Patent Publication Number: US-10330702-B2

Title: Wafer level integrated circuit probe array and method of construction

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE 
     This applications incorporates by reference in its entirety, the following applications: US-2010/0231251-A1 (U.S. Ser. No. 12/721,039) filed 10 Mar. 2010; U.S. Ser. No. 13/343,328 filed 4 Jan. 2012 as a CIP of Ser. No. 13/226,606 which claims priority to provisional 61/380,494 filed 7 Sep. 2010 and 61/383,411 filed 16 Sep. 2010 and US-2012/0092034-A1 (U.S. Ser. No. 13/276,893) filed 19 Oct. 2011 which itself is a CIP of Ser. No. 12/764,603 filed 21 Apr. 2010 which claims 61/171,141 filed 21 Apr. 2009, 61/257,236 filed 2 Nov. 2009 and 61/307,501 filed 24 Feb. 2010, U.S. Ser. No. 13/921,484 filed 19 Jun. 2013 and U.S. Ser. No. 61/950,404 filed 10 Mar. 2014. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     The present invention concerns integrated circuit fabrication and testing. More particularly, the present invention concerns a methodology and structure for testing multiple integrated circuit dies residing on a semiconductor wafer substrate. 
     Description of the Related Art 
     Conventional integrated circuit fabrication techniques normally involve the formation of several individual integrated circuit devices on a single semiconductor substrate, termed a wafer. After fabrication is completed the wafer is normally cut or scribed to separate the individual integrated circuit devices into individual devices, commonly called singulated devices or die, or into rows of devices, commonly called strips. Usually the individual singulated integrated circuit devices, “chips”, called dies or dice, are spaced apart from one another on the wafer to accommodate the cutting tool used to segment the wafer. The wafer thus has the appearance of a series of integrated circuit dies (dice) separated by intersecting lines that accommodate the cutting operation. These lines are commonly referred to as scribing lines, streets or lanes. Such dice can be placed into IC packaging and wires connected from the die to leads within the IC package. Testing can then be done on the package leads or contacts, which are relatively speaking much larger than the contact on the IC dies. The technology used for testing IC leaded packages therefore is not particularly analogous to wafer level testing and we have found principles from IC packed lead testing will not work without substantial modification and inventive input. 
     In many instances it is deemed advantageous to test the electrical functionality of the individual integrated circuit dies either at the wafer level or at the strip level. That is, before the wafer is segmented and the individual integrated circuit dies are separated from one another. Typically this testing is performed by placing a series of test probes in contact with electrical input and output (I/O) pads, or bonding pads or bumps or balls that are formed on an exposed surface of each integrated circuit die. These I/O pads are usually connected to elements of a leadframe if the integrated circuit die is subsequently packaged. An example of such a tester is shown in U.S. Pat. No. 5,532,174 to Corrigan. 
     Semiconductor integrated circuit devices (“die”) can also be tested while they are still present on the semiconductor wafer on which they were formed. Such wafer level testing is traditionally accomplished on a per-die basis, in which probe tips are brought into contact with bond pads or balls for a given die using precision wafer handling system commonly called a wafer prober. For each application a specifically designed spatial configuration of probes are matched to the spatial array of bonding pads or balls in what is commonly called a probe array. In the wafer prober, either a single die or a plurality of die may be stimulated and tested through the probe tips via a tester. In the case where a single die is tested for each wafer prober index step, the probe array is commonly called single site. In the case where 2 or more die are tested for each wafer prober index step, the probe array is commonly called multi-site. After single or multisite die are tested, the wafer prober system indexes to the next die or set of die which are similarly tested, etc. The probe array are commonly fastened onto a Printed Circuit Board (PCB) element to enable routing of signal lines to connect with Test system; said assembly of probe array and PCB are commonly called a probe card. 
     However, wafer prober and large probe array systems also exist which are capable of testing an entire semiconductor wafer, either all dies (i.e. chips) on the wafer simultaneously or a significant fraction of the dies on the wafer simultaneously. Typically such large probe array systems are of limited testing capability for process step called “wafer sort” so simply identify which dies on the wafer can make electrical contact and which dies don&#39;t exhibit electrical contact or for burn in. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The following summary is intended to assist the reader in understanding the full disclosure and the claims. The claims define the scope of the invention, not this summary. 
     Disclosed is a test contact pin assembly or probe array for temporary contact with a test pads on a wafer level integrated circuit device wherein the test pads includes metallic film, electroplated bump, post structure or solder ball material affixed to make electrical connection with test die on the wafers. The disclosed test contact pin assembly incorporates at least one upper terminal pin or probe, further having a longitudinal extension, at least one lateral flange or some other contact surface, and a contact surface for electrically contacting lower terminal pin or probe. The disclosed test contact pin assembly further incorporates at least one lower terminal pin having a contact surface for electrically contacting upper terminal pin, and a foot, said pins being held intact by bias forces which maintain the contacts surfaces together but in a slideable relationship to each other. There may also be an elastomeric material of predetermined height when in an uncompressed state, said material surrounding the pins to create said bias force and maintain the surface in slideable electrical contact. There may also be a rigid top surface located atop said elastomeric material, said up-stop surface including at least one aperture to receive a portion of said longitudinal extension. Said up-stop surface may also include and at least one channel, having an up-stop wall and a recess to receive and contact at least one flange or other contact surface on the pin, said channel being sized to be large enough to receive said flanges with minimum frictional contact the sidewalls; so that said up-stop surface provides an upward stop limit for the upper pin by virtue of its contact with the flanges. The channels in this configuration, providing a keying function to prevent contact rotations, may be a depression, recess or upstanding walls which have a similar confining effect. Alternatively, said channels being sized to be receive said flanges may be incorporated into an additional element in the construction placed immediately adjacent the up-stop surface. 
     The up-stop surface is fixed in position at a predetermined distance above said foot or other bottom boundary layer, said distance being less than the height of the uncompressed elastomeric material plus the height of at least one of the flanges, so that the elastomeric material is in a precompressed condition before the upper pin comes in contact with the IC pad. The predetermined location for the up-stop surface provides a precision datum when used in conjunction with the lateral flange element of the upper terminal pin. This pre-compressed condition provides a loading force for the upper terminal pin against the precision up-stop surface. Furthermore, the pre-compressed condition also provides a more uniform bias force against the pins as they contact the IC pads. Without precompression, the initial travel of the pins would have a lower responsive force than if the elastomer was not in pre-compressed condition. 
     Also disclosed is a contact/probe/pin array assembly for making temporary contact of test pad on a wafer level integrated circuit device having an upper probe pin, configured to move downwardly along a Z-axis when in contact with said pads or balls, the pin having longitudinal upper portion, having a top and a bottom end a pair of laterally extending flanges (or other stop engagement members), having a predetermined width and an upper edge, said flanges extending from said bottom end of said upper portion. There may also be a lower portion extending beyond said flanges, a lower pin in slideable contact with the upper pin at said lower portion and an up-stop plate being rigid plate. 
     The material for the up-stop plate is preferably of a substantially insulating and non-hydroscopic material. Furthermore, for testing over temperature ranges common for wafer probing, the material for up-stop plate is preferably with a linear coefficient of expansion that is as close as possible to that of the silicon wafer. The up stop plate may have a bottom (or other contact) surface including a plurality of spaced part, recesses sized to just receive said flanges with minimal frictional contact, and to confine said flanges in a predetermined orientation, at least one upper edge of said flanges contacting said bottom surface of the said plate to define an upper travel limit for said pin; so that the pins are confined against rotational movement and have an upper travel limit defined by said plate thereby keeping said pins aligned in all axes while permitting movement along the Z-axis. Alternatively the up-stop plate may have a flat bottom surface against which is provided an additional element with plurality of recesses sized to receive said flanges. In either case, the recesses or channels are preferably designed with sufficient depth such that required z-axis movement never pushes said flanges out of the channel. Also disclosed is a method of providing a plurality of coplanar or non coplanar, or multiple plane contact pin tips to test pads on a wafer level integrated circuit, having all for some of the steps, in any order, of forming a top plate, hereafter referred to as pin guide or probe guide (the term pin and probe being used interchangeably), with apertures for said pins, so that said crowns protrude from said apertures; forming a stop element on each pin; forming an up-stop portion on the underside of said top plate; configuring each pin to engage between the stop element and up-stop to limit upward Z-axis travel of the pin forming a channel in the underside of the top plate, said channel being sized to receive a portion of the pin so that rotation of the pin in the channel is restricted so that the Z-axis upper travel limit of the pins are limited by the up-stop contact. The pin travel is limited so that said flange never fully exits the channel 
     The pin guide plate may be fabricated by either machining or molding processes and may be preferably composed of a ceramic material or glass filled composite. 
