Abstract:
An interface for making blind-mate connections between a test head of an automatic test system and a device interface board (DIB) includes floating brackets that are individually and compliantly coupled to the test head. The floating brackets each include a plurality of blind-mate connectors and alignment pins for engaging alignment holes within the DIB. When the DIB is pulled down against the test head, the floating brackets can individually move in compliance with applied forces to align the blind-mate connectors with complementary connectors on the DIB.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    Not Applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         Reference to Microfiche Appendix  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    This invention relates generally to electrical interfaces for making large numbers of electrical connections simultaneously and quickly, and, more particularly, to using such electrical interfaces for making connections between different portions of an automatic system for testing electronic devices.  
         DESCRIPTION OF RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 C.F.R. 1.97 AND 1.98  
         [0006]    Automatic test equipment (ATE) for testing integrated circuits includes two principle components—a tester and a peripheral. The tester includes electronic hardware and software for exercising devices under test (“DUTs”), to ensure that the devices work properly before they are shipped to customers. The peripheral includes mechanisms for automatically transferring DUTs to a test site, in rapid succession for testing by the tester, and for transferring the DUTs away from the test site once testing is complete. By operating together, the tester and the peripheral can test large numbers of devices very quickly.  
           [0007]    At the interface between the tester and the peripheral lies a device interface board, or “DIB.” Different DIBs are generally used for testing different types of electronic devices, so DIBs are designed to be easily removable and interchangeable.  
           [0008]    In a normal testing arrangement, a DIB is attached either to the peripheral or to a portion of the tester called the “test head.” A manipulator physically positions the test head in alignment with the peripheral and causes the test head and peripheral to mechanically “dock.” The act of docking sandwiches the DIB between the test head and the peripheral and allows electrical signals to pass between the tester and DUTs for testing.  
           [0009]    Test systems generally convey electrical signals between the test head and the DIB using blind-mate connectors. As known to those skilled in the art, “blind-mate” describes a connection scheme in which two parts of a connector, such as a male part and a female part, can be mated by virtue of their positioning and alignment, generally by pressing together two separable portions of an assembly. Blind-mate connectors are often used in modular electronic systems, in areas that are enclosed or inaccessible. They are generally designed to overcome slight misalignments between their mating parts and to automatically seat themselves as their parts come together. In automatic test equipment, blind-mate pogo pins generally extend from the test head to mate with conductive pads on the DIB. In addition, blind-mate RF connectors may also extend from the test head, for mating with complementary blind-mate RF connectors on the DIB.  
           [0010]    Test systems customarily provide coarse alignment mechanisms for aligning the DIB with the test head. For example, in the Tiger test system, which is manufactured by Teradyne, Inc., of Boston, Mass., the DIB includes alignment bushings for engaging alignment pins on a peripheral. Alignment pins also extend from the test head, for engaging bushings on the peripheral. First the DIB is attached to the peripheral; then the peripheral is docked with the test head. By aligning the DIB with the peripheral and then aligning the peripheral with the test head, the DIB becomes coarsely aligned with the test head. Depending upon alignment accuracy, as well as the dimensions and tolerances of the blind-mate connectors, this coarse alignment may be adequate to ensure that the blind-mate connectors align.  
           [0011]    Increasingly, ATE manufactures are designing test heads with smaller connectors, and these connectors are being more closely spaced than before. As a result, the coarse alignment between the test head and DIB may not be adequate to ensure that the blind-mate connectors at the interface mate.  
           [0012]    One prior approach to overcoming this problem has been to provide the connectors with enough play to individually overcome misalignments. FIGS. 1 and 2 show an example of this approach. A test head includes an array  100  of connector blocks  110  for holding blind-mate connectors. The connector blocks  110  retain accurate positions, relative to the test head, using alignment pins  220  and  222 . Blind-mate pogo pins (not shown in FIG. 2) extend from holes  212  of a pin housing  214 . Blind-mate RF connectors  216  extend from individual holes  218  formed within L-shaped supports  210  of the connector blocks  110 . The holes  218  are oversized in relation to the RF connectors  216 . The extra space around each connector allows the RF connectors  216  to move and seat themselves when mating with connectors on the DIB.  
           [0013]    Although this approach works well for small misalignments, it fails when the misalignments become large in relation to the connector size and spacing. We have recognized that even highly precise alignment between the test head and the DIB does not ensure that all the connectors will align. The test head and the DIB are large assemblies constructed of many parts. Alignment errors accumulate across these large assemblies and between their constituent parts to misalign the connectors. What is needed, therefore, is a better way of aligning blind-mate connectors to account for these and other misalignments.  
         BRIEF SUMMARY OF THE INVENTION  
         [0014]    With the foregoing background in mind, it is an object of the invention to align blind mate connectors at an interface between different portions of a test system.  
