Patent Publication Number: US-9417263-B2

Title: Testing probe head for wafer level testing, and test probe card

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application is a divisional application of U.S. patent application Ser. No. 13/233,079, filed Sep. 15, 2011, now U.S. Pat. No. 8,832,933, which application is expressly incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to semiconductors, and more particularly to probes cards for testing integrated circuits formed on a semiconductor wafer. 
     BACKGROUND 
     Modern semiconductor fabrication involves numerous steps including photolithography, material deposition, and etching to form a plurality of individual semiconductor devices or integrated circuit chips (dice) on a single semiconductor silicon wafer. Typical semiconductor wafers produced today may be at least about 6 inches or more in diameter, with a 12 inch diameter wafer being one common size. Some of the individual chips formed on the wafer, however, may have defects due to variances and problems that may arise during the intricate semiconductor fabrication process. Prior to wafer dicing wherein the individual integrated circuit chips (dies) are separated from the semiconductor wafer, electrical performance and reliability tests are performed on a plurality of chips simultaneously by energizing them for a predetermined period of time (i.e., wafer level burn-in testing). These tests may typically include LVS (layout versus schematic) verification, IDDq testing, etc. The resulting electrical signals generated from each chip or DUT (device under test) are captured and analyzed by automatic test equipment (ATE) having test circuitry to determine if a chip has a defect. 
     To facilitate wafer level burn-in testing and electrical signal capture from numerous chips on the wafer at the same time, DUT boards or probe cards as they are commonly known in the art are used. Probe cards are essentially printed circuit boards (PCBs) that contain a plurality of metallic electrical probes that mate with a plurality of corresponding electrical contacts or terminal formed on the wafer for the semiconductor chips. Each chip or die has a plurality of contacts or terminals itself which must each be accessed for testing. A typical wafer level test will therefore require that electrical connection be made between well over 1,000 chip contacts or terminals and the ATE test circuitry. Accordingly, precisely aligning the multitude of probe card contacts with chip contacts on the wafer and forming sound electrical connections is important for conducting accurate wafer level testing. Probe cards are typically mounted in the ATE and serve as an interface between the chips or DUTs and the test head of the ATE. 
     As semiconductor fabrication technology advances continue to be implemented, the critical dimension or spacing between electrical test contact pads and bumps (i.e. “pitch”) of dies or chips on the semiconductor wafer continues to shrink. The present major trend in semiconductor fabrication is moving towards 3D IC chip packages with heterogeneous chip stacking. Such 3D IC chip packages include DUTs having a TSV (through silicon via) electrical interconnect structure with corresponding micro bump testing contact fine pitch arrays with a micro bump pitch of less than 50 microns (m). 
     A technology bottleneck occurs that is associated with existing known testing probe card designs and assembly techniques that do not readily support such small testing pad micro bump pitches as encountered on 3D IC chip packages. There are limitations associated with existing guide plate manufacturing having closely spaced holes which support small diameter (e.g. 25 microns) needle-like metal testing probe which are flexible and easily bent, guide plate assembly techniques, and probe handling required to manually insert the slender probes through small diameter probe holes (e.g. 30 microns) in the guide plates which is a time-consuming operation and results in all too frequent damage to the structurally thin and weak probes. 
     An improved testing probe card and method for fabricating the same is therefore desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the embodiments will be described with reference to the following drawings where like elements are labeled similarly, and in which: 
         FIG. 1  is a partial cross-sectional side view of an embodiment of a test probe card according to the present disclosure; 
         FIG. 2  is a perspective view of one embodiment of the testing probe head in  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional side view of one embodiment of the interposer in  FIG. 1 ; 
         FIGS. 4-8  show exemplary embodiments of testing probes useable in the testing probe card of  FIG. 1 ; 
         FIGS. 9-14  show exemplary sequential method steps for fabricating the testing probe head of  FIG. 2 ; 
         FIG. 15  is a block flow diagram showing the basic method steps in  FIGS. 9-14 ; 
         FIGS. 16-19  are scanning electron microscope images taken during fabrication of the testing probe head using the method shown in  FIGS. 9-14 ; and 
         FIGS. 20 and 21  show partial cross-sectional side views of an alternative embodiment of the testing probe head of  FIG. 2  with a probe guide plate. 
     
    
    
     All drawings are schematic and are not drawn to scale. 