     As disclosed this is a method of providing an uniform resilient upward bias force on a plurality of probe/pin against test pads on a wafer level having all or some of the steps, in any order, of, inserting an upper pin having an electrical contact surface, preferably in the form of a wedge, into an elastomer block, inserting a bottom pin having an electrical contact surface in contact with the electrical surface of the upper pin within said elastomeric block, and pre-compressing said block a predetermined amount by confining the block between upper and lower plates, which could include the PCB mounting surface. The pre-compression can be accomplished in various ways but the primary effect is to get an uniform z-axis resilience in response to pin contact with the IC pads. Without pre-compression, the resilient force is highly non uniform due to the ‘slack’ in the elastomer in its initial compression. Resilient biasing forces are the product of elastomeric material and patterning such that variations of required force may be optimized for particular customer requirements. 
     Also disclosed are methods of precisely aligning the pin guide plate to the retainer plate which mounts probe array to printed circuit board (P CB) when used with integrated circuit testing apparatus. Said retainer plate includes alignment pins to provide accurate registration to the PCB during test. One such method of precisely aligning a pin guide plate requires corners within a retainer plate having like corners and sized to receive said pin guide plate, for use an integrated circuit testing apparatus, comprising any or all of the following steps in any order:
         a. accurately locating a registration corner and adjacent sidewalls of said retainer plate and said pin guide plate,   b. loosely inserting said pin guide into said retainer,   c. Inserting bias elements in the sidewalls of at least a diagonally adjacent corner to said one corner and biasing said pin guide into and said registration corner,
 
so that the pin guide is aligned into said registration corner.
       

     The method can also include inserting bias elements in to at least two corners. 
     The method can also include inserting bias element into all corners aside from the registration corner. 
     The method can also include cutting away or forming the registration corner or the corner on the pin guide (or both) so that the corners themselves do not touch or meet but that their sidewalls extending away from the corners will precisely engage. This avoids the problem that the corners are slightly mismatched and prevent proper engagement of the sidewalls for alignment since it is easier to machine accurate sidewalls than corners. 
     The disclosure also includes an alignment system for precision alignment of test pins in an integrated circuit tester comprising any or all of the following elements:
         a. pin guide plate, having at least two corners, one of said corners being the registration corner and the other being the driven corner, said corners having sidewall extending therefrom;   b. a retainer plate for receiving said guide plate, said retainer having a aperture generally sized to receive said guide plate and likewise having at least two corners; said retainer including sidewalls extending away from said corners, one of said corners being a registration corner and defining, together with the guide plate, the precision location for the test pins; the other of said corners being the driving corner;   c. said sidewalls of said driving corner including recesses therein;   d. said sidewalls of said driven corner of said guide plate including recesses;   e. elastomeric material fitted in said driving and driven recesses for biasing the pin guide plate from the driven corner into the registration corner of said retainer plate,
 
so that the guild plate is precision registered with the retainer by virtue of the mating of registration corners under bias force.
       

     The alignment system may also include the radius of said driven corner being enlarged so that when said pin guide corner is inserted therein, contact is substantially made between sidewalls. 
     The alignment system may also include the radius of said driving corner being decreased so that when said pin guide corner is inserted therein, contact is substantially made between sidewalls. 
     The alignment system may also include the use of cylindrical elastomers as bias elements. 
     Another method disclosed to precisely aligning a pin guide plate within a retainer plate requires alignment pins. 
     Another method disclosed to precisely align the pin guide plate within the retainer plate requires the steps of pre-registration and gluing the elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a subset of components of a wafer prober system and a wafer. 
         FIG. 2  is a schematic view of a probe array as affixed to a probe card Printed Circuit Board (PCB) said assembly also commonly referred to as probe card. 
         FIG. 3  is a top plan view of a probe array. 
         FIG. 4  is an isometric view of the probe array in  FIG. 2 . 
         FIG. 5  is a side perspective view of the prober array in  FIG. 3  with portions broken away. 
         FIG. 6  is a side plan schematic view of a pair of probes in an uncompressed state. 
         FIG. 7  is a view like  FIG. 6  with the probes in a compressed state. 
         FIG. 8  is a side plan schematic view like  FIG. 6  but with a contact ball illustrated and additional layers shown. 
         FIG. 9  is a view like  FIG. 8  except with the pin shown in a compressed state. 
         FIG. 10  is an isometric view of the top portion of the array shown in  FIG. 3 . 
         FIG. 11  is an isometric view of the bottom side of the portion of the array shown in  FIG. 10 . 
         FIG. 12  is a view like  FIG. 11  with pins removed. 
         FIG. 13  is a view like  FIG. 10  with the pins removed. 
         FIG. 14  is a side view of the array of  FIG. 3  with portions broken away. 
         FIG. 15  is a top plan view of the elastomer layer. 
         FIG. 16  is a side view of the elastomer layer. 
         FIG. 17  is a top plan view of a top ceramic plate. 
         FIG. 18  is a bottom plan view of the plate in  FIG. 17 . 
         FIG. 19  is a bottom plan view like  FIG. 18  except shown retention posts. 
         FIG. 20  is bottom isometric view of the pin guide plate with retention posts as seen from the bottom. 
         FIG. 21  is a view like  FIG. 20  with the perspective rotated 180 degrees. 
         FIG. 22  is a view like  FIG. 20  of the bottom of the pin guide but with a Kapton® cartridge inserted over retention posts. 
         FIG. 23  is a view like  FIG. 22  but rotated to a different perspective. 
         FIGS. 24   a - f  are views of an individual upper pin with double edge crown and recess in the following views: a: top plan, b: side plan, c: front plan, d: other side plan, e: side perspective, f: bottom plan. 
         FIGS. 25   a - f  are views of an individual upper pin with a 4 point crown with lateral recess in the following views: a: top plan, b: side plan, c: front plan, d: other side plan, e: side perspective, f: bottom plan. 
         FIGS. 26   a - f  are views of an individual upper pin with a 4 point crown with central recess in the following views: a: top plan, b: side plan, c: front plan, d: other side plan, e: side perspective, f: bottom plan. 
         FIGS. 27   a - f  are views of an individual upper pin with a wedge crown in the following views: a: top plan, b: side plan, c: front plan, d: other side plan, e: side perspective, f: bottom plan. 
         FIGS. 28   a - f  are views of an individual upper pin with a chisel crown in the following views: a: top plan, b: side plan, c: front plan, d: other side plan, e: side perspective, f: bottom plan. 
         FIGS. 29   a - f  are views of an individual upper pin with a double chisel crown in the following views: a: top plan, b: side plan, c: front plan, d: other side plan, e: side perspective, f: bottom plan. 
         FIG. 30  is perspective view of probe tips/crowns overlayed with an example Kelvin contact system. 
         FIG. 31  is a top plan view of the probe tips overlayed with an example Kelvin contact system. 
         FIG. 32  is a close of up of one Kelvin contact system in  FIG. 31 . 
         FIG. 33  is a perspective view of a pin array. 
         FIG. 34 a    and  FIG. 34 b    are side plan views like  FIGS. 5 and 6  showing a ball contact of a DUT in initial engagement ( 34   a ) and final engagement ( 34   b ) with the pin fully downwardly depressed. 
