhered with a conductive adhesive, etc.) at one end to cap  1314  and at another end to post  1316 . 
     The process illustrated in  FIGS. 14-17  is an example only, and many variations are possible. For example, the order in which the operations are performed can be changed. As another non-limiting example, as mentioned above, post  1316  need not be used. Consequently, the operation shown in  FIG. 16  can be skipped, and wire  1312  can be connected from cap  1314  directly to terminal  114  in  FIG. 17 . 
       FIGS. 18A and 18B  illustrate another non-limiting example of an embodiment of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  1804  according to some embodiments of the invention.  FIG. 18A  shows a perspective view and  FIG. 18B  shows a side-cross sectional view of spring contact structure  1804 . Spring contact structure  1804  can comprise conductive material  1812  in a hollow portion  1810  of a carbon nanotube column  1808 , which can be attached to terminal  114  of substrate  102 . Carbon nanotube column  1808  can be, for example, a column of vertically aligned carbon nanotubes. As mentioned, column  1808  can include a hollow portion  1810 , which as shown can extend the length of column  1808 . Generally speaking, column  1808  can be formed using any of the techniques described herein and variations thereof for forming columns of vertically aligned carbon nanotubes. Hollow portion  1810  can be formed in the same or similar way as hollow portion  210  of  FIGS. 2A and 2B . Although column  1808  and hollow portion  1810  are shown with a square-type cross-section, other types of cross sections are equally contemplated including without limitation a circular cross-section. 
     As shown in  FIGS. 18A and 18B , hollow portion  1810  can be filled with an electrically conductive material  1812 , which can be any electrically conductive material that can be deposited into hollow portion  1810 . (For ease of illustration, hollow portion  1810  is shown in  FIGS. 18A and 18B  partially filed with conductive material  1812 , but hollow portion  1810  can be fully filed with conductive material  1812 .) In some embodiments, conductive material  1812  can have a greater electrical conductivity than column  1808 . In some embodiments, conductive material  1812  can comprise a conductive material with a relatively low melting point that can be deposited into hollow portion  1810  while melted and then allowed to cool. For example, conductive material  1812  can be solder. As another non-limiting example, conductive material  1812  can be a curable material that is deposited into hollow portion  1810  in a flowable or semi-flowable state and then cured, causing the conductive material  1812  to solidify inside hollow portion  1810 . For example, conductive material  1812  can be a curable conductive epoxy. Alternatively, conductive material  1812  can remain in a liquid or semi-liquid state and be functional in the liquid or semi-liquid state. As yet another example, conductive material  1812  can be a resilient electrically conductive polymer. Although not shown in  FIGS. 18A and 18B , a conductive cap (e.g., like cap  214  including any variation of cap  214  discussed herein) can be attached (e.g., soldered, welded, adhered with an epoxy, etc.) to the upper (as oriented in  FIGS. 18A and 18B ) end of column  1808 , and conductive material  1812  can extend within hollow portion  1810  from terminal  114  to the conductive cap (not shown) if present. 
     Column  1808  can provide dominant mechanical characteristics of spring contact structure  1804  and can thus be a non-limiting example of mechanical component  106  in  FIG. 1 . The conductive material  1812  and cap (not shown), if present, can provide dominant electrical characteristics of spring contact structure  1804  and thus be a non-limiting example of electrical component  108  of  FIG. 1 . If the cap (not shown) is not present, conductive material  1812 , which as discussed above, can fill hollow portion  1810  and thus provide a direct electrical connection from terminal  114  to the end of column  1808  opposite terminal  114 , can by itself be a non-limiting example of electrical component  108  of  FIG. 1 . 