     DETAILED DESCRIPTION 
     This description of illustrative embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present disclosure. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the disclosure are illustrated by reference to the embodiments. Accordingly, the disclosure expressly should not be limited to such embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the disclosure being defined by the claims appended hereto. 
     As the term may be used herein in describing metallic test probes, rigid shall have its customary meaning of a structure that is generally deficient in or devoid of flexibility. 
       FIG. 1  shows one exemplary embodiment of a probe card according to principles of the present disclosure. A probe card  200  generally includes a testing printed circuit board (PCB)  210 , space transformer  240 , interposer  230 , and testing probe head  260  having a laterally extending array including a plurality of testing probes  300  configured and arranged to engage mating testing contacts disposed on a DUT (device under test). Testing PCB  210  includes conventional DUT testing circuitry and active devices as will be well known to those skilled in the art. Testing PCB  210  includes a bottom surface  214  and a top surface  212  that includes an array of electrical contacts for interconnecting with corresponding contacts on the automatic test equipment (ATE) (not shown) for performing wafer level DUT testing. In one embodiment, testing PCB  210  may be made of silicon. Testing PCB  210  includes conventional wafer testing circuitry that is operative to apply an electrical load to a DUT  100  on the wafer, and to receive and process return electrical signals from the DUT which in some embodiments may be associated with wafer level DUT burn-in performance and reliability tests. 
     Testing probe card  200  further includes a mounting assembly  270  which includes a fixing or mounting ring  220  for securing the probe card to the ATE in a conventional manner. In some embodiments, mounting ring  220  may be made of a suitable metal such without limitation as stainless steel, aluminum, or titanium. 
     With continuing reference to  FIG. 1 , mounting assembly  270  in some embodiments may further include an upper metal support plate  272  and lower metal support plate  274  which are positioned in spaced apart relationship. A compressible deformable member such as an elastomeric or rubber insert  276  may be interspersed between the upper and lower support plates  272 ,  274  in some embodiments as shown to add fleixibility to the relatively rigid testing probes  300  and testing probe head  260 . The compressible insert  276  further functions to compensate for potential non-planarity of the testing probe tips, enhance positive contact between the probe tips and testing contacts on the DUTs, and absorb the initial contact impact stresses of engaging the testing probe head  260  with the DUT. Mounting assembly  270  may be secured to mounting ring  220  in any suitable manner including via threaded fasteners  261  as shown. With continuing reference to  FIG. 1 , space transformer  240  is disposed between interposer  230  and testing probe head  260 . Space transformer  240  includes a substrate that receives and secures the lower ends  252  of a plurality of conductive metal wire leads  250  which pass through the substrate. In some embodiments, the ends of the wire leads  250  may be coupled to contact pads (not shown) disposed on the lower surface of the space transformer similar to surface contact pads  261  shown in  FIG. 14 . In some embodiments, the space transformer  240  substrate may be a multi-layered organic (MLO) or multi-layered ceramic (MLC) interconnect substrate. The upper ends  254  of wire leads  250  are electrically connected to contacts on the upper surface  212  of the testing PCB  210 . The pitch or spacing of lower ends  252  may be smaller or finer than the upper ends  254 . An adhesive  256  may be applied on top of space transformer  240  to support and fix the wire leads  250  in place in relation to the space transformer. In one representative embodiment, the adhesive may be any thermally cured adhesive from common suppliers such as Henkel, 3M, Shinetsu and Loctite. 
     Space transformer  240  may include one or more guide pins  242  as shown in  FIG. 1  which may be aligned with and received in mating sockets  244  disposed in mounting assembly  270  to facilitate mounting the space transformer to the mounting assembly. Space transformer  240  may be supported from mounting assembly  270  and/or testing PCB  210  via threaded fasteners  261  or any other suitable means. In one embodiment, as shown, space transformer  240  may be mounted to both testing PCB  210  and the mounting assembly  270 . 
