Abstract:
The present invention is directed to a structure comprising a substrate having a surface; a plurality of elongated electrical conductors extending away from the surface; each of said elongated electrical conductors having a first end affixed to the surface and a second end projecting away from the surface; there being a plurality of second ends; and a means for positioning and maintaining the plurality of the second ends in substantially fixed positions with respect to each other. The structure is useful as a probe for testing and burning in integrated circuit chips at the wafer level.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to an apparatus and test probe for integrated circuit devices and methods of use thereof  
         BACKGROUND OF THE INVENTION  
         [0002]    In the microelectronics industry, before integrated circuit (IC) chips are packaged in an electronic component, such as a computer, they are tested. Testing is essential to determine whether the integrated circuit&#39;s electrical characteristics conform to the specifications to which they were designed to ensure that electronic component performs the function for which it was designed.  
           [0003]    Testing is an expensive part of the fabrication process of contemporary computing systems. The functionality of every I/O for contemporary integrated circuit must be tested since a failure to achieve the design specification at a single I/O can render an integrated circuit unusable for a specific application. The testing is commonly done both at room temperature and at elevated temperatures to test functionality and at elevated temperatures with forced voltages and currents to burn the chips in and to test the reliability of the integrated circuit to screen out early failures.  
           [0004]    Contemporary probes for integrated circuits are expensive to fabricate and are easily damaged. Contemporary test probes are typically fabricated on a support substrate from groups of elongated metal conductors which fan inwardly towards a central location where each conductor has an end which corresponds to a contact location on the integrated circuit chip to be tested.  
           [0005]    The metal conductors generally cantilever over an aperture in the support substrate. The wires are generally fragile and easily danage and are easily displaceable from the predetermined positions corresponding to the design positions of the contact locations on the integrated circuit being tested. These probes last only a certain number of testing operations, after which they must be replaced by an expensive replacement or reworked to recondition the probes.  
           [0006]    [0006]FIG. 1 shows a side cross-sectional view of a prior art probe assembly  2  for probing integrated circuit chip  4  which is disposed on surface  6  of support member  8  for integrated circuit chip  4 . Probe assembly  2  consists of a dielectric substrate  10  having a central aperture  12  therethrough. On surface  14  of substrate  10  there are disposed a plurality of electrically conducting beams which extend towards edge  18  of aperture  12 . Conductors  16  have ends  20  which bend downwardly in a direction generally perpendicular to the plane of surface  14  of substrate  10 . Tips  22  of downwardly projecting electrically conducting ends  20  are disposed in electrical contact with contact locations  24  on surface  25  of integrated circuit chip  4 . Coaxial cables  26  bring electrical signals, power and ground through electrical connectors  28  at periphery  30  of substrate  10 . Structure  2  of FIG. 1 has the disadvantage of being expensive to fabricate and of having fragile inner ends  20  of electrical conductors  16 . Ends  20  are easily damaged through use in probing electronic devices. Since the probe  2  is expensive to fabricate, replacement adds a substantial cost to the testing of integrated circuit devices. Conductors  16  were generally made of a high strength metal such as tungsten to resist damage from use. Tungsten has an undesirably high resistivity.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to provide an improved high density test probe; test apparatus and method of use thereof.  
           [0008]    It is another object of the present invention to provide an improved test probe for testing and burning-in integrated circuits.  
           [0009]    It is another object of the present invention to provide an improved test probe and apparatus for testing integrated circuits in wafer form and as discrete integrated circuit chips.  
           [0010]    It is an additional object of the present invention to provide probes having contacts which can be designed for high performance functional testing and for high temperature burn in applications.  
           [0011]    It is yet another object of the present invention to provide probes having contacts which can be reworked several times by resurfacing some of the materials used to fabricate the probe of the present invention.  
           [0012]    It is a further object of the present invention to provide an improved test probe having a probe tip member containing a plurality of elongated conductors each ball bonded to electrical contact locations on space transformation substrate.  
           [0013]    A broad aspect of the present invention is a test probe. having a plurality of electrically conducting elongated members embedded in a material. One end of each conductor is arranged for alignment with contact locations on a workpiece to be tested.  