           [0015]    To achieve the foregoing object, as well as other objectives and advantages, an interface for making blind-mate connections between a first portion of a test system and a second portion of a test system includes a plurality of floating brackets individually and compliantly coupled to the first portion of the test system. Blind-mate connectors are attached to each floating bracket, for mating with complementary blind-mate connectors attached to the second portion of the test system. In compliance with applied mating forces, the floating brackets are individually moveable with respect to the first portion of the test system, for aligning and mating the blind-mate connectors of the first portion of the test system with the blind-mate connectors of the second portion of the test system.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]    Additional objects, advantages, and novel features of the invention will become apparent from a consideration of the ensuing description and drawings, in which— 
         [0017]    [0017]FIG. 1 is an isometric view of an array of blind-mate connectors used in a test head of an automatic test system, according the prior art;  
         [0018]    [0018]FIG. 2 is an isometric view of a single connector block from the array of FIG. 1;  
         [0019]    [0019]FIG. 3 is an isometric view of a connector block in accordance with the invention;  
         [0020]    [0020]FIG. 4 is an exploded, isometric view of the connector block of FIG. 3;  
         [0021]    [0021]FIG. 5 is an isometric view of a mating block, for use on a DIB, for mating with the connector block of FIGS. 4 and 5; and  
         [0022]    [0022]FIG. 6 is an isometric view of a device interface board (DIB), and a portion of an array of blind-mate connectors with which the DIB mates.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    [0023]FIGS. 3 and 4 show a connector block  300  in accordance with the invention. The connector block  300  is similar in many respects to the connector block  110  of FIG. 2, and preferably can be used in place of the connector block  110 . Like the connector block  110 , the connector block  300  has an L-shaped support  310 , a pogo-pin housing  214  (pins not shown), and alignment pins  320  and  322  for aligning the connector block  110  within the test head. The manner of providing RF connectors on connector block  300  differs markedly, however, from the manner of providing them on the connector block  110 .  
         [0024]    In contrast with the prior connector block  110 , wherein the RF connectors  216  are mounted to the support  210 , the RF connectors  316  of the connector block  300  are instead mounted to a floating bracket  312 . The floating bracket  312  is compliantly mounted to the support  310  of the connector block  300  via cylindrical fasteners, such as screws  318   a  and  318   b . The screws  318   a  and  318   b  pass through holes  412  in the floating bracket  312 . The screw  318   a  preferably extends into a hole  424  of the support and is captured within a threaded portion thereof (not shown). The screw  318   b  preferably extends through the support  310 , where it is captured in a threaded region of another component (not shown) below the support.  
         [0025]    Preferably, the screws also pass through shoulder washers  410  disposed within the holes  412 . The shoulder washers  410  have an inner diameter that is approximately 3 mm larger than the diameters of the necks of the screws  318   a  and  318   b . This mismatch in diameter allows the floating bracket  312  to move along a horizontal plane relative to the support  310  through a substantial range of compliance. Four springs  422  are disposed within holes  424  of the support  310  to bias the floating bracket  312  in an upper position relative to the support  310 . Two of these springs are preferably positioned concentrically around the screws  318   a  and  318   b , and two are positioned around pins  414 . The pins  414  reside within holes  424 , where they keep the springs vertically oriented. The screws  318   a  and  318   b  respectively have shoulders  318   c  and  318   d  that abut corresponding shoulders (not shown) within the holes  424 , to define bottom-most positions to which the screws can be advanced. With the screws  318   a  and  318   b  advanced to these bottom-most positions, the floating bracket  312  can be made to move through a vertical compliance range on the springs  422 . The springs  422  are preferably positioned and specified to provide enough upward force to overcome the insertion force of the RF connectors  316  with their counterparts on the DIB, while still allowing vertically compliant movement in response to docking forces.  
         [0026]    The floating bracket  312  is preferably made of steel, and the support  310  is preferably made of aluminum. To reduce ground loops and interference within the test system in which it is used, the floating bracket  312  is preferably electrically insulated from the support  310 . Insulating sheets  416 , preferably made of Delrin®, are placed between the floating bracket  312  and the springs  422  (Delrin® is a registered trademark of E. I. du Pont de Nemours and Company). To reduce wear on the insulating sheets, steel sheets  418  are preferably affixed to the bottoms of the insulating sheets  414  using sheets  416  of double-stick tape. Thus, the Delrin® contacts the floating bracket  312 , but the springs  422  rub against the steel. The shoulder washers  410  and the pins  414  are preferably made of insulative plastic.  
         [0027]    Unlike the prior RF connectors  216 , which are individually floated, the RF connectors  316  of the connector block  300  are floated as a group. A pair of alignment pins  314  extends from the floating bracket  312 . The alignment pins  314  are preferably steel and are press fit or screwed into the floating bracket  312 . The alignment pins  314  are positioned and arranged to engage alignment holes adjacent to mating connectors on the DIB. The alignment pins and holes have beveled or rounded ends, which allow the pins to seat themselves within the holes when the DIB is pressed against the test head. As the alignment pins seat themselves, the floating brackets compliantly move into precise alignment with the DIB, and the RF connectors  316  accurately mate.  
         [0028]    The floating brackets  312  allow for initial horizontal misalignments of approximately±1.5 mm. Individual connectors simply cannot provide this much play at the connector sizes and spacing desired. Because the RF connectors are aligned as groups, however, their misalignments can be overcome without requiring significant additional space.  
