Probe card stiffener with decoupling

A stiffener for a probe card assembly can include decoupling mechanisms disposed within radial arms of the stiffener. The decoupling mechanisms can be compliant in a direction along a radial direction of said radial arm and rigid in a direction perpendicular to said radial arm. The decoupling mechanisms can decouple the stiffener from thermally induced differential radial contraction and expansion of the stiffener relative to the cardholder to which the stiffener is mounted. This can reduce thermally-induced vertical translation of the probe card assembly.

BACKGROUND

Microelectronic devices (e.g. dies) are typically manufactured in large number on a semiconductor wafer. For various reasons, the devices may fail to perform correctly. Accordingly, as a part of the manufacturing process, various tests of the microelectronic devices are typically performed. Tests can include, for example, functional tests, speed tests and sorting, and burn-in testing. Testing can be performed at the wafer level (e.g., before the microelectronic devices are separated from each other in a process called singulation) to allow failed to devices to be identified before packaging the devices.

To perform tests on the microelectronic devices, temporary electrical connections to the devices are made. For example, a wafer can be placed into a prober, and the wafer placed onto a movable stage. The stage can be moved to bring the wafer into contact with a probe card assembly. The probe card assembly can include many probes that are arranged to make temporary pressure-based electrical contacts to corresponding terminals (e.g., aluminum bond pads) on the microelectronic devices. Alignment of the wafer and probe card assembly can be performed using optical systems. Testing can involve sending signals to and from the wafer through the probes.

Because of the small sizes of the terminals and probes, it is challenging to ensure and maintain proper alignment between the probe card assembly and the wafer. Typically, the probe card assembly is mounted (e.g., bolted or otherwise fixed in position) into the prober to maintain a fixed position of the probe card assembly relative to the stage. Various adjustment mechanisms can be provided in the prober, probe card assembly, or both to allow alignment operations (e.g., tilt adjust) to be performed to place the tips of the probes into parallel alignment with the surface of the stage (and thus, into alignment with terminals of the wafer).

Maintaining proper alignment can be complicated when temperature variations are present, as most materials change dimension as a function of temperature. It is often advantageous to test the microelectronic devices over a range of temperatures. To this end, heating or cooling elements can be included in the stage or other portions of the prober to heat or cool the microelectronic devices during testing. Moreover, even if heating or cooling elements are not included, operation of the microelectronic devices during testing may generate heat. The resultant heating or cooling can cause the wafer, probe card assembly, and the prober to expand or contract, changing the positions of the probes relative to the terminals. For example, differential changes in the dimension of the probe card assembly relative to the mounting structure (e.g., cardholder) of the prober to which the probe card assembly is mounted can cause bowing or bending of the probe card assembly. If the bowing is toward the stage, one or more of the probes may press against the electronic devices with too much force and damage the devices or the probes. Conversely, if the bowing is away from the stage, one or more of the probes may fail to make reliable electrical contact with the terminals of the electronic devices, resulting in erroneous test results.

SUMMARY

In some embodiments of the invention, a probe card assembly is provided. The probe card assembly can include a wiring substrate. The wiring substrate can have internal electrical traces which connect to a tester interface disposed on a first surface of the wiring substrate. A probe head having a plurality of probes can be disposed proximate to a second surface of the wiring substrate and can include electrical connections between the probes and the internal electrical traces of the wiring substrate. The probes can be arranged to contact an electronic device to be tested. A stiffener can be disposed proximate to the first surface. The stiffener can have a plurality of attachment mechanisms disposed distally from the main body. A plurality of decoupling mechanisms can be disposed between the main body and the attachment mechanisms. The decoupling mechanism can be compliant in a radial direction and rigid in one or more other directions.

In some embodiments of the invention a stiffener is provided. The stiffener can include a main body portion and a plurality of radial arms disposed within a plane and extending radially outward from the main body portion. The main body portion can include first attachment mechanisms positioned for attachment to a probe card substrate. The radial arms can include second attachment mechanisms for attachment to a cardholder of a prober. A decoupling mechanism can be disposed within each of the arms between the main body portion and the second attachment mechanism. The decoupling mechanism can accommodate movement in a radial direction along a radial axis of the arm, and can resist movement in one or more directions perpendicular to the plane.