     In some embodiments, carbon nanotube column  1808  can be mechanically decoupled (as defined above) from conductive material  1812  and/or, if present, cap (not shown). Similarly, in some embodiments conductive material  1812  and/or, if present, cap (not shown) can be electrically decoupled (as defined above) from carbon nanotube column  1808 . In some embodiments, carbon nanotube column  1808  can be elastically deformable in a particular elastic range while conductive material  1812  is not elastically deformable, by itself, over all or part of the elastic range of the carbon nanotube column  1808 . Conductive material  1812  can, however, be plastically deformable over the particular elastic range. Cap (not shown), if present, can be rigid over the particular elastic range. In some embodiments, conductive material  1812  and, if present, cap (not shown) can have a significantly lower electrical resistance than carbon nanotube column  1808 . 
     There are many possible uses and applications for spring contact structure  104  (including without limitation spring contact structures  204 ,  904 ,  1304 , and  1804  and any variations of those spring contact structures described herein).  FIG. 19  illustrates a non-limiting example in which spring contact structure  104  can be part of a probe card assembly for testing DUT  1922 . DUT  1922  (which can be an acronym for device under test) can be any electronic device or devices to be tested, including without limitation one or more dies of an unsingulated semiconductor wafer, one or more semiconductor dies singulated from a wafer (packaged or unpackaged), one or more dies of an array of singulated semiconductor dies disposed in a carrier or other holding device, one or more multi-die electronic devices, one or more printed circuit boards, or any other type of electronic device or devices.  FIG. 19  shows an exemplary probe card assembly  1940  and a simplified block diagram of a test system  1900  in which the probe card assembly  1940  can be used to test DUT  1922  according to some embodiments of the invention. As will be seen, spring contact structures  1906 , spring contact structures  1910 , and/or electrically conductive resilient probes  1914  can comprise spring contact structures  104 . Alternatively, spring contact structures  1906 , spring contact structure  1910 , and/or probes  1914  can be other types of contact structures. 
     As shown in  FIG. 19 , the probe card assembly  1940  can comprise a wiring substrate  1902 , an interposer  1908 , and a probe head  1912 . Brackets  1916  and/or other suitable means can hold the wiring substrate  1902 , interposer  1908 , and probe head  1912  together. The wiring substrate  1902  can be a printed circuit board, ceramic substrate, or the like. The wiring substrate  1902  can include electrical connectors  1904  configured to make electrical connections with a plurality of communications channels  1920  to and from a tester  1918 . Connectors  1904  can be pads for receiving pogo pins, zero-insertion-force connectors, or any other electrical connection device suitable for making electrical connections with communications channels  1920 . Electrically conductive paths (not shown) can be provided through the probe card assembly  1940  to provide electrical connections from individual electrical connections in connectors  1904  (each such individual electrical connection can correspond to one of communication channels  1920 ) to electrically conductive resilient probes  1914 , which can contact input and/or output terminals  1924  of DUT  1922 . Those conductive paths (not shown) through the probe card assembly  1940  can comprise electrically conductive connections, such as traces and/or vias (not shown), from the connectors  1904  through the wiring substrate  1902  to electrically conductive terminals (not shown) on the wiring substrate  1902  in contact with spring contact structures  1906 ; electrically conductive connections, such as vias (not shown), through interposer  1908  electrically connecting the spring contact structures  1906  with spring contact structures  1910 ; and electrically conductive connections, such as traces and vias (not shown), through the probe head  1912  between electrically conductive terminals (not shown) on the probe head  1912  in contact with the spring contact structures  1910  and probes  1914 . In this way, a plurality of signal paths comprising the communications channels  1920 , the above-described conductive paths through the probe card assembly  1940 , and the probes  1914  are provided between the tester  1918  and the input and/or output terminals  1924  of DUT  1922 . 
