Abstract:
An apparatus for processing electronic circuit devices includes an infeed station, a first inspection station, an inverter station, a second inspection station, a sorting station, and an outfeed station. A linear transport mechanism having side edges transports a first work piece containing a plurality of electronic circuit devices through the stations along a linear path. The inverter station holds an empty second work piece above the transport mechanism in an inverted orientation. The inverter station also includes an elevator for lifting the first work piece vertically into an abutting relationship with the second work piece, and an inverting mechanism for inverting the first and second work pieces while maintaining them in the abutting relationship to position the electronic devices in the second work piece in the inverted orientation. The inverter station executes the work piece inverting action while maintaining the work pieces above the linear transport mechanism and between the side edges of the linear transport mechanism. Thus, the electronic circuit devices are inspected at the first inspection station in a first orientation in the first work piece, and are inspected at the second inspection station in an inverted orientation in the second work piece.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of 35 U.S.C. §119 of co-pending provisional patent applications No. 60/052,698, filed Jul. 16, 1997 and Ser. No. 60/073,885, filed Feb. 6, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an apparatus and method for inspecting and handling devices that are semi-constrained in compartmented trays. More particularly, the invention relates to an apparatus and method for conveying devices contained in trays to and through multiple inspection and handling stations. 
     BACKGROUND OF THE INVENTION 
     Semiconductor devices such as integrated circuit chips need to be precisely fabricated since exact precision is required to insure that such devices have an exact predetermined geometry. Although such fabrication produces high quality results, defective devices are fabricated that have geometry variations in coplanarity, span and sweep as well as mark defects in content, legibility, contrast, orientation and quality, which are outside tolerances for acceptable devices. Accordingly, inspection of the devices is necessary to ascertain whether the devices meet exacting acceptance standards. The inspection stages generally include both camera and laser inspections. 
     The semiconductor devices to be inspected are typically provided in compartmented trays which have multiple rows and columns of pockets into which the devices are placed. Trays typically hold between 50 and 100 devices, and the trays are often configured to be stackable. 
     Machines of the type to which this invention relates have been used in the past. In that regard it has been proposed to cycle a tray loaded with semiconductors from an input module through intervening inspection modules and a pick-and-place module to an outfeed module, and to achieve an inversion of the semiconductors between the inspection modules. A desire in connection with such machines is ongoing to increase the speed and reliability of processing the semiconductors and to do so without complicating the structure or system. 
     Accordingly, among the objects of this invention are to improve the speed and reliability of the inspection and/or otherwise processing of such semiconductors and to do so without complicating either the machine&#39;s structure or the process. 
     SUMMARY OF THE INVENTION 
     For the achievement of these and other objects, this invention proposes to transport trays loaded with semiconductor devices through the infeed, inspection, pick-and-place (PNP) and outfeed modules, and an inverter module, along a linear path. That is, the transport moves the loaded tray in a straight line to and through the modules with the various operations being performed on the tray and the semiconductor devices carried in the tray, with the tray positioned on or in registry with that linear path. Consistent with that format, the inversion of the tray between inspection modules is accomplished by displacing the devices while in a tray vertically from the linear path, rotating the devices 180 degrees while they are still held captive in the tray, and returning the devices to the liner path, again in a tray. In executing the inversion, the inverter module is loaded with a pre-positioned empty, transfer tray which cooperates with an incoming loaded carrier tray to achieve the inversion. In the course of carrying out the inversion step, the pre-positioned tray becomes a carrier tray and exits the inverter module as a carrier tray loaded with the semiconductor devices. What had been the carrier tray remains in the inverter module and awaits arrival of a subsequent, incoming carrier tray. The tray left in the inverter module is itself rotated 180 degrees to be in the proper orientation for cooperation with the next incoming carrier tray and becomes a pre-positioned tray. 
     Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an inspection handler apparatus; 
         FIG. 2  is a plan view of a typical compartmented tray; 
         FIG. 3  is a schematic front view of the inspection handler apparatus; 
         FIG. 4  is a schematic plan view of an infeed module of the inspection handler apparatus; 
         FIG. 5  is a front elevation view of an inverter module including a tray inverter apparatus; 
         FIG. 6  is a side elevation view of the inverter module; 
         FIG. 7  is a top view of the inverter module; 
         FIG. 8  is a top view of a vertical transport assembly for the tray inverter apparatus; 
         FIG. 9  is a side view of the vertical transport assembly; 
         FIG. 10  is a top view of a tray holder shown lowered to a position on top of a pair of guide rails and engaging two device trays that are each disposed in the upside-down position; 
         FIG. 11  is a sectional view through line  11 — 11  in  FIG. 10 ; 
         FIG. 12  is a partial sectional view through line  12 — 12  in  FIG. 10 ; 
         FIG. 13  is a front elevation view of a tray holder and front guide rail in  FIG. 10 ; 
         FIG. 14  is a top view of a lever and a cam; 
         FIG. 15  is a partial sectional view through line  15 — 15  in  FIG. 14 ; 
         FIG. 16  is a partial sectional view through line  16 — 16  in  FIG. 10 ; 
         FIG. 17  is a plan view of an alternative tray inverter holder assembly embodying the invention; 
         FIG. 18  is an enlarged partial view of the tray inverter holder assembly as shown in  FIG. 17 ; 
         FIG. 19  is a sectional view taken along line  19 — 19  of  FIG. 18 ; 
         FIG. 20  is a plan view of an upper outer pawl; 
         FIG. 21  is an end view of the upper outer pawl of  FIG. 20 ; 
         FIG. 22  is a plan view of a lower outer pawl; 
         FIG. 23  is an end view of the lower outer pawl of  FIG. 22 ; 
         FIG. 24  is a plan view of a tray; 
         FIG. 25  is a sectional view taken along line  25 — 25  of 
         FIG. 24 ; and 
         FIG. 26  is a side view of two nested trays. 
       Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components or steps set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various other ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As previously mentioned, the infeed module, scanner module, package vision inspection (PVI)module, PNP module and outfeed modules can be of well-known construction and operation. For that reason, those modules have been illustrated schematically and will not be described in detail. The inverter module will be described in detail, and parts of the overall tray transport arrangement will be as well so as to define the linear path along which the trays are moved. 
     Addressing first the modules other than the inverter module, the machine  10  can be viewed as starting with an infeed module  100  and proceeding downstream from that module, there is a scanner module  200 , an inverter module  300 , a Package Vision Inspection (PVI)  400 , a pick-and-place (PNP) module  450 , and an outfeed module  500 . Associated with the PNP module is a tray module  700  and a taper module  900 , one located on each side of PNP module  450 . All of these elements are supported on a sub-base  52 . The sub-base  52  is located above a storage area  54  which houses the process and control equipment, such as a computer system for controlling the overall operation of machine  10 . The storage area  54  is protected by various access doors  56  that provide access to storage area  54 . Monitors  851  and  852  are provided for monitoring machine operation. 
     A typical tray  12  is illustrated in FIG.  2 . Trays for containing semiconductor devices include JEDEC style trays. The tray  12  has multiple columns and rows of pockets  14  into which devices are housed. Tray  12  include a first surface  16 , a second surface  18 , a first corner  20 , a second corner  22 , a third corner  24 , a fourth corner  26 , a side edge  28 , a side edge  30 , an end edge  32 , an end edge  34  and preferably notches  36  in the side edges  28  and  30 . The corner  26  is preferably slightly bevelled and is used to determine the orientation of the tray. The tray  12  is adapted to be transported through inspection handler apparatus  10  leading with end edge  32 . 
     In the tray semiconductor devices such as leaded devices are normally oriented leads down (live bug) and ball grid array (BGA) devices are normally oriented balls up (dead bug). 
     A number of the trays  12 , loaded with semiconductor devices or other types of units, are stacked at the infeed module against columns  11 . The stacked trays are supported by singulators  13 . The singulators have fingers (not shown), which are extendable from and retractable into the singulators by conventional actuators  99 . These actuators can be electrically or pneumatically operated. When a tray is to be delivered to the transport  17 , the singulator fingers are retracted and the stack lowers with the lower-most tray engaging transport  17 . Fingers  99  are again extended to engage and hold the tray which is second from the bottom and the lower-most, released tray is moved along path  42  by transport  17 . Transport  17  includes a belt  19  which carries a pusher  101  and is driven by a reversible stepper motor  21  through a belt assembly  23 . The pusher moves a tray  12  from the infeed module to the entrance or staging area for the scanner inspection module  200 . The pusher is returned to the left hand of the infeed module to await subsequent delivery of another tray  12  for transport to the scanner module. 