In some embodiments of the invention a method of using a probe card assembly is provided. The method can include obtaining a probe card assembly. The probe card assembly can include a probe head having resilient probes, a stiffener having a main body coupled to the probe head and a plurality of radial arms extending radially outward from the main body in an x-y plane. A decoupling mechanism can be disposed within each radial arm between the main body and an attachment mechanism disposed at the end of the radial arm distal from the main body. The method can also include installing the probe card assembly into a prober. The installing can include fixing the attachment mechanisms to a cardholder of the prober. Another operation in the method can be varying a temperature of the probe card assembly such that a radial dimensional change of the probe card assembly occurs relative to the cardholder. The decoupling mechanisms can respond to the radial dimensional change to maintain a substantially constant position of the main body relative to the cardholder in a z direction perpendicular to the x-y plane.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

This specification describes exemplary embodiments and applications of the invention. The invention, however, is not limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. Moreover, the Figures may show simplified or partial views, and the dimensions of elements in the Figures may be exaggerated or otherwise not in proportion for clarity. In addition, as the terms “on,” “attached to,” or “coupled to” are used herein, one object (e.g., a material, a layer, a substrate, etc.) can be “on,” “attached to,” or “coupled to” another object regardless of whether the one object is directly on or attached to or coupled to the other object or there are one or more intervening objects between the one object and the other object. Also, directions (e.g., above, below, top, bottom, side, up, down, under, over, upper, lower, horizontal, vertical, “x,” “y,” “z,” etc.), if provided, are relative and provided solely by way of example and for ease of illustration and discussion and not by way of limitation. In some figures, “x,” “y,” and “z” axes are provided in accordance with a right-hand coordinate system for ease of discussion and illustration but not by way of limitation. With reference to particular directions or orientations, the term “substantially” may be used, by which it is to be understood that the recited direction or orientation need not be exact, but may include deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations, conversion factors, rounding off, and other factors known to skill in the art. Similarly, the term “about” means quantities, dimensions, sizes, formulations, parameters, shapes and other characteristics need not be exact, but may be approximated and/or larger or smaller, as desired, reflecting acceptable tolerances, conversion factors, rounding off, measurement error and the like and other factors known to those of skill in the art. In addition, where reference is made to a list of elements (e.g., elements a, b, c), such reference is intended to include any one of the listed elements by itself, any combination of less than all of the listed elements, and/or a combination of all of the listed elements. In addition, where reference is made to a range of values, such reference is intended to include not only the explicitly recited range, but also all the individual values and sub-ranges encompassed within that range.

FIGS. 1A-1Billustrates a schematic side view depiction of a test system, shown generally at100, which can address some of the aforementioned challenges. Referring toFIG. 1A, the test system100can include a prober102and a test head104. A cutaway126provides a partial view of the inside of the prober102. A device to be tested, referred to herewith as a device under test (DUT)112, can be placed onto a stage106. The DUT can be for example: a microelectronic device, a wafer comprising a plurality of unsingulated dies, a carrier holding a wafer, a carrier holding a plurality of singulated dies, dies forming a multi-chip module, and the like. The stage can be movable to position the DUT112in a horizontal plane (e.g., directions labeled “x” going left and right across the page and “y” going in and out of the page) and a vertical direction (e.g., direction labeled “z” going up and down the page). A probe card assembly108can be mounted into the prober102and can include probes124. The probes124can be arranged in a pattern which corresponds to terminals128of the DUT112. For example, as shown inFIGS. 1A and 1B, contact portions (e.g., distal ends) of the probes124can be disposed generally in a plane156that corresponds to a plane (not shown) of terminals128of the DUT112. The stage can be moved vertically to bring the probes124into contact with the terminals128to form temporary pressure electrical connections between the probes and the terminals. Testing can include exchanging electrical signals between the DUT112and the test head104through the probes124and terminals128. For example, test signals can be sourced and sinked from a tester (not shown) which connects to the test head104through a cable110. Alternatively or in addition, test signals can be sourced and sinked from the test head104using electronics (not shown) in the test head. As another example, electronics (not shown) of the probe card assembly108can source or sink test signals or perform processing (e.g., conversion) of test signals.

The probe card assembly108can include a stiffener120, wiring substrate121, and probe head122. The wiring substrate121can be, for example a printed circuit board material, and can include multiple layers (not shown) of an insulating material on which conductive traces (not shown) are formed thereon and vias (not shown) are formed between to provide electrical connections. For example, the wiring substrate121can comprise a ceramic, organic, or printed circuit board substrate comprising electrically conductive pads (not shown) on one surface of the substrate and internal conductive paths connecting those pads to terminals (not shown) on another surface of the substrate. As shown in detail inFIG. 1B, the wiring substrate121can have a first, upper surface152and a second, lower surface154opposite the first surface. The stiffener120can be disposed opposite the first surface152and the probe head122can be disposed opposite the second surface154, although other arrangements are possible. The probes124can be disposed on the probe head122.

The probe head can include one or more substrates (e.g., printed circuit boards, organic layers, ceramic layers, and the like, similar to the wiring substrate121) on which the probes are mounted (e.g., to conductive terminals). The probe head122can be coupled to the stiffener120, for example as described further below.