     The configuration of probe card assembly  1940  shown in  FIG. 19  is exemplary only and is simplified for ease of illustration and discussion. Many variations, modifications, and additions are possible. For example, although the probe card assembly  1940  is illustrated in  FIG. 19  as having three substrates—the wiring substrate  1902 , the interposer  1908 , and the probe head  1912 —the probe card assembly  1940  can have more or fewer than three substrates. For example, probe head  1912  can be attached and/or electrically connected directly to the wiring substrate  1902 , which can eliminate interposer  1908 . As another non-limiting example, the probe card assembly  1940  can have more than one probe head  1912 , and each such probe head  1912  can be independently adjustable. As another non-limiting example, spring contact structures  1906 ,  1910  can be mounted on interposer  1908  to contact terminals (not shown) on wiring substrate  1902  and probe head  1912 , or spring contact structures  1906  can be mounted on wiring substrate  1902  to contact terminals (not shown) on interposer  1908 , or spring contact structures  1910  can be mounted on probe head  1912  to contact terminals (not shown) on interposer  1908 . As another non-limiting example, probes  1914  can be replaced with terminals (not shown) on probe head  1912  arranged to contact spring contact structures (not shown) disposed on DUT  1922 . In general, positions of spring contact structures and corresponding terminals with which they make be swapped. 
     DUT  1922  can be tested as follows. Terminals  1924  of DUT  1922  can be pressed against probes  1914 , causing probes  1914  to form temporary, pressure based electrical connections with terminals  1924 . The tester  1918  can generate test signals, which can be provided through the communications channels  1920 , probe card assembly  1940 , and probes  1914  to input terminals  1924  of DUT  1922 . Response signals generated by DUT  1922  can be sensed by probes  1914  in contact with output terminals  1924  of DUT  1922  and provided through the probe card assembly  1940  and communications channels  1920  to the tester  1918 . The tester  1918  can analyze the response signals to determine whether DUT  1922  responded properly to the test signals and, consequently, whether DUT  1922  passes or fails the testing. The tester  1918  can alternatively or in addition rate the performance of DUT  1922 . 
     Spring contact structure  104  is not limited to use in a test system or probe card assembly like those illustrated in  FIG. 19 .  FIG. 20  illustrates a non-limiting example in which spring contact structures  104  can be used in a test socket.  FIG. 20  illustrates an exemplary test socket  2000  having a substrate  2010 , terminals  2012 , and spring contact structures  2014 , which can be spring contact structure  104 . As shown in  FIG. 20 , test socket  2000  can be used to test electronic devices such as electronic devices  2016   a ,  2016   b , which can be like DUT  1922 .  FIG. 20  depicts electronic device  2016   a  being pressed against spring contact structures  2014  of the test socket  2000 , and  FIG. 20  depicts electronic device  2016   b  in the process of being pressed against the spring contact structures  2014 . In some embodiments, substrate  2010 —which can be a wiring substrate with electrical contacts for connecting to a test controller and internal wiring connecting the electrical contacts to contact structures  2014 —can be connected to a test controller, which can control testing of electronic devices  2016   a  and  2016   b.    
       FIGS. 21 and 22  illustrate in cross section additional non-limiting examples of embodiments of the spring contact structure  104  of  FIG. 1  in the form of spring contact structures  2104 ,  2204  according to some embodiments of the invention. The spring contact structure  2104  of  FIG. 21  is generally similar to the spring contact structure  204  of  FIGS. 2A and 2B , except that an electrically conductive wire  2112  having a serpentine shape is used. Electrically conductive wire  2112  can be disposed in the hollow portion  210  of carbon nanotube structure  208 . Electrically conductive wire  2112  can be electrically connected to electrically conductive cap  214  and to terminal  114  of substrate  102 . Electrically conductive wire  2112  can be similar to wire  212  described above. Because the wire  2112  is serpentine shaped, the length of the wire  2112  can be longer than the height of carbon nanotube structure  208 . 
     The spring contact structure  2204  of  FIG. 21  is also generally similar to the spring contact structure  204  of  FIGS. 2A and 2B , except than an electrically conductive wire  2212  having a spiral or coiled shape is used. Electrically conductive wire  2212  can be similar to wire  212  described above. Wire  2212  can be longer than length of carbon nanotube structure  208 . Other arrangements similar to  FIGS. 21 and 22  can be used where the conductive wire is replaced by an electrically conductive material such as steel wool or foamed porous metal structure. 