           [0014]    In a more particular aspect of the present invention, the other end of the elongated conductors are electrically connected to contact locations on the surface of a fan-out substrate. The fan-out substrate provides space information of the closely spaced electrical contacts on the first side the fan-out substrate. Contact locations having a larger spacing are on a second side of the fan out substrate.  
           [0015]    In yet another more particular aspect of the present invention, pins are electrically connected to the contact locations on the second surface of the fan out substrate.  
           [0016]    In another more particular aspect of the present invention, the plurality of pins on the second surface of the fan-out substrate are inserted into a socket on a second fan-out substrate. The first and second space transformation substrates provide fan out from the fine pitch of the integrated circuit I/O to a larger pitch of electrical contacts for providing signal, power and ground to the workpiece to be tested.  
           [0017]    In another more particular aspect of the present invention, the pin and socket assembly is replaced by an interposer containing a plurality of elongated electrical connectors embedded in a layer of material which is squeezed between contact locations on the first fan-out substrate and contact locations on the second fan-out substrate.  
           [0018]    In another more particular aspect of the present invention, the test probe is part of a test apparatus and test tool.  
           [0019]    Another broad aspect of the present invention is a method of fabricating the probe tip of the probe according to the present invention wherein a plurality of elongated conductors are bonded to contact locations on a substrate surface and project away therefrom.  
           [0020]    In a more particular aspect of the method according to the present invention, the elongated conductors are wire bonded to contact locations on the substrate surface. The wires project preferably at a nonorthogonal angle from the contact locations.  
           [0021]    In another more particular aspect of the method of the present invention, the wires are bonded to the contact locations on the substrate are embedded in a elastomeric material to form a probe tip for the structure of the present invention.  
           [0022]    In another more particular aspect of the present invention, the elongated conductors are embedded in an elastomeric material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a schematic cross-section of a conventional test probe for an integrated circuit device.  
         [0024]    [0024]FIG. 2 is a schematic diagram of one embodiment of the probe structure of the present invention.  
         [0025]    [0025]FIG. 3 is a schematic diagram of another embodiment of the probe structure of the present invention.  
         [0026]    [0026]FIG. 4 is an enlarged view of an elastomeric connector electrically interconnecting two space transformation substrates of the structure of FIG. 2.  
         [0027]    [0027]FIG. 5 is an enlarged view of the probe tip within dashed circle  100  of FIG. 2 or  3 .  
         [0028]    [0028]FIG. 6 shows the probe tip of the structure of FIG. 5 probing an integrated circuit device.  
         [0029]    FIGS.  7 - 13  show the process for making the structure of FIG. 5.  
         [0030]    [0030]FIG. 14 shows a probe tip structure without a fan-out substrate.  
         [0031]    [0031]FIG. 15 shows the elongated conductors of the probe tip fixed by solder protuberances to contact locations on a space transformation substrate.  
         [0032]    [0032]FIG. 16 shows the elongated conductors of the probe tip fixed by laser weld protuberances to contact locations on a space transformation substrate.  
         [0033]    [0033]FIG. 17 shows both interposer  76  and probe tip  40  rigidly bonded to space transformer  60 .  
         [0034]    [0034]FIG. 19 shows a more detailed view of the blade cutting process  
         [0035]    [0035]FIG. 20 shows the blade of FIG. 19 partially entering the wire.  
         [0036]    [0036]FIG. 21 shows the severed wire of FIG. 20.  
         [0037]    [0037]FIG. 22 shows the severed wire of FIG. 21 coated with a coating.e.  
         [0038]    [0038]FIG. 23 a  shows a cross-sectional view of the tip of the wire of FIG. 22.  
         [0039]    [0039]FIG. 23 b  shows a top view of the tip of the wire in FIG. 22.  
         [0040]    [0040]FIG. 24 shows cutting the wire with two blades.  
         [0041]    [0041]FIG. 25 shows cutting the wire with a sharp blade and a flat blade or anvil.  