The stiffener120can be plate-like rigid structure and can include a rigid material (e.g., metal) which resists warping or bending due to mechanical loads or thermal gradients. The stiffener120can be a monolithic assembly, or the stiffener can be assembled from a number of components. For example, the stiffener120can be machined or cast in a single body. Alternatively, the stiffener can include a main body portion and one or more arms which are attached to the main body portion. In some embodiments, the stiffener120can be made of aluminum, steel (e.g., stainless steel), titanium, nickel, low-CTE nickel-steel alloys (e.g., Invar material, nickel-cobalt ferrous alloys (e.g., to match particular CTE requirements, e.g. Kovar material)), graphite epoxy, metal matrix materials, ceramics, etc. In addition, alloys of any of the foregoing materials or mixtures of any of the foregoing materials with other materials can be used. The stiffener can be more rigid than the wiring substrate121, the probe head122, or both, and thus can provide structural rigidity to the probe card assembly108. The probe head122can be coupled to the stiffener120so that forces applied to the probe head are passed through to the stiffener, helping to provide rigidity to the probe head. For example, attachment mechanisms130can connect the probe head122to the stiffener120. For example, the attachment mechanisms can be fasteners that fix the probe head122in position relative to the stiffener. As another example, the attachment mechanisms can be adjustment mechanisms to allow for adjustment of the planarity and orientation of the probe head. For example, adjustment mechanisms can include differential screws, biasing springs, actuators, and similar components.

One non-limiting example of an attachment and adjustment mechanism for coupling a probe head to a stiffener is illustrated in U.S. Pat. No. 7,671,614. Other intermediate assemblies (not shown), such as for example, one or more interposers and/or space transformers can also be included between the wiring substrate121and the probe head122. While only a single probe head122is illustrated, more than one probe head can be included if desired. Non-limiting examples of probe head assemblies and attachment and adjustment techniques are disclosed in U.S. Pat. Nos. 5,974,662, 6,483,328, 6,509,751, 5,806,181, 6,690,185, 6,640,415, Application Publication No. 2001/0054905, U.S. Patent Application Publication No. 2002/0004320, U.S. Patent Application Publication No. 2002/0132501 and U.S. patent application Ser. No. 11/165,833, entitled “Method And Apparatus For Adjusting A Multi-Substrate Probe Structure,” filed Jun. 24, 2005.

The probes124can be resilient and can include an electrically-conductive material to allow an electronic signal to be transmitted through the probe. Non-limiting examples of probes112include composite structures formed of a core wire bonded to a conductive terminal (not shown) on the probe head122that is over coated with a resilient material as described in U.S. Pat. Nos. 5,476,211, 5,917,707, 6,336,269. Probes124can alternatively be lithographically formed structures, such as the spring elements disclosed in U.S. Pat. Nos. 5,994,152, 6,033,935, 6,255,126, 6,945,827, U.S. Patent Application Publication No. 2001/0044225, and U.S. Patent Application Publication No. 2004/0016119. Still other non-limiting examples of probes are disclosed in U.S. Pat. Nos. 6,827,584, 6,640,432, 6,441,315, and U.S. Patent Application Publication No. 2001/0012739. Other non-limiting examples of probes124include conductive pogo pins, bumps, studs, stamped springs, needles, buckling beams, etc.

On or within the probe head122, electrical connections132(e.g., traces, vias, or both) can electrically connect the probes124to electrical connections134(e.g., traces, vias, or both) on or within the wiring substrate121, which can electrically connect to test connectors114, which can be electrically connected to the test head104. The test connectors114can be, for example, zero insertion force connectors, pogo pins, flexible wiring, and the like. The test connectors114can extend from the wiring substrate121upward between radial arms133of the stiffener120, or upward through holes (not shown) in the stiffener120. Alternatively, or in addition, the electrical connections134can connect to electronic circuitry (not shown) disposed on the wiring substrate121. The electrical connections132,134and probes124can thus provide electrical signal paths which can be used by the tester (not shown), test head104, and/or circuitry (not shown) to write test data to and receive response data from the DUT112. The wiring substrate121can be fixedly attached to the stiffener120, or can float between the stiffener120and the probe head122. For example, the wiring substrate121can be mechanically coupled to, but radially decoupled from, the stiffener120. Non-limiting examples of wiring substrates and attachment techniques are disclosed in U.S. Pat. No. 7,285,968 and U.S. Patent Pub. No. 2007/0126440.

The probe card assembly108can be mounted into the prober102by fixing the probe card assembly to a cardholder142(e.g., a head plate or insert ring) of the prober. For example, the stiffener120and the cardholder142can each include holes136,144to receive fasteners146(e.g., screws, bolts, and the like) used to secure the probe card assembly108in place. Other techniques can be used to secure the probe card assembly108in position, including for example, clamping and the like. Holes136are therefore just one non-limiting example of an attachment mechanism that can be included in the probe card assembly108, and other attachment mechanisms, including clamping surfaces, screws, mechanical interlocks, and the like can be used. As illustrated inFIGS. 1A,1B, and2B, the cardholder142can comprise a structure with a central opening150into which portions of the probe card assembly108extend. For example, the cardholder142can comprise a ring structure, and all or part of the wiring substrate121and the probe head122can be disposed or extend into the opening150.

