Cryogenic Probe Card

Abstract

The probe card includes a support element having a first side and a second side opposite the first side. A plurality of probe tips extend outwardly from the first side of the support element, the probe tips configured to contact components of a device under test (DUT). A plurality of vias extend through the support element from the first side to the second side, each of the vias connected to a respective probe tip of the plurality of probe tips. A plurality of conductive traces are formed on the support element, each of the traces connected to a respective via in the plurality of vias, and electrical signals can be provided to or received from the probe tips through the conductive traces.

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 165,105, entitled "CRYOGENIC PROBE CARD," filed March 23, 2021, which is incorporated herein by reference in its entirety.

[0002] Government Interest Statement This invention was made with government support under Contract Nos. W909MY-19-P-0032 and W909MY-21-C-0005 awarded by the U.S. Army. The U.S. Government has certain rights in this invention. [Background technology]

[0003] Probe cards are used to test the functionality and connectivity of components of an integrated circuit. A probe card can include multiple probes, each configured to make electrical contact with a respective component of an integrated circuit (IC). The functionality or connectivity of the components in electrical contact with the probes can then be tested by electrical signals input to or received from the IC by the probes. Traditionally, due to various applications and design requirements, probe cards have included probes spaced 20 microns or more apart from each other. Therefore, conventional probe cards are not well suited to testing the functionality and connectivity of components of an IC that are spaced closer than 20 microns apart from each other. Summary of the Invention

[0004] The following is a brief summary of subject matter described in more detail herein. This summary is not intended to be limiting on the scope of the claims.

[0005] Described herein is technology related to probe cards for testing ICs. More specifically, described herein is a cryogenic probe card suitable for testing elements of an IC at low temperatures (e.g., about 0° C. or less, about 200 K or less, or about 150 K or less). Furthermore, described herein is a probe card suitable for testing elements of an IC spaced less than 20 microns apart from one another.

[0006] An exemplary probe card includes a probe platform including a support element, multiple probe tips, multiple vias, and multiple conductive traces. The support element can be a substantially solid element configured to house, hold, or support the probe tips. The probe tips extend outward from a bottom surface of the support element. The probe tips are conductive elements configured to contact a device under test (DUT) to facilitate testing the functionality or electrical connectivity of the DUT. The probe tips can be positioned closely together on or within the support element. For example, the probe tips can be positioned less than 20 microns, less than 10 microns, or less than 1 micron apart from each other. The multiple vias can be configured such that each via is connected to a respective probe tip of the multiple probe tips. The vias extend from the bottom surface of the support element to the top surface of the support element. The multiple conductive traces can be positioned on the top surface of the support element, each connected to a respective via in the multiple vias. Thus, electrical signals can be provided to or received from the probe tips via the conductive traces on the top surface of the support element.

[0007] The support element can include a central platform, a plurality of arms, and an annular portion disposed around the central platform and connected to the central platform via the arms. The central platform can include probe tips mounted thereon. As the probe card moves toward the surface of the DUT, the probe tips contact elements on the surface of the DUT. The elements of the DUT exert a force on the probe tips that opposes the movement of the probe tips toward the DUT. The support element can be configured to allow the central platform to flex along the line of motion of the probe card in response to the elements of the DUT exerting a force on the probe tips. By way of example and not limitation, the arms of the central platform can be thin and narrow relative to their length, thereby providing sufficient flexibility to allow the central platform to flex. Flexing of the central platform, including the probe tips, can prevent the probe tips from damaging the elements of the DUT when they contact those elements.

[0008] An exemplary probe card may further include a circuit board to which the probe platform may be attached. The circuit board may be configured to facilitate handling or attachment of the probe card or to facilitate electrical connection between the probe card and other test elements, such as various electrical meters or measurement devices (e.g., voltmeters, ammeters, ohmmeters, etc.) or power sources (e.g., voltage or current sources). In exemplary embodiments in which the support element includes multiple arms and / or annular portions, the probe platform may be attached to the circuit board by the arms and / or annular portions of the probe platform. Each of the multiple conductive traces of the probe platform may extend to the circuit board and electrically connect with a respective electrical contact on the circuit board. The electrical contacts on the circuit board may be configured to facilitate connection of test elements to the multiple conductive traces. For example, the electrical contacts may be or include any of a variety of connectors, such as coaxial connectors (e.g., BNC connectors), plugs, pins, sockets, etc.

[0009] Some DUTs, such as some types of focal plane arrays (FPAs), are configured to operate in very cold environments. To test the functionality of such devices, the probe card must be able to withstand the low temperatures at which these devices operate. The circuit board may further include multiple flexures configured to allow deflection due to thermal expansion or contraction of the circuit board and / or the probe card platform. By way of example, the probe platform may be a substantially flat element. The flexures of the circuit board may be configured to deflect in a direction substantially parallel to the plane of the probe platform to reduce mechanical stresses caused by different thermal expansion / contraction rates between the probe platform and the circuit board. The flexures may further be configured to resist deflection in a direction perpendicular to the plane of the probe platform. For example, the flexures may be configured to resist deflection of the probe platform caused by forces applied to the probe pins when the probe pins contact the DUT.

