Patent Publication Number: US-2023140379-A1

Title: High performance interposer

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 63/272,737, filed on Oct. 28, 2021, under Attorney Docket No. A1245.70004US00 and entitled “TALL HEIGHT INTERPOSER WITH FORMED SHUNTING EXTENSION,” which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     This patent application relates generally to interconnection systems and more particularly to systems with interposers that provide multiple electrical connections between components, including sockets providing multiple connections between a semiconductor chip and a printed circuit board. 
     Electronic systems are frequently assembled by integrating components that each performs specific functions, such as processors, memories, transceivers or other communications interfaces. Such an approach enables different component manufacturers to specialize in the design and manufacture of their components, leading to better performing components. Further, using the same components in multiple electronic systems enables mass production of each component, which provides economies of scale. 
     Interconnections between components in an electronic system are often provided by a printed circuit board (PCB), which contains multiple layers of conductive structures, including signal traces that can pass electrical signals from one location on the printed circuit board to another. Connections may be made to the conductive structures inside the PCB using holes, drilled fully or partially through the board and then plated with metal. These plated holes, sometimes called vias, are electrically connected to conductive structures within the board through which the holes pass. Connection points on the components, sometimes called leads, might also be connected to the vias, completing a connection between the component and the traces or other conductive structures in the PCB. Connection between leads of the component and the vias might be made, for example, by inserting the lead into the via or by forming a pad on the surface of the PCB on top of the via and connecting the lead to the pad. 
     Connections between the lead on the component and the via may be made in various ways, such as by using solder or by shaping the contact to generate a spring force on the via or a pad attached to the via. In some systems, a component may be attached to a PCB through a socket. The socket has contacts that are connected at a mounting portion to the vias on the PCB and mating portions at the other end that are connected to leads on a component. In some instances, the lead on the component may be a pad on a surface of the component and the mating portions of the contacts of the socket may be compliant so that they exert a force against the pads when the component is pressed into the socket. The socket may include latching structures to hold the component in the socket and press it against the mating portions of the contacts. 
     A socket may include an interposer, which is a component that can make multiple connections between a printed circuit board and a component pressed against the interposer. Interposers may be made with molded plastic housings and metal contacts inserted in channels in the housing. Interposers may be attached to the printed circuit board in any of multiple ways. For example, solder balls may be attached to the mounting portions of the contacts and the interposer may be attached to the PCB in a reflow solder operation. In other interposers, the mounting portions of the contacts may be spring fingers designed to press against pads on a surface of the PCB. Screws or other hold down structures may ensure that the interposer is pressed against the PCB so that the spring fingers are compressed and generate a desired contact force. 
     The contacts in the interposer are frequently positioned in an array with mounting portions aligned with pads on the PCB and mating ends aligned with pads on the component being connected to the PCB. Each contact may carry a signal or be connected to ground. The pattern of the contacts in the array, and their function as signal or ground conductors, may be selected to provide good integrity of signals passing through the interposer. Signal carrying contacts, for example, may be positioned between ground contacts. Also, the signal carrying contacts may be positioned in pairs that carry differential signals. However, constraints, such as the position or function of the pads on the PCB or on the component pressed into the interposer may preclude an arbitrary positioning of signal and ground contacts. 
     SUMMARY 
     Some embodiments relate to A contact for an interposer, the contact comprising an intermediate portion; a first compliant arm extending from the intermediate portion in a first direction, the first compliant arm comprising a first contact region; and a projection extending from the intermediate portion in a second direction perpendicular to the first direction, the projection comprising a first bent portion forming a first strip that is angled relative to the first direction and facing the first contact region. 
     In some embodiments, the projection further comprises a second bent portion forming a second strip parallel to the first strip; and the contact further comprises a second compliant arm extending from the intermediate portion in a direction opposite the first direction, the second compliant arm comprising a second contact region facing the second strip. 
     In some embodiments, the first bent portion extends from the projection in a third direction perpendicular to both the first and second directions. 
     In some embodiments, the first arm is more compliant in the first direction than it is in the third direction. 
     In some embodiments, the contact further comprises a tab extending from the intermediate portion in the third direction, wherein the tab is parallel to the first strip. 
     In some embodiments, the intermediate portion lies substantially in a third plane perpendicular to the second direction. 
