PATENT ABSTRACT
An apparatus for interfacing a test head to a peripheral system is provided. The apparatus includes a first unit having a first connection member for providing electrical communication with the peripheral system, a second unit having a second connection member for providing electrical communication with the test system, and pivot members coupling the first unit and the second unit. The pivot members enable motion in the following sequence as one of the first and second unit moves towards the other: a) pivotal motion between the first connection member and the second connection member; and b) linear motion which decreases linear distance between the first connection member and the second connection member while maintaining respective contact surfaces of the first and second connection members in parallel.

PATENT DESCRIPTION
[0001]    This application is a Divisional of U.S. patent application Ser. No. 11/199,646, filed Aug. 9, 2005, which is a Continuation of U.S. patent application Ser. No. 11/180,133, filed Jul. 13, 2005, the entire disclosure of which is expressly incorporated by reference herein. The U.S. patent application Ser. No. 11/180,133 further claims the benefit of U.S. Provisional Application No. 60/587,437, filed Jul. 13, 2004. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of electronic interfacing and more specifically to electronic interfacing during semiconductor testing. In particular, an apparatus and method are disclosed for performing electronic interfacing in order to perform semiconductor testing. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the manufacture of integrated circuits (ICs) and other electronic devices, testing with automatic test equipment (ATE) is performed at one or more stages of the overall process. 
         [0004]    A special handling apparatus is used to place one or more devices under test (DUT or DUTs) into position for testing. In some cases, the special handling apparatus may also bring the DUT or DUTs to the proper temperature and/or maintain it at the proper temperature to be tested. The special handling apparatus is of various types including “wafer probers” or “probers” for testing unpackaged devices on a wafer and “device handlers” or “package handlers” for testing separated or non-separated packaged parts; herein, “peripheral” or “peripherals” will be used to refer to all types of such apparatus. Also the acronym DUT may be used to refer to either a single device under test or a set of devices simultaneously under test. 
         [0005]    The electronic testing itself is provided by a large and expensive ATE system. The DUT requires precision, high-speed signals for effective testing. Accordingly, the “test electronics” within the ATE, which are used to test the DUT, are typically located in a “test head,” which must be positioned as close as possible to the DUT. The test head is extremely heavy: the size and weight of the test heads have grown from a few hundred pounds to as much as three to four thousand pounds. 
         [0006]    In order to use a test head to test integrated circuits, the test head is typically “docked” to a peripheral. When docked, the test head must be located as close as possible to the peripheral&#39;s test site in order to minimize signal degradation. A test head positioning system, including a test head manipulator and a docking apparatus, may be used to position the test head with respect to the peripheral and may be designed to facilitate flexible docking and undocking of a test head with a variety of peripherals. With the test head in docked position, a batch of devices, generally all of the same type, may be tested. In general a set of DUTs are tested simultaneously in parallel. Depending upon the overall system the number of DUTs in a set may range from one to 16 or more in a packaged device handler. In wafer probing the number of devices tested at one time has grown to dozens with an ultimate goal of testing all devices on the wafer in parallel. The peripheral places each set of DUTs in turn in position to be tested. For the purposes of this document “DUT” will hereinafter refer to either a single device under test (i.e., a set of one) or a set comprising a plurality of devices to be tested simultaneously. 
         [0007]    After the testing of a particular DUT type is complete, the test head may be undocked from the peripheral and moved away from using a test head manipulator. If desired, another DUT type may be loaded into the peripheral, and the test head is docked again to the peripheral to perform electronic testing. When changing over from testing one type of device to another, it is usually necessary to reconfigure the system by changing one or more units such as Performance Boards, DUT boards, and/or probe cards which adapt the test head and peripheral to the particular DUT. More will subsequently be said about such units. 
         [0008]    It is furthermore often desirable to dock a given test head with different peripherals from time to time. For example, testing may be performed with a certain packaged device handler for a time, and then it may be desired to change to another packaged device handler. In other situations, it may be desired to change over from a wafer prober to a packaged device handler or conversely. In such cases the test head is undocked from the original peripheral, which is then moved out of the way. The new peripheral is then moved into place, and the test head is docked with it. In other situations both peripherals are in position to be used, and the test head may be undocked from the first peripheral and then moved to and docked with the second peripheral. It is often also desirable to move the test head away from a peripheral to perform maintenance. Thus, it may be required to easily dock and undock the test head with a variety of different peripherals. In all of these situations the heavy test head is typically maneuvered from position to position using a test head manipulator. 
         [0009]    An electrical “interface system” or “interface” connects the test head with the peripheral&#39;s test site where the DUT is electrically tested. Generally, a performance board is attached to the test head to adapt the test head to a particular type of DUT or family of DUT types. The performance board generally includes conductive paths from the test electronics in the test head to a set of conductive pads arranged in a planar pattern. A second board for contacting the DUT is also provided. If the testing is performed on a prober type of peripheral, the DUT-contacting board is typically a probe card having needle like conductive contacts used to make electrical connection to the tiny connection pads on the chip itself. If packaged parts are tested using a handler, a DUT board including suitable contact devices to electrically connect with the “pins” of the DUT is used. Thus, a DUT board might include an appropriate test socket. In many situations the probe card or DUT board has conductive pads in a planar pattern that is the same as that of the DIB or load board. An interface system provides mechanical coupling and electrical interconnections between the performance board and the DUT-contacting board. In many situations the DUT-contacting board may be held in place by the interface unit which in turn is secured to the peripheral. In other situations the DUT-contacting unit may be held by the peripheral and the interface is separately aligned and secured to the peripheral. Typically, spring-loaded electrical contacts, commonly known as spring pins or Pogo Pins®, are disposed on each side of the interface to provide the electrical signal paths between the conductive pads on the probe card or DUT board and the conductive pads on the DIB or Load Board attached to the ATE. In situations where the contact patterns on the performance board are the same as on the DUT-contacting board, double-ended, spring pins may be used to realize the signal paths and electrical contacts. The interface may include hundreds or thousands of such electrical contacts, which are of necessity small and fragile. Typically, the contacts are arranged in a generally planar fashion on each side of the interface. When the test head is docked to the peripheral through the interface, electrical connections are thus made by the contacts on the two sides of the interface between the probe card or DUT board and performance board attached to the test head. 