     Interposer  230  provides an electrical interface between the conductive wire leads  250  in the space transformer  240  and contacts on the testing probe head  260 . Referring to  FIG. 1 , interposer  230  may be a passive interposer formed of a substrate containing a plurality of vertically-oriented cylindrical conductive vias  232  that pass completely through the substrate. In one embodiment, as shown in  FIG. 3 , the substrate may be a made of a compressible material such as without limitation silicone rubber to add flexibility to the testing probe card  200  for absorbing initial contact stresses occurring when engaging the testing probe head  260  with the DUT during testing and/or to conform to and compensate for possible DUT or probe non-planarity situations. An upper portion of a compressible interposer  230  may include a thin flexible polymer mesh  234  disposed proximate to or on the top surface and a lower portion may include a sheet  236  made of a relatively more rigid material disposed proximate to or on the bottom surface. In some embodiments, sheet  236  may be without limitation FR-4 or FR-5 (UL grade designation for Flame Retardant Class 4 or 5) glass reinforced epoxy laminate sheet made of woven fiberglass cloth and an epoxy resin binder that is flame resistant. The conductive vias  232  in one embodiment may be made of any suitable conductive metal powder such as without limitation tungsten, copper, nickel, and alloys thereof. 
     In alternative embodiments, interposer  230  may have a relatively rigid substrate construction being made of a relatively non-compressible material. Such materials may include without limitation a silicon substrate, FR-4/FR-5 glass reinforced epoxy laminate sheet, or other suitable rigid materials used for interposes. The cylindrical conductive vias  232 , which are disposed in the rigid substrate and may be TSVs in some embodiments where a silicon substrate is used, may be made of any suitable conductive material including without limitation tungsten, copper, nickel, or alloys thereof. In some embodiments, a rigid interposer may include a redistribution layer fabricated on one surface (called an RDL). Thus the interposer  230  could physically and electrically convert the dense/finer pitch pads facing the probe side to the pads with relaxed pitch on the wiring side. 
     Interposer  230  may be mounted below and to the underside of space transformer  240  by any suitable means commonly used in the art, such as without limitation via threaded fasteners  261  in some embodiments as shown in  FIG. 1 . 
     Referring again to  FIG. 1 , testing probe head  260  includes a support substrate  262 , a plurality of conductive metallic through vias, for example through-substrate vias or through-silicon vias (TSV)  264 , and a plurality of corresponding conductive metallic testing probes  300  electrically and structurally coupled to the vias. In some embodiments, support substrate  262  may be formed by a conventional semiconductor substrate material such as silicon commonly used in the art. 
     Referring to  FIGS. 1 and 14 , vias  264  may be made of any suitable conductive material including without limitation metals such as copper or tungsten. Vias  264  extend completely through support base  262  and may be terminated at each end by a relatively flat and broadened conductive metallic surface contact pad  266 . Vias  264  function to transfer electrical test signals through the support base substrate both to and from testing PCB  210  for testing the dies or DUTs  100 . Vias  264  and contact pads  266  are formed in support substrate  262  by conventional photolithography, etching, and material deposition techniques used in fabricating semiconductors in silicon wafers. 
     Referring to  FIGS. 1 and 14 , the upper set of contact pads  266  are configured, dimensioned, and spaced apart to make electrical contact with vias  232  in interposer  230  when the testing probe head  260  is mounted on the interposer. Accordingly, the upper contact pads  266  may have a lateral spacing or pitch that matches the pitch of vias  232  to eliminate the need for redistribution layer conductors to alter pitch spacing. The lower set of contact pads  266  will be electrically coupled to testing probes  300  as further described herein. 
     Referring to  FIGS. 1 and 14 , testing probes  300  extend outwards from and generally perpendicular in some embodiments to support substrate  262  as shown. Probes  300  are configured and arranged for mating with corresponding test contacts  110  on a DUT  100  to be tested. Testing probes  300  may have a pitch Pp that matches the pitch Pt of test contacts  110 . In one exemplary embodiment, pitches Pp and Pt may be about 40 microns. In some embodiments, test contacts  110  may be test pads or microbumps as shown in  FIG. 1  such as those found on a 3D IC package. Testing probes  300  provide conductive paths for electrically connecting testing PCB  210  with the DUTs  100  in the wafer for wafer level burn-in testing. 
     Referring to  FIGS. 1, 4, and 14 , testing probes  300  are generally pin-like and vertically elongated may have a relatively rigid shaft with a structural beam-like construction and configuration. In some embodiments, probes  300  may be cantilevered from support substrate  262  without intermediate or dual support near opposing upper and lower ends of each probe. Each probe has a base portion  302  attached to support substrate  262 , a tip portion  304  with a free end defining a tip  303  configured for engaging test contacts  110  on DUT  100 , and an intermediate portion  305 . In other embodiments, as shown in  FIG. 21  for example and further described herein, an intermediate alignment and support guide plate  332  may be provided to help support and prevent lateral permanent deformation and non-planarity of the probe tips, in addition to possible breakage during repetitive use and thermal cycles from applying an electrical load to wafers being tested. 