[0010] The above summary presents a simplified overview in order to provide a basic understanding of some aspects of the systems and / or methods described herein. This summary is not an extensive overview of the systems and / or methods described herein. It is not intended to identify key / critical elements or to delineate the scope of such systems and / or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1 is a perspective view of the top surface of an exemplary probe card. [Figure 1B] FIG. 1B is a perspective view of the bottom of the exemplary probe card shown in FIG. 1A. [Figure 2A] FIG. 2 is a perspective view of an exemplary probe card support element. [Figure 2B]FIG. 2B is a partial perspective view of the probe card support element shown in FIG. 2A. [Figure 2C] FIG. 2C is a partial perspective view of the bottom of the probe card support element shown in FIGS. 2A and 2B. [Figure 3] FIG. 2 is a top view of an exemplary platform for supporting probe tips of a probe card. [Figure 4] 1 is a cross-sectional view of an exemplary support element of a probe card. [Figure 5] FIG. 2 is a partial perspective view of the probe card shown in FIGS. 1A and 1B. [Figure 6] FIG. 2 is a cross-sectional view of the probe card shown in FIGS. 1A and 1B. [Figure 7] FIG. 10 is a top view of another exemplary support element. [Figure 8A] 1A-1C illustrate exemplary processing steps for forming a probe tip support element. [Figure 8B] 1A-1C illustrate exemplary processing steps for forming a probe tip support element. [Figure 9] 10A-10C illustrate exemplary processing steps for forming another probe tip support element. [Figure 10] FIG. 1 is a flow diagram illustrating an exemplary method for forming a probe card.

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] Various techniques relating to probe cards having closely spaced probe elements and suitable for cryogenic operation are now described with reference to the drawings, wherein like numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be apparent, however, that such aspects may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form to facilitate description of one or more aspects. Furthermore, it should be understood that functions described as being performed by particular system components may be performed by multiple components. Similarly, for example, a component may be configured to perform functions described as being performed by multiple components.

[0025] Furthermore, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or." That is, unless otherwise specified or clear from the context, the phrase "X uses A or B" is intended to mean any of the natural inclusive permutations. That is, the phrase "X uses A or B" is satisfied by any of the following examples: X uses A, X uses B, or X uses both A and B. Furthermore, the articles "a" and "an," as used in this application and the appended claims, should generally be construed to mean "one or more" unless otherwise specified or clear from the context that the singular form is intended.

[0026] Furthermore, as used herein, the terms "component" and "system" are intended to encompass computer-readable data storage comprised of computer-executable instructions that, when executed by a processor, cause certain functions to be performed. Computer-executable instructions may include routines, functions, etc. It should also be understood that a component or system may be localized on a single device or distributed across several devices. Furthermore, as used herein, the term "exemplary" is intended to mean serving as an example or instance of something and is not intended to indicate a preference.

[0027] 1A and 1B, perspective views of an exemplary probe card 100 are shown. Referring now only to FIG. 1A, a perspective view of a top surface 102 of the probe card 100 is shown. Referring now only to FIG. 1B, a perspective view of a bottom surface 104 of the probe card 100 is shown. Referring again to FIGS. 1A and 1B together, the probe card 100 includes a probe platform 106 and a circuit board 108. The probe platform 106 is configured to support a plurality of conductive probes (e.g., shown in FIG. 2C ) according to various embodiments described in more detail below. The circuit board 108 is configured to support the probe platform 106 and facilitate electrical connections between elements of the probe platform 106 and other equipment used with the probe card 100 to test the functionality or connectivity of elements on an IC DUT. The circuit board 108 can be, for example, a printed circuit board (PCB) on which various components are formed or connected.

[0028] The probe card 100 can be used to test the functionality or connectivity of elements of a DUT by lowering the probe card 100 onto the DUT until the probes on the underside 110 of the probe platform 106 contact the elements of the DUT being desirably tested. Alternatively, the DUT can be placed on a stage and raised towards the probe card 100 until the elements of the DUT contact the probes on the underside 110 of the probe platform 106.

[0029] The probe platform 106 includes a support element 112. The support element 112 is configured to support a plurality of conductive probes (e.g., as shown in FIGS. 2C and 3). As described in more detail below, the support element 112 holds the probes in a stable arrangement to facilitate establishing contact between the probes and elements of the DUT. The support element 112 further includes, supports, or comprises various components to facilitate forming electrical connections between the probes and test equipment connected to the probe card 100. As used herein, the probe platform 106 is intended to refer to the support element 112 as well as the various components contained thereon / in it.