         [0010]    A typical interface common in the art is an apparatus with two hingeably connected units. The bottom unit or first unit attaches to the peripheral and holds the probe card or DUT board in a proper alignment for testing. The lid unit, or second unit, contains the electrical contacts used to complete the electrical signal paths between the probe card or DUT board and the performance board attached to the test head. Preparation for testing begins with the interface attached to a peripheral by the first unit and in an open position. A probe card or DUT board is placed into the first unit, properly aligned, and secured. A performance board is attached to the test head. The second unit is then pivoted towards and locked against the first unit to bring the electrical contacts on the one side of the second unit into contact with the probe card. The test head is then docked to the peripheral, making contact between the electrical contacts on the other side of the second unit and the conductive pads on the performance board, thus completing the electrical connections between the test head and the peripheral&#39;s test site. The DUT is then positioned for testing by the peripheral, completing the connection between the DUT and the test head; and the electrical signal tests are then run. Once testing is complete, the test head may be undocked from the peripheral. The interface is unlocked, and the second unit is moved away from the first unit. The probe card or DUT board may be removed to allow for installation of another probe card or DUT board for testing further device types. 
         [0011]    It is well understood that, when docking the test head, the test head is typically first planarized with respect to the interface, aligned linearly in two dimensions, and aligned rotationally about an axis perpendicular to the plane of the interface. The test head may then be advanced along a linear path into a docked position. The docking apparatus desirably provides a means to establish the final docked distance (or “height”) between the test head and the peripheral such that the electrical contacts are satisfactorily mated (that is, with sufficient compression, to assure a low resistance connection) and such that the test head does not over-travel and thus damage or destroy the contacts. Interfaces are typically changed when operation is switched from one peripheral to another; indeed, each peripheral may have its own interface attached to it. Further, it is typical that when a single peripheral is used to first test devices of one type and then reconfigured to test devices of another type, the interface may either be changed from a first type to a second type or the probe card (or DUT board) may be changed from a first type to a second type. Generally, the docked height requirement may be different for each testing set up. It is most desirable to have a system where an interface may remain in place on the peripheral and to have a capability to easily change probe cards and/or to reconfigure the interface to change over from one DUT type to another. 
         [0012]    The prior art is described with reference to  FIG. 16 .  FIG. 16  has been adapted from U.S. Pat. No. 6,114,869. Referring to  FIG. 16 , signal interface system  1  includes a first ring unit  3  attached by hinge assembly  8  to second ring unit  11 . Second ring unit  11  includes spring-loaded contacts  42 . When the interface is closed, spring-loaded contacts  42 , held in “POGO tower”  10  engage fixed conductive pads  55  contained on probe card (or DUT board)  6 , which is contained in first ring unit  3 . As is generally well known and discussed in the &#39;869 patent, it is preferred that when closing an interface of this type second ring unit  11  is first pivoted downwards to a position where the plane of spring-loaded contacts is parallel to the plane of contacts in first ring unit  3 . Then the plane of spring-loaded contacts in second ring unit  11  is moved vertically downwards to make compressive contact with the contacts of first ring unit  3 . In opening the interface, the reverse procedure is preferred. In this way the contacts are not scraped against one another in a destructive manner. This is accomplished in the interface of  FIG. 16  by mounting “POGO tower”  10  to second ring unit  11  with springs. A fixed hinge enables second unit  11  to be rotated to a position where the plane of the spring-loaded contacts  42  is essentially parallel to and spaced slightly apart from the plane of conductive pads  55 . Rotating lock ring  16  by means of handle  4  moves “POGO tower”  10  downwards or upwards respectively bringing spring-loaded contacts  42  into or out of engagement with conductive pads  55 . Although this approach is protective of the contacts in normal operation, it is disadvantages in the event second unit  11  is closed abruptly with excessive force (i.e., slammed shut) in which case POGO tower  10  may bounce to such a degree that contacts  42  could be damaged. Additionally, repeatability of planarity between contacts  42  and conductive pads  55  prior to rotating handle  4  is dependent upon the mounting springs having uniform characteristics throughout their lives. 
       SUMMARY OF THE INVENTION 
       [0013]    An apparatus for interfacing a test head to a peripheral system includes a first signal unit having a first connection member for providing electrical communication with the peripheral system, a second signal unit having a second connection member for providing electrical communication with the test system, and pivot members coupling the first signal unit and the second signal unit. The pivot members enable motion in the following sequence as the second signal unit moves toward the first signal unit: a) pivotal motion between the first connection member and the second connection member; and b) linear motion which decreases linear distance between the first connection member and the second connection member while maintaining respective contact surfaces of the first and second connection members in parallel. The pivot members also enable motion in the following sequence as the second unit moves away from the first unit: a) linear motion which increases linear distance between the first connection member and the second connection member while maintaining respective contact surfaces of the first and second connection members in parallel; and b) pivotal motion between the first connection member and the second connection member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of a signal delivery system in accordance with an exemplary embodiment the present invention. 
           [0015]      FIG. 2  is a perspective view of the signal delivery system of  FIG. 1  showing a second unit fully pivoted away from a first unit and struts fully extended. 
           [0016]      FIG. 3  is an exploded perspective view of the signal delivery system of  FIG. 1 . 
           [0017]      FIG. 4  is a perspective view of a probe card tray. 
           [0018]      FIG. 5  is a perspective view of a prober adapter ring. 
           [0019]      FIG. 6A  is a perspective view of a first ring. 
           [0020]      FIG. 6B  is a bottom view of the first ring of  FIG. 6A . 
           [0021]      FIG. 7A  is a perspective view of a compression ring. 
           [0022]      FIG. 7B  is a side view of the compression ring of  FIG. 7A . 