     Testing probes  300  may be of any suitable length, transverse cross-sectional shape, and configuration to fit the intended application so long as suitable pitch spacing Pp may be provided to match the pitch Pt of testing contacts  110  on the DUT  100  for wafer level testing. In some embodiments, testing probes  300  may have a generally rectilinear (e.g. square or rectangular) cross-sectional shape (viewed transverse to the axis or length of the probe), which in some embodiments may result from one exemplary probe fabrication technique that may be used such as reverse wire electrical discharge machining (“R-WEDM”) commonly used for MEMS manufacture, as further described herein. In one exemplary embodiment for wafer level testing of 3D IC packages, probes  300  may have an approximate cross-sectional width (measured across each flat side) of about 20 microns to support testing of a plurality of 20 micron diameter microbump test contacts  110  in a 40 micron pitch Pt testing contact array on a DUT  100 . The pitch Pp of such probes  300  in testing probe head  260  may correspondingly be about 40 microns also. 
       FIGS. 4-8  show some of the possible embodiments and configurations of testing probes formed according to principles of the present disclosure. The testing probes have a free end opposite support substrate  262  with a tip  303  configured and dimensioned for contacting a corresponding testing pad  110  on a DUT  100 .  FIG. 4  shows a single probe  300  having a rectangular or square beam shape. Probe  300  has a uniform transverse cross-section in size for its entire length.  FIG. 5  shows substantially the same configuration, but probe  310  has a tapered or reduced width pyramidal shaped tip portion  304  for engaging correspondingly smaller diameter testing microbump contacts  110  on a DUT  100 .  FIG. 6  depicts a probe  320  having a curved beam shape with a tip portion  304  which is axially offset from base portion  302  to add flexibility to the probe. Probe  320  otherwise may have a uniform transverse cross-section for its entire length as shown, or alternatively may have a tapered tip portion  304  configured similarly to  FIG. 5 . Also, as further shown in  FIG. 6 , any of the probes may have rounded tips for enhancing engagement with test contacts  110  on DUT  100  (shown in  FIG. 1 ) which are formed during fabrication of the probes and probe array. 
     Each testing probe shown in  FIGS. 4-8  may be considered to have a base portion  302 , a tip portion  304  with a free end defining a tip  303 , and an intermediate portion  305  similarly to that shown in  FIG. 4 . 
     Exemplary probes  330  and  340  shown in  FIGS. 7 and 8 , respectively, are similar in configuration to the probes shown in  FIGS. 4 and 5 . However, probes  330  and  340  have a stopper  306  formed on at least one lateral side of the probe. Stopper  306  protrudes laterally outwards from probes  330 ,  340 , and are dimensioned and configured to engage an intermediate alignment and support guide plate  332  as shown in  FIGS. 20 and 21 . These figures show probes  330  mounted through guide plate  332 ; however, the same principle applies to probes  340  with stoppers  306 . 
     Guide plate  332  may be mounted on support substrate  262  of testing probe head  260  via spacers  338  which space the guide plate away from substrate  262  forming a gap therebetween, as shown in  FIGS. 20 and 21 . In some embodiments, a guide pins  334  may be provide to align and mount guide plate  332  to substrate  262  via the spacers  338 . In other embodiments, guide pins  334  may be omitted. Guide plate  332  and spacers  338  may be made of an electrically non-conductive and insulating material to avoid shorting the electrical signals passing through probes  300  during testing of the DUTs  100 . In some embodiments, the guide plate  332  and spacers  338  may be one integral unitary structure/part which is made of single material such as without limitation machinable ceramic, silicon, or silicon nitride. In other embodiments, the guide plate and spacers may be formed as two or more separate parts which are joined together such as glued by adhesives or mechanically fastened by screws. 
     With continuing reference to  FIGS. 7-8 and 20-21 , guide plate  332  may contain a plurality of apertures  336  configured and dimensioned to receive at least one end and a portion of probes  330  (or probes  340 ) therethrough. An aperture  336  is therefore provided for each through silicon via  264  in support substrate  262  of the test probe head. Apertures  336  are laterally arranged and spaced to have a pitch that matches the pitch of vias  264  so that the apertures are each concentrically aligned with a corresponding via below. During assembly, one end of probes  330  or  340  are inserted through apertures  336  until the laterally extending stoppers  306  engage guide plate  332 , thereby limiting the insertion depth of the probes. 