As introduced above, most materials change dimension as a function of temperature. Accordingly, temperature changes can cause changes in dimension of the cardholder142, the probe card assembly108(e.g., stiffener120), or both. For example, differences in the thermal coefficient of expansion (CTE) in the stiffener120and the cardholder142can result in distance between attachment mechanisms (e.g., holes136) of the probe card assembly108changing relative to the distance between corresponding attachment mechanisms (e.g., holes144) of the cardholder142. For example, heating can cause the stiffener120to expand a greater amount than the probe cardholder142, and the resulting mechanical stress can cause the stiffener to bow. Such bowing can be undesirable, as it can result in the probes124moving away from a nominal position. Matching the CTE of the stiffener120to the cardholder142may not be practical due to several factors. For example, some cardholders142are made of low CTE material which is very expensive (e.g. made from Nobinite or Invar materials); use of such expensive materials drives up the cost of the probe card assembly. For example, some nickel-iron alloys provide CTE of less than about 1.5 ppm per degree Celsius. In other cases, a probe card user may have different probers which have cardholders made of different materials. As the different cardholders have different CTE, either multiple probe cards (using different materials for the stiffeners) would be needed to avoid CTE mismatches will be present. Moreover, even if the CTE of stiffener120and the cardholder142are matched, differences in temperature between the stiffener and cardholder can still cause dimensional mismatches.

To reduce movement of the probe card assembly108caused by the foregoing effects, the stiffener120can include a plurality of decoupling mechanisms138. For example, the decoupling mechanisms can be disposed within each of radial arm portions133of the stiffener. In general, the decoupling mechanisms can be disposed within any portions of a stiffener in a position which allows for decoupling portions of the stiffener120from dimensional changes of the cardholder142. For example, the decoupling mechanisms138can be positioned between the attachment mechanisms (e.g., holes136) and a main body portion131of the stiffener120. Alternatively or in addition, decoupling mechanisms138′ can be provided in the cardholder142as also shown inFIG. 1B. Thus, decoupling mechanisms138′ can be used in place of decoupling mechanisms138or in addition to decoupling mechanisms138. Decoupling mechanisms138′ located in the cardholder142can be structurally and functionally like decoupling mechanisms138and can comprise any embodiment disclosed herein for decoupling mechanisms138.

Regardless of where located, the decoupling mechanisms138can respond to induced forces by changing dimension. For example, the decoupling mechanisms can absorb part or all of the dimensional changes of the stiffener120relative to the cardholder142to which the stiffener is attached. For example, the decoupling mechanisms138can shear in a radial direction (e.g., within the horizontal (x-y) plane) to absorb radial expansion or contraction of the stiffener. For example, the decoupling mechanisms138can be compliant in a direction along the radial arm allowing the decoupling mechanism to absorb dimensional changes along the longitudinal axis of the radial arm133by expanding or contracting to change the length of the radial arm (e.g., elastically responding to compression or tension along the axis of the radial arm). The decoupling mechanism138can maintain rigidity in one or more other directions (e.g., a direction perpendicular to the radial arm to resisting bending or vertical displacement of the radial arm). For example, the decoupling mechanism can be rigid in the z direction, to maintain the rigidity of the stiffener with respect to forces applied to the probes124. For example, the decoupling mechanism138can be compliant in one axis while being rigid in two other axes.

The amount of decoupling is dependent upon the amount of compliance provided by the decoupling mechanism138, and thus, the decoupling mechanism can be designed to provide a desired amount of decoupling. In some embodiments, the amount of decoupling can be selected to tune the thermally induced stress levels on the probe card assembly108and the cardholder142. Those thermally induced stress levels can result in thermal movement (e.g., deformation and translation vertically (parallel to the “z” axis) inFIGS. 1A,1B, and2B) of the stiffener120and the cardholder120, and the amount of decoupling selected for the decoupling mechanism138can be such that the total thermal movement of the stiffener120and the cardholder120result in no appreciable movement of the contact ends of the probes124at a given temperature over a predetermined temperature range. The amount of decoupling provided by the decoupling mechanism138can thus be tuned, for example, to maintain the contact ends of the probes124in a plane (e.g.,156) and to keep the plane (e.g.,156) from appreciably moving even as the temperature changes within a predetermined temperature range.