         FIG. 35 . is a perspective view like  FIG. 33  but of an alternate embodiment with long pins. 
         FIG. 36 a    and  FIG. 36 b    are side plan views of the alternate embodiment in  FIG. 35  with long pins, showing a ball contact of a DUT in initial engagement ( 36   a ) and final engagement ( 36   b ) with the pin fully downwardly depressed. 
         FIG. 37  is a top plan view of a probe card plate, guide plate/pin guide and pin arrays. 
         FIG. 38  is a top perspective view of the guide plate/pin guide and arrays of  FIG. 37 . 
         FIG. 39  is a top perspective view of the probe card plate/retainer of  FIG. 37   
         FIG. 40  is an exploded bottom perspective of the combination of  FIGS. 38 and 39 . 
         FIG. 41  is a close up partial perspective top view of a portion of a corner of the retainer. 
         FIG. 42  is a close up partial perspective top view of a portion of one array showing the elastomer insert. 
         FIG. 43  is a close up partial perspective top view of a portion of a corner of the probe card plate/retainer showing an elastomer. 
         FIG. 44  is a cross sectional view of a pin guide, elastomer and retainer taken along an edge near a corner. 
         FIG. 45  is an exploded view of a probe card/retainer, guide plate/retainer and pin arrays. 
         FIG. 46  is an exploded view of a pin array. 
         FIG. 47  is a top plan view of the pin array in  FIG. 46 . 
         FIG. 48  is a close up bottom plan view of the pin guide in  FIG. 46 . 
         FIG. 49  is a cross section taken along lines  48   a - 48   a.    
         FIG. 50  is a perspective view of the pin array in  FIG. 45 . 
         FIG. 51  is a perspective view of a pin guide in  FIG. 45 . 
         FIG. 52  is a top perspective view of a single pin and elastomeric bias element. 
         FIG. 53  is a bottom perspective view of  FIG. 52 . 
         FIG. 54 a - d    are views of a guide plate in  FIG. 45 .  FIG. 54 d    is a close of the circled area in  FIG. 54   a.    
         FIG. 55  is a top up view of a staged guide plate. 
         FIG. 56  is a close up view of the plate in  FIG. 55  on circle A. 
         FIG. 57  is a side plan view of a portion of the retainer and pin array of  FIG. 45 . 
         FIG. 58  is a side plan view of a single pin pair of  FIG. 57 . 
         FIG. 59  is an alternative embodiment of the retainer and pin array of  FIG. 57 . 
         FIG. 60  is a further embodiment of the retainer and pin array with a counter bore alignment feature. 
         FIG. 61  is a further embodiment of the retainer and pin array with a keyway alignment feature. 
         FIG. 62  is a further embodiment of the retainer and pin array with an alternate keyway alignment feature. 
         FIG. 63  is a further embodiment of the retainer and pin array with a square keyhole alignment feature. 
         FIG. 63 a    is top plan view of a square keyhole. 
         FIG. 64  is a further embodiment of the retainer and pin array with a cross cut alignment feature. 
         FIGS. 64 a - d    show top view of various embodiments of cuts through the top layer  64   a  being cross cut,  64   b  being diagonal,  64   c  being left flap and  64   c  be right flap. 
         FIG. 65  is top view of the pin guide pin array. 
         FIG. 66  is a side plan view, with portions broken away, showing a leadbacker, alignment plate, a probe guide and a retainer with alignment pins. 
         FIG. 67  is an exploded view like  FIG. 46  of a pin array according to a further embodiment. 
         FIG. 68  is a view like  FIG. 45  of a probe card/retainer, guide plate/retainer and pin arrays. 
         FIG. 69  is a side plan view of  FIG. 68 . 
         FIG. 70  is a perspective view with portions broken away of a pin array within housing. 
         FIG. 71  is a close up plan view of the pin array of  FIG. 70 . 
         FIGS. 72 a - d    are views of a pin pair according to another embodiment.  FIG. 72 a    is a side view,  72   b  is an end view,  72   c  is a perspective view and  72   d  is a top view. 
         FIGS. 73 a - d    are view like  FIG. 72  except the pin pairs are rotated to be side by side, as can be seen when comparing  FIGS. 72 d  and 73 d   .  FIG. 73 a    is a side view,  73   b  is an end view,  73   c  is a perspective view and  73   d  is a top view. 
         FIG. 74  is a side view like  FIG. 57  with portions broken away of a pin pair according to another embodiment, but showing a tapered top or ceramic later with straight probes. 
         FIG. 75  is a top view of a Kapton® keying/anti-rotation layer used to prevent pin rotation and having slightly undersided oval or oblong holes. 
         FIG. 76  is a view like  FIG. 74  except the top layers have a funnel structure for easier pin insertion. 
         FIG. 76 a    is a view like  FIG. 76  except with straight probes. 
         FIG. 77  is a perspective view of the subject matter of  FIG. 76 . 
         FIG. 78  is a layer like  FIG. 75  except the holes are rectangular keyed to the shape of the pins to prevent rotation. 
         FIG. 79  is a perspective view showing two guide plates of  FIG. 78  with pins. 
         FIG. 80  is close up view of the shaded area in  FIG. 78  showing pin guide flaps (see  FIG. 81  for detail). 
         FIG. 81  is a close up view of an alternative embodiment where the guide plate holes have flaps similar to those shown in  FIG. 64 . 
         FIG. 82  is a top view of pins and a guide plate showing relief slots. 
         FIG. 82 a    is a view like  FIG. 82  but with contact points/nubs. 
         FIG. 83  is a side perspective view of  FIG. 82 . 
         FIG. 83 a    is view like  FIG. 83  but with contact points. 
         FIG. 84  is a close up top view of the relief slots. 
         FIG. 84 a    is a view like  FIG. 84  but with contact points. 
         FIG. 85  is a perspective view of  FIG. 84 . 
         FIG. 85 a    is a view like  FIG. 85  but with contact points. 
         FIG. 86  is a top view like  FIG. 82  showing an alternate flap structure. 
         FIG. 87  is a side view of  FIG. 86 . 
         FIG. 88  is a side view of  FIG. 86  rotated 90 degrees. 
         FIG. 89  is a perspective view of  FIG. 87 . 
         FIG. 90  is a housing with guide plate. 
         FIG. 91  is a side plan view of a pin array, die under test (DUT) and a ball guide plate used to align the ball contacts on a DUT with pins. 
         FIG. 92  is a perspective view of a pin array with a ground plane on the upper surface. 
         FIG. 93  is a plan view of  FIG. 92 . 
         FIG. 94  is a perspective view of a housing with portion broken away showing a press fit pin into the load board and a slip fit pin to maintain the two piece housing together. 
         FIG. 95  is a side view of  FIG. 94 . 
         FIG. 96  is a side view of  FIG. 95  rotated 90 degrees. 
         FIG. 97  is a top view of a pin orientation according to a DUT with non-aligned contacts. 
         FIG. 98  is a perspective view of  FIG. 97 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     A typical IC wafer contains between 1 k-22 k dies typically organized in a regular matrix separated by horizontal and vertical scribe lines, for later cutting into individual dies or chips to be mounted in an IC enclosure with leads or contacts. This disclosure is primarily directed to testing of an individual dies or groups of dies in an array such as a pattern of generally geographically adjacent dies, or multiple arrays simultaneously, before they are cut along the scribe lines, whereafter, each die is inserted into an IC package with leads or contacts. 
     In the preferred embodiment, as shown in  FIGS. 1 and 2 , a probe array of contacts  10  is held, preferably close press fit registration to prevent movement, into a pin guide plate/pin guide  12  which itself is affixed onto probe retainer  14  by means of a retainer. Said retainer may include a picture frame opening which has a stepped ledge to accommodate a like ledge on the pin guide plate  12 . It is preferable to restrict freedom of lateral movement by means of alignment pins press fit into retainer to secure registration relative to the probe card or PCB. This retainer may be fastened to the probe card via screw fasteners or the like. 