     Advantageously, the foregoing probe assembly with guide plate  332  is intended to provide improved probe planarity (i.e. tips of probes terminating and falling uniformly along a single plane defined by the probe tips) and better positioning of the probes for completing the reflow soldering assembly further described herein. Stoppers  306  are spaced between the ends of the probes  330 , and in one embodiment may be located closer towards the base portion  302  than the tip portion  304  of each probe. Guide plate  332  therefore provides both intermediate lateral/transverse support of each probe via apertures  336  and axial support via stoppers  306  thereby enhancing the structural strength of this testing probe head  400 . 
     A completed testing probe head  400  with guided and supported testing probes  330  is shown in  FIG. 22 . 
     It will be appreciated that in some embodiments, at least one but not all of the testing probes need to have stoppers to limit the insertion depth of the full probe array. Since the probes are still collectively attached to the temporary workpiece base  301  as shown in  FIGS. 10A and 10B , only a few space apart probes  330  or  340  of the design as shown  FIG. 7 or 8  need to be provided in the probe array to effectively limit the insertion depth all the probes in the array through guide plate  332 . Accordingly, in some embodiments, the probe array may include a combination of both probes  300  or  310  with straight shafts (see, e.g.  FIGS. 4 and 5 ) with at least one probe  330  or  340  having a stopper  306 . 
     An exemplary method for fabricating test probes  300  and assembling test probe head  260  as shown in  FIGS. 1 and 14  will now be described. Specific reference is made to  FIGS. 9-15 , with  FIG. 15  showing a flow chart of the basic fabrication process steps involved in making testing probe head  260 . The various process steps that may be used including photolithography, material deposition, material removal, machining, forming, and others to be described below refer to conventional processes known and commonly used in MEMS (micro-electro-mechanical systems) or semiconductor fabrication unless otherwise noted. 
     Referring to  FIGS. 9 and 15 , a workpiece W is first provided in the form of a monolithic block of bulk raw material from which probes  300  will be formed is provided in the first step. The block of material is dimensioned so that a complete laterally extending array of testing probes  300  for the testing probe head  260  may be fabricated from the single block of material simultaneously. In the embodiment shown, where a rectilinear probe array (i.e. square or rectangular) is to be fabricated, the raw material block has a complementary rectilinear configuration. 
     The block of raw material for workpiece W will be selected based on the material intended for the testing probes  300 . In some embodiments, the raw material may be any conductive metal or metal alloy suitable for use as testing probes. In some representative embodiments, without limitation, the raw material may be tungsten palladium, tungsten carbide, palladium, cobalt, nickel, hard gold, soft gold, tungsten, rhenium, rhodium, or alloys thereof. In other embodiments, the raw material may be an electrically conductive non-metallic material such as carbon-nanotube in bulk shape. 
     In the next step shown in  FIGS. 10 and 15 , the testing probe array containing a plurality of individual probes  300  is next formed from the monolithic block of raw material. In one embodiment, reverse wire electrical discharge machining (“R-WEDM”) commonly used for MEMS manufacture may be used to machine the probes. This process is capable of accurately producing a testing probe array with sufficiently small probe pitch Pp suitable for mating with 3D IC package microbump arrays pitch Pt (see also  FIG. 1 ). In some embodiments, pitch Pp may be about 40 microns or less. 
     With continuing reference to  FIGS. 10 and 15 , one end of the bulk raw material block or workpiece W or will serve as a temporary expendable common base  301  for supporting the individual testing probes  300  during the probe formation and fabrication process until attached to support substrate  262 . In one embodiment, R-WEDM may be used to cut or form completed probes in an essentially two-part, bi-directional machining process, which will be further described for convenience with reference to the arbitrary X-Y-Z coordinate system drawn in  FIG. 2  with respect to the fabrication base  301 . The completed testing probe  300  array will correspondingly extend laterally in both the X and Y directions, as well as in the Z direction normal to the base  301  defining the height or length of the completed test probes. 