           [0023]      FIG. 7C  is another side view of the compression ring of  FIG. 7A . 
           [0024]      FIG. 8A  is a perspective view of a second ring. 
           [0025]      FIG. 8B  is a side view of the second ring of  FIG. 8A . 
           [0026]      FIG. 8C  is another perspective view of the second ring of  FIG. 8A . 
           [0027]      FIG. 9A  is a perspective view of a compression ring with various cross sectional views indicated. 
           [0028]      FIG. 9B  is a further perspective view of the compression ring shown in  FIG. 9A . 
           [0029]      FIG. 9C  is a cross-section of compression ring  110  at cross-section A-A of  FIG. 9A . Cam follower  122  is also shown. 
           [0030]      FIG. 9D  is a cross-section of compression ring  110  at cross-section B-B of  FIG. 9A . Cam follower  122  is also shown. 
           [0031]      FIG. 9E  is a cross-section of compression ring  110  at cross-section C-C of  FIG. 9A . Cam follower  122  is also shown. 
           [0032]      FIG. 9F  is a cross-section of compression ring  110  at cross-section D-D of  FIG. 9A . Cam follower  122  is also shown. 
           [0033]      FIG. 10A  is a perspective view of a module housing ring. 
           [0034]      FIG. 10B  is a side view of the module housing ring of  FIG. 10A . 
           [0035]      FIG. 10C  is another perspective view of the module housing ring of  FIG. 10A . 
           [0036]      FIG. 11  is a perspective view similar to  FIG. 2  showing an alignment feature of a probe card of the signal delivery system of  FIG. 1  and illustrating the removal/insertion of a probe card. 
           [0037]      FIG. 12  is a perspective view similar to  FIG. 1  with part of the pivot block and the pivot support plate cut away to show elements of the pivot assembly.  FIGS. 13A  though  13 E are side cut-away views similar to  FIG. 12  showing the elements of the pivot assembly in various positions. 
           [0038]      FIG. 14  is a perspective view of a dummy module. 
           [0039]      FIG. 15  is an exploded perspective view of a dummy module. 
           [0040]      FIG. 16  is a perspective view of a prior art signal delivery system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]      FIG. 1  is a perspective view of a signal delivery system  5  in accordance with an exemplary embodiment of the present invention. Signal delivery system  5  is depicted in a closed position, in which first signal unit  32  and second signal unit  34  (hereinafter “signal units” when discussed as a pair) are in contact with one another and are substantially parallel to one another. 
         [0042]      FIG. 2  shows a perspective view of signal delivery system  5  of  FIG. 1  in an open position, in which first signal unit  32  and second signal unit  34  are angularly distanced from each another. 
         [0043]    An exemplary embodiment of the present invention includes pivot members which connect the signal units and which constrain the types of motion which occurs between the signal units as they are drawn together or drawn apart. In an exemplary embodiment, the pivot members include struts  31  and pivot assembly  50 , all of which are shown in  FIGS. 1 and 2 . 
         [0044]    Pivot assembly  50  connects first signal unit  32  and second signal unit  34  and assists and restricts motion between the two units to pivoting motion and linear motion. Further details of how pivot assembly  50  assists and restricts the movement of the signal units are described below in  FIGS. 12 and 13A  to  13 E. 
         [0045]    Strut  31  opposes forces which tend to compress its length. In one embodiment, strut  31  consists of a strut cylinder  36  and a strut piston  38 . As strut  31  is compressed, strut piston  38  is pushed into strut cylinder  36 , thereby decreasing the volume of the inside of strut cylinder  36 . In one exemplary embodiment, strut cylinder  36  contains a gas which, as it is compressed, provides the force which opposes the reduction of the length of strut  31 . In another exemplary embodiment, strut cylinder  36  contains a spring which, as it is compressed, provides the force which opposes the reduction of the length of strut  31 . 
         [0046]    One end of strut  31  is connected to first signal unit  32 . The other end of strut  31  is connected to second signal unit  34 . The connection of strut  31  to first signal unit  32  is closer to pivot assembly  50  than is the connection of strut  31  to second signal unit  34 . This arrangement causes any compression of strut  31  to provide forces that tend to generally pivot second ring unit  34  away from first signal unit  32 . In one instance, struts  31  provide a controlled, cushioned descent of second ring unit  34 . In another instance, struts  31  hold signal delivery system  5  open. 
         [0047]    An exemplary assembly of the signal units will now be generally described with reference to  FIG. 3 . A specific, detailed description of the various signal units of signal delivery system  5  will then follow. A description of how the signal units are assembled into signal delivery system  5  will then be provided with reference to  FIG. 3 . 
         [0048]    A general description of the signal units is first provided. Referring now to  FIG. 3 , an exemplary embodiment of the present invention is shown in which the signal units exist in the form of circular rings. Second signal unit  34  consists of a second ring  120 , a module housing  130 , and at least one signal module  132 . First signal unit  32  consists of a prober adapter ring  90 , a first ring  100 , a probe card  40 , a probe card tray  80 , and a compression ring  110 . In this illustrative embodiment a probe card is used; however, a DUT board could just as well be used. In this event probe card tray  80  would be used to hold the DUT board. 
         [0049]    A detailed description of each ring of signal delivery system  5  now follows. Shown in  FIG. 4  is a perspective view of probe card tray  80 . Support annulus  86 , which defines an interior surface of probe card tray  80 , contains a plurality of probe card alignment pins  82 . The outer edge of the upper major surface of probe card tray  80  has a plurality of alignment pins  84  and screw holes  88 . In an exemplary embodiment, the top surface of support annulus  86  is lower than the upper major surface of probe card tray  80  to establish a desired distance between a device under test (not shown) and probe pin  132 C (not shown) of signal module  132  when signal delivery system  5  is closed. 