     In some embodiments, the first compliant arm comprises a first curved region positioned, along a length of the first compliant arm, between the intermediate portion and the first contact region, wherein the first curved region has a first convex region facing in the first direction and a first concave region facing away from the first direction. 
     In some embodiments, the first compliant arm further comprises a pair of wings positioned adjacent to the first curved region. 
     In some embodiments, the first contact region comprises a second curved region having a second concave region and a second convex region, wherein the second convex region faces the first strip and the second concave region faces away from the first strip. 
     In some embodiments, the projection is made from a portion of a metal sheet, wherein, when the portion of the metal sheet is planar, the projection has a T-shape or a π-shape. 
     In some embodiments, the contact has a height along the first direction in a fully compressed state in excess of 1.8 mm. 
     In some embodiments, the contact has a width along the second direction in the fully compressed state in excess of 1 mm. 
     In some embodiments, the first strip substantially lies in a plane perpendicular to the first direction. 
     Some embodiments relate to an interposer comprising an insulative member comprising a plurality of channels extending in a first direction from a first surface of the insulative member to a second surface of the insulative member opposite the first surface; and a plurality of contacts held in the plurality of channels, each of the plurality of contacts comprising: an intermediate portion; a first compliant arm extending from the intermediate portion in the first direction, the first compliant arm comprising a first contact region exposed at the first surface of the insulative member and a second contact region, wherein the first contact region is positioned, along a length of the first compliant arm, between the intermediate portion and the second contact region; and a projection extending from the intermediate portion in a second direction perpendicular to the first direction, the projection comprising a first strip configured to touch the second contact region of the first compliant arm. 
     In some embodiments, the interposer further comprises a second compliant arm extending from the intermediate portion in a direction opposite the first direction, the second compliant arm comprising a third contact region exposed at the second surface of the insulative member and a fourth contact region, wherein the third contact region is positioned, along a length of the second compliant arm, between the intermediate portion and the fourth contact region. The projection further comprises a second strip configured to touch the fourth contact region of the second compliant arm. 
     In some embodiments, the first compliant arm and the first strip are configured such that the second contact region of the first compliant arm wipes against the first strip when the first compliant arm is compressed. 
     In some embodiments, the second compliant arm and the second strip are configured such that the fourth contact region of the second compliant arm wipes against the second strip when the second compliant arm is compressed. 
     In some embodiments, the intermediate portion lies substantially in a first plane; the projection lies substantially in a second plane; the first strip lies substantially in a third plane; and the first, second and third planes are mutually perpendicular to each other. 
     In some embodiments, each of the plurality of contacts further comprises a tab extending from the intermediate portion and engaging with a wall of the respective channel. 
     In some embodiments, the plurality of contacts are slidably retained in the respective channels in the first direction. 
     In some embodiments, the plurality of contacts have heights along the first direction in excess of 1.8 mm. 
     Some embodiments relate to a method for connecting a first electronic component with a second electronic component through an interposer comprising a plurality of contacts, each contact comprising an intermediate portion, a projection, a first complaint arm and a second compliant arm, the method comprising: forming a first conductive path from the first electronic component to the second electronic component such that the first conductive path extends through the intermediate portion, wherein forming the first conductive path comprises placing the first compliant arm in contact with the first electronic component and the second compliant arm in contact with the second electronic component; and moving the first electronic component and the second electronic component together to form a second conductive path, at least partially in parallel with the first conductive path, from the first electronic component to the second electronic component such that the second conductive path extends through the projection, wherein forming the second conductive path comprises: deflecting the first compliant arm into contact with the projection; and deflecting the second compliant arm into contact with the projection. 
     In some embodiments, the first conductive path has a current density that extends through the intermediate portion to a greater extent than it extends through the projection. 
     In some embodiments, the second conductive path has a current density that extends through the projection to a greater extent than it extends through the intermediate portion. 
     In some embodiments, deflecting the first compliant arm into contact with the projection comprises pressing the first compliant arm against a first strip of the projection, and wherein: the intermediate portion lies substantially in a first plane; the projection lies substantially in a second plane; the first strip lies substantially in a third plane; and the first, second and third planes are mutually perpendicular to each other. 
     In some embodiments, the method further comprises further deflecting the first compliant arm to wipe against the first strip. 
     In some embodiments, further deflecting the first compliant arm causes a distal end of the first compliant arm to move closer to the intermediate portion. 
