Abstract:
A load board feeder is secured to the center portion of a test head. The load board feeder uses a lift mechanism to control the movement of a locator block in vertical directions. A load board rests on the locator block and a location device on the locator block ensures alignment of the load board with a test head. When the load board feeder lowers the load board, the load board is properly seated on the test head without damaging delicate pogo pins.

Description:
FIELD OF THE INVENTION 
     The present invention relates to load boards for testing integrated circuits, and particularly to mounting a load board onto a test head. 
     DESCRIPTION OF RELATED ART 
     A test head and a load board are used to test the functionality of newly manufactured integrated circuits. The integrated circuits to be tested are connected to a load board prior to testing. The test head provides power and controls the flow of electricity to the integrated circuits attached to the load board  325  (FIG. 9) during testing. As seen in FIG. 3, a test head  310  may be circular in shape and have an aperture through the middle. Channel cards  315  are arranged around the circumference of the interior aperture  312  and contain pogo pins  320  on the upper surface of the channel cards  315 . As seen in FIG. 12, pogo pins  320  are spring loaded pins, for example the pin portion  322  is able to recede into the spring containing portion  324 , that provide electrical contact between the test head channel cards  315  and the load board  325  via slots  326  on the underside of the load board  325 . 
     Load boards are electromechanical printed circuit boards used for testing the functionality of integrated circuits. A load board is latched onto a test head, and therefore, must be properly aligned with the test head so that the pogo pins  320  correctly contact the load board. Proper alignment ensures electrical contact between the test head channel cards  315  and the load board  325  so that the test head fully conducts testing of the integrated circuits. A schematic depiction of a load board  325  in electrical contact with the pogo pins  320  of a test card  315  that is connected to a test head  310  is provided in FIG. 13. A slot  326  on the underside of the load board  325  is depicted as the contact point between the pogo pins  320  and the load board  325 . 
     Load boards are normally manually positioned onto test heads, leading to several concerns. Manually positioning a load board onto a test head makes it difficult to properly align the load board with the test head, which may result in improper contact of the pogo pins  320  with the load board  325 . As a result, load boards are often shifted or adjusted after initial manual positioning in order to align the load board with the test head. However, the pogo pins  320  that the load board is already in contact with are spring loaded, and therefore, easily bent or broken. A damaged pogo pin  320  requires replacement of the channel card  315  that the damaged pogo pin  320  is part of, each channel card normally being very expensive. Replacing a channel card  315  also leads to test head down time, which delays production and causes additional expense. 
     SUMMARY OF THE INVENTION 
     There is a need to prevent bent and broken pogo pins on a test head channel card related to testing integrated circuits. There is also a need to ensure that load boards are properly aligned with test heads. These needs and others are addressed by the present invention, which provides alignment of the load board with the test head, and an automated system for positioning the load board onto the test head. According to the present invention, a load board feeder is installed into the center aperture of a test head. The load board feeder has a location device that engages the load board when the load board is properly aligned with the test head. The load board feeder also comprises a mechanism for lowering the load board into its seating place on the test head, without a damaging impact to the pogo pins on the test head channel cards. This mechanism prevents undue damage to the delicate pogo pins on the test head channel cards that may occur during manual positioning and alignment of the load board. 
     Accordingly, one aspect of the invention relates to a load board feeder for positioning a load board onto a test head that has an aperture through its center. The load board feeder comprises a base and a body connected to the base. An attachment device is connected to the body and is used to attach the load board feeder to the test head. A lift mechanism is connected to the base and vertically moves a block that is attached to the lift mechanism. The block contains the load board location device and serves as a resting place for the load board prior to positioning the load board onto the test head. 
     In certain embodiments, the load board feeder is cylindrically shaped, and contains a load board location device on a circular block. The load board location device comprises a circular plate attached to the block and a disk that engages the block and the plate. The circular block has a circular cavity that is not concentric with the center of the block. Likewise, the circular plate has a non-concentric, circular hole that aligns with the circular cavity in the block. The outer diameter of the circular disk is just small enough to allow the circular disk to fit within the circular hole and cavity. The top of the circular disk protrudes above the top of the plate, thereby providing an engagement element for a load board. 