     The pin guide plate  12  abuts the PCB probe card  11  when assembled. The preferred material for the plate is a machineable ceramic such as Macor® or Photoveel® but Torlon® or other composite may be used alternatively. The PCB includes a plurality of traces which connect signal lines from the probe array to connectors for the Test systems. Probe card plate/retainer  14  comprised of PCB, retainer and probe array is mounted in a “wafer prober” (not shown) which is a robotic machine which holds the probe cards and the wafer  8 , atop a chuck  6  and preferably moves the wafer into position and then in contact with the plate guide  12 . Alternatively, the plate could be moved and the wafer immobilized, but this is uncommon with current wafer prober systems. The wafer prober robot is well known in the art and sold by companies such as TEL (Tokio Electron) TSK Solutions/Accretech, and Electroglass (EG). Prior art probe arrays were constructed using micro spring pins, buckling beams and cantilevered structures, all of which suffered from poor performance particularly at higher frequencies, where their capacitance and inductance were limiters. 
     The prober robot locates the position of the array by a known camera system which locates fiducial markings on the pins or other fiducial markings on the array and brings the wafer into contact with selected pins for testing, as will be explained herein. The camera system typically includes an upwardly and downwardly pointing camera, one for calibrating location on the wafer and the other to calibrate on the pin array. Once calibrated, the movement of both/either is tracked and the prober should know the exact number of steps to each die on the wafer. 
     An array  10  is a package of contact pins  22 / 62  which form apart of a multi-layer package. This package  10  has a pin guide plate  20  with a plurality of apertures  22  through which the upper portion of probe pins  42  protruding, as shown in  FIGS. 3-4 . In  FIGS. 11-14 , it can be seen that the preferred construction of the apertures  32  is circular with a central portion having a being a plurality of rectangular slots or channel  96  with parallel side walls sized to receive the cross bar flange portion  44   a - 44   b  of pin  422  which have a like cross section. The resultant channel structure maintains alignment of the pins and prevents rotation thereof consequently controlling the orientation of the entire pin. Rotation is a twisting or torqueing action which would make the planar contact surfaces  52 / 53  ( FIG. 6 ) no longer be coplanar and hence have less electrical contact surface in common. 
     Upper probe portion of pins  42  can be seen more clearly in  FIGS. 5-7 , wherein each has a crown  40  which makes contact with the die, an elongated body  42  which preferably has, as mentioned, a squarish or rectangular cross section. Other cross sections are possible, such as circular, oval, triangular, keyed (with a keyway), etc., if the cross sections are used to mate with a like shape in aperture  32 , or a portion thereof, to maintain rotational alignment of the upper pin instead of or in addition to channels  96 . Alternatively a separate element may be provided with the channel elements to receive probe cross-bar elements. 
     The preferred method of preventing rotation and maintaining alignment of pin  42  is accomplished by creating channels  96  in the pin guide plate  20 , as can be seen most clearly in  FIGS. 5, 10, 11, 12, 13, 18, 19, 20  and  21 . These channels are preferably formed or cut in the material in parallel spaced apart sidewalls  97  ( FIG. 12 ) creating recesses or depressions  96  with an aperture  32  in the channel upper interior wall to allow the passage of the upper pin portion  42 . The aperture  32  may be circular or be likewise shaped with parallel spaced apart sidewalls sufficient to allow passage of portion  42 , but also prevent its rotation. Since these parallel walls spaced apart sidewalls  97  already accomplish this function, one or the other may be dispensed with unless both are desired walls  97  are preferably sized to provide low resistance (and may be coated with low resistance materials such as Teflon®) by being spaced apart sufficiently to not make contact with the pin when properly oriented, but close enough that if the pin rotates, it will immediately engage the walls and be reoriented. The channels receive cross bar flanges  44   a - 44   b  and prevent their rotation or change in alignment, so that they provide good alignment with the greatest amount of contact area for the lower pin at their contact surfaces  52 / 64  ( FIG. 6 ).  FIGS. 21-22  show the top pins  22  in place from their bottom view in different perspectives. Also shown in  FIGS. 21-22  are alignment posts  55  around the periphery of pin guide plate  20 . Alignment posts  55  maintain alignment of various layers such as the bottom Kapton® layer. 
     At the bottom of body  42  are left and right cross bar flange sections  44   a - 44   b  one of which includes an optional recess  48  is used as a fiducial mark to help the assembler or machine which is the right or left hand side of the pin as seen from above. It may also be used for alignment purposes. These flanges also operate as a key for a keyway slot in the Kapton® layer  92  (see below) and in the bottom surface of the pin guide plate  20 . 
     The cross bar flange section  44   a - b  provide an upper limiter for upper portion  42 . In the preferred embodiment is critical that all of the crowns — 40  be maintained in a very coplanar or multi-planar relationship to each other, preferably within 30 microns of each other. In alternative embodiments, it may be desirable to have pin heights in multiple planes according to the arrangement of the DUT. For conventional semiconductor wafer processes, the wafer test pads, bumps or balls are assumed to be likewise very planar so contact of each crown onto the wafer must be at a relatively equal pressure to prevent damage to the wafer. This is achieved by having the crowns coplanar the pin deflection pressure likewise relatively equal. For novel 3D wafer processes, there may be requirements for multiple planes at differing heights for wafer test pads, bumps or balls, but the presumption is that the planarity requirement for each plane would be likewise required to be coplanar within 30 microns. 
     The bottom portion  50  of the upper pin  22  is characterized by having a generally planar portion  52  which is wedge shaped to slideably engage/mate with a like planar surface  64  of lower pin  62 . Surfaces  52  and  64  slide by each other during compression. Both pins are conductive and thus carry signals to the load board  70  at the rocker foot  66  of lower pin  62 . The arcuate shaped based of foot  66  is preferred, though other forms such as flat or having a semi-circular or partial cylindrical protuberance  67  in the center of the foot, are possible. Foot  66  may be arcuate, either across its entire base or just a portion as shown at the hemispherical or half or partial cylindrical protrusion  67 . This creates a “rocker” base which allows the foot to adapt to variations in the load/contact board. This protrusion is preferably equidistant from the ends of the base/foot or that it is central to an axis running through the midpoint or center of gravity of the pin. The semicircular shape may also be substituted with other shapes that permit a rocking action. This rocking action provides helps remove any oxide on the protrusion or the contact load board. The further advantage of having a protrusion of any shape, though preferably a partial cylinder as shown is that the force per unit area on the load board is increased thereby increasing the quality of the electrical contact with the board. The protrusion is arcuate similar to a truncated cylinder but having walls that slope generally smoothly into the remaining portion of the foot. Pin guide  20  is preferably made of a ceramic material or Macor® such as SiC Technide® C18, SiN Technide® 310Shapal M Soft®, Photoveel L (Ferrotec), Photoveel®, MM500 Mccalex®, or other materials with low expansion coefficients. Alternatively, composite materials such as Torlon 5030® may satisfy some applications with more constrained thermal or humidity exposure. 
     The preferred material can be predictably formed or milled to great tolerance of known thickness, very flat, and have a low coefficient of thermal expansion and be non-hydroscopic to avoid expansion due to variable weather conditions. Chip test houses where this device will be used are not always well temperature and humidity controlled, so the pin guide plate material must be sufficiently stable to deliver the pin crowns  40  in a coplanar state. Top plate  20  must also be millable or formable to have the rectangular channels  96  mentioned above. 
     Pins  22  and  62  are upwardly biased relative to each other by, for example, an elastomer  80  which surrounds, at least in part, the pins. This provides an upward bias against cross bar flanges  44   a - 44   b . The lower pin is in fact driven downwardly against the load board by the same elastomer, which thereby creates a solid electrical contact therewith. Elastomer  80  may include a top and bottom layer of Kapton® or other somewhat elastic material  122  as a further means to hold the pins within the elastomer at the narrowed neck regions in the pins  54 . In the preferred embodiment Kapton® layers  122  have apertures larger than the narrowed neck regions  54  of the pins but smaller than the wider portions  50 ,  68  so that the pins will be resiliently confined between Kapton® layers. 