For example, a given change in temperature may result in a thermal movement Maof the stiffener120and a thermal movement Mbof the cardholder142. As illustrated inFIG. 1B, movement Macan be, in this example, in the positive “z” direction, and movement Mbcan be in the negative “z” direction. If, for example, Mais greater than Mb, decoupling mechanisms138, can be configured to allow radial arms133to move in the “x,y” plane and thereby reduce movement Maby approximately the difference between Mband Maso that there is no (or no appreciable) movement of plane156. Alternatively, if decoupling mechanisms138′ are in the cardholder142, decoupling mechanisms138′ can be configured to increase movement Mbby approximately the difference between Mband Maso that there is no (or no appreciable) movement of plane156.

Various non-limiting detailed examples of decoupling mechanisms are described further below.

FIGS. 2A-2Dillustrate one example of a probe card assembly200, which can for example be used within the test system100ofFIG. 1A(e.g., used in place of probe card assembly108). The probe card assembly200can include a stiffener plate202(which can be like stiffener120), a wiring substrate204(which can be like wiring substrate121), and a probe head assembly222(which can be like probe head122). As shown inFIGS. 2B and 2C, the probe head assembly222can include a plurality of probes224(which can be like probes124). The wiring substrate204can include test head connectors208(which can be like test connectors114). As shown, contact ends of the probes224can be in the plane156discussed above.

The wiring substrate204can be attached to the stiffener plate202such that the wiring substrate204can expand and contract radially. That is, the wiring substrate204can move radially with respect to the stiffener plate202and the probe head assembly222. This can reduce the forces on the stiffener plate202caused by expansion or contraction of the wiring substrate204in response to changes in the ambient temperature. A mechanical fastener214(e.g. a screw or a bolt) can be used to secure the wiring substrate204to the stiffener plate202at one location (e.g., at the center) of the wiring substrate204. The fastener214can pass through (or thread through) a hole in the stiffener plate202and thread into a threaded hole (or insert)252in the wiring substrate204. Additional attachments to the wiring substrate204can loosely attach the wiring substrate204to the stiffener plate202so that it can expand or contract radially relative to the fastener214. For example, additional fasteners212,232(e.g., bolts and nuts) can prevent the wiring substrate204from rotating with respect to the stiffener plate202. The fasteners212can pass through holes246in the wiring substrate204which are elongate to provide space for expansion and contraction of the wiring substrate204. Lubrication, bearings, or other means (not shown) can be provided on surfaces of the wiring substrate204to facilitate movement of the wiring substrate with respect to the stiffener plate202and the probe head assembly222.

Mechanical fasteners216can mechanically attach the probe head assembly222to the stiffener plate202. Mechanical fasteners216can thus be a non-limiting example of a plurality of first attachment mechanisms. As shown inFIG. 2C, mechanical fasteners216can pass through holes242in the wiring substrate204. Extra space can be provided in the holes242in the wiring substrate204through which the mechanical fasteners216pass. Consequently, the probe head assembly222need not be attached directly to the wiring substrate204. In this way, the wiring substrate204can also be thermally decoupled from the probe head assembly222.

Mechanical fasteners216can comprise any suitable means for securing the probe head assembly222to the stiffener plate. For example, the mechanical fasteners216can be screws or bolts216(e.g., as shown inFIG. 2C) that pass through threaded holes (not shown) in the stiffener plate and engage threaded holes (not shown) in the probe head assembly222. Alternatively, the mechanical fasteners216can be more complicated structures that provide additional functions. For example, the mechanical fasteners can be configured not only to secure the probe head assembly222to the stiffener plate202but also to control the orientation of the probe head assembly222(and thus the probes224) with respect to the stiffener plate202. Another example of a mechanical fastener216is a differential screw.

The stiffener plate202can include a main body portion201and a plurality of radial arms210. Although eight radial arms210are shown, a larger or smaller number of radial arms can be used. The radial arms210can extend radially outward from the main body portion201and can be disposed in a plane (e.g., the x-y plane). As can be seen inFIGS. 2B and 2C, the radial arms210can include tabs226disposed at the ends of the radial arms distal from the main body201. The tabs226can be inserted into corresponding slots in the wiring substrate204. The slots can include extra clearance space around the tabs to provide thermal decoupling of the stiffener plate202and wiring substrate204. A second attachment mechanism, such as for example holes206, can be disposed at the ends of the radial arms210. The holes206can correspond to holes134in the cardholder142so that the probe card assembly200can be attached to the cardholder142by fasteners228(e.g., bolts) that pass through the holes206in the radial arms210and into or through holes134in the cardholder142(or tester head plate). InFIG. 2B, the cardholder142is shown in dashed lines as are bolt/nut pairs for bolting the probe card assembly200to the cardholder142, since these are not necessarily parts of the probe card assembly. Because the stiffener202can be fixed to the cardholder142and the probe head assembly222can be fixed to the stiffener202, the stiffener202can provide mechanical stability to the probe head assembly222.