     Accordingly, another aspect of the invention relates to a method of seating a load board onto a test head having an aperture through its center. A load board feeder, comprising a lift mechanism and a location device for aligning a load board with a test head, is attached within the center aperture of a test head. The load board feeder is brought to its raised position and a load board is placed onto the load board feeder. The load board is adjusted so that it engages the load board location device. The load board is aligned with the test head when the load board engages the load board location device. The lift mechanism is activated to lower the load board into its seating position on the test head and the load board is latched to the test head. 
     Other advantages of the present invention will become readily apparent from the following detailed description, simply by way of illustration of the best mode contemplated of carrying out the invention. The invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are illustrative in nature, not restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
     FIG. 1 depicts an embodiment of a load board feeder of the present invention. 
     FIG. 2 depicts an exploded view of the load board feeder depicted in FIG.  1 . 
     FIG. 3 depicts a test head utilized with the embodiment of a load board feeder shown in FIG.  1 . 
     FIG. 4 depicts air hoses for the load board feeder shown in FIG. 1 passing through the center aperture of the test head shown in FIG.  3 . 
     FIG. 5 depicts the load board feeder shown in FIG. 1 positioned for insertion into the center aperture of the test head shown in FIG.  3 . 
     FIG. 6 depicts the load board feeder shown in FIG. 1 inserted into the center aperture of the test head shown in FIG.  3  and attached to the center ring of the test head shown in FIG.  3 . 
     FIG. 7 depicts a load board stiffener (without a load board for clarity) properly seated on the load board feeder depicted in FIG.  6 . 
     FIG. 8 depicts a bottom view of a load board attached to a load board stiffener containing a central insert placed in the load board stiffener. 
     FIG. 9 depicts the load board attached to the load board stiffener as shown in FIG. 8 seated on the load board feeder depicted in FIG.  6 . 
     FIG. 10 depicts the embodiment of a load board feeder shown in FIG. 1 in the up position. 
     FIG. 11 depicts the embodiment of a load board feeder shown in FIG. 1 in the down position. 
     FIG. 12 depicts pogo pins clear of the load board when the embodiment of a load board feeder shown in FIG. 10 is in the up position. 
     FIG. 13 depicts pogo pins contacting the load board when the embodiment of a load board feeder shown in FIG. 11 is in the down position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An apparatus for aligning and seating a load board onto a test head in a testing arrangement for testing integrated circuits is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
     FIG. 1 depicts an embodiment of a load board feeder according to the present invention. The load board feeder allows a load board to be properly aligned with a test head before the load board is positioned onto the test head. The load board feeder also mechanically lowers the load board onto the test head. By aligning and mechanically lowering the load board onto the test head, the load board feeder prevents the delicate pogo pins of the channel cards from becoming bent or broken, as is common when a load board is manually positioned onto a test head. 
     Assembly of an Embodiment of the Invention 
     Referring to FIGS. 1 and 2, components and assemblage of an embodiment of the present invention are described. A top ring  10 , used to attach the load board feeder  200  to a test head, has fastening apertures  11  and pillar fastening apertures  13  therethrough. The fastening apertures  11  and the pillar fastening apertures  13  are counter sunk to allow the top of a flat head screw to lie flush with the surface of the top ring  10 . 
     Pins  15  are inserted into pin apertures  12 , for example by using a press fit, in the underside of the top ring  10 . When the load board feeder  200  is attached to a test head  310  (FIG.  3 ), the pins  15  align with pin holes (not shown in FIG. 3) in the center ring  300  surrounding the center aperture  312 . The pins  15  are not equally spaced around the circumference of the top ring  10 , thus ensuring that the load board feeder is properly aligned with the test head  310  when the pins  15  are aligned with the pin holes. 
     Base plate pillars  20  serve as a body for the load board feeder. The present invention is not limited to pillars for a body, as other mechanical elements connecting the base plate  70  and the top ring  10  provide the same function. For example, a cylinder with a cut-out for an air tube  109  is employed in certain embodiments instead of the pillars  20 . The base plate pillars  20  are attached, for example, to a base plate  70  via threaded studs  72 . Each end of a base plate pillar contains a threaded stud aperture  71 , of which one receives a threaded stud  72 , thus joining the base plate pillar  20  to the base plate  70 . The opposing end of the base plate pillar  20  rests against the underside of the top ring  10 . A pillar fastening aperture  13  through the top ring  10  permits a screw to fasten the top ring  10  to the base plate pillar  20  via a threaded stud aperture  71 . The pillar fastening apertures  13  are counter sunk to allow the top of a flat head screw to lie flush with the surface of the top ring  10 . 