       FIG. 23  illustrates in cross section another non-limiting example of an embodiment of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  2304  according to some embodiments of the invention. The spring contact structure  2304  can include a carbon nanotube structure  2308 , electrically conductive wire  2312 , and electrically conductive cap  214 . Carbon nanotube structure  3208  can be disposed on terminal  114  of substrate  102  and can include a hollow portion  2310 . Electrically conductive wire  2312  can be disposed in the hollow portion  210 , and an electrically conductive cap  214  can be disposed on an end of the carbon nanotube structure  3208 . The wire  2312  can electrically connect to the terminal  114  and to the cap  214 . Wire  2312  can be generally similar to wire  312  as described above. 
     Wire  2312  can include a ball  2302  at the end. For example, wire  2312  can be attached to terminal  114  by wire bonding equipment. Spring contact structure  2304  can therefore be made as follows. Wire  2312  can be bonded to terminal  114 . Carbon nanotubes can be grown on terminal  114 . For example, carbon nanotube structure  2308  can be, as discussed above, vertically aligned carbon nanotubes grown on terminal  114 . As another non-limiting example, carbon nanotube structure  2308  can be grown on a seed material (not shown) on terminal  114 . Carbon nanotubes do not grow from the portion of the terminal  114  covered by ball  2302 , therefore a gap G can be formed between wire  2312  and carbon nanotube structure  2308 , thus creating hollow portion  2310  in the carbon nanotube structure  2308 . In other words, a space is created between the wire  2312  and the carbon nanotube structure  2308 . 
       FIGS. 24A-25C  illustrate another non-limiting example of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  2404  according to some embodiments of the invention. As shown in a top view in  FIG. 24A  and in cross section view in  FIG. 24B , spring contact structure  2404  can comprise a carbon nanotube structure  2408  having a space  2410  along the length of the structure. For example, space  2410  can be created by removal of a portion of a grown column, for example by laser ablation, etching, cutting etc. As another non-limiting example, space  2410  can be created by growing carbon nanotubes having the desired shape. For example, carbon nanotubes can be grown on growth material (not shown) patterned on the terminal  114  as generally described above. 
     Disposed in space  2410  can be an electrically conductive structure  2412  (e.g., a wire or prebent wire). The electrically conductive structure  2412  can be electrically connected (e.g., attached) to the terminal. The electrically conductive structure can extend the length of the carbon nanotube structure  2408 . A cap  2414  (e.g., like cap  214  in  FIG. 2A ) can be attached to an upper end of the carbon nanotube structure  2408  as shown in  FIG. 24B  and electrically connected to electrically conductive structure  2412 . 
     As seen best in cross section view in  FIG. 24C , the conductive structure  2412  can be bent to bias the conductive structure  2412 . When bent in such a manner, the conductive structure can therefore move in a predetermined direction when the spring contact structure  2404  is compressed. For example, when a downward force is applied to the cap  2414 , this can cause the carbon nanotube structure  2408  to compress at portions of base end  2416  (moving from the position show in dotted lines to the position shown in solid lines). Conductive structure  2412  can flex outward, moving in generally the direction of the bend. This can help to avoid movement of the conductive structure  2412  from interfering with mechanical properties of the carbon nanotube structure  2408  or damaging the carbon nanotube structure  2408 . 
     The carbon nanotube structure  2408  can provide dominant mechanical characteristics of spring contact structure  2404  and can thus be a non-limiting example of mechanical component  106  in  FIG. 1 . The conductive structure  2412  and cap  2414  can provide dominant electrical characteristics of spring contact structure  2404  and thus be a non-limiting example of electrical component  108  of  FIG. 1 . In some embodiments, carbon nanotube structure  2408  can be mechanically decoupled (as defined above) from conductive structure  2412  and cap  2414 , and/or conductive structure  2412  and cap  2414  can be electrically decoupled (as defined above) from carbon nanotube structure  2408 . In some embodiments, conductive structure  2412  and cap  2414  can have a significantly lower electrical resistance than carbon nanotube structure  2408 . Alternatively, carbon nanotube structure  2408  can be electrically conductive. Cap  2414  can be like any of cap  214 ,  914 ,  1314  and variations thereof described above. 