     The upper limit of travel of the upper pin  22  in the Z-axial direction for the Z-height is defined by engagement of the up-stop surface  90  and some portion of pin  22  which engages the up-stop. In the preferred embodiment, it is cross bar flanges  44   a - 44   b , but it could be any protrusion on the pin for this purpose. It is possible that other surfaces of probe guide  20  and other portions of pin  22  form the combination of an up-stop  90 ,  190 ,  390  for the upper pin. It is the top travel point for that pin. The lower surface up-stop of plate  20  is located such that the protrusion of crowns  40  will all be located in the same plane. The preferred protrusion of the crown may be for example 75 microns. 
     Is it also desirable to have the upward force of pin  22  to be relatively uniform through its travel. This is achieved by pre-compression/pre-loading of the elastomer  80 . In  FIG. 6 , pin  22  is precompressed downwardly by up-stop surface  90  of probe guide  20  so that when pin  22  engages the wafer and is compressed, the force response to compression is relatively uniform. If the pin was not compressed, the elastomer would exhibit a much less uniform response, with less force at the beginning of the downward pin deflection that later. The elastomer exhibits better uniformity when it is already compressed state. The preferred pre-compression may be for example 80 microns. 
     The crown or tip  40  performs several functions. First, of course, it makes electrical contact with the wafer test pad or electrode. Wafer test pad may be include the forms of metallic film, electroplated bump or solder ball. In alternate embodiments, the crown may each have Kelvin style contact (force and sense) in order to confirm a reliable test, as known in the art. 
     The crown also has the need to shed any debris which may accumulate between contact tests. 
     Finally, the crowns also need to provide fiducial recognition for the camera system in the prober which will align the array with the wafer at precise points. The camera system must be able to recognize the crown and the center of the crown by recognizable artifacts on the crown, whether they are there for other reasons, or solely for the purpose of enhancing the reliability of recognition. For example a cross hair, such as “xx” could be placed in the base of the crown as a point of recognition. If each crown included such a marking, or if the corners of the array were so marked, or other known combination, the computer could calculate the position of the entire array. It may also be desirable to provide side illumination (i.e. orthogonal to the travel of the pin) to provide greater contrast to the position calibration camera of the probe, since the crown has facets which will reflect side illumination upwardly and provide a very bright spot in an otherwise dark field. 
     Various crown shapes are possible.  FIGS. 24 a - f , 25 a - f , 26 a - f , 27 a - f , 28 a - f  and 29 a   - f  illustrate several embodiments. Each embodiment is the same except for the crown  40  which varies by figure. In  FIG. 24  the crown is has two parallel spaced apart ridges  240   a - b  formed in a chisel shape with an arcuate hemispherical valley  240   c  therebetween. In  FIG. 25  crown  40  further includes a cross hemispherical valley  240   d  orthogonal to valley  240   c , which is shown alternatively as a v-shaped valley, though it could also be hemispherical. This creates 4 points on the crown.  FIG. 26  is similar to  FIG. 25  except that all valleys  250   e - f  are v-shaped created sharp flat walled facets from the crown points. In  FIG. 27  the crown is a chisel shape with a single flat sloped wall  240   g  creating a wedged crown. In  FIG. 28  the crown is a double chisel with converging flat sidewalls  240   h - i . In  FIG. 29 , the crown is inverted from  FIG. 28  where the sidewalls  240   j - k  slope inwardly toward a bottom valley line. 
     Interposed between the pin guide top plate  20  and the elastomer  80  is a retaining layer  122  preferably of Kapton® polyamide film from Dupont or equivalent. This layer maintains the pins in place before the top surface is applied. 
       FIG. 11  illustrates the upper portion of the array  10  with cross bar flanges  44   a - 44   b  sitting in the channels  96 . The lower pins  62  could also be sitting a like plate with channels, but this is typically not necessary. 
     Both upper and lower pings  22  and  62  are at least in part potted into elastomer  80  which is shown in further detail in  FIG. 15 . The pins are placed in the space voids  81  while the octagonal voids  83  provide take up space to be used during compression and precompression. Without space, the elastomer would have a less uniform resistance/response to compression because the compressed elastomer would have no place to go. Voids  81  are typically square or rectangular, and of smaller than the cross section of that portion of the pin  50 ,  68  which is captured therein. This provides a bias force which maintains contact surfaces  52 ,  64  in planar registration for maximum electrical surface contact. 
       FIGS. 8 and 9  are similar to  FIGS. 6 and 7  except that they include ball/pad  120  in contact with crown  40 . In addition they also show a Kapton® layer  122  on both the upper and lower surfaces of the elastomeric layer  80 . This layer  122  includes apertures (not shown) large enough to permit insertion of the portion of the pin shown. 
       FIGS. 30, 31 and 32  are views of the array in  FIG. 4  but also including circuitry for Kelvin contacts. Kelvin sensing circuits are known in the art and provide a way to minimize test errors. They require additional contacts to make several points of contact on each pad, isolated, mechanically independent probes which are very small and closely spaced. 
     In  FIG. 31 , crown  40  is a wedge structure with two longitudinal ridges separated by a recess or valley. Placed within the valley is a polyamide or other insulator  124  which sits in and straddles the recess between peak pin contacts  150   a - b  which in this case are inverse wedge shaped per  FIGS. 29 a - f   . The sidewalls of the peaks  150   a - b  cradle the Kelvin insulator  124  and provide sufficient to support for the insulator to keep relatively coplanar with peaks  150   a - b . It is also possible that only the distal end  126  of the insulator is supported by a portion of the crown. Applied atop of the insulator is a conductive trace 130 which supplies the other conductor in the Kelvin circuit (typically the sense lead, with the force conductor being the crown ridges). This conductive trace run back from each of the crowns along leads  132  to the Kelvin circuitry. Because the Kelvin trace occludes the recess in the crown, any fiducial marking in the crown is unavailable to the camera system. Thus the fiducial mark may be placed on the trace or insulator as identified with “xx” at  134 . 
     An alternative embodiment is shown is  FIGS. 35-36 . 
     In the previous embodiment, as shown in  FIGS. 33-34 , pins  42  and  66  as previously described (see  FIGS. 6-9 ). Contact balls/pads  120  are shown in cross section. At the point where the top of pin  42  first engages ball  120  ( FIG. 34 a   ), there is a large gap  43  between an adjacent ball  120   a  and the surface of plate  20 . If however ball  120   a  is misshapened, or is a “double ball” (defect) there is a chance that the gap  45  will be nonexistent and ball  120   a  will physically strike the surface of plate  20  potentially causing damage. Note that “ball” need not be round, but means any protruding contact surface on a DUT. To avoid these consequences if defective ball shapes or heights, the embodiment in  FIGS. 35-36  account for this. 
     To the extent the elements from one embodiment to the other are similar, the numerical designation has been designated with  300  series numbers, i.e.  42  is similar to  342 . A solution to the problem set forth above, is to increase the length of that portion  410  of pin  342  which extends above plate  20  when the DUT is in test position (i.e. pin  342  is maximally displaced as show). The pin travel distance (stroke) is defined as the distance the upper pin travels between in-test and out of test positions. The pin travel is preferably limited so that the flanges never leave the channel in the prior embodiment, it was desirable, for many reasons, to have the portion of pine  42  which extended beyond surface  20  as small as possible. As can be seen in  FIG. 7 , the exposed portion of the pin in test mode, is virtually flat with surface  20  whereas in  FIGS. 35-36  the pin height in test position  410  is substantially greater, at least sufficient to prevent ball  320   a  from contacting the surface of  20  even if it is a double height ball, a 1.5 height ball or other misshapened form. In non-test mode the pin height above plate  20  is indicated as  412 . Thus in this embodiment, the pin height in test position is sufficient that another ball, typically an adjacent ball will not touch the surface of plate  20 . One such limit would be that the pin apex is never lower than 50% or 10-50%, of the height of a contact ball, or just sufficient that any ball contact will not contact the surface regardless of its height. 