         [0042]    [0042]FIGS. 26 a    26   b  and  26   c  show cutting the wires with opposed blades where the blades have different cutting surfaces to form different tip shapes.  
         [0043]    [0043]FIGS. 27 a ,  27   b  and  27   c  shows the tips of FIG. 26 coated with a coating.  
         [0044]    [0044]FIG. 28 shows a side view of a plurality of wires with the fee ends positioned in place by a positioning apparatus.  
         [0045]    [0045]FIG. 29 is a top vie of the positioning apparatus of FIG. 28.  
         [0046]    [0046]FIG. 30 shows a side view of a plurality of wires with the fee ends positioned in place by another positioning apparatus.  
         [0047]    [0047]FIG. 31 is a top vie of the positioning apparatus of FIG. 28. 
     
    
     DETAILED DESCRIPTION  
       [0048]    Turning now to the figures, FIGS. 2 and 3 show two embodiments of the test assembly according to the present invention. Numerals common between FIGS. 2 and 3 represent the same thing. Probe head  40  is formed from a plurality of elongated electrically conducting members  42  embedded in a material  44  which is preferably an elastomeric material  44 . The elongated conducting members  42  have ends  46  for probing contact locations on integrated circuit devices  48  of wafer  50 . In the preferred embodiment, the workpiece is an integrated circuit such as a semiconductor chip or a semiconductor wafer having a plurality of chips. The workpiece can be any other electronic device. The opposite ends  52  of elongated electrical conductors  42  are in electrical contact with space transformer (or fan-out substrate)  54 . In the preferred embodiment, space transformer  54  is a multilevel metal/ceramic substrate, a multilevel metal/polymer substrate or a printed circuit board which are typically used as packaging substrates for integrated circuit chips. Space transformer  54  has, in the preferred embodiment, a surface layer  56  comprising a plurality of thin dielectric films, preferably polymer films such as polyimide, and a plurality of layers of electrical conductors, for example, copper conductors. A process for fabricating multilayer structure  56  for disposing it on surface  58  of substrate  60  to form a space transformer  54  is described in U.S. patent application Ser. No. 07/695,368, filed on May 3, 1991, entitled “MULTI-LAYER THIN FILM STRUCTURE AND PARALLEL PROCESSING METHOD FOR FABRICATING SAME” which is assigned to the assignee of the present invention, the teaching of which is incorporated herein by reference. Details of the fabrication of probe head  40  and of the assembly of probe head  40  and  54  will be described herein below.  
         [0049]    As sown in FIG. 2, on surface  62  of substrate  60 , there are, a plurality of pins  64 . Surface  62  is opposite the surface  57  on which probe head  40  is disposed. Pins  64  are standard pins used on integrated circuit chip packaging substrates. Pins  64  are inserted into socket  66  or plated through-holes in the substrate  68  which is disposed on surface  70  of second space transformer  68 . Socket  66  is a type of pin grid array (PGA) socket such as commonly disposed on a printed circuit board of an electronic computer for receiving pins from a packaging substrate. Second space transformer  68  can be any second level integrated circuit packaging substrate, for example, a standard printed circuit board. Socket  66  is disposed on surface  70  of substrate  68 . On opposite surface  70  of substrate  68  there are disposed a plurality of electrical connectors to which coaxial cables  72  are electrically connected. Alternatively, socket  68  can be a zero insertion force (ZIF) connector or the socket  68  can be replaced by through-holes in the substrate  68  wherein the through-holes have electrically conductive material surrounding the sidewalls such as a plated through-hole.  
         [0050]    In the embodiment of FIG. 3, the pin  64  and socket  66  combination of the embodiment of FIG. 2 is replaced by an interposer, such as, elastomeric connector  76 . The structure of elastomeric connector  76  and the process for fabricating elastomeric connector  76  is described in copending U.S. patent application Ser. No. 07/963,364 to B. Beaman et al., filed Oct. 19, 1992, entitled “THREE DIMENSIONAL HIGH PERFORMANCE INTERCONNECTION MEANS”, which is assigned to the assignee of the present invention, the teaching of which is incorporated herein by reference and of which the present application is a continuation-in-part thereof, the priority date of the filing thereof being claimed herein. The elastomeric connector can be opted to have one end permanently bonded to the substrate, thus forming a FRU (field replacement unit) together with the probe/substrate/connector assembly.  