         [0050]      FIG. 5  depicts a perspective view of an exemplary peripheral adapter unit in the form of peripheral adapter ring  90 . A peripheral adapter unit (also referred to as a probe adapter) is used to enable an interface to be used with a variety of different makes and models of peripherals. Peripheral adapter ring  90  adapts signal delivery system  5  to a peripheral (not shown). The interior surfaces of peripheral adapter ring  90  include two cylinders which have a central axis common to peripheral adapter ring  90 : a lower interior cylinder  93  and an upper interior cylinder  94 , which has a diameter greater than that of lower interior cylinder  93  to form edge  97 . The exterior surfaces include two cylinders which have a central axis common to peripheral adapter ring  90 . These include a lower exterior cylinder  95  and an upper exterior cylinder  96 , which has a diameter greater than that of lower exterior cylinder  95  to define support edge  98 . Peripheral adapter ring  90  sits on support edge  98  within a circular cutout in a peripheral and contains a plurality of fastener holes  92  through which a fastener such as a bolt, screw, or other device passes to anchor it to the peripheral. Internal recessed slots  91   a,b,c  and holes  99   a,b,c  are used to align and secure with screws first ring  100 , which is next described. Recessed slots  91   a  include two holes  99   a,b ; recessed slots  91   b  do not include holes; and recessed slots  91   c  include single holes  99   c  (not visible) each. 
         [0051]    Shown in  FIGS. 6A and 6B  are various views of first ring  100  which exemplifies a first subunit in an exemplary embodiment of the present invention. Turning now to  FIG. 6A , there is shown a perspective view of first ring  100  which is described generally by the following cylindrical portions which have a central axis common to first ring  100 : interior cylinder  101 A, lower exterior cylinder  101 B, and upper exterior cylinder  101 C, which has a diameter greater than lower exterior cylinder  101 B to establish support edge  101 D. Also included on the exterior of first ring  100  are bosses  1001   a,b,c , which correspond respectively with recessed slots  91   a,b,c  respectively in peripheral adapter ring  90 . Referring also to the bottom view of first ring  100  shown in  FIG. 6B , bosses  1001   a  have two holes each corresponding respectively to holes  99   a,b  in recesses  91   a ; bosses  1001   b  do not have holes, and bosses  1001   c  have single holes  1019   c  correspond respectively to holes  99   c . First ring  100  fits within peripheral adapter ring  90 . The fit of bosses  1001   a,b,c  within their respective recesses  91   a,b,c  provides initial alignment of the two parts. Alignment pins (not shown) fitted for example between holes  99   b  and  1019   b  provide precise alignment between the two. The alignment pins may be fitted permanently to either holes  99   b  or  1019   b . The alignment pins are short, coming into play after first ring  100  has been partially inserted into peripheral adapter ring  90 . Holes  99   a  and  99   c  are threaded to receive mounting screws which are passed through holes  1019   a  and  1019   c  respectively to secure first ring  100  to peripheral adapter ring  909 . 
         [0052]    First ring  100  contains a plurality of fastener holes  106  which pass entirely through it in a direction parallel to the central axis and are available to help secure interface unit  5  to a peripheral. Threaded screw receiving holes  1016  are provided to receive screws for attaching a hinge assembly  50  (see  FIG. 3 ) to first ring  100 . On the top major surface of first ring  100  there are a plurality of alignment pins  104  and pins  108 . Pins  104  are alignment pins that serve to align second ring  120  with first ring  100 ; and spring-loaded plunger pins  104  are spring loaded plungers which serve to bias second ring  120  in position when the unit is partially closed. Along the interior surface described by interior cylinder  101 A there is attached a plurality of guide cam followers  102  which have a cylindrical shape. The axes of guide cam followers  102  are radially aligned toward the central axis of first ring  100  and are generally uniformly spaced about first ring  100 . Finally, there is shown a compression handle pin slot  103  formed in the top major surface of first ring  100 . 
         [0053]    Shown in  FIG. 6B  is a bottom view of first ring  100  shown  FIG. 6A . The bottom view shows that the axes of guide cam followers  102  are radially aligned toward the central axis of first ring  100  and that fastener holes  106  pass completely through the walls of first ring  100  from the top major surface of first ring  100  to the bottom major surface. 
         [0054]    An embodiment of the present invention comprises a compression unit.  FIGS. 7A to 7C  illustrate various views of compression ring  110 , which exemplifies the compression unit. Referring now to  FIG. 7A  there is shown a perspective view of compression ring  110  which has a generally cylindrical shape with a central axis  119  and top surface  111 . The plane of surface  111  is preferably perpendicular to the central axis of the cylinder defining compression ring  110 . For purposes of the following discussion, “up” is considered to be in a direction indicated by arrow  119   a  along central axis  119 . Attached to top surface  111  by screws  112 A is a compression handle  112  with a compression handle pin  113 . Within the wall of compression ring  110  is a plurality of guide cam slots  114 , which generally form an arc referenced from the central axis of compression ring  110 . Guide cam slots  114  are parallel to top surface  111 . Also included within the wall of compression ring  110  is at least one camming slot  115  which comprises a second camming surface  116 , and at least one first camming surface  118 . Second camming surface  116  makes a smooth connection with first camming surface  118  which slopes up away from camming slot  115  toward top surface  111  of compression ring  110 . The end of camming slot  115  where first camming surface  118  meets second camming surface  116  is open. Additionally, first camming surface  118  extends above top surface  111 . Camming slot  115  is not entirely parallel to surface  111 . Proceeding from the point where surface  116  meets surface  118 , camming slot  115  first slopes away from surface  111 ; near the closed end of slot  115 , slot  115  changes from being sloped to being parallel to surface  111 . 
         [0055]    The slopes of camming surfaces  116  and  118  in the radial direction from axis  119  are of interest. First we define “alpha” as the angle between the plane defined by surface  111  and the slope of either camming surface  116  or camming surface  118  in the radial direction. Then for camming surface  116 , alpha is zero everywhere; that is, camming surface  116  is everywhere parallel to surface  111 . However, the slope of camming surface  118  in the radial direction varies along its circumferential length so that camming surface  118  is in effect “twisted.” For camming surface  118 , alpha is zero at the point where it meets camming surface  116 . Proceeding along the length of camming surface  118  from where it meets camming surface  116  to its uppermost point, the magnitude of alpha monotonically increases. At all points of non-zero alpha camming surface  118  is tilted downwards and away from the inside of compression ring  110 . 
