Abstract:
A method and apparatus for testing through the connector of a circuit card. The apparatus includes a block, which may be tapered, to offset the force applied when engaging the connector. The block is adjustably mounted to accommodate testing of different-sized circuit cards.

Description:
This application is a divisional of U.S. Pat. application Ser. No. 08/963,235, filed on Nov. 3, 1997, which has been allowed. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to a method and apparatus for preventing lateral motion of a circuit card. More specifically, this invention relates to a method and apparatus for supporting a circuit card while testing through a connector on the circuit card. 
     BACKGROUND OF THE INVENTION 
     Circuit cards are often tested to ensure that the circuitry within the card and the components on the card are present and functional. If a circuit card includes a connector, it is desirable to also test the connector. If a circuit card is tested without testing the connector the circuit card may successfully pass the test while not having the connector installed or while having a non-functional connector installed. 
     Circuit cards can be tested using a test fixture  100  as shown in FIG. 1, for example. The test fixture  100  includes a first plate  110  having locating pins  112 ,  114 . The locating pins  112 ,  114  are located corresponding to the location of apertures in a circuit card  120 . The locating pins  112 ,  114  are used to properly position the circuit card  120 . The circuit card  120  shown in FIG. 1 is aligned in the test fixture  100  with the locating pins  112 ,  114  protruding through the apertures of the circuit card  120 . 
     A probe block  130  including probes  116  is attached to the first plate  110 . A backer gate  140  includes probes  142  and posts  144 . The probes  142 ,  116  contact the circuit card  120  to test components on the circuit card  120  or the circuitry of the circuit card  120 . Each probe  142 ,  116  contacts a designated signal on the circuit card  120 . The posts  144  prevent the force of the probes  116  of the probe block  130  from bowing the circuit card  120 . 
     Circuit cards  120  often include connectors  150  mounted on the circuit cards  120  as shown in FIG.  1 . The probes  142 ,  116  can be used to test components on or the circuitry of the circuit card  120  but will not test the connector  150 . To test the connector  150 , a side access unit  160  engages the connector  150  with side probes  162 . When the side probes  162  engage the connector  150 , the side probes assert a force in the “A” direction upon the connector  150 . Because the connector  150  is mounted on the circuit card  120 , the force in the “A” direction is applied indirectly to the circuit card  120 . 
     The number of side probes  162  needed to conduct a test increases as the number of connectors  150  on a circuit card  120  increases and as the number of pins on a connector  150  increases. The force in the “A” direction increases as the number of side probes  162  used to interconnect with the connector  150  increases. 
     The lateral motion of the circuit card  120  due to the force applied by the side probes  162  is opposed by the locating pins  112 ,  114  which are used to position the circuit card  120 . As the number of side probes  162  increases, however, the force may become excessive and the locating pins  112 ,  114  may bend or the apertures in the circuit card  120  may elongate, thus allowing the circuit card  120  to move laterally. This results in damaged locating pins  112 ,  114  or a damaged circuit card  120 . If the probes  142 ,  116  were in contact with the circuit card  120  when the side probes  162  caused the circuit card  120  to move laterally, the probes  142 ,  116  may also be bent and damaged. 
     In addition to costs resulting from the damage to the locating pins  112 ,  114 , to the probes  116 ,  142 , and to the circuit card  120 , lateral movement of the circuit card  120  will result in the circuit card  120  being incorrectly positioned. The probes  116 ,  142  are located to contact signals on the circuit card  120 . Successful contact with the signals on the circuit card  120  depends on the circuit card  120  being in a desired location. When the circuit card  120  is incorrectly positioned, the probes  116 ,  142  may not contact their designated signals on the circuit card  120 . The probes  116 ,  142  may contact an incorrect signal or no signal. This may result in a test failure of a circuit card  120  that is properly functional or result in test failures that are erroneously attributed to a misaligned circuit card  120 . 
     An edge block  170  as shown in FIG. 1 may be used to offset the force in the “A” direction applied by the side probes  162 . The use of an edge block  170  is effective when the distance “B”, which is the length of the circuit card  120  that extends past the locating pin  114 , equals the distance between the locating pin  114  and the edge block  170 . Due to manufacturing tolerances, however, the distance “B” on circuit cards  120  is inconsistent. The distance “B” typically varies by ±0.51 mm (±20 mils). 