         [0051]    [0051]FIG. 4 shows a cross-sectional view of structure of the elastomeric connector  76  of FIG. 3. Connector  76  is fabricated of preferably elastomeric material  78  having opposing, substantially parallel and planar surfaces  80  and  82 . Through elastomeric material  78 , extending from surface  81  to  83  there are a plurality of elongated electrical conductors  85 . Elongated electrical conductors  84  are preferably at a nonorthogonal angle to surfaces  81  and  83 . Elongated conductors  85  are preferably wires which have protuberances  86  at surface  81  of elastomeric material layer  78  and flattened protuberances  88  at surface  83  of elastomeric material layer  78 . Flattened protuberances  88  preferably have a projection on the flattened surface as shown for the structure of FIG. 14. Protuberance  86  is preferably spherical and flattened protuberance  88  is preferably a flattened sphere. Connector  76  is squeezed between surface  62  of substrate  54  and surface  73  of substrate  68  to provide electrical connection between end  88  of wires  85  and contact location  75  on surface  73  of substrate  68  and between end  88  or wires  85  and contact location  64  on surface  62  of substrate  54 .  
         [0052]    Alternatively, as shown in FIG. 17, connector  76  can be rigidly attached to substrate  54  by solder bonding ends  88  of wires  85  to pads  64  on substrate  54  or by wire bonding ends  86  of wires  85  to pads  64  on substrate  54  in the same manner that wires  42  are bonded to pads  106  as described herein below with respect to FIG. 5. Wires  85  can be encased in an elastomeric material in the same manner as wires  42  of FIG. 5.  
         [0053]    Space transformer  54  is held in place with respect to second space transformer  68  by clamping arrangement  80  which is comprised of member  82  which is perpendicularly disposed with respect to surface  70  of second space transformer  68  and member  84  which is preferably parallely disposed with respect to surface  86  of first space transformer  54 . Member  84  presses against surface  87  of space transformer  54  to hold space transformer  54  in place with respect surface  70  of space transformer  64 . Member  82  of clamping arrangement  80  can be held in place with respect to surface  70  by a screw which is inserted through member  84  at location  90  extending through the center of member  82  and screw into surface  70 .  
         [0054]    The entire assembly of second space transformer  68  and first space transformer with probe head  40  is held in place with respect wafer  50  by assembly holder  94  which is part of an integrated circuit test tool or apparatus. Members  82 ,  84  and  90  can be made from materials such as aluminum.  
         [0055]    [0055]FIG. 5 is a enlarged view of the region of FIG. 2 or  3  closed in dashed circle  100  which shows the attachment of probe head  40  to substrate  60  of space transformer  54 . In the preferred embodiment, elongated conductors  42  are preferably wires which are at a non-orthogonal angle with respect to surface  87  of substrate  60 . At end  102  of wire  42  there is preferably a flattened protuberance  104  which is bonded (by wire bonding, solder bonding or any other known bonding technique) to electrically conducting pad  106  on surface  87  of substrate  60 . Elastomeric material  44  is substantially flush against surface  87 . At substantially oppositely disposed planar surface  108  elongated electrically conducting members  42  have an end  110 . In the vicinity of end  110 , there is optimally a cavity  112  surrounding end  110 . The cavity is at surface  108  in the elastomeric material  44 .  
         [0056]    [0056]FIG. 6 shows the structure of FIG. 5 used to probe integrated circuit chip  114  which has a plurality of contact locations  116  shown as spheres such as a C4 solder balls. The ends  110  of conductors  42  are pressed in contact with contact locations  116  for the purpose of electrically probing integrated circuit  114 . Cavity  112  provides an opening in elastomeric material  44  to a permit ends  110  to be pressed towards and into solder mounds  116 . Cavity  112  provides a means for solder mounds  116  to self align to ends  110  and provides a means containing solder mounds which may melt, seep or be less viscous when the probe is operated at an elevated temperature. When the probe is used to test or burn-in workpieces have flat pads as contact locations the cavities  112  can remain or be eliminated.  