       FIG. 25  illustrates a cross section view of another non-limiting example of the spring contact structure  104  of  FIG. 1  in the form of spring contact structure  2504  according to some embodiments of the invention. Spring contact structure  2504  is generally similar to spring contact structure  2404  of  FIGS. 24A-24C , except that conductive structure  2512  is provided having a different shaped bend than conductive structure  2412 . Accordingly, movement of conductive structure  2512  when compressed can be generally in a vertical direction, as compared to conductive structure  2412 , which moves generally in a horizontal direction. 
       FIGS. 26A-26B  illustrate in cross section view another non-limiting example of a process for making spring contact structures that are embodiments of the spring contact structure  104  in  FIG. 1 . 
     As shown in  FIG. 26A , an electrically conductive structure  2612  (e.g. a wire) can be coupled to terminal  114  of substrate  102 . For example, conductive structure  2612  can be attached to (e.g., bonded, soldered, welded, adhered with an electrically conductive adhesive, etc.) or formed on (e.g., deposited, plated, grown, etc.) terminal  114 . Terminal  114  can comprise a growth material  2616  suitable for growing carbon nanotubes, for example as described above. Alternatively, terminal  114  can be coated with a growth material (e.g., using physical deposition). Conductive structure  2612  (or a portion of conductive structure  2612 ) can also be coated with a growth material  2616 . 
     Carbon nanotubes  2618 ,  2620  can be grown from the growth material. For example, carbon nanotubes  2618  can be grown horizontally from conductive structure  2612  and carbon nanotubes  2620  can be grown vertically from terminal  114 . 
     If desired, mold  2602  can be placed around terminals  114  and conductive structure  2612 . Mold  2602  can guide the growing carbon nanotubes  2618 ,  2620  (and in particular, horizontally growing carbon nanotubes  2618 ) to form a column  2608  as shown in  FIG. 26B . The mold  2602  can be removed after growing the carbon nanotubes, for example by physical removal, etching, etc. An electrically conductive cap  2614  can be attached the column  2608  if desired. Conductive cap  2614  can make electrical connection to conductive structure  2612 , electrically connecting terminal  114  and cap  2614  together. Conductive cap  2614  can be like any of cap  214 ,  914 ,  1314  and variations thereof described above, and conductive structure  2612  can be like any of conductive structure  212  and  912  and variations thereof described above. Accordingly, conductive structure  2612  is a non-limiting example of electrical component  108  of  FIG. 1 , and column  2608  is a non-limiting example of the mechanical component  106  of  FIG. 1 . 
       FIGS. 27A-27B  illustrate in cross section view another non-limiting example of a process for making spring contact structures that are embodiments of the spring contact structure  104  in  FIG. 1 . 
     As shown in  FIG. 27A  an electrically conductive structure  2712  (e.g. a wire) can be coupled to first surface  2730  of growth material  2716 . Conductive structure  2712  can be like conductive structure  2612  and can be attached or grown in a similar manner. 
     Growth material  2716  can be suitable for growing carbon nanotubes, for example as described above. Growth material  2716  can be disposed in a trench. For example, a trench can be formed by wet or dry etching and growth material can be deposited by physical deposition to form first surface  2730  and angled second surface  2732 . For example, wet etching can be performed on silicon using KOH. Dry etching can be performed on silicon using reactive ion etching. Growth material can also be disposed on additional surfaces  2734  adjacent to the trench. Growth material can also be disposed (not shown) on the electrically conductive structure  2712 , similar to as shown in  FIGS. 26A-B . 