     Some embodiments relate to an electronic device, comprising a first printed circuit board (PCB) comprising a first plurality of pads; a second PCB parallel to the first PCB and separated from the first PCB along a first direction by a distance between 1.9 mm and 10 mm, the second PCB comprising a second plurality of pads; an electronic component mounted on the first PCB, wherein the second PCB at least partially covers the electronic component; and an interposer disposed between the first PCB and the second PCB, the interposer having a plurality of contacts placing the first plurality of pads in electrical communication with respective pads of the second plurality of pads. 
     In some embodiments, each contact of the plurality of contacts comprises: an intermediate portion; a first compliant arm in contact with a respective pad of the first plurality of pads and extending from the intermediate portion in the first direction, the first compliant arm comprising a first contact region; and a projection extending from the intermediate portion in a second direction perpendicular to the first direction, the projection comprising a first bent portion forming a first strip that is angled relative to the first direction and facing the first contact region. 
     In some embodiments, the projection further comprises a second bent portion forming a second strip parallel to the first strip; and each contact further comprises a second compliant arm in contact with a respective pad of the second plurality of pads and extending from the intermediate portion in a direction opposite the first direction, the second compliant arm comprising a second contact region facing the second strip. 
     In some embodiments, the first bent portion extends from the projection in a third direction perpendicular to both the first and second directions. 
     The foregoing features may be used separately or in any suitable combination. The foregoing is a non-limiting summary of the invention, which is defined by the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
         FIG.  1    is an exploded perspective view of an electronic assembly including an interposer, in accordance with some embodiments. 
         FIG.  2 A  is a perspective view of an interposer including an array of contacts, in accordance with some embodiments. 
         FIG.  2 B  is a side view of the interposer of  FIG.  2 A , in accordance with some embodiments. 
         FIG.  3 A  is a side view of a stamped portion of a metal sheet, in accordance with some embodiments. 
         FIG.  3 B  is a perspective view of a contact obtained by bending the stamped portion of  FIG.  3 A , in an uncompressed state, in accordance with some embodiments. 
         FIG.  3 C  is a perspective view of the contact of  FIG.  3 B , in a compressed state, in accordance with some embodiments. 
         FIG.  3 D  is a cross sectional side view of a portion of the interposer of  FIG.  2 A  including a contact in an uncompressed state, in accordance with some embodiments. 
         FIG.  3 E  is a cross sectional side view of a portion of the interposer of  FIG.  2 A  including a contact in a compressed state, in accordance with some embodiments. 
         FIG.  3 F  is a top view of the interposer of  FIG.  2 A , in accordance with some embodiments. 
         FIG.  4 A  is a side view of another stamped portion of a metal sheet, in accordance with some embodiments. 
         FIG.  4 B  is a perspective view of a contact obtained by bending the stamped portion of  FIG.  4 A , in an uncompressed state, in accordance with some embodiments. 
         FIG.  4 C  is a perspective view of the contact of  FIG.  4 B , in a partially compressed state, in accordance with some embodiments. 
         FIG.  4 D  is a perspective view of the contact of  FIG.  4 B , in a fully compressed state, in accordance with some embodiments. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The inventors have recognized and appreciated techniques for making an interposer to support electrical connections through the interposer with high signal integrity while simultaneously meeting the mechanical requirements for a high density electronic device. Those interposers may enable high integrity connections between arrays of contact points on a first substrate (e.g., a printed circuit board) and arrays of contact points on a second substrate (e.g., another printed circuit board or a semiconductor chip). These high integrity connections may be supported even for a relatively large separation between the first and second substrate and a relatively high density of connections. 
     Interposers as described herein may support an electronic device with a mezzanine or stacking configuration, such that the electrical interface of the first substrate is in a plane parallel to the plane of the electrical interface of the second substrate. For example, the first substrate may include pads formed on a top surface of the first substrate and the second substrate may include pads formed on a bottom surface of the second substrate, where the top surface of the first substrate is parallel to the bottom surface of the second substrate. During operation, the pads on the first substrate are electrically connected to the pads of the second substrate through the interposer. With interposers as describe herein, the first and second substrates may be separated by a sufficient distance to enable components mounted on either first or second substrate to occupy the space between the substrates. While such a configuration enables a high density of electronic components, constructing an interposer that spans that separation and meets the electrical and mechanical requirements of a high speed, high density electronic system poses challenges. 