         [0057]    FIGS.  7 - 13  show the process for fabricating the structure of FIG. 5. Substrate  60  with contact locations  106  thereon is disposed in a wire bond tool. The top surface  122  of pad.  106  is coated by a method such as evaporation, sputtering or plating with soft gold or Ni/Au to provide a suitable surface for thermosonic ball bonding. Other bonding techniques can be used such as thermal compression bonding, ultrasonic bonding, laser bonding and the like. A commonly used automatic wire bonder is modified to ball bond-gold, gold alloy, copper, copper alloy, aluminum, Pt, nickel or palladium wires  120  to the pad  106  on surface  122  as shown in FIG. 7. The wire preferably has a diameter of 0.001 to 0.005 inches. If a metal other than Au is used, a thin passivation metal such as Au, Cr, Co, Ni or Pd can be coated over the wire by means of electroplating, or electroless plating, sputtering, e-beam evaporation or any other coating techniques known in the industry. Structure  124  of FIG. 7 is the ball bonding head which has a wire  126  being fed from a reservoir of wire as in a conventional wire bonding apparatus. FIG. 7 shows the ball bond head  124  in contact at location  126  with surface  122  of pad  106 .  
         [0058]    [0058]FIG. 8 shows the ball bonding head  124  withdrawn in the direction indicated by arrow  128  from the pad  106  and the wire  126  drawn out to leave disposed on the pad  106  surface  122  wire  130 . In the preferred embodiment, the bond head  124  is stationary and the substrate  60  is advanced as indicated by arrow  132 . The bond wire is positioned at an angle preferably between 5 to 60° from vertical and then mechanically notched (or nicked) by knife edge  134  as shown in FIG. 9. The knife edge  134  is actuated, the wire  126  is clamped and the bond head  124  is raised. The wire is pulled up and breaks at the notch or nick.  
         [0059]    Cutting the wire  130  while it is suspended is not done in conventional wire bonding. In conventional wire bonding, such as that used to fabricate the electrical connector of U.S. Pat. No. 4,998,885, where, as shown in FIG. 8 thereof, one end a wire is ball bonded using a wire bonded to a contact. location on a substrate bent over a loop post and the other of the wire is wedge bonded to an adjacent contact location on the substrate. The loop is. severed by a laser as shown in FIG. 6 and the ends melted to form balls. This process results in adjacent contact locations having different types of bonds, one a ball bond the other a wedge bond. The spacing of the adjacent pads cannot be less than about ˜20 mils because of the need to-bond the wire. This spacing is unacceptable to fabricate a high density probe tip since dense integrated circuits have pad spacing less than this amount. In contradistinction, according to the present invention, each wire is ball bonded to adjacent contact locations which can be spaced less than 5 mils apart. The wire is held tight and knife edge  134  notches the wire leaving upstanding or flying leads  120  bonded to contact locations  106  in a dense array.  
         [0060]    When the wire  130  is severed there is left on the surface  122  of pad  106  an angled flying lead  120  which is bonded to surface  122  at one end and the other end projects outwardly away from the surface. A ball can be formed on the end of the wire  130  which is not bonded to surface  122  using a laser or electrical discharge to melt the end of the wire. Techniques for this are described in co-pending U.S. patent application Ser. No. 07/963,346, filed Oct. 19, 1992, which is incorporated herein by reference above.  
         [0061]    [0061]FIG. 10 shows the wire  126  notched (or nicked) to leave wire  120  disposed on surface  122  of pad  106 . The wire bond head  124  is retracted upwardly as indicated by arrow  136 . The wire bond head  124  has a mechanism to grip and release wire  126  so that wire  126  can be tensioned against the shear blade to sever the wire.  