     In the preferred embodiment, the travel of pin  342  is greater than pin  42 . When  FIGS. 7 and 36   a  are compared the distal tail  412  may be allowed to travel up to but preferably not touching the foot of pin  366 . The actual downward pin travel is preferably controlled by the prober that puts the wafer into the test socket. As the pins are driven toward each other, if the proper fails, there are several possible hard stops in the system where are preferably not needed. For example contact between the lower portion of cross bar flanges  344   b  with the proximal end of pin  366  but also the distal end of pin  342  against the foot of pin  366  as shown in  FIG. 36 b   . The elastomer in this configuration is shown in the preferred embodiment which has two thinner layers of less resilient elastomer  414 ,  418  surrounding a more elastic layer  416  which provides most of the bias force against the pins. Thus if the upper pin were to bottom out, at  412 , the lower layer  418  would separate the pins from contact because the distal end of pin  342  will remain as an interposer. 
     The consequence of allowing this additional travel is that the elongated lateral portion  342  of the pin are taller than in the previous embodiment and alignment channels  396  are deeper. Specifically the depth of channel groves  396  must be equal to or greater than the differential between the exposed height of the pin when the pin is in test and non-test positions (i.e.  412  less  410 ). In the preferred embodiment the height of cross bar flange  344   a  be must be likewise equal to or greater than that differential to maintain the keying effect of channels  396 . Whether by the above formula or otherwise, it is preferable that the lateral alignment portion  342  must stay at least partially engaged with the channels  396  during the entire pin travel to keep the pin grooved against rotation. 
     Further details of the structure for insertion of the guide plate  12  into the probe card plate or retainer  14  follows and is shown in  FIGS. 37-43 . 
     Registration of the retain  14  with guide plate  12  is important for the prober to know where exactly the pin arrange is located relative to the IC. Since the dimensions are very small, a solution in this disclosure is to insure that the guide plate, which has many probe arrays is reliably aligned with the probe card plate. 
     Instead of trying to align the guide plate with every corner of the probe card plate, which is extremely difficult, it is possible to align along two (or three) edges thereof and bias the guide plate into reliable position with respect to those two (or three) edges. This is much more predictable than trying to align against  4  edges. 
     In  FIG. 37 , retainer  14  has 4 corners  502   a - d , each having intersection edges  504   a - h , in pairs as shown. In  FIG. 39 , these edges can be seen with the guide plate removed. In one embodiment, corner  502   c  is designated the “registration or reference corner”, though any corner is acceptable. Therefore at least edges  504   e - f  will be used for registration of the guide plate by means of biasing of the plate into that corner. In the preferred embodiment, edges  504   g  and  504   d  will also provide registration as they are in line with corner  504   c  edges. The driving corner which is diagonally opposite the registration corner is the primary location for bias elastomers. It is also possible that the remaining two corners can have elastomer bias. It is also possible that there are more or less than 4 corners such as in the case of a triangle or polygon but the same principles for precision alignment apply, namely that there is a registration corner (or more precisely, sidewalls adjacent that corner) which are precisely milled/formed for alignment and the remaining edges/corners of the shape can be used to drive the pin guide into that registration corner. 
       FIG. 43  provides a close up view of corner  502   a  illustrates the biasing mechanism, which is preferably provided by recesses  506   a  and  506   b  being provided in the sidewall. These recesses/notches are longitudinal along a portion of the sidewall and have a depth sufficient to receive and elastomeric cylindrical member  510 . This member is also shown in  FIG. 42  which shows a corner of the guide plate/pin guide  12 , but it is the same member just shown in both locations. In the preferred embodiment, the corners of the pin guide  12  do not actually engage the corners of the retainer  14  because either the pin guide corners are cut away/reduced in radius or the retainer corners are cut deeper/increased radius. This insures that the sidewalls adjacent the corners are used for registration. If this was not done, a slight mismatch in the fit of the corners would prevent the sidewalls of the two parts from mating and providing precision registration. 
     At a minimum, one or two elastomers  510  are used to drive the pin guide  12  into the registration corner, but the preferred structure would provide elastomers in notches in all walls adjacent corners except that registration corner which must have material to material direct contact with no gaps. 
     To permit the insert of elastomers  510 , the upper edges of the sidewalls adjacent corners are cut away/beveled slightly and clearance is provide in along the corners of the retainer for the same reason. Even the registration corner can have this cut away even if it is not used in order to allow any corner to be the registration corner. The elastomers may be rubber cylinder or other biasing elements. They are preferably fitted after the pin guide  12  is inserted into the retainer  14  and then glued in place, though they may be glued first and then the pin guide inserted. Arrows  530  ( FIG. 39 ) illustrate the bias forces resultant from the elastomers, driving the pin guide into its registration corner. 
       FIG. 44  illustrates a cross sectional view of the intersection between the retainer  14  and pin guide  12  at a corner with the elastomer in place. In this embodiment the pin guide is inserted from the bottom so that ledge  520  engages a ledge  522  on the retainer to prevent push-though. Note that the pin guide could be inserted from the top also with appropriate changes in the ledge and stop. Cut away recesses  526  ( FIG. 38 ) may also be used to provide an insertion gap for removal of the guide. 
     The bias elastomer  512  resides in part in recess  506   b , but in the preference embodiments, it also has a like recess  511  in the pin guide  12  so that the elastomer is fully captured from escape. 
     Alternate Embodiments 
     Further embodiments are disclosed below. To the extent that elements are not specifically referred to, in general, they are the same or similar to like parts in the previous embodiments. Where possible the same or similar parts are referred to by a like reference number increased by 1000 or other leading digit. So for example, retainer  14  in  FIG. 2  may be similar to retainer  1014  in  FIG. 45 . This is done to avoid unnecessary repetition in this specification. 
     In the previous embodiments the pin guide  20  was preferably made of a ceramic material which included a plurality of channel features in up-stop surface to receive the flanges of wafer side pins. The use of slots  96 , however, may limit the arrangements of pins/probes to a regular (i.e. uniform) array. Alternative embodiments may separate the functionality of the pin guiding channels from that of the precision up-stop surface for purposes of improved flexibility for placement of test site locations or manufacturing options. For example, there may be circumstances where a unique arrangement of pins/probes that is not a rectilinear array is desirable. Further there are materials which are easier to laser cut but retain many of the necessary properties such as electrical insulation and durability but would make fabrication and customization easier. 
     Furthermore, to improve alignment of probes/pins on the DUT pads/balls, it is advantageous to high the tightest possible tolerance between probe size and aperture size. Rectangular probes in rectangular apertures are particularly advantageous, but casting of ceramic material with rectangular apertures is difficult and ceramic is not particularly amenable to laser cutting. 
     By replacing the channel elements portion of pin/probe guide  12  into two parts, an upper part  1012  and a lower part/up-stop  1020  which functions as an up-stop, it is possible to eliminate the channels  96  and thereby allow for smaller separation between pins (because there are no sidewall channels) and allow for non-uniform pin locations (again because there are no channels). So, in one embodiment a ceramic separate element, herein referred to as a probe guide plate  1012  is in abutment with a precision up-stop  1020 . The material selection for the up-stop plate  1020  may be broadened to include other materials which can be laser cut, such as Cerlex®, the aperture spacing and location can be easily altered for custom DUT pad layouts. 
     As will be explained elsewhere, there is an additional benefit to this combination layer approach, namely that rotation of probes can be inhibited by special modification of the up-stop plate  1020 . 
       FIG. 45  is an exploded view of an assembly with a top shipping plate  1102   a  retainer plate  1014 , a pin guide  1012 , a pin array  1010  (according to this embodiment) and a load board  1070 .  FIG. 46  shows the pin array  1010  in greater detail. 