     Interposers as described herein may include arrays of contacts designed to electrically connect points of contact on a first substrate to points of contact on a second substrate. The contacts may provide vertical compliance in one direction (e.g., towards the upper substrate or towards the lower substrate, but not both) or in two opposed directions (e.g., towards the upper substrate and simultaneously towards the lower substrate). The vertical compliance increases the interposer tolerance with respect to variations in the vertical extension of the various components that constitute the electronic assembly, including variations in the heights of the substrates and the interposer. 
     Further, each contact may provide two (or more) conductive paths between the points of contact. For example, a first conductive path may be established by simply causing a contact to touch two opposed pads, and a second conductive path may be established as a result of the compression of the contact as it is pressed against those pads. Multiple conductive paths lead to a reduction in the contact inductance and resistance and avoids electrical stubs, thereby improving signal integrity. Accordingly, some embodiments are directed to an interposer having contacts configured so that each contact, when compressed by a pair of opposed substrates, provides a first conductive path and a second conductive path parallel to the first conductive path. 
     The inventors have recognized and appreciated designs for interposer contacts to provide two (or more) conductive paths between parallel substrates separated by a relatively large distance. For example, parallel substrates may be separated from one another by a distance greater than 1.8 mm, such as between 1.9 mm and 10 mm or between 1.9 mm and 3 mm. As the distance between substrates increases, the thickness of interposers, and consequently, the height of the contacts must also be increased. Accordingly, contact heights in excess of 1.8 mm are required in some arrangements (the height being measured in the fully compressed state). 
     Such designs may be achieved without increasing the lateral extension (the width) of the contacts because doing so would otherwise reduce the density of contacts per unit volume within the interposer. For example, some interposers have a contact pitch of 1 mm or less. To support connections between similar components with a larger separation, an interposer may be provided with contacts with high aspect ratios (with relatively tall and thin geometries), as described herein. 
     Unfortunately, designing contacts with high aspect ratios and, simultaneously, to provide multiple parallel conductive paths is challenging from a mechanical standpoint. One approach is to design contacts with arms at each end that make electrical contact with each other. When such a contact is compressed between two substrates, both compliant arms bend inwardly. At some point along the bending range (e.g., halfway through the bending range), the arms directly touch one another, thereby forming an additional conductive path in parallel to the first conductive path. While this design works well for relatively short contacts, it does not provide reliable connections where the contacts are tall. Tall contacts require that the arms be sufficiently long to cover the additional contact height when they bend. However, increasing the length of an arm—without simultaneously increasing its lateral extent (because, as explained above, doing so would reduce the contact density)—leads to unreliable connections as the arms may be too compliant to form a reliable electrical connection or even to ensure that the arms will press against each other. 
     The inventors have recognized and appreciated that reliable operation of a high aspect ratio contacts may be provided by contacts with a rigid portion which both arms can touch when compressed. This design enables contacts with arbitrarily high aspect ratios. In this design, an additional conductive path is formed by causing the arms to touch the rigid portion. Contacts that include these rigid portions can be designed with shorter arms than would be necessary in the absence of a rigid portion. In one example, a contact includes an intermediate portion, a pair of compliant arms extending from the intermediate portion in opposite directions parallel to the mating direction, and a rigid portion protruding laterally from the intermediate portion. The rigid portion includes a pair of landing strips positioned at opposite ends of the rigid portion, where the landing strip are configured to contact a respective compliant arm as the compliant arm is compressed. Such a contact may be made by stamping a sheet of metal to form a unitary planar piece, and by bending this piece at multiple locations to provide the desired shape. 
       FIG.  1    is a perspective view of an electronic assembly including an interposer, in accordance with some embodiments. Electronic assembly  1  includes substrates  14  and  18 , an interposer  10  and another electronic component  17 . In some embodiments, substrates  14  and  18  may be part of respective electronic components. For example, substrate  14  may be a PCB (e.g., a motherboard) and substrate  18  may be a semiconductor card (e.g., a processor card), for example. In such arrangements, interposer  10  may be a portion of a chip socket including mounting hardware attached to substrate  14  (not shown for simplicity of illustration). Alternatively, substrate  18  may also be a PCB or a connector carrying cables connected to a device positioned outside assembly  1 . 