     If the distance “B” is less than the distance from the locating pin  114  to the edge block  170 , the force in the “A” direction will not be offset by the edge block  170  until the locating pins  112 ,  114  have bent or the apertures in the circuit card  120  have elongated. If the distance “B” is greater than the distance from the locating pin  114  to the edge block  170 , the circuit card  120  will not fit on the first plate  110 . 
     To overcome the shortcomings of conventional circuit card testing, a new test apparatus is provided. An object of the present invention is to provide an apparatus for preventing the lateral movement of a circuit card. A related object is to provide an improved test apparatus for testing circuit cards by preventing lateral motion of the circuit card during testing. Another object of the present invention is to prevent lateral motion of a circuit card during testing when the location of the end of the circuit card is variable. 
     SUMMARY OF THE INVENTION 
     To achieve these and other objects, and in view of its purposes, the present invention provides an apparatus that opposes the lateral movement of a circuit card. Lateral movement of the circuit card is prevented by engaging an end of the circuit card. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
     FIG. 1 is a conventional circuit card testing apparatus; 
     FIG. 2A is a sectional view of a first exemplary embodiment according to the present invention; 
     FIG. 2B is a top view of a variation of the present invention incorporating the exemplary embodiment shown in FIG. 2A; 
     FIG. 3 is a sectional view of a second exemplary embodiment according to the present invention; 
     FIG. 4 is a sectional view of a third exemplary embodiment according to the present invention in a first position; and 
     FIG. 5 is a sectional view of the third exemplary embodiment, shown in FIG. 4, in a second position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawing, wherein like reference numerals refer to like elements throughout, FIG. 2 shows a test system according to a first exemplary embodiment of the invention. In FIG. 2, the present invention is implemented in an apparatus  200  for testing a circuit card  120 . The apparatus  200  opposes lateral motion of a circuit card  120  by engaging an end  222  of the circuit card  120 . The end  222  of the circuit card  120  is engaged by a card block  230 . The card block  230  is adjustably mounted to a first plate  210 . The card block  230  can be adjustably mounted using a spring  232 , for example. 
     For testing a circuit card  120 , the circuit card is placed upon the first plate  210  with apertures in the circuit card  120  aligned with the locating pins  112 ,  114  of the first plate  210 . The backer gate (or second plate)  140  is lowered to a position above the circuit card  120  as shown in FIG.  2 . The probes  142 ,  116  contact the circuit card  120  for testing components or circuitry of the circuit card  120 . The posts  144  contact the circuit card  120  to prevent the circuit card  120  from bowing due to upward pressure of the probes  116  of the probe block  130 . 
     When the side probes  162  of the side access unit  160  interconnect with the connector  150 , the bolt  234  is released to allow the spring  232  to drive the card block  230  into the end  222  of the circuit card  120 . Thus, the force in the “A” direction exerted by the side probes  162  to interconnect with the connector  150  is opposed by the card block  230  asserting an opposing force against the edge  222  of the circuit card  120 . By balancing the force exerted by the card block  230  and the force exerted by the side probes  162 , the locating pins  112 ,  114  and probes  142 ,  116  are not damaged and the probes  142 ,  116  contact the circuit board  120  at desired locations. Because the card block  230  is adjustably mounted, the card block  230  can be used to engage the end  222  of the circuit card  120  even if the distance “B” from the locating pin  114  to the end  222  of the circuit card  120  varies. 
     The number and type of connectors  150  mounted on a circuit board  120  may vary. As the number of connectors  150  increases or the number of pins per connector  150  increases, the number of side probes  162  required will also increase. This results in an increased force in the “A” direction upon the circuit card  120 . To compensate for changes in the force exerted by the side probes  162 , the spring  232  may be changed or its tension adjusted. 
     As shown in FIG. 2B, multiple adjustable card blocks  230  may be used to compensate for differences in the force exerted by the side probes  162  between different circuit cards  120 . When the force exerted by the side probes  162  decreases, the bolts  234  of a decreased number of card blocks  230  will be released. When the force exerted by the side probes  162  increases, the bolts  234  of an increased number of card blocks  230  will be released. The force exerted by one or more card blocks  230  is adjusted to closely match the force exerted by the side probes  162 . Thus the force on the locating pins  112 ,  114  is minimized to prevent damage to the locating pins  112 ,  114 , the probes  142 ,  116 , or to the circuit card  120 . 