[0030] 2A-2C, various views of the probe platform 106 are shown. Referring only to FIG. 2A, a perspective view of the support element 112 is shown. Referring only to FIG. 2B, a partial perspective view of the central platform 114 of the support element 112 is shown. Referring only to FIG. 2C, a partial perspective view of the underside of the central platform 114 of the support element 112 is shown.

[0031] Referring again to FIG. 2A , the support element 112 includes a central platform 114, an annular portion 116, and a plurality of arms 118 extending from the central platform 114 to the annular portion 116. While not shown in FIG. 2A , the central platform 114 includes a plurality of probes disposed thereon. For example, referring briefly to FIG. 3 , a view facing the underside 300 of an exemplary central platform 302 is shown, with the central platform 302 including a plurality of probe tips 304 extending therefrom. While the central platform 302 is shown as including nine probe tips 304, it should be understood that virtually any number of probe tips 304 can be included on the central platform 302. The probe tips 304 can have a conical shape extending from the underside 300 of the platform 302 (i.e., off-page) such that each of the probe tips 304 terminates at a point 306. In other embodiments, the probe tips 304 can have a pyramidal shape.

[0032] It should be understood that the probe tips 304 can occupy only a small portion of the underside 300 of the central platform 302. In other embodiments, the probe tips 304 can be distributed across substantially the entire underside 300 of the central platform 302. Furthermore, the placement of the probe tips 304 can desirably be based on the placement of the elements of the DUT being tested. For example, if the probe card 100 is intended to be used to test the functionality or connectivity of a DUT having regularly spaced elements, the probe tips 304 of the central platform 302 can be regularly spaced at the same intervals as the elements of the DUT. In exemplary embodiments, the distance d1 between the first probe tip 308 within the probe tip 304 and the second probe tip 310 within the probe tip 304 can be less than 20 microns, 10 microns or less, or 1 micron or less. In still further embodiments, the distance d1 can be less than 1 micron, 500 nanometers or less, or 250 nanometers or less.

[0033] Referring again to FIG. 2A , the support element 112 is configured to allow deflection of the central platform 114 in a direction perpendicular to the surface 119 of the support element 112. Additionally, the support element 112 is configured to resist deflection of the central platform 114 along a plane parallel to or coplanar with the surface 119 of the support element 112. By way of example and not limitation, the arms 118 can be thin and narrow relative to their length so that the arms 118 are rigid in a plane parallel to the surface 119 and can deflect in a direction perpendicular to the surface 119. Thus, when the central platform 114 is subjected to an upward force resulting from a probe tip below the central platform 114 contacting the DUT, the central platform 114 can exhibit some upward deflection from its initial position. This deflection can prevent contact damage to the DUT caused by the probe tip. The rigidity of the arms 118 in the plane parallel to the surface 119 prevents the probe tip attached to the central platform 114 from becoming misaligned with components of the DUT.

[0034] Referring now to FIG. 2B, a partial perspective view of the central platform 114 is shown. The central platform 114 may have a plurality of conductive traces 120 formed thereon. Each of the conductive traces 120 extends from the central platform 114 along a respective arm 118 of the support element 112. The conductive traces 120 may be formed as a metallization layer on the support element 112, as described in more detail below. Each of the conductive traces 120 is connected to a respective via 122 that extends through the central platform 114 from a top surface 124 of the central platform 114 to a bottom surface 126 of the central platform 114. Each of the vias 122 is connected to a respective probe tip that extends downward from the bottom surface 126 of the central platform 114. As shown in FIG. 2B, the arms 118 of the support element 112 may be configured to have a thickness t1 that is less than the overall thickness t2 of the central platform 114. Thus, the central platform 114 and the probes disposed thereon may extend lower than other portions of the probe card 100. This configuration can help prevent portions of the probe card 100 other than the probes from contacting the DUT when the probe card 100 is moved toward the DUT at an angle offset from the plane of the DUT.

[0035] 2C , there is shown a partial perspective view of the bottom surface 126 of the central platform 114. Elements of the probe platform 106, such as the conductive traces 120 and vias 122, are shown for purposes of illustration, but it should be understood that in some embodiments, these features may not be visible from the bottom surface 126 of the central platform 114. However, in some embodiments in which the support platform 112 is formed of a substantially transparent material, the traces 120 and vias 122 may be visible from the bottom surface 126 of the central platform 114.