     In electronic assembly  1 , the electrical interface of substrate  14  is in a plane parallel to the plane of the electrical interface of substrate  18 . In the example of  FIG.  1   , substrate  18  includes pads  16  formed on the bottom surface of substrate  18 , and substrate  14  includes pads  12  formed on the top surface of substrate  14 , where the bottom surface of substrate  18  is parallel to the top surface of substrate  14 . During operation, pads  16  are in electrical contact with pads  12  via interposer  10 . 
     The separation between the substrates, and consequently, the thickness of interposer  10  (along the z-axis) may be sufficiently large to allow electronic component  17  to fit near interposer  10  under substrate  18 . In some embodiments, electronic component  17  has a height in excess of 1.8 mm. Electronic component  17  may include, for example, a bank of memory cards or may be a connector terminating a plurality of cables carrying signals that pass through interposer  10  to components on substrate  18 . In some embodiments, the lateral extension of substrate  18  is such that electronic component  17  lies at least partially under substrate  18 . As a result, substrates  18  at least partially covers electronic component  17 . In these embodiments, in order to ensure a reliable connection between substrates  18  and  14 , interposer  10  (and, consequently, contacts  100 ) should be designed to be taller than electronic component  17 . 
     Interposer  10  may be mounted to substrate  14  (using posts, bolts, latches, or other hardware not shown for simplicity), and electrical connections may be formed via spring-loaded contacts. For example, interposer  10  may include compliant beams at the bottom side of interposer  10 . Latching structures (not shown in  FIG.  1   ) may retain interposer  10  in place on substrate  14 , thereby allowing the spring-loaded contacts to produce a force towards substrate  14 . Further, substrate  18  may be pressed into the top surface of interposer  10 . Electronic assembly  1  may include posts, bolts, latches, or other hardware (not shown in  FIG.  1   ) to hold substrate  18  to the interposer and to press the substrate against the mating portions of the interposer contacts. In some embodiments, the upper mating portions of the contacts of the interposer  10  may be compliant and may exert a force against pads  16  when substrate  18  is pressed against the interposer. Similarly, the lower mating portions of the contacts of the interposer  10  may be compliant and may exert a force against pads  12  when substrate  14  is pressed against the interposer. 
       FIG.  2 A  is a perspective view illustrating an interposer  10  in additional detail, in accordance with some embodiments. Interposer  10  includes an insulative member  11  serving as the interposer housing. Insulative member  11  includes a top surface  13  and a bottom surface  15 , which opposes top surface  13 . Insulative member  11  holds an array of contacts  100 , which may be arranged in an array, here shown as a rectangular array with rows and columns, for example. Each contact  100  includes an upper mating portion that is exposed at top surface  13  and a lower mating portion that is exposed at bottom surface  15 . Being exposed outside the interposer housing, the upper mating portions allow for electrical connections with substrate  18  and, similarly, the lower mating portions allow for electrical connections with substrate  14 . Insulative member  11  may include channels through which the bodies of the contacts are passed and retained. 
     In some embodiments, each contact of an interposer  10  may provide two (or more) parallel conductive paths electrically connecting a pad  12  with a pad  16 . Providing multiple parallel conductive paths may reduce the overall contact inductance and the overall contact resistance and short out electrical stubs that would otherwise be formed by the distal portions of the contact arms, thereby improving signal integrity.  FIG.  2 B  is a cross sectional view of an interposer  10 , in accordance with some embodiments. This depiction illustrates that one of the contacts  100 , which includes an upper mating portion exposed at the top surface  13  and a lower mating portion exposed at the bottom surface  15 , forms two parallel paths through its length (labeled “first conductive path” and “second conductive path” respectively). Although not illustrated, the other contacts  100  may be designed in a similar fashion. 
     Some embodiments relate to contacts designed to provide parallel conductive paths while simultaneously ensuring reliable mechanical connections. Some such embodiments relate to contacts with tall and thin geometries. These geometries allow the contacts to satisfy contact density requirements while also providing sufficient play to accommodate electronic components of varying dimensions. As one example, a contact may have a height (along the z-axis, which is perpendicular to the substrates connected by interposer  10 ) that is greater than 1.8 mm (such as between 1.9 mm and 3 mm or between 1.8 mm and 10 mm) in the fully compressed state and may have a width (along the x-axis) less than 1 mm (such as between 0.2 mm and 0.8 mm) in the fully compressed state. 