     Carbon nanotubes  2718 ,  2720 ,  2722  can be grown from the growth material. For example, vertically oriented carbon nanotubes  2718  can be grown from first surface  2730 . Angled carbon nanotubes  2720  can be grown from angled surface  2732  toward conductive structure  2712 . Additional carbon nanotubes  2722  can also be grown vertically from the additional surfaces  2734 . Horizontally oriented carbon nanotubes can be grown from the electrically conductive structure  2712  if it is also coated with growth material. As shown in  FIG. 27B , carbon nanotubes  2718 ,  2720 ,  2722  can form a column  2708  around the conductive structure  2712 . If desired, a mold (not shown) like mold  2602  can be used to guide growth of carbon nanotubes  2718 ,  2720 ,  2722 . 
     If desired, a conductive cap  2714  can be attached to column  2708 . Cap  2714  can be in contact with conductive structure  2712 , thus electrically connecting terminal  114  to cap  2714 . Conductive cap  2714  can be like any of cap  214 ,  914 ,  1314  and variations thereof described above, and conductive structure  2712  can be like any of conductive structure  212  and  912  and variations thereof described above. Accordingly, contact structure  2704  is a non-limiting example of a spring contact structure  104 , wherein conductive structure  2712  is a non-limiting example of electrical component  108  of  FIG. 1 , and column  2708  is a non-limiting example of the mechanical component  106  of  FIG. 1 . 
       FIGS. 28A-34B  illustrate another non-limiting example of a process for making spring contact structures that are an embodiment of the spring contact structure  104  in  FIG. 1 . 
     As shown in top view in  FIG. 28A  and in cross section view in  FIG. 28B , a growth material  2804  can be disposed on a substrate  2802 . Substrate  2802  can be like substrate  102 . Growth material  2804  can be suitable for growing carbon nanotubes, for example as described above. As shown in top view in  FIG. 29A  and cross section view in  FIG. 29B  a masking material  2902  can be deposited onto growth material  2804  and substrate  2802 . Masking material  2902  can be, for example, a photo resist. As shown in top view in  FIG. 30A  and cross section view in  FIG. 30B , masking material  2902  can be patterned to provide a hole  3002  to expose growth material  2804  and to form a trench  3004 . For example, one or more operations of depositing masking material, exposing masking material, and removing exposed (or unexposed) portions of masking material can be performed to create the hole  3002  and trench  3004  using a photolithographic process. 
     As shown in top view in  FIG. 31A  and in cross section view in  FIG. 31B  conductive material  3102  can be deposited into hole  3002  and trench  3004 . For example, conductive material  3102  can be deposited by deposition, plating, or other suitable means. Conductive material  3102  can be a metal, such as copper, gold, aluminum, or other such material including alloys of the foregoing. As another non-limiting example, conductive material  3102  can comprise a bundle of conductive nanotubes. The conductive material can thus form a post  3104  (corresponding to hole  3002 ) extending vertically from growth material  2804  and beam  3106  (corresponding to trench  3004 ) extending horizontally from post  3104 . As shown in top view in  FIG. 32A  and cross section view in  FIG. 32B , the masking material  2902  can be removed after forming post  3104  and beam  3106 , to leave the post and beam free standing. If desired, an adhesion material (not shown) can be deposited onto the growth material  3104  before the conductive material  3102  to enhance adhesion of the post  3104  to the growth material  2804 . 
     As shown in top view in  FIG. 33A  and cross section view in  FIG. 33B , the beam  3106  can then be reformed to form an elongate conductive structure  3302 . For example, the substrate  2802  can be spun (e.g., in a centrifuge) so that centrifugal forces cause the beam  3106  to stand up and reorient into a vertical position by permanent plastic deformation. Although conductive structure  3302  is shown as a perfectly straight column, it will be appreciated that, depending upon the particular conductive material  3102  and process conditions under which the substrate  2802  is spun, the resulting conductive structure  3302  may have a smaller or a larger kink (corresponding to the junction between the post  3104  and the beam  3106  of the deposited conductive material  3102 ). Any such kink is not illustrated in  FIG. 33A  for simplicity. 