     R-WEDM is basically an automated CNC (computer numerical control) process generally utilizing a thin single strand of metal discharge cutting wire held between computer-controlled moveable guides. The discharge wire is electrically energized and fed through the bulk raw material or workpiece W, which may be submerged in a tank of dielectric fluid such as deionized water, to make a series of cuts. The wire may be articulated in numerous directions and orientations to make machine components having a variety of configurations. Electrical discharges or sparks from the wire cuts or erodes the workpiece material. Electric discharge machines (EDM) are commercially available from various companies, such as for example GF AgieCharmilles of Lincolnshire, Ill. 
     One embodiment of an R-WEDM process used for forming embodiments of a testing probe array according to the present disclosure may utilize a micro-sized brass discharge wire  402 . In one non-limiting representative example, discharge wire  402  may have a diameter of about 20 microns that may be used for producing a test probe array with a pitch spacing of about 40 microns and individual testing probe widths of about 20 microns. The diameter of the wire used will be based at least in part on the pitch spacing and final width (in both X and Y directions) of the testing probes  300 , and also must compensates for the spark or electrical discharge produced by the wire  402  which will cut a path or kerf larger than the diameter of the wire itself (i.e. overcut). 
     Initially, the probe bulk material block or workpiece W (see  FIG. 9 ) is first mounted and secured in an EDM machine capable of implementing the R-WEDM process. Next the discharge wire  402 , which is typically supported by wire guides, is positioned near one of the lateral sides of the workpiece W and spaced axially inwards (in the Z axis direction) a short distance from the end of temporary workpiece base  301  (see  FIG. 10 ). 
     With reference now to  FIGS. 2, 10A, and 15 , the first part of the two-part, bi-directional R-WEDM probe cutting process involves cutting a plurality of channels Cy extending across workpiece W in the Y axis direction. In one embodiment, this may be accomplished by advancing energized discharge wire  402  progressively and horizontally in a first axial X-axis direction across the bulk material block or workpiece W in the X-Y plane (see dashed wire path in  FIG. 10A ). Wire  402  has a length that extends completely across the workpiece W in the Y axis direction so that channels Cy used to form probes  300  may be fully cut for all probes simultaneously across the full width of the workpiece. As the discharge wire  402  axially advances, the wire is then intermittently and repetitively moved vertically into and out of the workpiece W in the Z axis direction (along the Y-Z plane) to form a plurality of channels Cy extending in the Y axis direction and transverse to the X-axis direction of motion of the discharge wire  402 . Channels Cy are spaced apart along the X axis leaving concomitantly a plurality of individual rectilinear-shaped sheets of probe material which are spaced apart in the X direction, but have continuous width across the workpiece W in the Y axis direction (see, e.g. scanning electron microscope images in  FIGS. 16 and 17 ). 
     The depth of channels Cy cut into the workpiece W along the Z-axis do not extend completely through the workpiece as shown in  FIG. 10A  leaving temporary workpiece base  301  intact for supporting the plurality of probes to be formed for the entire probe formation process. 
     Accordingly, referring to  FIG. 10A , the first part of the foregoing probe cutting process involves temporarily stopping axial motion of discharge wire  402  at a plurality of predetermined axial intervals or cutting positions X1 . . . Xn (where n=number of X axis axial cutting positions) to cut channels Cy. The discharge wire W is therefore horizontally and axially moved to a first cutting position X1, the wire is then moved into and out of workpiece W along the Z axis to form a first channel Cy, wire  402  is then moved to the next axial cutting position Xn, the wire is then moved vertically again to cut a second channel Cy, and so on until the desired number of channels Cy are cut. The probes  300  now have been partially formed with the desired axial width and spacing or pitch of the probes along the X axis; the width and pitch of the individual probes along the Y axis yet to be cut as described below. 
     The foregoing process is controlled by the automated CNC process and R-WEDM machine with the appropriate axial cutting positions, depth of cuts in the Z-axis, and other relevant process parameters including controlled movement of the discharge wire  402  being preprogrammed into the machine processor. It is well within the ambit of one skilled in the art to program and control the R-WEDM machine cutting process to achieve the desire location, depth, and size of the cuts to be made in workpiece W. 