     The load board feeder base plate  70  provides a platform for attaching the base plate pillars  20 , and a pneumatic jig cylinder  45 . Slide bushings  65  and block guide shafts  60  are also attached to the base plate  70 . For example, the pneumatic jig cylinder  45  is fastened via screws  74  that protrude through apertures  73  in the base plate  70 . Also by way of example, the slide bushings  65  have flanges  66  at one end. The slide bushings  65  protrude through apertures  64  so that the flanges  66  contact the underside of base plate  70 , and the slide bushing  65  passes through the base plate  70 . Screws (not shown) through the flange  66  fasten the slide bushings  65  to the base plate  70 . 
     Guide shafts  60  pass through the slide bushings  65 . Each guide shaft  60  has a stop  80  attached to a guide shaft end to prevent the guide shaft  60  from becoming disconnected from the base plate  70 . For example, the stops  80  could be welded or fastened by screws to the end of the guide shafts  60 . 
     A load board locator block  40 , is attached to the pneumatic jig cylinder  45 . For example, the locator block  40  could be welded to the pneumatic jig cylinder  45 , or the end of the pneumatic jig  45  could be threaded and received by a threaded aperture in the bottom of the locator block  40 . The load board locator block  40  has at least a circular cavity  41  in its upper surface. A locating disk  50  is configured to fit within the cavity  41  on the upper surface of the load board locator block  40 . 
     A load board locator plate  30  is fastened to the upper surface of the load board locator block  40 , and contains an aperture  31  therethrough that allows the locating disk  50 , placed in the cavity  41 , to pass through the load board locator plate  30 . There can be a press fit between the locating disk  50  and the aperture  31  and/or the cavity  41 , but the present invention does not require a press fit. The locator plate  30  is fastened, for example, by screws that are counter-sunk to lie flush with the surface of the locator plate  30 . The locator plate  30  protects the locator block  40  from wear. 
     Load board locator block guide shafts  60  freely slide through the slide bushings  65 , and are attached to the underside of the load board locator block  40  by welds, threads, or other attachment. The locator block guide shafts  60  work with the slide bushings  65  to provide smooth movement of the locator block  40  when the pneumatic jig cylinder  45  moves the locator block  40 . The guide shaft stoppers  80 , attached to the ends of the load board locator block guide shafts  60 , prevent the pneumatic jig cylinder  45  from raising the load board locator block  40  too far above the load board feeder base plate  70 . 
     Preferably, the above components are made from aluminum so that the weight of the load board feeder is kept to a minimum and heat generated by the test head does not adversely affect the load board feeder. However, the present invention is not limited to aluminum as a construction material. 
     A control box  90  houses a mechanical air switch control  95 . Air control valves  100  are attached to the mechanical air switch  95  and provide control of pressurized air for operation of the pneumatic jig cylinder  45 . A tube fitting  105  controls the pressurized air supply to the mechanical air switch  95 . Two tube fittings  110  provide pressurized air into and out of the pneumatic jig cylinder  45 . The tube fittings  110  are connected to the air controllers  100  by air supply tubes  109 . 
     Test Head Configuration 
     The test head described is a M973 Teradyne Tester Test Head which has a hollow center, however, any test head having a hollow center may be used with the present invention. The test head  310  depicted in FIG. 3 has a circular aperture  312  through the test head center. The upper surface of the aperture  312  forms a ring  300 . As shown in FIG. 3, the inner portion of the center ring  300  has been removed, i.e., by milling, leaving a lip  306 . The lip  306  assists centering the load board feeder  200  by surrounding top ring  10  when the load board feeder  200  is seated onto the test head  310 , however, the lip  306  is not necessary. Apertures  305  drilled into the center ring  300  are threaded so as to provide a place for fasteners, for example screws, to fasten the load board feeder  200  via top ring  10  to the test head  310 . Other methods, for example, riveting or welding, could also be used to attach the load board feeder  200 , via top ring  10 , to the test head  310 . 
     The test head  310  also contains channel cards  315  that are used to control testing of load boards. Pogo pins  320  on top of the channel cards  315  provide electrical contact between the channel cards, and therefore the test head, and a load board  325  (FIG.  9 ). Supports  302  ensure the rigidity of the test head  310 . 