         [0062]    After the wire bonding process is completed, a casting mold  140  as shown in FIG. 11 is disposed on surface  142  of substrate  60 . The mold is a tubular member of any cross-sectional shape, such as circular and polygonal. The mold is preferably made of metal or organic materials. The length of the mold is preferably the height  144  of the wires  120 . A controlled volume of liquid elastomer  146  is disposed into the casting  140  mold and allowed to settle out (flow between the wires until the surface is level) before curing as shown in FIG. 13. Once the elastomer has cured, the mold is removed to provide the structure shown in FIG. 5 except for cavities  112 . The cured elastomer is represented by reference numeral  44 . A mold enclosing the wires  120  can be used so that the liquid elastomer can be injection molded to encase the wires  120 .  
         [0063]    The top surface of the composite polymer/wire block can be mechanically planarized to provide a uniform wire height and smooth polymer surface. A moly mask with holes located over the ends of the wire contacts is used to selectively ablate (or reactive ion etch) a cup shaped recess in the top surface of the polymer around each of the wires. The probe contacts can be reworked by repeating the last two process steps  
         [0064]    A high compliance, high thermal stability siloxane elastomer material is preferable for this application. The compliance of the cured elastomer is selected for the probe application. Where solder mounds are probed a more rigid elastomeric is used so that the probe tips are pushed into the solder mounds where a gold coated aluminum pad is being probed a more compliant elastomeric material is used to permit the wires to flex under pressure so that the probe ends in contact with the pad will move to wipe over the pad so that good electrical contact is made therewith. The high temperature siloxane material is cast or injected and cured similar to other elastomeric materials. To minimize the shrinkage, the elastomer is preferably cured at lower temperature (T≦60°) followed by complete cure at higher temperatures (T≧80°).  
         [0065]    Among the many commercially available elastomers, such as ECCOSIL and SYLGARD, the use of polydimethylsiloxane based rubbers best satisfy both the material and processing requirements. However, the thermal stability of such elastomers is limited at temperatures below 200° C. and significant outgassing is observed above 100° C. We have found that the thermal stability can be significantly enhanced by the-incorporation of 25 wt % or more diphenylsiloxane. Further, enhancement in the thermal stability has been demonstrated by increasing the molecular weight of the resins (oligomers) or minimizing the crosslink junction. The outgassing of the elastomers- can be minimized at temperatures below 300° C. by first using a thermally transient catalyst in the resin synthesis and secondly subjecting the resin to a thin film distillation to remove low molecular weight side-products. For our experiments, we have found that 25 wt % diphenylsiloxane is optimal, balancing the desired thermal stability with the increased viscosity associated with diphenylsiloxane incorporation. The optimum number average molecular weight of the resin for maximum thermal stability was found to be between 18,000 and 35,000 g/mol. Higher molecular weights were difficult to cure and too viscous, once filled, to process. Network formation was achieved by a standard hydrosilylation polymerization using a hindered platinum catalyst in a reactive silicon oil carrier.  
         [0066]    In FIG. 10 when bond head  124  bonds the wire  126  to the surface  122  of pad  106  there is formed a flattened spherical end shown as  104  in FIG. 6.  
         [0067]    The high density test probe provides a means for testing high density and high performance integrated circuits in wafer form or as discrete chips. The probe contacts can be designed for high performance functional testing or high temperature bum-in applications. The probe contacts can also be reworked several times by resurfacing the rigid polymer material that encases the wires exposing the ends of the contacts.  
         [0068]    The high density probe contacts described in this disclosure are designed to be used for testing semiconductor devices in either wafer form or as discrete chips. The high density probe uses metal wires that are bonded to a rigid substrate. The wires are imbedded in a rigid polymer that has a cup shaped recess around each to the wire ends. The cup shaped recess  112  shown in FIG. 5 provides a positive self-aligning function for chips with solder ball contacts. A plurality of probe heads  40  can be mounted onto a. space transformation substrate  60 . so that a plurality of chips can be probed an burned-in simultaneously.  