     With reference to  FIGS. 2, 10B, and 15 , the second part of the R-WEDM probe cutting process next involves cutting a plurality of channels Cx extending across workpiece W in the X axis direction perpendicular to and intersecting channels Cy already formed in  FIG. 10A  in the same manner previously described. In one embodiment, this may be accomplished by advancing energized discharge wire  402  progressively horizontally a second axial Y direction across the bulk material block or workpiece W within the X-Y plane. The second axial cut direction is therefore oriented 90 degrees from the first axial cut direction shown in  FIG. 10A . As the wire  402  axially advances, the wire is stopped at a plurality of Y-axis positions Y1 . . . Yn where the wire is vertically moved into and out of the workpiece W in the Z axis direction (in the X-Z plane) to cut channels Cx through the spaced apart sheets of probe material previously formed. Cutting channel Cx in the sheets of probe material forms a plurality of individual pillars at the intersections between channels Cy and Cx. The pillars each define an elongated probe  300 , which are now arranged spaced apart in both the X and Y directions (see also scanning electron microscope images in  FIGS. 17 and 18 ). The probes  300  each now generally have the desired final lateral or axial width and a pitch or spacing along both the X axis and Y axis. 
     In some embodiments, as shown in  FIG. 2 , the probes  300  formed via cutting channels Cy and Cx may have a rectilinear (i.e. square or rectangular) cross-sectional shape in the X-Y plane. It should be noted that in  FIGS. 10A and 10B , the free ends of the presently formed probes  300  shown (i.e. ends not still attached to temporary base  301 ) will actually define the base portion  302  of the probes for attachment to supporting substrate  262  as described below. 
     Referring now to  FIGS. 2, 11, and 15 , the testing probe head  260  fabrication and assembly process next continues with providing support substrate  262 . Substrate  262  already contains fully formed through silicon vias  264  and upper/lower contact pads  266  previously formed by conventional MEM or semiconductor fabrication processes well known in the art. A plurality of conventional conductive solder microbumps  268  are formed on one side of substrate  262  on contact pads  266  as shown in  FIG. 11  which will be used to electrically interconnect each probe  300  to a corresponding contact pad and via  264 . 
     Referring now to  FIGS. 2, 12, and 15 , the testing probes  300  are next physically and electrically connected to conductors in support substrate  262  of testing probe head  260 . In one embodiment, the probes may be connected to substrate  262  using solder joints. To accomplish this, the workpiece W with plurality of completed testing probes  300  is advanced toward substrate  262 . The free ends of each finished testing probe  300  pillar shown in  FIG. 10B  are then abuttingly engaged with a corresponding solder bump  268  on substrate  262  and held in position. The probe-substrate assembly may then be moved to a reflow soldering oven and heated to melt the solder bumps  268  using any suitable heat source such as hot gas, infrared heat, etc. The melted solder flows and creates a physical and electrical connection to the free ends of the testing probes  300 , which will define base portion  302  of each probe. The assembly now appears as shown in  FIG. 12  with base portion  302  of each probe attached to support substrate  262  and opposite tip portion  304  of each probe still attached to temporary fabrication base  301 . 
     Referring now to  FIGS. 2, 13, and 15 , temporary base  301  is next severed and removed from the probe assembly. In one embodiment, R-WEDM may be used to laterally cut across the probes  300  in either the X or Y axial direction more proximate to the base  301  than substrate  262 . This final cutting step will define the finished height or length of the testing probes  300 . 
     The completed testing probe head  260 , as shown in  FIGS. 2 and 14 , is now ready for mounting to testing probe card  200 .  FIGS. 18 and 19  show scanning electron microscope images of an actual testing probe assembly formed according to an embodiment of the present disclosure using R-WEDM. 
     It will be noted that the workpiece W and R-WEDM machining process may be conducted in any suitable orientation other than the foregoing orientations provided merely for convenience in describing the process. The disclosure is therefore not limited to R-WEDM machining in any particular orientation so long as the testing probes  300  may be properly fabricated. 
     There are numerous advantages of the foregoing probe formation process. First, all testing probes  300  are simultaneously formed and mounted to the testing probe head in a single solder reflow operation as opposed to being individually assembled on a piece-meal basis as in prior manual probe mounting operations. This results in more precise dimensional accuracy of the testing probes and significantly less time to assemble the probes to the testing probe head. The present process is also fully automated and eliminates manual handling and potential damage of the probes resulting in lower reject rate. The present probes also have a more rigid and durable constructions than prior flexible testing probes or pins. Furthermore, the present probe fabrication and testing probe head assembly steps permit high probe count and fine/smaller pitch spacing of probes to meet the demand for 3D IC package microbump arrays on DUTs. 