     Another exemplary embodiment of the present invention is shown in FIG.  3 . The apparatus  300  includes a card block  330  that opposes the lateral motion of the circuit card  120  by engaging the end  322  of the circuit card  120 . For testing a circuit card  120 , the circuit card is placed upon the first plate  310  with apertures in the circuit card  120  aligned with the locating pins  112 ,  114  of the first plate  310 . The backer gate  340  is lowered to a position above the circuit card  120  until the tapered side  331  of the card block  330  engages the end  322  of the circuit card  120 . The first plate  310  has a cavity  335  into which the card block  330  is inserted. The probes  142 ,  116  contact the circuit card  120  for testing components or circuitry of the circuit card  120 . The posts  144  contact the circuit card  120  to prevent the circuit card  120  from bowing due to upward pressure of the probes  116  of the probe block  130 . 
     When the side probes  162  of the side access unit  160  interconnect with the connector  150 , the force in the “A” direction exerted by the side probes  162  to interconnect with the connector  150  is opposed by the card block  330 . The card block  330  prevents lateral motion of the circuit card  120  in the “A” direction and prevents the force exerted by the side probes  162  from damaging the locating pins  112 ,  114  or the probes  142 ,  116 . 
     Another exemplary embodiment of the present invention is shown in FIG.  4 . The apparatus  400  includes a card block  430  that opposes the lateral motion of the circuit card  120  by engaging the end  422  of the circuit card  120 . The card block  430  is adjustably mounted on the bottom  442  of the backer gate  440  by a bolt  434  and a spring  433 . The spring  433  pushes the block  430  downward away from the backer gate  440  and toward the first plate  410 . 
     The card block  430  has a first side  431  and a second side  432 . The second side  432  is tapered and opposite the first side  431 . When the backer gate  440  is lowered to a position above the first plate  410 , the card block  430  enters a cavity  435  in the first plate  410  until the second side  432  of the card block  430  engages the end  422  of the circuit card  120 . The backer gate  440  is lowered to its desired position above the first plate  410  and the tension of the spring  433  maintains the position of the card block  430 . Preferably, the first side  431  of the card block  430  is adjacent the sidewall  436  of the cavity  435 , and the sidewall  436  may support the card block  430  laterally in opposing a force in the “A” direction. 
     The card block  430  as shown in FIG. 4 has reached the bottom of the cavity  435 . The depth and width of the cavity  435  and the size and taper of the card block  430  are designed so the bottom of the card block  430  will only reach the bottom of the cavity  435  when the distance “B” of the circuit card  120  is a minimum. 
     As shown in FIG. 5, as the distance “B” increases, the extent to which the card block  430  extends into the cavity  435  decreases. The depth and width of the cavity  435  and the size and taper of the card block  430  are designed so the top of the card block  430  is not adjacent the bottom of the backer gate  440  unless the distance “B” is at a maximum as shown in FIG.  5 . 
     The present invention allows testing of circuit cards without lateral motion of the circuit cards. This can be implemented with existing probe blocks and minor modifications to the top plate and to the backer gate of a testing system. The application of the present invention is not limited to preventing lateral motion of circuit cards of a single product type. 
     The present invention is also not limited to blocking the end of a circuit card. The end or edge of a component on the circuit card can be blocked. For example, the end of a connector may be blocked to oppose the force exerted by side probes interconnecting with the connector. Blocking a component such as a connector must be done carefully to avoid damaging the soldered connections of the connector to the circuit card. 
     The present invention has been described above with regard to preventing the lateral motion of a circuit card in a single direction. The teachings of this invention can be applied to oppose lateral forces in multiple directions upon a circuit card. This may be necessary, for example, when a circuit card has connectors mounted on more than one end of the circuit card. 
     Although illustrated and described herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention. The present invention has been described as implemented for preventing lateral motion of a circuit card during testing. The applications of the present invention are not limited, however, to circuit card testing.