Abstract:
A test fixture which holds multiple circuit boards in an edge-to-edge configuration for testing includes a sliding interconnect mechanism which is located between the circuit boards under test. The interconnect mechanism includes an interconnect board on which are mounted pairs of inter-wired frame connectors which mate with the connectors on each of the printed circuit boards to be tested and electrically interconnect the boards. The interconnect mechanism includes guide pins on which the interconnect mechanism slides to accurately align the frame and board connectors and an actuating mechanism to move the interconnect mechanism into position to securely mate the aligned connectors. The actuating mechanism can also be reversed to unmate the connectors and release the boards under test after the tests are completed.

Description:
FIELD OF THE INVENTION 
     This invention relates to test fixtures for electronic circuits and, more particularly, to test fixtures for simultaneously testing multiple printed circuit boards. 
     BACKGROUND OF THE INVENTION 
     Complex electronic circuits generally require extensive testing to ensure reliability and quality. This testing often involves measuring electrical parameters at selected points on the circuit board while the circuit is in operation. Modern circuit boards are often multilayered and have components and signal connections on both sides of the board so that it is necessary to have access to both sides in order to complete the testing. Because space is generally limited when circuit boards are mounted in a carrier or mounting device in the final product, it is often difficult to obtain access to the points on the circuit board necessary to complete testing. Consequently, during testing operations, circuit boards are often mounted in special test fixtures. The board can be inserted into such a fixture and temporarily held in place while power and ground are applied to the board so that the selected electrical parameters can be measured when the board is in its actual operational state. 
     In some cases, it is necessary for several boards to be tested simultaneously because the electronic circuits on each board interact with circuits on the other boards and the boards must be electrically connected together during the test procedure in order to fully test each board. Circuit boards are normally electrically connected to the remainder of the circuitry by means of connectors which establish multiple simultaneous connections. In the case of complex boards, such as mother boards, connections of the board to its normal mounting arrangement may be accomplished by several multiple connector pairs which together require a significant amount of force to mate and unmate. 
     Consequently, it is desirable to provide a test fixture in which multiple circuit boards can be inserted and electrically connected together during testing. 
     It is further desirable to provide a test fixture in which multiple circuit boards can be connected with an interconnect mechanism which can be quickly connected and released without requiring time-consuming alignment of the connector portions. 
     SUMMARY OF THE INVENTION 
     In accordance with one illustrative embodiment of the invention, a test fixture holds multiple circuit boards in an edge-to-edge configuration. A sliding interconnect mechanism is mounted on the test fixture and is located between the circuit boards under test. The interconnect mechanism includes an interconnect board on which are mounted pairs of inter-wired frame connectors which mate with the connectors on each of the printed circuit boards to be tested and electrically interconnect the boards. The interconnect mechanism includes guide pins on which the interconnect mechanism slides to accurately align the frame and board connectors and an actuating mechanism to move the interconnect mechanism into position to securely mate the aligned connectors. The actuating mechanism can also be reversed to unmate the connectors and release the boards under test after the tests are completed. 
     In accordance with one embodiment of the invention, the sliding interconnect mechanism comprises a rigid mounting plate which supports the board to insure alignment accuracy and the strength needed for multiple matings and unmatings of the frame connectors on the interconnect board with the connectors on the circuit boards under test. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective view of the interconnect mechanism showing the interconnect board and the screw mechanism. 
     FIG. 2 is an exploded diagram of the interconnect mechanism. 
     FIG. 3 is a picture of an illustrative test fixture showing the inventive interconnect mechanism mounted on the test fixture. 
     FIG. 4 is an underside view of the same test fixture illustrating in more detail how the interconnect mechanism is mounted on the test fixture. 
     FIG. 5 is a perspective view of the test fixture showing printed circuit boards under test mounted in the test fixture with peripheral boards inserted into the boards under test. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of the inventive interconnect mechanism. The interconnect mechanism comprises a circuit board  1  which contains the inter-wired frame connectors  4 - 11  that establish the electrical connections for testing purposes. Board  1  contains a number of circuit traces on its lower side (not shown) which interconnect the frame connectors  4 - 11 , that are mounted on board  1 . Alternatively, the frame connectors may be wired together with discrete wiring. The circuit board  1  is mounted on a rigid frame  2 . For example, rigid frame  2  may be comprised of metal, such as aluminum. Frame  2  supports board  1  to provide mechanical rigidity to hold the connectors in position during the mating and unmating operations. 
     As shown in FIG. 1, four male frame connectors,  4 ,  5 ,  6  and  7  are illustrated which connectors are opposed by four female frame connectors,  8 ,  9 ,  10  and  11 . This connector configuration would be used to interconnect two printed circuit boards under test that would be plugged together during normal operation conditions. Other connector configurations may also be used. The connectors  4 - 11  include conventional pins and sockets which have been omitted from FIG. 1 to clarify the figure. In addition, the female connectors  8  and  9  contain a locating pin  14  in which fits into a hole in the printed circuit board under test and aligns the frame connectors with the board connectors as the printed circuit board under test is mated with the interconnect board. A similar locating pin  16  is associated with female connectors  10  and  11 . Male connectors  4  and  5  have a hole  15  associated therewith which receives the locating pin from the female connectors (not shown) on the associated circuit board under test. A similar hole  17  also accepts a locating pin from the mating female connectors (not shown) on the circuit board under test. 
     In the connector arrangement shown in FIG. 1, the frame connectors are arranged in pairs. For example, male connector  4  has a corresponding female connector  8 . Similarly, male connector  5  has a corresponding female connector  9 . As mentioned previously, the pins and sockets in these connectors can be connected together in parallel to allow two printed circuit boards under test which would normally be plugged together to be plugged separately into the circuit board  1 . In this manner, the printed circuit boards can be tested in an edge-to-edge configuration as will be illustrated in FIG.  5 . Similarly, connectors  6  and  7  are arranged in pairs with female connectors  10  and  11 . 