     It will be appreciated that if a testing probe head  400  with guided testing probes  330 ,  340  as shown in  FIG. 21  is to be fabricated, the free probe ends are simply inserted through apertures  336  in guide plate  332  (see  FIG. 20 ) prior to solder reflow process shown in  FIG. 12  and described above. The other fabrication process steps process steps described herein remain the same with exception that the R-WEDM machining step for probes  330 ,  340  will include forming stoppers  306  as part of the process. 
     It will further be appreciated that any of the testing probe configurations shown in  FIGS. 4-8  and other may be formed using R-WEDM in some embodiments. The computer-controlled R-WEDM machines are capable of moving discharge W in a plurality of other directions along multiple axes other than merely the X, Y, and Z axes. Accordingly, numerous intricate shapes and contours may be cut to form testing probes having a wide variety of configurations adapted to suit the intended testing application. 
     According to one embodiment of the present disclosure, a test probe card for wafer level testing includes a mounting assembly, a printed circuit board including wafer level testing circuitry which is supported by the mounting assembly, and a testing probe head including a probe array comprising a plurality of rigid metallic testing probes. The testing probes are fixedly attached to and cantilevered from a silicon substrate including a plurality of metal through silicon vias. The testing probes are electrically coupled to the vias and arranged to engage a corresponding testing contacts in a device under test in a semiconductor IC package. The probes are operable to receive and transmit electrical signal between the printed circuit board and device under test for conducting wafer level testing. In some embodiments, the testing probes are fixedly attached to the silicon substrate via a base portion of the probe which is soldered to the vias or conductive surface contact pads coupled to the vias. The probes may be soldered using flip chip soldering reflow process. In some embodiments, the testing probe card may further include a guide plate disposed between opposite ends of the test probes. The guide plate includes a plurality of apertures through which the testing probes are inserted. At least one testing probe includes a stopper positioned to engage the guide plate and thereby limit the insertion depth of the at least one testing probe through the guide plate for proper positioning of the probe. 
     In one embodiment according to the present disclosure, a method for fabricating a semiconductor test probe head includes: providing a workpiece made of an electrically conductive material; cutting a plurality of first channels in the workpiece in a first axial direction using an electric discharge wire; cutting a plurality of second channels in the workpiece in a second axial direction using the electric discharge wire, the first and second channels intersecting and forming a plurality of a pillars defining testing probes at the intersections between the first and second channels; and connecting the probes to electrical conductors formed in a support substrate, the probes and substrate defining a testing probe head. Cutting of the first and second channels may be performed using reverse wire electric discharge machining (R-WEDM) in an electric discharge machine. The connecting step may be performed by soldering the probes to the conductors or surface contact pads coupled to the vias through use of solder bumps and a soldering reflow process. 
     In another embodiment, a method for fabricating a semiconductor test probe head includes: (a) providing a workpiece made of an electrically conductive metallic material, the workpiece defining an X-Y-Z coordinate system; (b) mounting the workpiece in an electric discharge machine having an articulating electric discharge wire; (c) advancing the discharge wire in a first direction along the X axis; (d) intermittently moving the discharge wire through the workpiece in a second direction along the Z axis at a plurality of intervals spaced along the X axis, the wire cutting a plurality of first channels in the workpiece extending in the Y axis direction; (e) advancing the discharge wire in a third direction along the Y axis; (f) intermittently moving the discharge wire through the workpiece in the second direction along the Z axis at a plurality of intervals spaced along the Y axis, the wire cutting a plurality of second channels in the workpiece extending in the X axis direction; (g) forming an array of testing probe pillars defined by the first and second channel cuts; (h) providing a support substrate comprised of silicon having a plurality of metallic through silicon vias; and (i) soldering the probes to the conductors, wherein the support substrate and testing probe pillars define a testing probe head. 
     While the foregoing description and drawings represent or exemplary embodiments of the present disclosure, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present disclosure may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes and/or control logic as applicable described herein may be made without departing from the spirit of the disclosure. One skilled in the art will further appreciate that the disclosure may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the disclosure, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present disclosure. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the disclosure being defined by the appended claims and equivalents thereof, and not limited to the foregoing description or embodiments. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the disclosure, which may be made by those skilled in the art without departing from the scope and range of equivalents of the disclosure.