[0036] The probe platform 106 includes a plurality of probe tips 128 and a second plurality of conductive traces 130 on the bottom surface 126 of the central platform 114. As described in more detail below, the probe tips 128 can be formed directly on the bottom surface 126 of the central platform 114. In other embodiments, the probe tips 128 can be formed within the bulk of the central platform 114 and subsequently exposed by selectively removing material from the bottom surface 126 of the central platform 114 (e.g., by etching, electro-discharge machining, ablation, etc.). The probe tips 128 can be arranged in any configuration suitable for testing components of the DUT. In a non-limiting example, if the DUT is a focal plane array (FPA) having a plurality of light-sensitive pixel cells (LSPCs) disposed thereon, the number and spacing of the probe tips 128 can be configured to align with the plurality of LSPCs such that each of the probe tips 128 contacts a respective LSPC of the FPA.

[0037] The second plurality of conductive traces 130 can facilitate connections between the probe tips 128 and the first plurality of conductive traces 120 on the top surface 124 of the central platform 114. For example, if the spacing between the probe tips 128 is small (e.g., less than 20 microns), some manufacturing processes used to form the vias 122 may not be suitable for forming vias 122 small enough to be placed in direct alignment with the probe tips 128. The second conductive traces 130 can fan outward from the cluster of probe tips 128 to provide more space for placing the vias 122.

[0038] However, in some embodiments, the second plurality of traces 130 is omitted, and the probe tips 128 are directly connected to the conductive traces 120 on the top surface 124 of the central platform 114 through the vias 122. For example, the vias 122 can be formed by multiphoton absorption-based three-dimensional semiconductor fabrication techniques, such as those described in U.S. Patent Application No. 16 / 498,960. Using such techniques, the vias 122 can be formed to have dimensions small enough to be closely packed together, similar to the probe tips 128. Referring now to FIG. 4, a cross-sectional view of another exemplary central platform 400 of a probe platform support element is shown. The central platform 400 includes a plurality of probe tips 402-408, a corresponding plurality of vias 410-416, and a plurality of conductive traces 418-424. The probe tips 402-408 extend outward from a bottom surface 426 of the central platform 400. Conductive traces 418-424 are formed on a top surface 428 of the central platform 400 opposite a bottom surface 426 of the platform 400. Vias 410-416 extend directly between the probe tips 402-408 and the conductive traces 418-424, respectively, without additional conductive traces being formed on the bottom surface 426 of the platform 400.

[0039] Using three-dimensional semiconductor fabrication techniques, via 122 can also be formed to be angled relative to probe tip 128 and / or surfaces 124, 126 of central platform 114. Referring again to FIG. 4 , vias 412, 414 are shown as substantially vertical and straight vias. In other words, vias 412, 414 extend directly upward along a straight line from probe tips 404, 406 to traces 420, 422, respectively. In contrast, via 410 is substantially straight but is angled relative to surfaces 426, 428 of platform 400 and probe tip 402 to which via 410 is connected. Furthermore, via 416 has a non-linear, curved shape. Angled and non-linear vias can be used to facilitate routing of conductive paths between probe tips 128 and top-surface conductive traces 120 in embodiments with many closely packed probe tips.

[0040] Referring again to FIG. 2C , the central platform 114 can include multiple alignment features 132. In some embodiments, the alignment features 132 are disposed on the bottom surface 126 of the central platform 114. In these embodiments, the support element 112, including the central platform 114, can be formed from a material that is substantially transparent to visible wavelengths of light. By way of example and not limitation, the support element 112 can be formed from silicon carbide, diamond, gallium nitride, sapphire, glass, or other transparent material. In various embodiments, the support element 112 and / or the central platform 114 can have a transmittance of 50% or more, 75% or more, or 90% or more to visible wavelengths of light. In further embodiments, the support element 112 and / or the central platform 114 can have a transmittance of greater than 90%, 95% or more, or 99% or more to visible wavelengths of light. The transparency of the central platform 114 facilitates alignment of the probe tip 128 with the elements of the DUT being desirably tested. The alignment features 132 can further aid in aligning the probe tips 128, especially when the probe tips 128 are small and closely spaced. By locating the alignment features 132 on the same bottom surface 126 of the central platform 114 as the probe tips 128, the alignment features 132 can be more easily focused by the imaging objective at the same time that the probe tips 128 are focused. However, in some embodiments, the alignment features 132 can be located on the top surface 124 of the central platform 114.

[0041] The alignment features 132 may be formed by any of a variety of means. In a non-limiting example, the alignment features 132 may be formed by selective deposition of a material such as a metal or ink. In another example, the alignment features 132 may be formed by selectively removing material from the central platform 114 such that the alignment features form a distinguishable pattern. For example, the alignment features 132 may be formed by selective laser ablation, etching, etc. Although the alignment features 132 are shown as an array of dots, it should be understood that the alignment features 132 may be arranged or configured according to virtually any pattern.