The stiffener202can include decoupling mechanisms250disposed radially between the main body201and the holes206to decouple the stiffener from thermally induced movement as described above. For example, the decoupling mechanisms250can be disposed within each of the radial arms210between the main body201and the holes206. Alternatively or in addition, decoupling mechanisms250′ can be located in the cardholder142as also illustrated inFIG. 2B. Thus, decoupling mechanisms250′ can be used in place of decoupling mechanisms250or in addition to decoupling mechanisms250. Regardless of where located, the decoupling mechanisms250can, for example, be like decoupling mechanisms138. The decoupling mechanisms can accommodate movement in a radial direction (e.g., in the “x, y” plane in the figures) along a radial axis of the arms210while resisting movement in a direction perpendicular to the plane in which the radial arms are disposed. The decoupling mechanisms250can be more flexible in the radial (horizontal) direction (in the “x,y” plane in the figures) than the vertical direction (parallel to the “z” axis in the figures). As a non-limiting example, the decoupling mechanisms250can provide an amount of compliance in the radial direction that is greater than or equal to any of a factor of 1.5, 2, 3, 5, or 10 times the amount of compliance in the vertical direction. In other words, the decoupling mechanisms250can provide a vertical rigidity that is 1.5, 2, 3, 5 or 10 times the rigidity in the horizontal direction. Various types of decoupling mechanisms250can be used, as will now be described. Decoupling mechanism250′ located in the cardholder142can be structurally and functionally like decoupling mechanism250and can comprise any embodiment disclosed herein for decoupling mechanism250.

In some embodiments, the decoupling mechanism (e.g.,138,250) can comprise one or more slits within the radial arm (e.g.,133,210). For example,FIGS. 3A-3Billustrate one embodiment of a decoupling mechanism300which comprises a plurality of slits302disposed within a radial arm304(which can be radial arm133or radial arm210). While two slits302are shown, the number of slits can be 2, 3, 4, or any other suitable number. The slits302can be oriented substantially perpendicular to the longitudinal radial axis306of the radial arm304, wherein the longitudinal axis of the radial arm extends along the length of the radial arm, from the main body (not shown) to the end (not shown) of the radial arm. The slits302can be narrow (e.g., ‘A’ dimension between 50 micrometers to 1.5 millimeters) cuts that extend partially into the radial arm304(e.g., between 75% to 95% of the way through the radial arm) and completely across the width (e.g., ‘C’ dimension) of the radial arm. For example, one of the slits306can extend inward into the radial arm304from an upper surface306, and another one of the slits306can extend inward into the radial arm from a lower surface308. The slits302can be closely spaced (e.g. ‘B’ dimension between about 500 micrometers and 5 millimeters). Various ways of fabricating the slits302into the radial arm304can be used, including for example: electron discharge machining, physical sawing, water jet cutting, laser cutting, and the like.

Operation of the decoupling mechanism300can be understood in reference toFIGS. 4-5which show the decoupling mechanism alternatively in an expanded position (FIG. 4) and a contracted position (FIG. 5). The decoupling mechanism300, comprising slits302, is positioned in between a first portion310(e.g. a main body side) and a second portion312(e.g. a distal end) of the radial arm304. The slits302effectively create a beam portion314connected by hinge areas316to top of the first portion310and the bottom of the second portion312. Bending at the hinge areas316therefore allows for radial movement of the first portion relative to the second portion (e.g., movement within the x-y plane). For example, as shown inFIG. 4, movement of the first portion310and the second portion312away from each other can be accommodated by the hinge portions316bending slightly to provide a slight angle to the beam portion314. This can have the effect of increasing the length of the radial arm, for example in response to thermally-induced forces placing tension on the radial arm (e.g., a decrease in size of a stiffener relative to a cardholder to which it is fixed). Conversely, as shown inFIG. 5, movement of the first portion310and the second portion312toward each other can be accommodated by the hinge portions312bending in the opposite direction from that shown inFIG. 4, allowing the slits302to decrease in size. This can have the effect of decreasing the length of the radial arm, for example in response to thermally-induced forces placing compression on the radial arm (e.g. an increase in size of a stiffener relative to a cardholder to which it is fixed). In other words, the decoupling mechanism can have the effect of compensating for an increase or decrease in radial dimension (e.g., diameter) of the stiffener by a corresponding decrease or increase so that the overall radial dimension of the stiffener between fixed attachment points remains substantially constant (relative to the dimensions defined by the attachment points, which may also vary, for example, due to thermal effects).