         [0069]    An alternate embodiment of this invention would include straight wires instead of angled wires. Another alternate embodiment could use a suspended alignment mask for aligning the chip to the wire contacts instead of the cup shaped recesses in the top surface of the rigid polymer. The suspended alignment mask is made by ablating holes in a thin sheet of polyimide using an excimer laser and a metal mask with the correct hole pattern. Another alternate embodiment of this design would include a interposer probe assembly that could be made separately from the test substrate as described in U.S. patent application Ser. No. 07/963,364, incorporated by reference herein above. This design could be fabricated by using a copper substrate that would be etched away after the probe assembly is completed and the polymer is cured. This approach could be further modified by using an adhesion de-promoter on the wires to allow them to slide freely (along the axis of the wires) in the polymer material.  
         [0070]    [0070]FIG. 14 shows an alternate embodiment of probe tip  40  of FIGS. 2 and 3. As described herein above, probe tip  40  is fabricated to be originally fixed to the surface of a first level space transformer  54 . Each wire  120  is wire bonded directly to a pad  106  on substrate  60  so that the probe assembly  40  is rigidly fixed to the substrate  60 . The embodiment of FIG. 14, the probe head assembly  40  can be fabricated via a discrete stand alone element. This can be fabricated following the process of U.S. patent application Ser. No. 07/963,348, filed Oct. 19, 1992, which has been incorporated herein by reference above. Following this fabrication process as described herein above, wires  42  of FIG. 14 are wire bonded to a surface. Rather than being wire bonded directly to a pad on a space transformation substrate, wire  42  is wire bonded to a sacrificial substrate as described in the application incorporated herein. The sacrificial substrate is removed to leave the structure of FIG. 14. At ends  102  of wires  44  there is a flattened ball  104  caused by the wire bond operation. In a preferred embodiment the sacrificial substrate to which the wires are bonded have an array of pits which result in a protrusion  150  which can have any predetermined shape such as a hemisphere or a pyramid. Protrusion  150  provides a raised contact for providing good electrical connection to a contact location against which it is pressed. The clamp assembly  80  of FIGS. 2 and 3 can be modified so that probe tip assembly can be pressed towards surface  58  of substrate  60  so that ends  104  of FIG. 14 can be pressed against contact locations such as  106  of FIG. 5 on substrate  60 . Protuberances  104  are aligned to pads  100  on surface  58  of FIG. 5 in a manner similar to how the conductor ends  86  and  88  of the connector in FIG. 4 are aligned to pads  75  and  64  respectively.  
         [0071]    As shown in the process of FIGS.  7  to  9 , wire  126  is ball bonded to pad  106  on substrate  60 . An alternative process is to start with a substrate  160  as shown in FIG. 15 having contact locations  162  having an electrically conductive material  164  disposed on surface  166  of contact location  162 . Electrically conductive material  164  can be solder. A bond lead such as  124  of FIG. 7 can be used to dispose end  168  of wire  170  against solder mound  164  which can be heated to melting. End  168  of wire  170  is pressed into the molten solder mound to form wire  172  embedded into a solidified solder mound  174 . Using this process a structure similar to that of FIG. 5 can be fabricated.  
         [0072]    [0072]FIG. 16 shows another alternative embodiment of a method to fabricate the structure of FIG. 5.  
         [0073]    Numerals common between FIGS. 15 and 16 represent the same thing. End  180  elongated electrical conductor  182  is held against top surface  163  of pad  162  on substrate  160 . A beam of light  184  from laser  186  is directed at end  180  of elongated conductor  182  at the location of contact with surface  163  of pad  162 . The end  180  is laser welded to surface  163  to form protuberance  186 .  
         [0074]    In summary, the present invention is directed to high density test probe for testing high density and high performance integrated circuits in wafer form or as discrete chips. The probe contacts are designed for high performance functional testing and for high temperature burn in  
         [0075]    The probe is formed from an elastomeric probe tip having a highly dense array of elongated electrical conductors embedded in an elastomeric material which is in electrical contact with a space transformer.  
         [0076]    Blade Cutting:  
         [0077]    [0077]FIG. 19 shows another embodiment of the blade cutting process. The bond wire  126  is held stationary by the capillary bond head  124  against a knife edge  134 . The knife edge  134  is actuated and mechanically notched (or nicked) into the bulk of wire to a good depth.  