[0042] The probe card 100 may include various additional features to facilitate electrical connections between the probe tips 128 held by the support elements 112. For example, referring now to FIG. 5 , a partial perspective view of the bottom surface 104 of the probe card 100 is shown. Conductive traces 120 are shown extending along the arms 118 of the support elements 112 to the annular portion 116 of the support elements 112. At the annular portion 116 of the support elements 112, the conductive traces 120 terminate at electrical contacts 134. In an exemplary embodiment, the electrical contacts 134 may be flip-chip bump bonds joined to conductive traces 136 formed on the circuit substrate 108 of the probe card 100. Thus, the electrical contacts 134 may be located on the top surface of the support elements 112 (e.g., on the same side of the support elements 112 as the top surface 124 of the central portion 114). Thus, each of the conductive traces 120 on the support elements 112 may have a respective electrical contact 134 connected thereto. The traces 120 and corresponding contacts 134 are shown in a bottom-up view in Figure 5 for ease of illustration. Thus, the traces 120 and corresponding contacts 134 disposed on the top side of the support element 112 may not be visible from the underside of the support element 112. However, it should be understood that in at least some embodiments, the top surface traces 120 and contacts 134 may be visible from the bottom surface 104 of the probe card 100 due to the transparency of the support element 112 to visible wavelengths of light.

[0043] The contacts 134 are electrically connected to traces 136 included on the circuit board 108. Referring again to FIG. 1A , the traces 136 may be connected to connectors 138. It should be understood that each of the connectors 138 may thus be electrically connected to a different respective probe tip within the probe tip 128. The connectors 138 are configured to allow connections to be made between the probe card 100 and various electrical test equipment that may be used to test the functionality or connectivity of the DUT. For example, the connectors 138 are configured to interface with input / output terminals of electrical devices such as voltmeters, ammeters, ohmmeters, current sources, voltage sources, etc. In an exemplary embodiment, the connectors 138 may be or include any of a variety of connectors, such as coaxial connectors (e.g., BNC connectors), plugs, pins, sockets, etc.

[0044] In various embodiments, the traces 136 are disposed on the top surface 102 of the circuit board 108. In such embodiments, the circuit board 108 may further include a plurality of vias configured to connect the traces 136 of the circuit board 108 to the contacts 134 of the support element. However, it should be understood that in other embodiments, the traces 136 may be disposed on the bottom surface 104 of the circuit board 108, and in these embodiments, additional vias may not be necessary.

[0045] Referring now to FIG. 6, a cross-sectional view of an exemplary probe card 100 is shown. As shown in FIG. 6, probe tips 128 extend downward from a central platform 114 of the probe card 100. The probe tips 128 are connected to conductive traces 130 formed on a bottom surface 126 of the central platform 114. The conductive traces 130 fan out from the probe tips 128, which may be located proximate to the center of the central platform 114. Thus, the conductive traces 130 may provide sufficient spacing for the vias 122 to be electrically connected to only a single probe tip within the probe tip 128. However, as mentioned above, in embodiments in which the vias 122 may be small enough to avoid any one of the vias 122 contacting multiple probe tips 128 (e.g., having a diameter of 10 microns or less, 5 microns or less, or 1 micron or less), the bottom surface conductive traces 130 may be omitted, and the vias 122 may be located directly above each probe tip 128 (e.g., as shown in FIG. 4).

[0046] Continuing to refer to FIG. 6 , the vias 122 each extend through the central platform 114 from a respective trace in the traces 130 to the top surface 124 of the central platform 114. At the top surface 124 of the central platform 114, the vias 122 are connected to the top surface conductive traces 120. The top surface conductive traces 120 are electrically connected to contacts 134 (e.g., bump bonds). The contacts 134 may be connected to corresponding contacts 602 on the bottom surface 104 of the circuit board 108. The contacts 602 are then connected to vias 604 that extend through the circuit board 108 and electrically connect between the contacts 602 and conductive traces 136 on the circuit board 108. The conductive traces 136 are themselves connected to the connector 138. Thus, each of the probe tips 128 is electrically connected to a respective connector in the connector 138 via the traces 130, 120, 136, the vias 122, 604, and the contacts 134, 602. In some embodiments, the probe card can be formed by placing connectors 138 directly on support element 112 (eg, instead of contacts 134) and omitting circuit board 108 entirely.

[0047] As mentioned above, some DUTs that are desirably tested by probe cards, such as some types of FPAs, are configured to operate in very cold environments. To test the functionality of such devices, the probe card must be able to withstand the cryogenic temperatures at which these devices operate. Additionally, the probe card must be able to withstand the mechanical stresses caused by thermal expansion and contraction as the probe card cools and / or returns to room temperature.