Note that movements shown inFIGS. 4-5are exaggerated for illustration, and actual radial movement can be relatively small. For example, radial expansion and contraction may be less than500micrometers. In general, the amount of compliance provided can be proportional to the width (A-dimension) of the slits (as well as being a function of the stiffness of the material from which the radial arm304is constructed) with a larger width slit generally providing greater compliance. Accordingly, the dimensions of the slits can be selected to provide a desired amount of compliance. For example, as generally discussed above with respect to decoupling mechanisms138, the dimensions of the slits can be selected such that the amount of compliance is set so that thermally induced movement of the cardholder142at a given temperature is compensated for by a corresponding (e.g., approximately equal but opposite) thermally induced movement of the stiffener202at the given temperature over a predetermined temperature range (e.g., a desired operating temperature range). Thus, the dimensions of the slits can be selected so that the net thermally induced movement of the cardholder142and the stiffener202results in approximately zero movement of the contact ends of the probes124over a predetermined temperature range. This can result in no appreciable movement in the “z” directions of the plane156of the contact ends of the probes124.

While the decoupling mechanism300can provide compliance in the radial direction (e.g., allowing expansion and contraction of the radial arm304), the decoupling mechanism can maintain rigidity in directions other than the radial direction. In particular, the decoupling mechanism300can maintain rigidity in the vertical z-direction. This rigidity can be maintained because the hinge portion316can only readily bend in one direction (e.g., in response to axial loading along the radial axis) and does not readily bend in respond to forces oriented in other directions (e.g., forces perpendicular to the radial axis) or torsion (twisting) forces. In particular, the entire width of the radial arm304can essentially resist vertical (z-direction) forces (e.g., probe loading). Accordingly, a stiffener which includes decoupling mechanisms in each of the radial arms can maintain rigidity in the z-direction while being able to accommodate thermally-induced dimensional changes in the x-y plane (e.g., radial expansion/contraction). In general, the amount of rigidity maintained is proportional to the width (C-dimension) of the radial arm304(as well as being a function of the stiffness of the material from which the radial arm is constructed), with a wider radial arm generally providing greater rigidity.

Another embodiment of a decoupling mechanism600is illustrated inFIG. 6. The decoupling mechanism600can be disposed within the radial arm304, and can include two slits602, which can be oriented similarly as inFIGS. 3A-3B. The slits602can define a beam section614disposed between the slits. Within the beam section can be a hollow portion616. For example, the hollow portion616can be cut into a side surface of the radial arm, and can extend partially or completely through the radial arm. The hollow portion616can help to allow for deformation of the beam when radial (axial) loading is applied, increasing the compliance of the decoupling mechanism600in the radial (axial) direction.

A decoupling mechanism can include slits in other orientations. For example, as illustrated inFIG. 7, another embodiment of a decoupling mechanism700can include angled slits702between a first portion710(e.g., a main body side) and a second portion720(e.g., a distal end) of the radial arm304. The slits702can be at an angle (e.g., other than perpendicular) relative to the top surface306and bottom surface308of the radial arm304. Angled slits702can provide a different ratio of radial compliance to vertical compliance as compared to perpendicularly oriented slits (e.g.,302). In some embodiments, angled slits702can also improve (e.g., maximize) stiffness in the vertical direction inFIG. 7by reducing (e.g., minimizing) bending stresses in the radial arm304. As a non-limiting example, angle offsets from vertical (perpendicular) can include 10 degrees, 22.5 degrees, 30 degrees, 45 degrees, or any other suitable value.

Another example of a decoupling mechanism is illustrated inFIGS. 8A-8B. The decoupling mechanism can be disposed between a first portion310and a second portion312of the radial arm304. The decoupling mechanism can include stepped portions which provide opposing bearing surfaces802on each of the first portion310and the second portion312. Positioned between the bearing surfaces can be a bearings804. Although four bearings are shown here, the number of bearings can be more or less than four. A clamp806can hold the first portion310, second portion312, and the bearings804together. The clamp can allow the first portion310and second portion312to slide radial relative to each other, while holding the first portion and second portion rigidly together in other directions.

Another example of a decoupling mechanism is illustrated inFIG. 9. The decoupling mechanism can include facing stepped portions of a first portion310and second portion310of the radial arm304. The first portion310and second portion310can be held together by a flexible connector906which provides compliance in the radial direction902and rigidity in the vertical direction904. For example, the flexible connector can be a metal plate which has been machine to include a hole908to allow flexing in the radial direction while resisting flexing in the vertical direction. As another example, the flexible connector can be a material which has compliance characteristics that differ in different directions. The flexible connector906can be attached to the radial arm portions, for example, by pins910which pass through corresponding holes in the flexible connector. As another example, the flexible connector can be a material which provides different rigidity in different directions.