     As explained above, designing contacts to be tall and thin, and, simultaneously, to provide multiple parallel conductive paths is challenging. In some embodiments, this may be accomplished by causing the contact&#39;s upper arm and the contact&#39;s lower arm, when compressed, to touch a rigid portion positioned between those arms. The inventors have recognized and appreciated that such an arrangement provides more reliable connections relative to arrangements in which, when compressed, the arms directly touch one another. This is because inserting a rigid portion between the arms fills part of the vertical extension of the contact, thereby enabling a reduction in the vertical extension of the arms. Having shorter arms is advantageous in that the arms may have mechanical properties that ensure reliable connections when the contact is compressed. 
     In some embodiments, each contact  100  may be made of a unitary piece of conductive material. Contacts  100  may be fabricated, for example, by stamping a sheet of metal to cut out a piece with a predefined shape and by folding the stamped shape to provide the desired geometry. In some embodiments, the sheet has a thickness between 0.030 mm and 0.070 mm (e.g., 0.050 mm). Different materials may be used for the metal sheet, including copper alloys. In one example, the metal sheet may be made of a copper-nickel-silicon alloy. In some embodiments, plating such as one or more of nickel, gold, silver, or tungsten, among others may be applied to all or portions of the contact. Contact portions of the contact, for example, may be plated. 
       FIG.  3 A  illustrates a stamped portion of a metal sheet that may be formed into a contact, in accordance with some embodiments. At this stage (prior to being bent), the contact has a planar shape. The contact includes an intermediate portion  101 , which may be positioned generally in the middle of the contact (relative to the z-axis). Arm  102  extends from intermediate portion  101  in the upwards direction (along the z-axis) and arm  112  extends from intermediate portion  101  in the downwards direction (along the z-axis). Both arms  102  and  112  are elongated along the z-axis. The width of both arms, (relative to the x-axis) varies along the length of the arms. The arm portions closer to the intermediate portion  101  are wider than the distal arm portions. As a result, the elasticity of the arms varies along their lengths. Each arm includes a pair of wings  106  laterally extending from the arms. The wings  106  provide high hertzian contact pressure when the contact force is low, such as for a 0.050 mm thick material. The distal ends of the arms include widened portions  104  and  114 , respectively, which serve as the arms&#39; contact regions. Contact  100  further includes a projection  120  extending laterally (along the x-axis) from intermediate portion  101 . The projection may be sized to be substantially rigid with respect to the z-axis. In this example, projection  120  is T-shaped. Ends  122  and  132  are defined on opposite sides of projection  120  relative to the z-axis. A tab  103  extends from intermediate portion  101  opposite projection  120 . 
       FIG.  3 B  illustrates contact  100  upon being bent, in accordance with some embodiments. As can been appreciated by comparing  FIG.  3 A  with  FIG.  3 B , the contact has been bent at multiple locations. Projection  120  has been bent by approximately 90° relative to intermediate portion  101 . Intermediate portion  101  substantially lies in a yz-plane while projection  120  substantially lies in an xz-plane. 
     Ends  122  and  132  have been bent by approximately 90° relative to projection  120 . Once bent, ends  122  and  132  form a pair of landing strips. Landing strip  122  substantially lies in a first xy-plane and landing strip  132  substantially lies in a second xy-plane parallel to the first xy-plane. 
     Compliant arm  102  has been bent at multiple locations:  115 ,  117 ,  119  and  121 . Compliant arm  112  has been bent at multiple locations in a similar manner. When bent, the arms may be more compliant with respect to the z-axis than they are with respect to the y-axis. Each of the curved regions  115 ,  117 ,  119  and  121  defines a convex region and a concave region. The convex regions face away from arm  102  and the concave regions face the cavity formed among arm  102 , projection  120  and intermediate portion  101 . Wings  106  have been bent upwardly and wings  116  have been bent downwardly. Curved region  117  serves as a contact region with respect to a pad  16 . As pad  16  presses further into contact  100 , contact region  117  wipes against the pad, thereby improving the reliability of the mechanical connection. 