         [0056]      FIG. 7B  shows a side view of compression ring  110 . As is illustrated, first camming surface  118  slopes up from second camming surface  116  toward top surface  111  and extends beyond. Guide cam slot  114  is substantially parallel to top surface  111 . In an exemplary embodiment, second camming surface  118  and camming slot  115  are not parallel to top surface  111  but slope down away from the connection with first camming surface  118 , as previously described. 
         [0057]      FIG. 7C  shows another side view of compression ring  110 , illustrating the various slopes of first camming surface  118 , second camming surface  116 , and camming slot  115 . Also shown is guide cam slot  114  which has top and bottom surfaces generally parallel to top surface  111 . 
         [0058]    Depicted in  FIGS. 8A through 8C  are different views of second ring  120 .  FIG. 8A  is a perspective view of second ring  120  which has a generally cylindrical shape with a central axis. The interior portion of second ring  120  is described by a lower interior cylinder  124  and an upper interior cylinder  126  which has a larger diameter than lower interior cylinder  124  to form edge  125 . Attached to an outer surface of second ring  120  is a plurality of cam followers  122  which have a generally cylindrical shape and are aligned so that their cylindrical axes are approximately radial to the central axis of second ring  120 . The cylindrical portions of cam followers  122  freely rotate about their cylindrical axes. Also rigidly attached to an outer surface of second ring  120  is a handle  128 . Upper cam follower  52  and lower cam follower  53 , both of which have generally cylindrical shapes, are attached to a protruding portion of second ring  120  opposite handle  128 . Also included are guide block slots  129  to provide alignment with module housing  130 , which is described later. 
         [0059]      FIG. 8B  is a side view of second ring  120  and shows the placements of cam followers  122 , upper cam follower  52 , and lower cam follower  53 . Cam followers  122  are secured to an exterior surface of second ring  120  near the bottom major surface. Upper cam follower  52  and lower cam follower  53  are mounted to second ring  120  on a side opposite from where handle  128  is mounted as was previously described. 
         [0060]      FIG. 8C  illustrates a bottom perspective view of second ring  120 . From this view, four cam followers  122  can be seen. Fewer or more cam followers are contemplated. A bottom surface of second ring  120  also contains at least one alignment hole  129 . 
         [0061]    More detailed views of camming surface  118  are described with reference to  FIGS. 9A through 9F .  FIG. 9A  indicates four cross sections A-A, B-B, C-C, and D-D which are taken of camming surface  118 . Each of the four cross sections is defined by a plane that includes central axis  119 . Furthermore, the twisted configuration of camming surface  118  is more clearly shown in  FIG. 9B .  FIG. 9C  is a sectional view of compression ring  110  taken at section A-A. The portion of compression ring  110  shown in the figure is the inside curved section of compression ring  110 , which is also shown in  FIG. 9A . Camming surface  118  interplays with cam follower  122 , which is also shown placed against camming surface  118  at the position where the axis of its cylinder of cam follower  122  is in the plane defined by section A-A. As shown in  FIG. 9C , cam follower  122  is tilted so that the rotation axis of cam follower  122  is parallel with the top surface of camming surface  118 , and so that the cylindrical surface of cam follower is tangent to camming surface  118 . Thus, the cylindrical axis of cam follower  122  is at the previously defined angle alpha  117 . 
         [0062]    Next, in a similar manner,  FIG. 9D  illustrates camming surface  118  and cam follower  122  at cross section B-B. Compared to  FIG. 9C , in  FIG. 9D , camming surface  118  is lower than it appears in  FIG. 9C  and angle alpha  117  is smaller. Note, however, that the cylindrical axis of cam follower  122  is still substantially parallel with surface  118 .  FIG. 9E  similarly illustrates camming surface  118  and cam follower  122  at cross section C-C. In  FIG. 9E , camming surface  118  is still lower than it appears in  FIG. 9D , and angle alpha  117  is still smaller. Again, the cylindrical axis of cam follower  122  is parallel to camming surface  118 . Finally,  FIG. 9F  similarly illustrates camming surface  118  and cam follower  122  at cross section D-D. In  FIG. 9F , camming surface  118  is shown at the point where it meets camming surface  116 . The cylindrical axis of cam follower  122  is shown parallel with camming surface  116 , and the angle alpha  117  has become essentially zero. 
         [0063]    Thus, as cam follower  122  has moved along camming surface  118 , the cylindrical axis of cam follower  122  has changed its angle while, at the same time, staying parallel first with camming surface  118  and then camming surface  116 . This configuration reduces wear on camming surface  118  and cam follower  122 . 
         [0064]    Shown in  FIGS. 10A to 10C  are various views of module housing  130 . Shown in  FIG. 10A  is a perspective view of module housing  130  which has a generally cylindrical shape. Located within the cylindrical wall of module housing  130  is at least one module opening  134  which passes completely through from a first surface to a second surface (referred to hereinafter as “top” and “bottom” respectively). At least one spring-loaded alignment pin  136  is rigidly attached to a bottom surface of the ring. Spring-loaded alignment pin  136  is provided to provide alignment with the probe card or DUT board as the unit is closed. Not visible in  FIG. 10A  but shown in  FIG. 10B  is a second spring-loaded alignment pin  138  of a different diameter than that of pin  136 . Located around module opening  134  are a plurality of screw holes  133 A and module alignment pins  133 B. Mounting wings  130   a  protruding from module housing  130  provide a number of mounting holes for various purposes. Relatively large holes  131   a  are used for screws to secure module housing  130  to second ring  120 . Others are used to secure guide blocks  135 , which fit within guide slots  129  in second ring  120 , and to allow guide pins  136  to protrude through second ring  120  for the purpose aligning module housing  130  with second ring  120  as required for specific applications. 