     Alternatively, elongate conductive structure  3302  can be formed by attaching a wire or other conductive material to terminal  114 , which is reoriented by being spun as described above. 
     A carbon nanotube column  3402  can be formed using similar techniques as described above. For example, carbon nanotubes can be grown on growth material  2804  to form column  3402  around conductive structure  3302  as shown in top view in  FIG. 34A  and cross section view in  FIG. 34B . If desired, an electrically conductive cap  3414  can be attached to the column  3402  as shown in  FIG. 34B . Cap  3414  can be in contact with conductive structure  3302 . Cap  3414  can be like any of cap  214 ,  914 ,  1314  and variations thereof described above. Accordingly, contact structure  3404  is a non-limiting example of a spring contact structure  104  of  FIG. 1 , wherein conductive structure  3302  (and cap  3414 , if included) is a non-limiting example of electrical component  108  of  FIG. 1 , and column  3402  is a non-limiting example of the mechanical component  106  of  FIG. 1 . 
       FIGS. 35A-36B  illustrate another non-limiting example of a process for making spring contact structures that are an embodiment of the spring contact structure  104  in  FIG. 1 . 
     As shown in top view in  FIG. 35A  and cross section view in  FIG. 35B , contact structures can be formed on a substrate  3502 . Substrate  3502  can be like substrate  102 . The contact structures can have a base  3506  and a tip  3508 . The bases  3506  and/or tips  3508  can be formed in various ways. For example, pits can be etched into the substrate  3502  in the reverse shape desired for the tips  3508 . A masking material can be deposited and patterned to leave an opening over the pit and having a reverse shape of the bases  3506 . The bases  3506  and tips  3508  can then be formed by depositing conductive material into the pits and the openings, after which the masking material can be removed. A conductive structure  3512  can be coupled to the bases  3506 . For example, conductive structure  3512  can be like any of wire  212  and  912  and variations thereof, and made in a similar manner. As another non-limiting example, conductive structure can be like any of conductive structures  2412 ,  2212 ,  2312 ,  2412 ,  2512 ,  3302  and variations thereof and made in a similar manner. 
     As shown in top view in  FIG. 36A  and cross section view in  FIG. 36B , carbon nanotubes can be grown on the bases  3506 , to form contact structure  3604 . Carbon nanotubes can be grown using similar techniques as discussed above. For example, the bases  3506  can include a growth material or be coated with a growth material suitable for growing carbon nanotubes. The grown carbon nanotubes can form columns  3602 . If desired, a mold (not shown), like mold  2602  can be used to guide the growth of the carbon nanotubes. 
     Accordingly, contact structure  3604  is a non-limiting example of a spring contact structure  104  of  FIG. 1 , wherein conductive structure  3512  is a non-limiting example of electrical component  108  of  FIG. 1 , and column  3602  is a non-limiting example of the mechanical component  106  of  FIG. 1 . Contact structure  3604  can be assembled on the tip  3508 , transferred to another substrate, and the tip  3508  released from substrate  3502 , for example as described further below. Similarly, additional embodiments of processes for making contact structures can include forming contact structures like  204 ,  904 ,  1804 ,  2104 ,  2204 ,  2304 ,  2404 ,  2504 ,  2604 ,  2704 ,  3404  on a tip. 
     If desired, additional operations on spring contact structures can be performed. For example, spring contact structures can be integrated into an electrical device, such as a probe card assembly.  FIGS. 37-39B  illustrate additional operations in a process for making spring contact structures that can be applied to contact structures  3604  of  FIG. 36 . Although the additional operations are illustrated using the contact structures  3604 , the additional operations that can be applied to any of the contact structures and variations thereof disclosed herein (e.g., contact structures  204 ,  904 ,  1804 ,  2104 ,  2204 ,  2304 ,  2404 ,  2504 ,  2604 ,  2704 ,  3404 ). 