Probe card assemblies (e.g.,124,200) with stiffeners (e.g.,120,202) having decoupling mechanisms (e.g.,138,250,300,600,700) as described herein can be used to provide reduced thermal motion of the probe card. A probe card assembly can be installed into a prober (e.g.,102) by fixing attachment mechanisms (e.g.,136,206) of the probe card assembly to a cardholder (e.g.,142) of the prober. Once installed, the prober can be operated to bring the probes (e.g.,124,224) into contact with a device to be tested (e.g., DUT112). Typically, the probes make contact with terminals of the device with some minimal contact force (e.g., by additional movement or over-travel past the point of initial contact) to provide reliable electrical connections between the probes and the device. This can result in forces on the probes, which are communicated through the probe head to the stiffener. The stiffener can resist deformation by these forces. Once the electrical connections have been made, testing can proceed by communicating test signals through the probes to the device to be tested. Testing can include providing stimulus signals to the device to be tested and receiving response signals from the device to be tested. Response signals can be compared to an expect response to determine if the device to be tested is operating correctly.

During testing, temperature of the probe card assembly can be varied either intentionally or unintentionally, via direct or indirect heating or cooling. For example, heating or cooling of the stage on which the device to be tested is position can result in indirect heating or cooling of the probe card assembly. Variation in temperature of the probe card assembly can cause a dimensional change of the probe card assembly relative to the cardholder. For example, the probe card assembly can have a different coefficient of thermal expansion as compared to the coefficient of thermal expansion of the cardholder. As another example, the probe card assembly and the cardholder can be at different temperatures. The decoupling mechanisms can absorb these dimensional changes and differences, helping to reduce thermally-induced forces on the stiffener. This can help the stiffener to maintain the probes in a substantially constant position within the z plane.

Also, generally in accordance with the discussion above with respect to slits shown inFIGS. 4-5, any of the decoupling mechanisms disclosed herein can be configured to provide an amount of compliance in the probe card assembly that results in thermally induced movement in the probe card assembly at a given temperature that sufficiently offsets thermally induced movement of the cardholder at the given temperature over a predetermined temperature range to maintain contact ends of the probes in a plane. For example, any of the decoupling mechanisms138(or138′),250(or250′),300,600,700, and/or the decoupling mechanisms illustrated inFIGS. 8A,8B, and9can be configured to have an amount of compliance such that thermally induced movement of the cardholder142at a given temperature is sufficiently offset by thermally induced movement of the stiffener (e.g.,202) of the probe card assembly at the given temperature over a predetermined temperature range (e.g., a desired operating temperature range) to maintain contact ends of the probes in the plane156and keep the plane156from moving. The net thermally induced movement of the cardholder142and the probe card assembly can thus be configured such that the net movement of the contact ends of the probes124(and thus the plane156) is substantially zero over a predetermined temperature range.

In accordance with additional embodiments of the invention, decoupling mechanisms as disclosed herein can alternatively or in addition be provided in other portions of the test system. For example, referring toFIG. 1A, in some embodiments, decoupling mechanisms (not shown) can be included within the cardholder142in addition to or instead of the decoupling mechanisms138within the probe card assembly108. For example, the decoupling mechanisms can be disposed within the card holder between the holes144and a main portion of the card holder (e.g., between the holes and other structure (not shown) of the cardholder attached to or held by the prober). The decoupling mechanisms can be like any of the decoupling mechanisms disclosed above. As a particular example, the decoupling mechanisms shown inFIGS. 6-9can be used (e.g., the first portion310can be a first portion of the cardholder142and the second portion312can be a second portion of the card holder).

As another example, decoupling mechanisms can be used for attachment of the probe card assembly108to the card holder142. For example, in place of fasteners146a decoupling mechanism (not shown) can be used to attach the probe card assembly108to the card holder142. The decoupling mechanisms can be like any of the decoupling mechanisms shown above. As a particular example, the decoupling mechanisms shown inFIGS. 8A-8Band9can be used (i.e., the first portion310can be a probe card assembly and the second portion312can be an insert ring, or vice versa).

As will now be apparent, some embodiments of a stiffener and probe card assembly as disclosed herein can provide several advantages. In some embodiments, the decoupling mechanisms can be implemented as partial cuts into the arms of the stiffener, hence the stiffener can be a single piece, and few or no additional parts or tooling may be needed for handling the stiffener or assembling the probe card assembly. In some embodiments, the CTE of the stiffener need not match the CTE of the cardholder, hence less expensive materials can be used to fabricate the stiffener. In some embodiments, the same probe card design can provide low thermally-induced movement even when used in different types of probers which include cardholders made of different materials having differing CTE.

Although specific embodiments and applications of the invention have been described in this specification, these embodiments and applications are exemplary only, and many variations are possible. Accordingly, there is no intention that the invention be limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. For example, features shown in one embodiment can be combined with features shown in another embodiment. Accordingly, it is not intended that the invention be limited except as by the claims set forth below.