         [0065]      FIG. 10B  shows a side view of module housing  130 . Spring-loaded alignment pins  136  and  138  extend down vertically from a bottom surface of the ring. Alignment pins of different sizes are used to ensure that the probe card or DUT board is inserted in only one orientation.  FIG. 10C  shows another perspective view of module housing  130  similar to  FIG. 10A . 
         [0066]    Returning to  FIG. 3 , an explanation is now made of the manner in which assembled signal delivery system  5  is assembled. In an exemplary embodiment, signal module  132  is inserted through module opening  134  of module housing  130 . A module alignment pin  133 B is aligned with a module alignment hole  132 B (not shown) of the signal module  132  to guarantee proper insertion and alignment. Screw  132 A (not shown) is inserted into screw hole  133 A to secure signal module  132  to module housing  130 . In the embodiment shown in  FIG. 3 , module housing  139  has 16 module openings  134 , and can therefore contain as many as 16 signal modules  132 . Signal modules  132  can be manufactured in a range of types to provide for different numbers and patterns of electrical connections as well as different electrical and transmission line characteristics. Indeed, custom signal modules can often be designed for specific applications. All signal modules of all types are contained in housings which are of the same shape and form factor. Thus, the interface unit can be configured for different application by removing selected signal modules from a previous application and inserting different signal modules for a new application. Depending upon the application, module housing  130  may or may not be fully populated with signal modules. In place of a signal module, a dummy module described below may be used. The dummy module may lack electrical connection. The dummy module may be configured to produce the same compressive force as a signal module. Thus, the interface is easily and modularly reconfigurable. The components that comprise second signal unit  34  are now described. Module housing  130  is partially disposed within an interior opening of second ring  120 , described by upper interior cylinder  126 , and rests upon edge  125 . Guide blocks  135  and guide block slots  129  are used to properly align the two components. The two are secured by screws which pass through holes  131   a  in wings  130   a  of module housing  130  threaded into threaded holes  121  in second ring  120 . The assembly of module housing  130  and second ring  120  comprises second signal unit  34  (shown in  FIG. 1 ). 
         [0067]    The components that comprise first signal unit  32  are now described. Compression ring  110  is rotatably disposed within an opening of first ring  100 . Guide cam followers  102  which are attached to first ring  100  extend into corresponding guide cam slot  114  of compression ring  110  to prevent compression ring  110  from moving axially up or down within the opening of first ring  100 . The interplay between guide cam followers  102  and guide cam slots  114  also restricts the rotational movement of compression ring  110  to angular distances defined by the length of the arc traversed by guide cam slot  114 . Because guide cam slots  114  are horizontal, their interplay with cam followers  102  maintains surface  111  of compression ring  110  in a horizontal plane. 
         [0068]    Probe card tray  80  is secured to the bottom surface of first ring  100  by screws, which pass through fastener holes  106  of first ring  100  and engage screw holes  88  in probe card tray  80 . Alignment pins  84  guarantee a proper angular orientation between first ring  100  and probe card tray  80 . 
         [0069]    Probe card or DUT board  40 , rests on a support annulus  86  of probe card tray  80  and is secured thereto. Probe card alignment pins  82  of probe card tray  80  are inserted into alignment holes  42  to assure proper angular and rectilinear alignment between probe card tray  80  and probe card or DUT board  40 . Thus, the alignments of first ring  100  to probe card tray  80  and probe card tray  80  to probe card or DUT board  40  assure that the conductive pads on probe card or DUT board  40  will make proper contact with signal module  132 . 
         [0070]    As illustrated in  FIG. 11 , probe card or DUT board  40  can be inserted or removed from interface unit  5  when it is in an open position without need for any disassembly or reassembly of the rest of the unit. The probe card or DUT board may or may not be secured to probe card tray  80  depending upon the application. Generally, if the peripheral is a wafer prober, then the interface is secured to the top of the peripheral, and probe card  40  may be held in place by gravity. On the other hand, if the peripheral is of another type, then the interface could be secured vertically, at an angle, or in a reversed position on a bottom surface of the peripheral, In such cases probe card or DUT board  40  may be secured using screws. Alternatively, clips or other quick change device that are well known could be used to facilitate rapid changeover. 
         [0071]    Finally, first ring  100  is disposed within an opening of prober adapter ring  90  and support edge  101 D rests upon edge  97 . The two rings are aligned and attached as previously described. The assembly of compression ring  110 , first ring  100 , probe card  40 , and probe card tray  80 , and prober adapter ring  80  comprises first signal unit  32  (shown in  FIG. 1 ). 
         [0072]    The pivot members are now described.  FIG. 12 . is a rear, partially-cut-away, perspective view of pivot assembly  50  which couples first signal unit  32  with second signal unit  34 .  FIGS. 13A-13E  are partial cut-away side views of signal delivery system  5  showing pivot assembly  50  in greater detail and in various positions so that its structure and operation may be explained. Pivot assembly  50  is comprised of an upper cam follower  52 , a lower cam follower  53 , a pivot block  54 , a pivot support plate  56 , and a channel  58 . Ends of pivot block  54  and pivot support plate  56  have been cut away to reveal upper cam follower  52 , lower cam follower  53 , and channel  58 , all of which are not normally exposed as shown. It is seen that upper cam follower  52  is of larger diameter than lower cam follower  53 . The linear portion of channel  58  is slightly wider than the diameter of upper cam follower  52  and 50% to 100% wider than the diameter of lower cam follower  53 . 
         [0073]    A detailed description of the pivotal motion and linear motion of signal delivery system  5  is now provided. These figures may be viewed in order from  FIG. 13A  to  FIG. 13E  to illustrate movement of second signal unit  34  toward first signal unit  32 . Alternatively, these figures may be viewed in reverse order to illustrate movement of second signal unit  34  moving away from first signal unit  32 . 