     Seating and Fastening an Embodiment of a Load Board Feeder into a Configured Test Head 
     FIG. 4 depicts an initial stage of seating the load board feeder  200  shown in FIGS. 1 and 2 into a configured test head  310  shown in FIG.  3 . Air hoses  109  are fed from the underside of test head  310  through the center aperture  312  before being connected to the pneumatic jig cylinder  45 . As shown in FIG. 4, the load board feeder  200  is seated into the test head  310  from above the test head  310 . 
     FIG. 5 depicts aligning the load board feeder  200  with the center aperture  312  in the test head  310 . As shown in FIG. 5, the circumference of the base plate  70  is small enough to pass through the center aperture  312  of the test head  310 , therefore allowing the body of the load board feeder  200 , i.e., base plate pillars  20 , pneumatic jig cylinder  45 , and block guide shafts  60 , to pass through the center aperture  312 . However, the circumference of top ring  10  fits just within the lip  306  (FIG. 3) and rests on the center ring  300  of the test head  310 . Therefore, top ring  10  prevents the load board feeder  200  from passing completely through the center aperture  312  in the test head  310 . 
     FIG. 6 depicts the top ring  10  of the load board feeder  200  seated on center ring  300  of the test head  310 . Pins  15  in the underside of the top ring  10  match with pin holes (not shown) in the top of center ring  300  when the load board feeder  200  is properly aligned with the test head  310 . Screws pass through fastening apertures  11  in the top ring  10  and into threaded apertures  305  in the center ring  300 , securing the load board feeder  200  to the test head  310 . The top of the load board feeder  200  is substantially parallel with the tops of the channel cards  315 . When in the up position, as depicted in FIG. 6, the top of the load board feeder  200 , i.e., the locator plate  30 , is above the tops of the channel cards  315  and the pogo pins  320  protruding therefrom. Having the top of the load board feeder  200  above the pogo pins  320  ensures that when a load board  325  (FIG. 9) is mounted onto the load board feeder  200  there is no contact between the load board  325  and the pogo pins  320 , as depicted in FIG.  12 . 
     Mounting a Load Board onto an Embodiment of a Load Board Feeder 
     For clarity, FIG. 7 depicts a load board stiffener  400 , without a load board  325 , mounted onto the load board feeder  200 . Before mounting the load board stiffener  400  onto the load board feeder  200 , a stiffener insert  410  is attached in the center of the load board stiffener  400 . For example, the tolerance between the stiffener insert  410  and the inner opening of the load board stiffener  400  creates a press fit; or the stiffener insert  410  is held in place via screws or like fasteners; or welding, etc. It is relatively unimportant whether the stiffener insert  410  lies in the same plane as the top of the load board stiffener  400 , or is below the top of the load board stiffener  400  and co-planar, as long as the top of the load board stiffener  400  and the stiffener insert  410  are substantially parallel. A substantially parallel relationship between the load board stiffener  400  and the stiffener insert  410  ensures that when the stiffener insert  410  flatly contacts, i.e., is not tilted, the locator plate  30 , then the top of the load board stiffener  400  (and the load board  325  which is attached to the top of the load board stiffener  400 ) is substantially parallel with the top of the load board feeder  200 . When the load board stiffener  400  is mounted onto the load board feeder  200 , the load board stiffener  400  is placed so that the stiffener insert  410  rests upon the load board locator plate  30 . Then, the load board stiffener  400  is gently rotated until the locating disk  50  engages a locating aperture  420  in the stiffener insert  410 . The stiffener insert  410  flatly contacts the locator plate  30 , and is properly aligned with the test head  310 . 
     The under-side of a load board stiffener  400  is shown in FIG. 8 with a load board  325  attached to the top-side of the load board stiffener  400 . The load board  325  is viewed between the rigid struts  402  of the load board stiffener  400 , and shows that the underside of the load board  325  contains a plurality of slots  326 , each adapted to receive a channel card  315  and its associated pogo pins  320 . An insert  410  is attached to the center of the load board stiffener  400  as described previously. The insert  410  allows the load board stiffener to rest upon the locator plate  30  (FIG.  6 ). An aperture  420  in the insert  410  is dimensioned to receive the locating disc  50 . The load board  325  is fastened to the load board stiffener  400  in a predetermined manner so that when the locating disc  50  engages the aperture  420  the load board  325  is properly aligned with the test head  310 . The load board  325  is fastened to the load board stiffener  400 , for example, by screws or like fasteners. When the load board stiffener  400  with a load board  325  attached, as shown in FIG. 8, is mounted on the load board feeder  200 , in the same manner as shown in FIG. 7, the load board  325  is automatically properly aligned with the test head  310 . 