     In  FIG. 46  the preferred assembly includes lower pins/probes  1062 , which pass through a plate  1081  preferably of Kapton®, an elastomeric element  1080  and upper Kapton® plate  1092 , upper (wafer side) pins/probes  1042  and a up-stop  1020 , preferably made of a rigid dielectric material which can be laser cut. Cirlex® from Fralock Corp Valencia Calif., is the preferred material. Guide plate  1012  is preferably made of ceramic or other rigid dielectric material. 
       FIG. 47  shows a bottom (or PCB side) view of an assembled array  1010 .  FIGS. 48 and 49  provide top and cross-section views additional configurations of a probe guide element. 
       FIG. 50  is a top perspective view of the assembly  110 . 
     The probe guide  1012  and adjacent up top plate  1020 , in this embodiment, cooperate to provide the function of guide plate  20  but with significant enhancements, as explained below. In other words, the probe guide  1012  no longer performs all of the same functions of guide  20  which included an up-stop. Now the functions of guide  20  are split between  1012  and  1020  with resultant advantages. 
     In one aspect, the up-stop  1020  is preferably laser cut from a dielectric material to allow for easier customization of holes positions for guiding slot  1032 . Hole or slot patterns are shown in detail in  FIGS. 51, 54   a - d ,  55 - 56 . In these figures slots/apertures  1032  are shown as preferred rectangular apertures though round or other shaped apertures are also possible. It is noteworthy that  FIGS. 55-56  illustrate that the hole pattern may be irregular/non-rectilinear/arbitrary in order to customize the apertures to the requirements of the device under test (DUT) which may have pins/pads in various locations. Because the material can be laser cut, even with sharp corners such as rectangles shown, the pin array can be quickly customized. 
       FIGS. 52-53  show the various layers with the elastomer  1080  cut away to show a single probe pin cell. Kapton® layers may be affixed to the elastomer by adhesive  1091 . 
       FIG. 57  is a cross-sectional view of a 4 pin array with portions: probe tip  1040 , probe stem  1042  flanges  1044   a ,  1044   b , surfaces  1052 / 1064  generally corresponding to like parts in previous embodiments. It is possible that different tip configurations may be provided on different probes to accommodate different DUT configurations such a 3 dimensional contact planes. For example some contacts on the DUT may be pads, others, balls, microball, posts, etc. The tips and probe height can be selected to be appropriate for each contact on the DUT in the same array. Note however that in the preferred embodiment pin guide  1012  does not require slots  96  as in the previous embodiment. Slots  96  provided a means for preventing rotation of the pins, but cannot be used easily in the case of irregular pin layout ( FIG. 55 ). The preferred internal structure of guide  1012  is planar on opposed (top/bottom) surfaces with orthogonal apertures or pockets. The up-stop plate  1020  abuts the pin guide  1012 . The desired probe tip radium of less than 7-8 micrometers have been demonstrated for dual knife probe tips such as examples shown herein and this has been shown to be suitable with controlled die forces of 2-35 grams per site to provide good contact resistance to wafer dies with test pads, bumps and balls. Sharper structures have been demonstrated, but seem to be unnecessary for typical wafer test applications. Probe tip  1040  knife edge separation in the ranges of 50-150 microns have demonstrated usefulness for ball sizes 150 to 300 microns in diameter for marking off ball apex with large number of insertions between required cleaning stops. The knife edge separation distances preferably match the target die pad, bump or ball geometries. 
     In order to provide resistance to pin rotation or to improve the centering of the probe within the guiding bore, other structures are illustrated, though they are not exhaustive. 
     In  FIG. 60  illustrates one such pin centering structure. In this embodiment probe guide  1012 , at its aperture includes a counter bore/concave trough surrounding the aperture. Likewise, pin/probe  1042  also includes a protrusion  1042   a  which mates with the counter bore to center pin within the bore. 
     In  FIG. 61  an alternate keying system is illustrated. In this case a key  1042   b  protrudes into the keyway  1020   b  cut into up-stop  1020 . The key and keyway can also be a tapered fit for that misalignment is corrected on entry of the key into the keyway. 
     In  FIG. 62  the keying function above can also be practiced in the Kapton® layer  1092  with a key  1042   c  added to probe designed to extending into a receiving keyway  1062   c . These can be tapered as well. A counter bore arrangement in the lower layer  1092  can also be used. 
       FIGS. 63 and 63   a  illustrate the use of filling casting material into the round apertures  1032   a  to fill the gaps between them and the squarish pins/probes  1042 . A gap  2050  will necessarily exist between square pins and round bores and this casting method in precisely centered position is one way to improve centering. 
       FIG. 64  illustrates further probe/bore centering and keying structures wherein layer  1092  preferably Kapton® is cut in various forms to provide a guideway for the pin/probe  1042 . In  FIGS. 64 and 64   a , a cross cut in the Kapton® layer provides  4  flaps  2052  which provide a bias force to align the pin within the aperture and inhibit rotation. The cuts release flaps which are driven upwardly and away from the layer when the pin is inserted therethrough. The  4  flaps which are freed by the cross cut provide a bias force against the pin because of their natural resilience. In  FIG. 64 b    a diagonal cut  2054  is used and in  FIGS. 64 c  and 64 d    right and left hand flaps are cut in the layer to apply a bias force on the pin. The cross cut through the Kapton® layer frees a plurality of flaps which extend upwardly along the pin sidewalls. This provides a bias force against the pin in both x and y axes, thereby tending to prevent rotation of the pin. With the bias force from  4  sides, it also tends to center the pin within the aperture. The diagonal and flap cut have the same effect. Other cuts in the Kapton® layer can provide similar benefits. 
       FIG. 65  illustrates how aperture  1032   a  are populated by pins  1042  of varying cross sectional shape. The gap  2056  as measured between the inner periphery of the aperture and the corner/edge of the pin with the pin fully displaced against an opposite peripheral wall. In preferred embodiments the clearance gaps are minimized to constrain the array of probe tips to precisely space locations coincident with precise spacings of test pads or balls on wafer die. Preferred gap between pin corner and bore is less than 20 microns and further preferred gap is less than 10 microns. 
       FIGS. 67-98  illustrate alternate embodiments, but to the extent they portions are similar, they should be assumed to have the same function as previously described. 
       FIG. 67  show as system with a two part probe guide housing/probe card having an upper housing  2020  preferably of a thermally stable material like ceramic with a plurality of apertures  2022  through which upper pins/probes  2042  protrude to engage the die under test (DUT). The upper pins are arranged in an array whose orientation is maintained by an upper pin guide  2021 . A lower set up pins/probes  2062  sideably engaged the upper set and is maintained in an array by a lower pin guide  2023 . The arrays sit within a lower half of the housing  2020   a . The lower half may be Torlon® or ceramic or other material. Torlon® or other compliant/slightly elastic material is preferred for anchoring to the load board (see  FIG. 94 ). 
       FIG. 68  illustrates an alternate shaped two part housings which is mounted in a retainer plate  3010  which as an aperture  3012  sized to receive a portion of the probe guide housing  2020 . The retainer and the housing each have a plurality of aligned and preferably slotted apertures  3014  which receive a rod elastomer  3016 . The apertures are preferably slotted so that they elastomers can be inserted laterally, though that is not required. The elastomer are an elastic material which allows for the probe guide housing and retainer to respond to lateral shock of the DUT handler driving the guide sideways or downward without damage. If no elastomer or other elastic connection was provided, when a DUT impacted the probe guide, it might crack the ceramic material if it did not give way. 
       FIG. 69  shows this in side view. 
       FIG. 70  is a view of part of  FIG. 67  with portions cut away and in greater detail in  FIGS. 71-73 . 