         [0074]    Beginning with  FIG. 13A , there is shown a cut-away side view of signal delivery system  5  with ends of pivot block  54  and pivot support plate  56  cut away to expose upper cam follower  52 , lower cam follower  53 , and channel  58 .  FIG. 12A  shows signal delivery system  5  in its maximally open position in which second ring unit  34  is at its greatest angular distance from first ring unit  32 . In the open position, upper cam follower  52  is in a top region of channel  58 , and lower cam follower  53  is at a left side of channel  58 . As can be seen, the top of channel  58  contains a curved recess into which upper cam follower  52  nestles when signal delivery system  5  is maximally open. Thus, a substantial portion of the wall of upper cam follower  52  may be in contact with the wall surface of channel  58 . The curved recess is primarily for manufacturing convenience; other shapes such as a squared opening will provide the same operation as will be described below. It is only necessary that channel  58  has a closed end which will contain upper cam follower  52 . Also in the open position, lower cam follower  53  is located in a middle region of channel  58  and is in contact with a left wall of channel  58 . Strut  31  is maximally extended (or minimally compressed) in this open position. Angle  72  is the angle between the top surface of first ring  100  and the bottom surface of second ring  120  and is at a maximum as shown. The value of angle  72  is established by the contacts of upper cam follower  52  and lower cam follower  53  with channel  58 . Because angle  72  is at a maximum for the present illustration, upper cam follower  52  is nestled in an upper recess of channel  58 , and lower cam follower  53  is in contact with a left surface of a midsection of channel  58 . A force which tends to increase angle  72  presses upper cam follower  52  against the upper recess of channel  58  and presses lower cam follower  53  against the left wall. 
         [0075]      FIG. 13B  depicts a decrease in angle  72  as second signal unit  34  is pivoted towards to first signal unit  32 . As angle  72  decreases from its value in  FIG. 13A  to its value in  FIG. 13B , second signal unit  34  and lower cam follower  53  pivot about the central axis of upper cam follower  52 , and lower cam follower  53  ceases contact with and moves away from the left surface of channel  58 . As the pivoting progresses, lower cam follower  53  pivots until it makes contact with a right surface of channel  58 . During the motion between the stages shown in  FIGS. 13A and 13B , upper cam follower  52  remains nestled in the upper recess of channel  58  and rotates about its own axis. 
         [0076]      FIG. 13C  shows a further decrease in angle  72 . During the motion between the stages shown in  FIGS. 13B and 13C , upper cam follower  52  leaves its nestling position in the upper recess of channel  58  and skims along the top curve of channel  58 . The movement of upper cam follower  52  has a pivotal component as the axis of upper cam follower  52  pivots about the axis of lower cam follower  53 . Lower cam follower  53  also moves, both rotationally and linearly. The rotational movement of lower cam follower  53  is the result of upper cam follower  52  leaving its nestling position, which causes lower cam follower  53  to rotate about its axis. The linear motion of lower cam follower  53  is the result of upper cam follower  52  skimming along the curved upper surface of channel  58  and being pushed closer to the bottom of channel  58  to cause the central axis of lower cam follower  53  to move linearly toward the bottom of channel  58 . 
         [0077]    Referring now to  FIG. 13D , there is shown the next stage of the closing of second signal unit  34  against first signal unit  32 . Angle  72  is now approximately zero degrees as the two units are substantially parallel to one another. Between the stage shown in  FIG. 13C  and the stage in  FIG. 13D , upper cam follower  52  and lower cam follower  53  generally move down channel  58 . Lower cam follower  53  remains in contact with the right surface of channel  58  as it moves linearly downward. Upper cam follower  52  moves from the curved upper surface to the left surface of channel  58  and remains in contact with channel  58  during this movement. The shape of the curved upper surface of channel  58  causes upper cam follower  52  to pivot about the central axis of lower cam follower  53  and to move linearly closer to the bottom of channel  58 . The pivotal component of the motion of upper cam follower  52  causes lower cam follower  53  to rotate about its axis. At the stage shown in  FIG. 13D , lower cam follower  53  is now pressed against the right surface of channel  58 , and upper cam  52  is pressed against the left surface. 
         [0078]      FIG. 13E  shows the final stage in the progress of upper cam follower  52  and lower cam follower  53 . As in  FIG. 13D , angle  72  remains zero degrees. In the movement from the stage shown in  FIG. 13D  to that shown in  FIG. 13E , second signal unit  34  moves linearly closer to first signal unit  32 , and upper cam follower  52  and lower cam follower  53  move linearly closer to the bottom of channel  58 . Upper cam follower  52 , whose diameter is only slightly less than the width of channel  58 , essentially maintains contact with the left and right surfaces of channel  58 , and lower cam  53  maintains contact with the right surface. Signal delivery system  5  is shown in its maximally closed position in which second signal unit  34  is closed and locked against first signal unit  32 . Upper cam follower  52  rests now in the middle region of channel  58  in contact with a left wall and a right wall of channel  58 . Lower cam follower  53  is now in contact with the right wall of channel  58  in a lower region of channel  58 . Strut  31  is minimally extended (or maximally compressed) in this closed position. 
         [0079]    Closing and opening of signal delivery system  5  by an operator is now illustrated. When signal delivery system  5  is open, an operator grasps handle  128  and applies a generally downward force to pivot second signal unit  34  toward first signal unit  32 . As second signal unit  34  is pivoted toward first signal unit  32 , cam follower  122  comes into contact with first camming surface  118  and is drawn down along first camming surface  118  as pivoting continues. Because the axis of cam follower  122  is fixed, as it is drawn along first camming surface  118 , compression ring  110  rotates. Cam follower  122  is cylindrical in shape, and the side of the cylinder contacts camming surface  118 . Recall that it was previously explained that camming surface  118  is “twisted.” In particular the slope of camming surface  118  makes an angle alpha  117  with respect to a plane which is orthogonal to axis  119 ; and, furthermore, angle alpha  117  varies at different positions along camming surface  118 . Simply put, at all positions where cam follower  122  is in contact with camming surface  118 , angle alpha  117  has been designed to be equal to the corresponding angle  172 . In this way the contact between camming surface  118  and cam follower  122  is always a line along the side of cam follower  122  that is parallel to the axis of cam follower  122 . This reduces wear in comparison to a situation where the contact between the two is a point on the edge a camming surface  118 , which will eventually deform and detract from smooth operation. 