     An example of a load board stiffener  400 , with a load board  325  attached, mounted on a load board feeder  200  (not shown) attached to a test head  310  is depicted in FIG.  9 . In FIG. 9, the load board feeder  200  is in the up position, as shown in FIG. 10, and the load board  325  does not contact the pogo pins  320 , as shown in FIG.  12 . When the load board feeder  200  is moved to the down position, as shown in FIG. 11, the load board  325  contacts the pogo pins  320 , as shown in FIG. 13, and is approximately flush with the top of the test head  310 . 
     Operation of an Embodiment of a Load Board Feeder 
     A load board  325  is attached to a load board stiffener  400  as described above. A load board feeder  200  is attached to a test head  310  as described above. The load board  325  is then mounted onto the load board feeder  200 , and as described above, is automatically aligned with the test head  310 . 
     The mechanical air switch  95  is moved to the down position thereby activating the pneumatic jig cylinder  45  which lowers the load board  325  onto the test head  310 . Block guide shafts  60  provide smooth movement of the load board  325  so there is no adverse impact when the slots  326  on the underside of the load board  325  engage the pogo pins  320  on top of the channel cards  315 . By combining proper alignment of the load board  325  to the test head  310  with smooth, controlled movement of the locator block  40 , the load board feeder  200  ensures that pogo pins  320  correctly contact the load board  325  without damaging the pogo pins  320 . 
     FIG. 11 depicts the load board feeder  200  in the fully down position. Note that in the down position, the locator plate  30  is slightly below the top ring  10 , ensuring that the load board  325  engages the pogo pins  320  (FIG. 13) and is not held out of contact with any of the pogo pins  320  by the load board feeder  200 . When the load board  325  engages the channel cards  315 , the pogo pins  320  of an individual channel card  315  contact a slot  326  on the underside of the load board  325  having receptors  327  (FIG. 12) that engage the pogo pin portion  322 . As the load board  325  is seated, the springs in portion  324  of each pogo pin  320  compress. Spring compression within pogo pin portion  324  ensures that the load board  325  contacts all of the pogo pins  320  on the various channel cards  315  within the test head  310 , even when there are minor height variations between the channel cards  315 . Once the load board  325  is seated onto the test head  310 , the load board  325  is connected to the test head  310 . For example, this connection is accomplished by pressing a latch button (not shown) on the test head  310 . 
     To remove the load board  325  from the test head  310 , the load board  325  is disconnected from the test head  310 . For example, this disconnection is accomplished by pressing a de-latch button (not shown) on the test head  310 . The mechanical air switch  95  is moved to its up position, activating the pneumatic jig cylinder  45  which raises the locator block  40 . As previously described, the block guide shafts  60  provide smooth movement of the locator block  40 . This smooth movement ensures that the pogo pins  320  are not damaged by erratic movement of the load board  325  while separating from the pogo pins  320 . 
     Thus, the load board stiffener  400  with the load board  325  attached is raised to a point where the load board  325  is no longer contacting the pogo pins  320  (FIG.  12 ). Once the load board feeder  200  has reached its fully raised position (FIG. 10) the load board stiffener  400  with the load board  325  attached is removed from the load board feeder  200 . 
     The present invention provides pre-alignment of a load board with a test head before the load board is seated onto the test head. The present invention also moves the load board in a vertical direction in a smooth and controlled manner. By pre-aligning the load board with the test head, and smoothly engaging the load board with the test head, the present invention eliminates adverse impact upon the delicate pogo pins that are part of the channel cards in the test head that provide electrical contact between the test head and load board. The present invention significantly reduces the amount of damage caused to pogo pins from manually placing a load board onto a test head and adjusting the load board to properly align it with the test head once the load board is resting on the test head. By decreasing damage to the pogo pins, the present invention increases the amount of time that a test head is used for testing integrated circuits, and greatly reduces the frequency of replacing expensive channel cards. 
     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, the invention is not limited to the enclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.