[0048] The probe card 100 can be configured for use in a cryogenic environment. In an exemplary embodiment, the probe card 100 includes a plurality of flexures. Referring again to FIG. 1A , the circuit board 108 includes a plurality of flexures 140. The flexures 140 are attached to the support elements 112. For example, the flexures 140 can be attached to the support elements 112 by flip-chip bump bonding (e.g., by the contacts 134). In other embodiments, the flexures 140 can be attached to the support elements 112 by fasteners, adhesive, or other attachment means. The flexures 140 are configured to provide stiffness that resists movement of the support elements 112 in a direction perpendicular to the surface of the circuit board 108 (e.g., the top surface 102). The flexures 140 are further configured to allow expansion and contraction of the support elements 112 in a direction parallel to the plane of the surface 102. When the probe card is cooled from room temperature to cryogenic temperatures, the support elements 112 and the circuit board 108 contract at different rates due to different thermal expansion coefficients of the support elements 112 and the circuit board 108. Similarly, when the probe card 100 is heated to room temperature (e.g., for storage), the support elements 112 and the circuit board 108 expand at different rates. The flexures 140 allow the support elements 112 to expand / contract at a different rate than the circuit board 108, for example, in a direction parallel to the top surface 102 of the circuit board 108. As shown in FIGS. 1A, 1B, and 5, the flexures 140 can have a stepped profile. However, it should be understood that the flexures 140 can have virtually any design that allows the support element 112 to expand laterally (i.e., parallel to the plane of the surface 102) while maintaining electrical contact between the conductive traces 136, and are positioned on the flexures 140 such that movement of the flexures 140 relieves mechanical stress at the electrical contact points (e.g., contacts 134) between the electrical elements included in the support element 112 and the circuit board 108.

[0049] In some embodiments, an additional metallization layer may be formed on the support element 112 or the circuit board 108 to provide mechanical stress offset to any of the various other metallization layers (e.g., traces 120, 130, 136). For example, referring again to FIG. 6 , a metallization layer 606 is formed on an underside 608 of the support element 112 along one of the arms 118 of the support element 112. The metallization layer 606 may relieve mechanical stress on one of the arms 118 of the support element 112 caused by thermal expansion of the support element 112 due to different thermal expansion coefficients between the conductive trace 120 and the support element 112. Similarly, a metallization layer 610 may be formed on a flexure underside 612 of the flexure 140 to offset the mechanical stress of thermal expansion of the circuit board 108 relative to the conductive trace 136. The metallized layers 606, 610 may not be connected to either the support element 112 or the electrical components contained in the circuit board .

[0050] 1A and 1B, the circuit board 108 may include mounting holes 142. The mounting holes 142 may be used to mount the probe card 100 to a stage (not shown), which may be used to position the probe card 100 for testing a DUT.

[0051] Referring now to FIG. 7, another exemplary support element 700 is shown, including multiple flexures 702-706. The flexures 702-706 are arranged around and connected to a central platform 708, which may have multiple probe tips (not shown) formed thereon. The flexures 702-706 may have a switchback profile configured to provide the central platform 708 with vertical compliance (i.e., into or out of the page) and radial stiffness (i.e., within the plane of the support element 700). For example, the flexure 702 includes a switchback arm 710 having a first end 712 and a second end 714. The first end 712 connects to the central platform 708, and the second end 714 connects to an outer portion 716 of the support element 700. Switchback arm 710 is surrounded by a first void 718 and a second void 720 that extend through support element 700 (e.g., within a page). First void 718 of switchback arm 710 partially defines switchback arm 722 of flexure 706, and second void 720 of switchback arm 710 partially defines switchback arm 724 of flexure 704.

[0052] Support element 112 and / or support element 700 can be formed as a monolithic element. For example, support elements 112, 700 can be formed by selectively removing material from a wafer of semiconductor material. In an exemplary embodiment, opening 144 in support element 112 defined by the position of arms 118 can be formed by etching or diamond grinding material away from a circular, planar element (e.g., a silicon carbide wafer). In other embodiments, opening 144 can be formed by electrical discharge machining (EDM). In such an embodiment, a hole can be formed in the circular, planar element by drilling or plunge EDM. A conductive wire can then be threaded through the formed hole. The conductive wire can be used to form opening 144 by wire EDM.

[0053] Referring now to FIGS. 8A and 8B, multiple processing steps for forming a probe tip in a support element are shown. While multiple processing steps are shown in FIGS. 8A and 8B, it should be understood that intermediate processing steps between the illustrated steps can be performed. Furthermore, not all of the illustrated steps may need to be performed to practice the processes described herein. Referring now to FIG. 8A, at 802, a silicon wafer 803 is obtained. At 804, multiple pyramidal or conical pits 805 are formed in the silicon wafer by etching. In an exemplary embodiment, the pits can be formed by potassium hydroxide (KOH) etching. In other embodiments, the pits can be formed by a multiphoton absorption-based etching process. At 806, a metal layer 807 is deposited on the etched wafer 803. The metal layer 807 is deposited such that the metal fills the pits 805. The metal layer 807 can be formed from a material that is desirably used to form a probe tip in a probe card. In an exemplary embodiment, the metal layer is made of tungsten. At 808, metal layer 807 is cleaned of excess metal using a chemical mechanical polishing (CMP) process, leaving metal probe tips 809 shaped within pits 805. At 810, another metal layer 811 is deposited over wafer 803 and probe tips 809. In an exemplary embodiment, metal layer 811 is made of aluminum. At 812, excess portions of metal layer 811 not disposed above probe tips 809 are removed, leaving metal layer 813 over each of probe tips 809.