         [0078]    [0078]FIG. 20 shows that the wire separation process is completed when the knife edge is  134  actuated, the bond wire  126  is notched and the capillary bond head  124  is raised to sever the wire completely.  
         [0079]    [0079]FIG. 21 schematically shows the configuration of the Angled Flying Lead wire  126  after severing. The contact end contains a bump  142  and a small tailend  152 .  
         [0080]    [0080]FIG. 22 shows a layer  162  of contact metallurgy such as Au, Ni, Cu, Fe, Pd, Pt, Co, Ir, Ro, Ru, or their alloys are coated over the wire  126  and the bump  142 .  
         [0081]    [0081]FIG. 23 is an optical cross-sectional view and top views of the probe tips after severing and after being coated with a suitable contact metallurgy.  
         [0082]    [0082]FIG. 24 is yet another embodiment of the wire cutting process. A double knife edge  134  and  135  are used to notch the wire  126  simultaneously. As knife edges  134  and  135  are actuated simultaneously to notch the wire  126 , it has the advantages of severing higher tensile strength wire, keep the wire in accurate position and control the shape and position of the bump precisely.  
         [0083]    [0083]FIG. 25 shows a modification of the double knife edge cutting process, where one knife edge  134  maintains its sharp edge, while the other side uses a flat end  136 . By actuating both  134  and  136  simultaneously, the wire can be severed with one end bonded on the surface of the substrate  60 , while the other end is dangling in air.  
         [0084]    [0084]FIG. 26 shows a modification of the double blade cutting process. By creating special feature shape and size at the knife edges  134  and  135 , the bumps on the flat end of wire can be created with special shapes and sizes, such as the single bump  142 , double bumps  144  and a thin line of bump  146 . These bumps are subsequently coated with a suitable metal  148 , as shown in FIG. 27, selected from the group consisting of Au, Cu, Ni, Fe, Pd, Pt, Ir, Ro, Ru, Co, and their alloys.  
         [0085]    Mask Design  
         [0086]    [0086]FIG. 28 shows a schematic cross-sectional view of another embodiment of the compliant test probe. A thin laminate sheet consisting of Polymer  190 /Metal  192 /Polymer  194  layers is fabricated with an array of holes  196  corresponding to the ends of the probe wires. The laminate is aligned and placed over the array of wires  198  and supported with a frame  230 , which can be either rigid or compliant. The frame is attached to a substrate  60 . The holes on the top polymer layer  194  has the shape of an oval shape  196 . During the alignment and placement process the wire array is first entering into the large portion of the oval shaped hole, then shifted into the small hole and pressed against the wall. The second mask  203  which is made of a thin sheet of polymer and with holes  207  corresponding to the wires array is placed over the wire array  198  and laying on top of the first mask  194 . The wire array  198  first enters into the large portion of the oval hole  207  then shifted into the small holes and presses against the polymer wall. The polymer material  194 ,  203  and  190  can be replaced with any inorganic material, while the metal sheet should be a low thermal expansion material such as Invar, Cu/Invar/Cu, Mo or silicon to match the thermal expansion of the probe array to that of the silicon wafer.  
         [0087]    [0087]FIG. 29 is a top view of the dual mask design. The ends of the wire array  198  are tightly sandwiched and locked in place by the two small semi-circles from the top mask  203  and lower mask  194 .  
         [0088]    [0088]FIG. 30 shows a cross-sectional view of another embodiment of the thermal expansion matched mask design. In addition to the oval mask design as shown in FIGS. 28 and 29, a third mask with precision located holes  211  corresponding to the ends of the probe wires  198  are aligned and placed over the wire ends  1198  and sit on the surface of the second mask  203 . Again the holes in the mask are oval shaped. The ends of wires are held in the small semi-circle hole.  
         [0089]    [0089]FIG. 31 is a top view of the triple mask design where the ends of wires  198  are sandwiched and locked in place by the semi-circles of each oval shaped holes in the three masks.  
         [0090]    While the present invention has been described with respect to preferred embodiments, numerous modifications, changes and improvements will occur to those skilled in the art without departing from the spirit and scope of the invention.