     As a general matter upper and lower pins  2042 / 2062  are similar though their lengths can vary according to test requirements. The pins preferably have upper and lower longitudinal portions which meet at a cross bar portion. The longitudinal portions have at least one planar surface which mates with a like planar surface to provide an electrical contact path. The pins are electrically conductive, either by use of a metal or metallic coating. The cross bar is has a transverse section generally orthogonal to the longitudinal portions, and has a contact planar contact surfaces adjacent the upper and lower pin portions. These contact surfaces form part up an up and down stop surface to engage with like surfaces on the housing to limit the travel of the pins. Each pin has an upper probe section  2042   a / 2062   a  and a lower probe section  2042   b / 2062   b  and a cross member/crossbar  2044  therebetween. The longitudinal surfaces of the probe section is planer so that they can mate where they overlap at  3040  conduct electricity and yet be in slideable engagement with a minimum of electrical and mechanical resistance. 
     The upper pin  2042  is biased upwardly so that it is “spring loaded” against engagement with the DUT. This is accomplished with an elastomer  2080   a / 2080   b  which may be split into upper and lower portions for ease of assembly, 
     To prevent the elastomer from intrusion into the cross bars, a flat more rigid material  3041  in interposed therebetween. In this case a Kapton® layer of rigid and preferable deflectable material is used. 
     The tips of the pins/probes may be identical, top and bottom for interchangeability or different. The upper tip may be shaped according to tip disclosures herein or known in the art. The lower tip engages the load board and may be optimized for that engagement. 
     Note that elastomers  3040  are provided on both sides of the pins/probes so that they have lateral pressure from both sides for maximum electrical contact. This can be achieved with separate elastomer sections or a matrix elastomer with apertures for the pins/probes. 
       FIG. 74  illustrates tapering of the apertures  2022  of the upper pin guide. The preferred material for the tapered portion is Cirlex®. The tapering is narrow to wider from top to bottom. This is shown as a widening gap  2022   a  between the pin/probe  2042  and the inner wall of the aperture  2022 . The taper reduces friction and also makes insertion of the pins/probes easier during assembly. The preferred construction is in two halves to the pins/probes are loaded from inside of the halves. 
       FIG. 76  illustrates an alternate way to achieve the benefits of tapering the pin guide. It is to taper a portion of the pin/probe instead (or in addition). Pins  2042  are preferably narrower from their tip to the portion which passes through the guide  2020  at  3050 . The rest of pin need not be tapered since it will have no beneficial effect. Indeed, the tapering can also end at the top of the pin guide at  3052 . 
       FIG. 76 a    illustrates a further embodiment of this tapering concept. Where the upper probe guide  2020  is made of two layers  2025   a / 2025   b , it is possible to make the fit between  2025   b  (lower layer) looser than  2025   a  (upper layer) creating a “funnel” structure. This makes insertion of the pins from the underside easier because the pin can more easily enter the larger space in  2025   b . The gap at  3050  is greater than at  3052 . See  FIG. 77 . 
       FIGS. 75, 78-89  are directed to various embodiments for limiting the rotation of the pins. It is important that the planar mating surfaces of the pins be maintained in parallel abutting planes to maximize electrical contact surface area. The pins are free to slide longitudinally with respect to each other within the bounds of their pin stops (i.e. engagement of the cross member with a rigid plate) but they are subject to undesirable twisting/torqueing forces which can reduce the mating area. These forces can arise from engagement with the balls of the DUT which may be off center, shock or elsewhere. An anti-rotation keying layer  3042  is desirable. This layer can be the same as the anti-intrusion layer or separate. It may be adjacent to the anti-intrusion layer or placed elsewhere orthogonal to the pin. It can be on the upper and lower pin path or just the upper where the twisting forces are greatest. 
     The embodiment in  FIG. 75  shows a plate or mask  3042  plurality of apertures  2020  which are slightly undersized relatively to the cross section of the pins. In other words the area of the aperture is less than the cross sectional area of the pin. This engagement has a stabilizing effect. These apertures are shown as ovals or rectangles with rounded corners so that the corners of the pins engage with the rounded corners of the apertures. In such case the engagement is only at the corners for greater stability and less resistance. In the preferred embodiment the material used for this mask is capable of some deflection, and not entirely rigid. 
       FIGS. 78-81  illustrate an alternate solution for mask  3042 . In this case the apertures have inner perimeter space larger than the pin, so there would be no engagement, but extending from the inner peripheral edge of the aperture are protrusions or tabs  3060  which extend inwardly into the space defined by the aperture. These tabs are preferably in pairs extending from opposing sidewalls. There may be tabs from all sidewalls or only two. The tab is deflectable and flexible and when the pin inserted they deflect upwardly and away but maintain a balanced force on the pin to keep it centered and resist twisting.  FIG. 79  shows a mast on both upper and lower pins. The tabs can be fill just a portion of the sidewall from which them emanate, or fill the entire sidewall as shown in  FIG. 80 . 
       FIGS. 82 a -85 a    show a slightly different configuration wherein the tabs  3060  are formed as longitudinal bumpers or numbs which span the thickness of the mask later, rather than mere flaps in previous embodiment. 
       FIGS. 82-85  provide further solution to anti-twisting. In this case, the apertures are sized to be a close fit with the pin. In one embodiment, they also have tabs/projections  3062 , but in this case they do not bend or deflect. That means the aperture is nearly equal to, equal to or less than the cross sectional area of the pin. Because there may be so much more contact surface between the pin and aperture inner walls, anti-twisting is enhanced, but so is friction. To reduce the force on the pin, relief slots  3062  are provided in the mask, such as by punching the mask with narrow slot adjacent to but separated from the apertures and generally parallel therewith. This weakens the aperture wall adjacent the slot and reduces pressure and resistance. The slots can also be a plurality of spaced apart holes or other void shapes. 
       FIGS. 87-89  illustrate flaps which extend from all sidewalls of the apertures and are deflected upwardly when the pin is inserted. The flaps may be precut or just score lines which are opened on insertion of the pin. 
       FIGS. 90-91  illustrate a construction primarily intended for manual testing, i.e. insertions which are not done by a robot. These insertions are necessarily sloppy because they lack robotic precision. Consequently there is a need to provide a guide which will urge the DUT balls into the right place on the holder. It is also helpful to provide a level of cushion because manual insertion pressure is variable.  FIG. 90  show a housing  3010  and a ball guide plate  3070  with apertures  3072  located where the balls  3074  and pins are to be aligned. The ball guide provides pre-alignment of the balls and some degree of resilience when the ball guide is made of a compressible material. 
       FIGS. 92-93  illustrate the use of an RF shield/ground plane layer  3080 . In some applications, the DUT generates RF radiation under test. RF can interfere with the high frequency test signals on the pins. To minimize this the array can include a further ground plane RF shield plate  3080  which is preferably located adjacent (above or below) the anti-rotation layer  3042  and/or the anti-intrusion layer  3041 . This layer is preferably attached to ground. 
       FIGS. 94-96  illustrate the assembly of the housing upper and lower halves  2020  and  2020   a . In the preferred embodiment, the upper half  2020  is made of a thermally stable material, such a ceramic. The lower half is preferably made of a more compliant material such as Torlon®. To prevent movement between the halves, an aperture is made in both halves and a pin  3084  fills the space. The pin is a slip fit, i.e., it is under little or no compression when inserted, so it does not risk cracking the ceramic. Because the lower half  2020   a  is a more flexible, compliant material, it can be connected to the load board (not shown below the housing) by a press fit pin  3086  which is slightly larger than the aperture so that it remains firmly in place. 
       FIGS. 97-98  illustrate, the arrangement flexibility of the low profile pins  2042  with respect to their placement on the guide plate housing  2020 . Some DUTS have ball/contact placement which is not aligned in rows and in an irregular orientation. Because the pins have very low profile (i.e. lateral dimension), they can be oriented in any angular position without interfering with adjacent pins. To avoid shorting by adjacent cross bars  2044 . 
     The description of the invention and its applications as set forth herein is illustrative and is not intended to limit the scope of the invention. Variations and modifications of the embodiments disclosed herein are possible and practical alternatives to and equivalents of the various elements of the embodiments would be understood to those of ordinary skill in the art upon study of this patent document. These and other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.