       FIG.  3 B  illustrates a contact  100  in the uncompressed state. In such a state, the convex portion of contact region  104  faces, but does not touch, landing strip  122  and the convex portion of contact region  114  faces, but does not touch, landing strip  132 .  FIG.  3 C  illustrates a contact  100  in a fully compressed state. Contact between contact region  104  and landing strip  122  may occur halfway through the compression range of arm  102 , for example. Further compression beyond this point causes contact region  104  to wipe against landing strip  122 , as shown in  FIG.  3 C . Similarly, contact between contact region  114  and landing strip  132  may occur halfway through the compression range of arm  112 , for example. The range between the level of compression at which contact region  121  touches landing strip  122  and full compression is intended to provide tolerance with respect to height variations. 
     Throughout the compression cycle, contact  100  provides a non-linear force response to compression. As a connection is first made between an arm and a landing strip, the reaction force of the connection and the reaction force at the pad build quickly due to the kinematic geometry. As deflection progresses, both reaction forces soften in response to intentional kinematic changes. The distance between the physical contact tangency and virtual support of the arms increases, extending the beam length and creating a reduced spring rate. The benefit is a rapid build of force to institute a reliable electrical connection early in the mechanical bending range, and subsequently a reduced maximum reaction force near the maximum compression state. As a result, less wear occurs between mating interfaces, and less warpage occurs in the hardware supporting the interposer. This reduces packaging space and weight of assembly hardware. 
       FIG.  3 D  is a cross sectional view of an interposer illustrating a contact  100  in an uncompressed state and  FIG.  3 E  is a cross sectional view of the interposer illustrating a contact  100  in a fully compressed state, in accordance with some embodiments. In the depiction of  FIG.  3 D , pad  16  contacts the upper arm of contact  100  and pad  12  contacts the lower arm of contact, but no pressure is exerted on either ends. At this stage, a first conductive path is established from pad  16  to pad  12 . This conductive path extends through intermediate portion  101 . Although a portion of this conductive path may partially extend into projection  120 , this conductive path exhibits more current density in the intermediate portion than it does in the projection. 
     In some embodiments, contact  100  is not latched or anchored to the walls of channel  150 , but rather, is slidably retained in the channel. In this example, channel  150  has a constricted central portion, which prevents contact  100  from sliding out of channel  150 . As a result, contact  100  is free to move inside channel  150  in the vertical direction, thus balancing the relative forces applied at either ends of the contact. 
     In the depiction of  FIG.  3 E , pads  12  and  16  are pressed against contact  100 , thereby causing compression of the arms. When the arms contact projection  120 , a second conductive path is established that is parallel to the first conductive path. The presence of this additional conductive path reduces the inductance and resistance of contact  100 , thereby improving signal integrity. 
     In some embodiments, the height H of a contact (in the fully compressed state) exceeds 1.8 mm, 2 mm, 3 mm or 4 mm, for example. For example, height H may be between 1.9 mm and 2 mm, between 1.9 mm and 3 mm or between 1.9 mm and 10 mm, among other possible ranges. In one example, height H is 2.87 mm. In some embodiments, the width W of a contact is less than 1 mm (e.g., between 0.2 mm and 0.8 mm). Accordingly, this contact is tall and thin—for example, it has an aspect ratio (H/W) greater than or equal to 1.8 (e.g., between 1.8 and 5), greater than or equal to 2 (e.g., between 2 and 5) or greater than or equal to 3 (e.g., between 3 and 5). As a result, this contact allows for electronic assemblies in which the separation between two substrates exceeds 1.8 mm without necessarily reducing the contact pitch. 
       FIG.  3 F  is a top view of an interposer  10 , in accordance with some embodiments. This depiction illustrates an array of channels  150  each including a contact  100 . The contact pitch P equals the separation between adjacent contacts along the y-axis. In some embodiments, pitch P may be 1 mm or less. The small contact pitch is enabled by the relatively small width W. 
     In this example, each contact  100  is shaped so that the entirety of the contact is confined within the boundaries of the respective channel  150  with respect to the xy-plane. This confined arrangement allows a reduction in the size of the substrate pads without sacrificing contact location precision. Reducing the size of a pad improves the pad&#39;s electromagnetic performance. 