         [0080]    Pivoting continues until spring-loaded alignment pins  136  and  138  make contact with probe card or DUT board  40  in first signal unit  32  and spring-loaded pins  108  make contact with second ring  120 . At this point, compression ring has been rotated to a position where cam follower  122  is near camming slot  115 , and alignment pins  104  have entered alignment holes  129  to maintain alignment between first signal unit  32  and second signal unit  34  as signal delivery system  5  is further closed. First signal unit  32  is now supported against second signal unit  34  by spring pins  136  and spring-loaded pins  108 , and angle  72  is approximately zero degrees. 
         [0081]    The user then grasps compression handle  112  and rotates it to move camming slot  115  to accept cam follower  122 . As camming slot  115  is moved to accept cam follower  122 , the sloped upper surface of camming slot  115  presses cam follower  122  toward the bottom of compression ring  110 , and second signal unit  34  is pulled toward first signal unit  32  linearly until compression handle pin  113  engages compression handle pin slot  103 . The signal delivery system  5  is now fully closed and locked. 
         [0082]    An opening of signal delivery system  5  in which second signal unit  34  moves away from first signal unit  32  is accomplished by a reverse process of the closing of signal delivery system  5 , as discussed above. When signal delivery system  5  is closed, an operator grasps handle  128  and compression handle  112  and releases compression handle pin  113  from compression handle pin slot  103 . While applying a downward force on handle  128 , the user then rotates compression handle  112  to move camming slot  115  to eject cam follower  122 . As camming slot  115  is moved to eject cam follower  122 , the sloped upper surface of camming slot  115  pushes cam follower  122  toward the top of compression ring  110 . Second signal unit  34  is pushed away from first signal unit  32  linearly until cam follower  122  leaves camming slot  115 . At this point, first signal unit  32  is supported by spring pins  136  and spring-loaded pins  44  against second signal unit  34 , and angle  72  is approximately zero degrees. 
         [0083]    While continuing the rotation of compression ring  110 , the user allows second signal unit  34  to pivot away from first signal unit  32 , assisted by struts  31 . The user controls the assent of second signal unit  34  by applying downward or upward forces to handle  128 . Movement continues until signal delivery system  5  is fully open. 
         [0084]    As described above, the motions between first signal unit  32  and second signal unit  34  are assisted and constrained by pivot assembly  50 . Specifically, as signal delivery system  5  starts to close from a fully-open position, shown in  FIG. 13A , the shape of channel  58  and the contacts of upper cam follower  52  and lower cam follower  53  with surfaces of channel  58  restrict motion between first signal unit  32  and second signal unit  34  to pivotal motion. As the signal delivery system  5  nears a fully-closed position, shown in  FIG. 12D , the shape of channel  58  and the contacts of upper cam follower  52  and lower cam follower  53  with surfaces of channel  58  restrict motion between first signal unit  32  and second signal unit  34  to linear motion until signal delivery system  5  is fully-closed, as shown in  FIG. 13E . 
         [0085]    The linear motion in the final stage of closure of signal delivery system subjects spring-loaded pins  132 C to compression forces and virtually no bending or sheer forces, which as described above, are damaging to such pins over time. The present invention, by virtually eliminating the bending and sheer forces applied to pins  132 C, minimizes damage to pins  132 C. 
         [0086]    As previously explained, second signal unit  34  includes second ring  120 , module housing  130 , and at least one signal module  132 . The previous figures have shown module housing  130  completely populated with a plurality of signal modules. It is understood, however, that there may be some testing configurations where module housing  130  is not completely populated with signal modules. 
         [0087]    When a signal module  132  is in place and interface unit  5  is in its closed position, the signal module  132  provides pressure upon probe card  40  as a result of the force provided by spring loaded (i.e., pogo) pins. Without a signal module in place, the pressure normally applied by the spring-loaded pins of a signal module to probe card  40  is eliminated or reduced to zero. This will result in an imbalance about module housing  130 ; i.e., the pressure applied across the entire surface of probe card  40  that normally comes in contact with the signal modulesis undesireably not uniform. 
         [0088]    To address the above problem, it is desirable to have a dummy module in the location where a signal module is not installed. A perspective drawing of dummy module  210  is shown in  FIG. 14 . Dummy module  210  includes base unit  220 . A plurality of springs  252  are situated between base unit  220  and pressure plate  230 . Springs  252  are situated in holes with chamfered surfaces  250 . Pressure plate  230  includes protruding members  232 . Retaining plate  240  is situated above pressure plate  230 . Retaining plate  240  includes wells  244  in which are inserted shoulder screws  246 . Shoulder screws  246  extend through pressure plate  230  and into base unit  220 . Retaining plate mounting holes  242  and  248  are also included. Dummy module  210  is secured to module housing  130  by inserting screws into, for example, signal unit mounting holes  242  and  248  and engaging them with screw holes  133 A in module housing  130 . 
         [0089]    An exploded perspective view of dummy module  210  is shown in  FIG. 15 . Base unit  220  includes openings  251  with chamfered surfaces  250 . Springs  252  are inserted into openings  251 . Springs  252  are also inserted into pressure plate  230  through openings (not shown). Pressure plate  230  includes protruding members  232 . Protruding members  232  extend through openings  260  formed in retaining plate  240 . Shoulder screws  246  extend through openings in retaining plate  240 , through further openings in pressure plate  230  and are secured into base unit  220 . 
         [0090]    As previously explained, dummy module  210  is used in place of signal module  132  in second signal unit  34 . Springs  252  are chosen so that dummy module  220  provides an amount of pressure substantially equal, for example, to that which is provided by signal module  132 , thus desirably delivering a more uniform and balanced force around module housing  130  and across the surface area of probe card  40  which normally comes in contact with an interface. 
         [0091]    While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.