[0054] Referring now to FIG. 8B , at 814, a wafer 815 is obtained. The wafer 815 can be formed from virtually any material desirably used to form support elements of a probe card. In an exemplary embodiment, the wafer 815 comprises silicon carbide. At 816, via holes 817 are etched through the wafer 815. At 818, the via holes 817 are filled with a conductive metal to form vias 819. For example, the via holes 817 can be electroplated with copper to form the vias 819. At 820, a metal layer 821 is applied to the wafer 815. At 822, the metal layer 821 is etched to leave contacts 823 in electrical contact with the vias 819. At 824, another metal layer 825 is deposited on the bottom side of the wafer 815. At 826, the metal layer 825 is etched to form traces 827 connecting the probe tips 809 to the vias 819. At 828, the silicon wafer 803 and the probe tips 109 formed therein are aligned to the traces 827 formed on the second wafer 815, and the wafers are bonded together by a metal thermocompression process. At 830, the remaining portion of the silicon wafer 803 is etched away, leaving the probe tips 809 extending downward from the second wafer 815.

[0055] In other embodiments, the probe tips can be formed directly on the support elements. Referring now to FIG. 9 , an exemplary wafer 900 is shown. The wafer 900 can be constructed from a material (e.g., silicon carbide) that is desirably used to form support elements for probe cards. A plurality of voids 902-908 can be formed in the wafer 900 and filled with a conductive material. In an exemplary embodiment, the bottom of each of the voids 902-908 can be filled with a first conductive material (e.g., tungsten) to form a plurality of probe tips 910-916. The remaining portion of each of the voids 902-908 can form vias 918-924 filled with a second conductive material (e.g., copper). The bottom of the wafer 900 can be etched away to expose the probe tips 910-916. Conventional semiconductor etching techniques may not be suitable for forming the voids 902-908 at a pitch (i.e., the distance between the voids) fine enough to yield the desired pitch of the probe tips. Thus, the voids 902-908 can be formed by a multiphoton absorption-based etching process that is well suited to forming high aspect ratio voids in semiconductors. Forming the probe tip in the manner described with respect to Figure 9 may be well suited to embodiments in which a via is formed directly above the probe tip in the support element.

[0056] 10 illustrates an exemplary method for forming a probe card. While the methodology is shown and described as a series of operations performed in sequence, it should be understood and appreciated that the methodology is not limited by the order of the sequence. For example, some operations may occur in a different order than described herein. Additionally, some actions may occur simultaneously with other actions. Furthermore, in some instances, not all operations may be required to implement the methodology described herein.

[0057] Referring now to FIG. 10 , a method 1000 for facilitating the formation of a probe card is shown. The method 1000 begins at 1002, and at 1004, a support element is formed. The support element can be formed such that the support element has a first side and a second side opposite the first side. At 1006, a plurality of probe tips are formed on the support element. The probe tips can be formed to extend outward from the first side of the support element. In an exemplary embodiment, the probe tips are formed in an arrangement that matches the arrangement of components on a device desirably tested by the probe card. At 1008, a plurality of vias are formed through the support element such that the vias extend from the first side to the second side. Each of the vias is connected to a respective probe tip of the plurality of probe tips. At 1010, a plurality of conductive traces are formed. The conductive traces can be formed on the second side of the support element. Each of the conductive traces can be connected to a respective via in the plurality of vias such that each of the conductive traces is electrically connected to a single respective probe tip in the plurality of probe tips. The method 1000 completes at 1012 .

[0058] The foregoing description includes examples of one or more embodiments. Of course, it is not possible to describe every conceivable modification and variation of the above-described devices or methods for the purposes of describing the foregoing aspects, but those skilled in the art will recognize that many further modifications and permutations of the various aspects are possible. Accordingly, the described aspects are intended to encompass all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent the term "includes" is used in either the detailed description or the claims, such term is intended to be as inclusive as the term "comprising," as "comprising" is interpreted when used as a transitional term in the claims.