     In some cases, the number of connectors, and the specific connectors used in the system, may require a substantial amount of force to mate and unmate the connectors. For example, a conventional connector used to connect two circuit boards is a model HDM connector manufactured by Teradyne of Boston, Mass. When eight of these connectors are used, as illustrated in FIG. 1, approximately 40-60 lbs. of force is required to properly mate and unmate the connectors. When the interconnect mechanism is used to connect boards having such connectors, the mating force must be equally distributed across the entire connector array in order to avoid damaging the connectors. The rigid mounting plate  2  supports the circuit board  1  to properly apply the force. 
     In order to provide for a mating of the connectors without requiring an operator to manually align the connectors, the mounting plate  2  is provided with an alignment mechanism comprising alignment posts  18 ,  19 ,  20  and  21  which slide into holes in the test fixture as will be hereinafter described. Spacers  22 ,  23 ,  24  and  25  limit the travel of the interconnection mechanism relative to the text fixture to insure proper fit with the connectors on the printed circuit boards under test. Other guide mechanisms, such as jointed arms can also be used. 
     The board  1  is can be moved relative to the text fixture by means of an actuating mechanism which includes screw  12  which can be turned by a handle  13 . Screw  12  can also be turned via a socket  12 A which receives the bit of a conventional torque driver. Screw  12  fits into a threaded hole in the test fixture, as shown in FIGS. 4 and 5, and drives the interconnect mechanism up and down to properly mate and unmate the connectors. Other actuating mechanisms, such as levers or hydraulic mechanisms can also be used. 
     FIG. 2 is an exploded diagram of the interconnection mechanism illustrated in Figure and illustrates some additional features of the interconnection mechanism. In particular, screw  12  includes a head  29  and is inserted through holes  30  and  31  of the frame  2  and circuit board  1 , respectively, such that head  29  bears against the lower surface  2 B of frame  2  and draws the frame  2  upward as the screw  12  is turned. A snap ring  27  fits into groove  28  and bears against the upper surface  2 A of frame  2  so that the frame  2  is forced downwards as the screw is reversed in order to unmate the connectors. 
     The guide posts  18 - 21  pass through holes  32 - 35  in printed circuit board  1  and through holes  36 - 39  in frame  2 . Each of the guide posts  18 - 21  has a shoulder which rests against surface  2 A of frame  2  so that each guide post can be secured to frame  2  by means of nuts  26  which engage threaded ends of guide posts  18 - 21 . Tubular spacers  22 - 25  slide over guide posts  18 - 21 , through holes  32 - 35  of printed circuit board, respectively, and rest against the upper surface  2 A of the frame  2 . Printed circuit board  1  is secured to the frame  2  by means of screws  40 , as illustrated in FIG.  2 . 
     FIG. 3 shows the inventive interconnection mechanism mounted on an illustrative test fixture. Text fixture  50  consists of a housing that includes side panels  52  and  55  which are attached to side rails  53  and  54 . Rails  53  and  54  are separated by a number of spacers  56 ,  58 ,  60 ,  62  and  64  to form a platform which supports the printed circuit boards under test. Spacers  58  and  60  contain an adjustment block  66  mounted between them which has a threaded hole that accepts the screw  12 . In addition, spacers  58  and  60  contain vertical holes in which the guide posts  18 - 21  of the interconnection board slide. Spacers  58  and  60  may also have mounting plate  68  and  70  attached thereto for attaching various holddowns, of which holddowns  72 ,  74  and  76  are shown, for temporarily fastening the printed circuit boards under test to the test fixture. As shown in FIG. 3, when the screw  12  is turned, the interconnection mechanism is drawn upward as the guide posts  18 - 22  slide into the holes in spacers  58  and  60 . This upward movement causes the connectors  4 - 11  to mate with corresponding connectors on the underside of the printed circuit boards which are held in the fixture. Consequently, the printed circuit boards are electrically connected together and can be tested as a unit. 
     FIG. 4 shows the underside of the test fixture  50  illustrated in FIG.  3 . In this arrangement, the test fixture  50  is mounted on arms  82  and  84  which are pivotally attached to stands  78  and  80 . The pivoted connection allows the test fixture  50  to be swung up so that the underside of the printed circuit boards under test can be reached easily. FIG. 4 illustrates the inventive interconnection board in its uppermost position at which point the guide posts  18 - 21  have fully slid into their holes in spacers  58  and  60  such that the tubular spacers (spacers  24  and  25  are shown) contact the undersides of the fixture spacers  58  and  60  limiting the upward travel of the interconnection board. 
     FIG. 5 illustrates the illustrative test fixture  50  with printed circuit boards  90  and  92  inserted therein. The test fixture  50  mounts on a test bed  100  which may contain additional test equipment. Each of the printed circuit boards under test  90  and  92  contains additional peripheral boards which can be plugged into connectors on the printed circuit board under test. For example, peripheral boards  96  are plugged into printed circuit board under test  90  whereas printed circuit boards  98  are plugged into printed circuit board under test  92 . In particular, boards  90  and  92  are connected by means of the inventive interconnection board so that the whole structure is then electrically interconnected and can be tested as a unit. 
     Although an exemplary embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. For example, it will be obvious to those reasonably skilled in the art that, although the description was directed to a particular hardware configuration, other hardware could be used in the same manner as that described. Other aspects, such as modifications to the specific screw mechanism and guide arrangements disclosed which achieve the same function, as well as other modifications to the inventive concept are intended to be covered by the appended claims.