         [0029]    [0029]FIG. 5 shows an example of a mating bracket  500 . Mating brackets  500  are installed within a DIB and arranged to engage with corresponding connecting blocks  300 .  
         [0030]    Each mating bracket  500  includes a support  510  and RF connectors  514 . Alignment holes  512  are formed within the support  510  for receiving alignment pins from the corresponding floating bracket  312 .  
         [0031]    [0031]FIG. 6 shows a DIB  610  positioned above a partial array of connector blocks on a test head (and rotated to reveal its bottom surface). The DIB  610  includes a printed circuit board  612  and a stiffener  614  having a pair of internal supports  616 . The printed circuit board  612  includes conductive pads (not shown) for making contact with pogo pins extending from the connector blocks when the DIB is mated with the test head. Mating brackets  500  are mounted to the DIB  610  between the internal supports  616 . The mating brackets  500  include alignment holes  518  (see FIG. 5) for receiving alignment pins  622  extending from the internal supports  616 . They also include holes  516  for receiving screws, which fasten the mating brackets  500  to the internal supports  616 . The mating brackets  500  are thus held firmly in place, with substantially no compliance, within the DIB  610 .  
         [0032]    In the preferred embodiment, the RF connectors  316  and  514  are SSMP coaxial connectors. These connectors are available from Connecting Devices Incorporated (CDI) of Long Beach, Calif. As shown in FIG. 4, the RF connectors  316  on the connector block  300  each consist of three parts: a male cable termination  316   a ; a threaded cap  316   b ; and a female-female “bullet”  316   c . Coaxial cables (not shown) attach to bottoms of the cable terminations  316   a  and extend through holes  426  in the support  310 , where the cables connect to internal portions of the test head. The tops of the cable terminations  316   a  enter holes  428  in the floating bracket  312 . The threaded caps  316   b  are screwed to the tops of the cable terminations  316   a  to hold them firmly to the floating bracket  312 . Female-female bullets  316   c  are pressed into the tops of the threaded caps  316   b , where they make electrical contact with the male portions of the cable terminations  316   a . A lip at the outer circumference of each of the female-female bullets  316   a  engages a recessed detent (not shown) within each of the corresponding threaded caps  316   a . The detents tightly retain the bullets within the threaded caps.  
         [0033]    The RF connectors  514  on the mating bracket  500  are similar to the RF connectors  316  on the connector block  300 . They each include a male cable termination and a threaded cap (not shown separately). Significantly, however, the threaded caps of the connectors  514  do not contain interior detents. Therefore, the connectors  514  retain the bullets less strongly than do the connectors  316 , causing the bullets to remain with the test head when the test head and the DIB are separated.  
         [0034]    The floating blind-mate connection scheme described herein allows large numbers of blind-mate connectors to be aligned as groups, and thus provides a great deal of play for overcoming misalignments while requiring little additional space. This scheme allows extremely small connectors to be closely spaced while maintaining accurate alignment. This connection scheme is applicable in a number of areas. In particular, it is useful for conveying RF signals to a DIB. It is also useful for conveying high frequency digital signals, such as those used for high frequency serial testing.  
         [0035]    Alternatives  
         [0036]    Having described one embodiment, numerous alternative embodiments or variations can be made. The connection scheme described herein is presented in relation to the interface between a test head and a DIB. This is merely an example, however. The connection scheme can be used wherever different separable portions of a test system come together. At some time in the future, testers may be designed as integrated assemblies without separate test heads. In these instances, the invention could reside at the interface between the integrated tester and the DIB.  
         [0037]    The floating brackets have been described in connection with the test head rather than the DIB. This arrangement is more economical than the reverse arrangement—with the floating brackets attached to the DIB—because many different DIBs can be used with any given test system. Including the more complex hardware with the test head thus reduces overall cost. This design choice is not essential to the invention, however. Alternatively, the floating brackets could be provided on the DIBs, and the test head could employ fixed brackets. It is it also not strictly essential that the mating brackets be fixed. They could be made to float as well. Such an arrangement would be economically ill advised, however, as it would involve a duplication of complexity and expense, which could likely be avoided.  
         [0038]    As described herein, a different mating bracket is provided for each floating bracket. The invention does not require this direct correspondence, however. Alternatively, larger mating brackets could be used for engaging multiple floating brackets, or a single panel could be used for engaging all of the floating brackets.  
         [0039]    As described herein, the floating brackets include alignment pins for engaging alignment holes within the mating brackets. This could certainly be reversed, however, with the alignment pins extending from the mating brackets for engaging alignment holes within the floating brackets.  
         [0040]    The floating brackets  312  are shown and described as attaching to the supports  310  of the connector blocks using screws  318   a  and  318   b . However, fasteners other than screws could be used for attaching the floating brackets to the supports. For example, pins and E-clips could be used.  
         [0041]    Each of these alternatives and variations, as well as others, has been contemplated by the inventors and is intended to fall within the scope of the instant invention. It should be understood, therefore, that the foregoing description is by way of example, and the invention should be limited only by the spirit and scope of the appended claims.