Claims

1. A probe card, a probe platform, the probe platform comprising: a support element having a first surface and a second surface opposite the first surface, the support element including a central platform and an annular portion disposed around the central platform; a plurality of probe tips extending outwardly from the first surface of the central platform of the support element, the plurality of probe tips configured to contact components of a device under test (DUT); a plurality of vias extending through the support element from the first surface to the second surface of the central platform of the support element, each via connected to a respective probe tip of the plurality of probe tips; a plurality of conductive traces extending outward from the central platform toward the annular portion, each conductive trace connected to a respective via in the plurality of vias, through which electrical signals may be supplied to or received from the probe tip; 1. A probe card comprising: a circuit board having a bottom surface, a top surface, and an opening extending from the bottom surface to the top surface, the circuit board including a plurality of flexures extending inward toward the opening, the plurality of flexures attached to the annular portion of the support element, and compliance of the plurality of flexures configured to allow flexure of the circuit board in a direction parallel to the top surface.

2. 2. The probe card of claim 1, wherein the plurality of probe tips includes a first probe tip and a second probe tip, the first probe tip and the second probe tip being spaced apart from each other on the support element by less than 20 microns.

3. The probe card of claim 1 , wherein the support element is formed from at least one of silicon carbide, diamond, gallium nitride, sapphire, or glass.

4. The probe card of claim 3 , wherein the support element is formed from silicon carbide.

5. The probe card of claim 1 , wherein the support element is formed of a material that is substantially transparent to visible light.

6. The probe card of claim 5 , wherein the support element has a plurality of alignment features formed thereon.

7. The probe card of claim 6 , wherein the alignment features are formed on the first surface of the support element and are visible through the support element from the second surface of the support element.

8. 2. The probe card of claim 1, wherein the plurality of conductive traces are formed on the second surface of the support element, the probe platform further includes a second plurality of conductive traces disposed on the first surface of the support element, and the probe tip is connected to the via through the second plurality of conductive traces.

9. The probe card of claim 1 , wherein the vias extend vertically through the support element such that each of the vias is aligned with an axis of a respective probe tip of the plurality of probe tips.

10. The probe card of claim 1 , wherein each of the vias extends through the support element at an angle relative to an axis of a respective probe tip of the plurality of probe tips.

11. The probe card of claim 1 , wherein a first via in the plurality of vias has a non-linear shape.

12. The probe card of claim 1 , wherein the circuit board includes a plurality of contacts, each of the contacts electrically connected to a respective conductive trace in the plurality of conductive traces.

13. The support element 13. The probe card of claim 12, further comprising: a plurality of arms extending outward from between the central platform and the annular portion, each of the plurality of conductive traces extending along a respective arm within the arms.

14. The probe card of claim 13 , wherein the support element is a monolithic element.

15. forming a support element having a first surface and a second surface opposite the first surface, the support element including a central platform and an annular portion disposed about the central platform; forming a plurality of probe tips extending outwardly from the first surface of the central platform of the support element, the plurality of probe tips configured to contact components of a device under test (DUT); forming a plurality of vias extending through the support element from the first surface to the second surface of the central platform of the support element, each via connected to a respective probe tip of the plurality of probe tips; forming a plurality of conductive traces extending outward from the central platform toward the annular portion, each of the conductive traces connected to a respective via in the plurality of vias, such that electrical signals can be supplied to or received from the probe tip through the conductive traces; attaching the annular portion of the support element to a plurality of flexures of a circuit board, the circuit board having a bottom surface, a top surface, and an opening extending from the bottom surface to the top surface, the plurality of flexures extending inwardly toward the opening, and compliance of the plurality of flexures configured to permit flexure of the circuit board in a direction parallel to the top surface; A method comprising:

16. 16. The method of claim 15, further comprising forming a plurality of voids in the support element using a multi-photon absorption based semiconductor fabrication technique, wherein forming the plurality of vias comprises filling a first portion of each of the plurality of voids with a conductive material.

17. 17. The method of claim 16, wherein forming the plurality of probe tips comprises filling a second portion of each of the plurality of voids with a conductive material.

18. 1. A system comprising: a probe platform, the probe platform comprising: a support element having a first surface and a second surface opposite the first surface, the support element including a central platform and a plurality of arms extending outwardly from the central platform; a plurality of probe tips extending outwardly from the first surface of the central platform of the support element, the plurality of probe tips configured to contact components of a device under test (DUT); a plurality of vias extending through the support element from the first surface to the second surface of the central platform of the support element, each via connected to a respective probe tip of the plurality of probe tips; a plurality of conductive traces extending outwardly from the central platform along each of the arms, a first end of each of the conductive traces being connected to a respective via in the plurality of vias, and through which electrical signals may be supplied to or received from the probe tip; a circuit board having a bottom surface, a top surface, and an opening extending from the bottom surface to the top surface, the circuit board including a plurality of contacts, each of the contacts electrically connected to an opposite second end of a respective conductive trace in the plurality of conductive traces, the circuit board including a plurality of flexures extending inward toward the opening, the plurality of flexures attached to the support element of the probe platform via the contacts, and compliance of the plurality of flexures configured to permit flexure of the circuit board in a direction parallel to the top surface.

Images