     As shown in side view in  FIG. 37A , a filler material  3802  can be disposed onto the substrate  3502  and around and between the columns  3602 . The filler material  3802  can be, for example, acrylic polymer, polydimethylsiloxane (PDMS), or other low modulus materials like polyurethane. The filler material  3802  can help to hold the columns  3602  in place and strengthen the columns  3602  so that additional operations can be performed to the ends  3720  of the columns. For example, portions of the filler material  3802  and portions of the ends  3720  can be removed by grinding, lapping, and similar processes. This can expose the conductive structures  3512  at ends  3720  of the columns  3602 . For example, exposing the conductive structures  3512  can make it easier to form an electrical connection (e.g., to a tip). The removal of ends  3720  can also help to planarize the ends  3720  of the columns. In other words, by planarizing, the resulting columns can have a substantially uniform length (height above the substrate  3802 ). Following lapping (or similar processes), portions of the filler material can be removed (e.g., by etching) to leave the ends  3702  of the columns exposed, as shown in side view in  FIG. 37B . Base portions  3722  of the columns can remain anchored in the filler material  3802 . 
     As shown in top view in  FIG. 38A  and side view in  FIG. 38B , the ends  3720  of the columns  3602  can be inserted into openings  3704  in another substrate  3702 . Substrate  3702  can be like substrate  102 . 
     As shown in top view in  FIG. 39A  and cross section view in  FIG. 39B , the columns  3602  can be attached to substrate  3702 . For example, a joining material  3902  (e.g., solder, plating material, conductive epoxy, etc.) can join ends  3720  of columns  3602  to substrate  3702 . The joining material  3902  can be electrically conductive and can contact the conductive structure  3512 , thus electrically connecting the contact structure  3506  to the joining material  3902 , and electrical conductors (not shown) on substrate  3702 . The joining material  3902  can also provide mechanical anchoring of the columns  3602  to substrate  3702 . The contact structures  3604  can be released from substrate  3502  after being joined to substrate  3702 , leaving tip  3508  and base  3506  free and exposed. All or some of filler material  3802  can also be removed. 
     Accordingly, columns  3602  and conductive structure  3512  embedded in the column can be a spring contact structure  3904  that is an embodiment of the spring contact structure  104  of  FIG. 1 . The base  3504 , tip  3508 , and conductive structure  3512  are an example of the electrical component  108  of  FIG. 1 , and the column  3602  is an example of the mechanical component  106  of  FIG. 1 . 
     Returning to  FIG. 19 , any of the contact structures shown in  FIGS. 21-39B  (e.g., spring contact structures  2104 ,  2204 ,  2304 ,  2404 ,  2504 ,  2604 ,  2704 ,  3402 ,  3604 ,  3904 ) and variations thereof can be used in a probe card. For example, any of the contact structures can be used as spring contact structures  1906  and/or  1910 . Alternatively or in addition, any of the contact structures and variations thereof can be used as probes  1914 . Accordingly substrate  102 ,  2802 ,  3502 ,  3702  can be a probe head, part of a probe head, interposer, test board, wiring substrate, or the like 
     Returning to  FIG. 20 , any of the contact structures shown in  FIGS. 21-34B  (e.g., spring contact structures  2104 ,  2204 ,  2304 ,  2404 ,  2504 ,  2604 ,  2704 ,  3402 ,  3604 ,  3904 ) and variations thereof can be used as spring contacts  2014  in the test socket  200 . 
     Although the discussion above has generally shown one or two spring contact structures, it is to be understood that many spring contact structures can be made and used in the manners described above. Accordingly, a device using spring contact structures can include hundreds, thousands, tens of thousands, or more spring contact structures. 
     Although specific embodiments and applications of the invention have been described in this specification, these embodiments and applications are exemplary only, and many variations are possible. Accordingly, there is no intention that the invention be limited these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. For example, features shown in one embodiment can be combined with features shown in another embodiment. Spring contacts illustrated herein can be made using processes different from those described, and the processes described herein can be used to make different types of spring contacts than those illustrated. Accordingly, it is not intended that the invention be limited except as by the claims set forth below.