       FIGS.  4 A- 4 D  illustrate an alternative implementation of contact  100 , in accordance with some embodiments.  FIG.  4 A  illustrates a stamped portion of a metal sheet that may be formed into a contact. At this stage (prior to being bent), the contact has a planar shape. The contact of  FIGS.  4 B- 4 D  is obtained by bending the planar element of  FIG.  4 A  in the same manner described above in connection with  FIG.  3 B .  FIG.  4 B  illustrates the contact of  FIG.  4 A  once it has been bent. In this depiction, contact  100  is uncompressed. In  FIG.  4 C , contact  100  is partially compressed and the mating regions touch the respective landing strips. In  FIG.  4 D , the contact is fully compressed. This design operates according to the same principle of operation as described above in connection with  FIGS.  3 A- 3 F . Relative to the implementations of  FIG.  3 A- 3 F , the implementations of  FIG.  4 A- 4 D  may be used for larger separations between substrates  14  and  18 . For example, the height H of the contact of  FIG.  4 A  may exceed 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm in some embodiments. In one example, height H is 7.75 mm. 
     The contact includes an intermediate portion  101 , a projection  120  extending laterally from the intermediate portion, and a pair of arms  102  and  112  extending in opposite direction along the z-axis. Arms  102  and  112  have widths that vary along their lengths. Widened portions  104  and  114  are formed at the distal end of the arms. Ends  122  and  132  extend from projection  120  in opposite directions. In this arrangement, projection  120  is n-shaped. Two supports connect projection  120  to intermediate portion  101 , with an opening  131  being formed between the supports. Opening  131  reduces the amount of material requiring bending. This reduces the forming force and reduces the variability of the material formed above and below the opening. 
     Connecting the projection to the intermediate portion by means of two supports increases the rigidity of the projection relative to T-shaped projections. Tabs  103  laterally extend from intermediate portion  101  opposite projection  120 . 
     Having thus described several embodiments, it is to be appreciated various alterations, modifications, and improvements may readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. 
     For example, some contacts are described as signal contacts. Similar contacts may be used as ground contacts. In some embodiments, signal and ground contacts may be differentiated based on shape, with the ground contacts being wider than signal contacts of some or all of their length. Alternatively, they may be differentiated by position, with signal contacts being positioned in pairs between ground contacts, for example in a ground, signal, signal, ground (GSSG) pattern, where adjacent signal contacts form a differential pair. Alternatively, the contacts may be arranged in a signal, ground, signal (SGS) pattern. The ground contacts may electrically connect to a ground plane of substrate  14 . 
     A chip socket has been described as an example of a component containing an interposer. Techniques as described herein may be used to construct an interposer used for any suitable purpose, such as to join two parallel printed circuit boards. Similarly, a printed circuit board was used as an example of a substrate with conductive structures to be connected to another device through an interposer. Techniques as described herein may be used to connect any suitable substrate to another electronic component. 
     Further, exemplary materials were described for portions of the interposer. Other materials may be used. 
     In some configurations, a semiconductor device with a Ball Grid Array or Land Grid Array may be connected to the board through the interposer. Alternatively, or additionally, the component may be the end of a flexible printed circuit. Accordingly, it should be appreciated that a component with a substrate having contact pads thereon may be pressed against the interposer to make electrical connections. 
     In some embodiments, a compressive force is applied to an interposer as a result of a lid being closed with some mechanism to bias the lid towards the interposer. That mechanism may include spring-like members with camming surfaces formed as part of the frame, for example. Similar spring-like members may be formed as part of a sheet-metal shell surrounding the frame and/or the interposer. 
     Terms signifying direction, such as “upwards” and “downwards,” were used in connection with some embodiments. These terms were used to signify direction based on the orientation of components illustrated or connection to another component, such as a surface of a printed circuit board to which a termination assembly is mounted. It should be understood that electronic components may be used in any suitable orientation. Accordingly, terms of direction should be understood to be relative, rather than fixed to a coordinate system perceived as unchanging, such as the earth&#39;s surface. 
     Further, though advantages of the present invention are indicated, it should be appreciated that not every embodiment of the invention will include every described advantage. Some embodiments may not implement any features described as advantageous herein and in some instances. Accordingly, the foregoing description and drawings are by way of example only. 
     Various aspects of the present invention may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. 
     Also, the invention may be embodied as a method, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. 
     Also, circuits and modules depicted and described may be reordered in any order, and signals may be provided to enable reordering accordingly. 
     Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. 
     All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. 
     The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” 
     As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. 
     The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. 
     Also, the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof herein, is meant to encompass the items listed thereafter (or equivalents thereof) and/or as additional items.