     Transport guide members  59  and  61  extend from the infeed module a short distance into the scanner module as does transport  17 . This cooperates in the transfer of the tray  12  from transport  17  to transport  35 . 
     While in the scanner module, laser unit  25  inspects the upper, exposed surfaces of the semiconductor devices in the tray. The laser is conventional and is moveable on both an x and y axis as illustrated by the arrows  27  and  29 , and thus is capable of traversing the entire tray to inspect all of the semiconductor devices. 
     Movement of the tray into and through the scanner module is accomplished by transport  35 , which includes a belt  103  carrying a transport mechanism  105  engageable with the underside of the tray. The belt is driven by a reversible stepper motor  31  and a pulley arrangement  33 . Transport  35  delivers the tray to inverter module  300 . Guide rails  63  and  65  in the scanner module and the inverter module, respectively, are in line and parallel and further define the linear path  42  as do transports  17  and  35 . It will be noted that two trays are illustrated as being in the scanner module at the same. This is the preferred arrangement as it reduces the overall time for processing the trays as is more completely described in U.S. Pat. No. 5,668,630 assigned to the assignee of this application. Reliance is placed on that patent should details of the scanner be necessary to an understanding of this invention. 
     The operation within the inverter module will be described hereinafter. 
     Transport  35  extends from the inverter module through the PVI module  400 , PNP module  450 , to the outfeed module  500  and transports a tray serially through those modules. Guide members  67  and  69 ,  71  and  73 ,  75  and  77 , and  79  and  81  are generally relatively aligned and parallel to each other and the linear path to further define that path. For convenience, the guide members have been illustrated as separate members in each station. As desired various of the modules may share guide members. All of the guide members associated with all of the modules, including the inverter module, can be adjustable to vary their relative spacing in a direction transverse to linear path  42  to accommodate trays of different widths. 
     In the PVI module, the surface of the semiconductor devices opposite to the surface inspected in the scanner module is inspected by a conventional camera arrangement  410 . As may be required for proper viewing of the semiconductor devices in the tray, the camera arrangement  37  is moveable vertically as illustrated by arrows  41 . It is also moveable on an x and y-axis as illustrated by arrows  39  and  43  so that the camera can traverse the entire upper exposed surfaces of all of the semiconductor devices in the tray. 
     After inspection in the PVI module is complete, the tray is transported to the PNP module  450 . The PNP module  450  includes a conventional precisor assembly  45  having a downwardly-projecting vacuum cup  49  with assembly  45  including a conventional vacuum-producing mechanism that cooperates with cup  49  to produce a lifting vacuum. 
     Assembly  45  is moveable vertically as illustrated by arrows  47  to engage a semiconductor device, remove that device from the tray and transport that device to a pre-selected area. The semiconductor devices removed can be either a “good” device or “reject” device. The assembly  45  is moveable on a y axis (indicated by arrow  51 ) to displace the unit from linear path  42 . The precisor assembly  45  can move the selected device to a tray station  700 , where it will be loaded into another tray. Alternatively, the selected unit may be moved to a taper module  900  where the selected device will be loaded into a carrier tape. When moved to the tray station, the selected unit can be either a “good” or “reject” device. When moved to the taper module, the selected unit will be a “good” device to be packaged in the carrier tape for delivery to a customer for the devices. 
     The tray station  700  may be of the type commonly used in the industry. For purposes of this application, it should be noted that carrier tape  906  is unwound from a supply reel  908  and drawn past the PNP module  450  where individual devices are placed in each compartment of the carrier tape. Downstream of that placement, a sealing tape (not shown) is adhered to and closes the open surface of the carrier tape. The closed carrier tape is wound onto a spool  912 . 
     Turning now to the inverter module, transport  170  takes a tray as it leaves the scanner module on transport  150 . Transport  170  is shown as a continuous assembly moving a tray through the inverter module, PVI module, PNP module and the outfeed module. The inverter module also includes a pair of spaced guide rails  202  and  204  arranged parallel to each other and the linear path  42 . 
     Returning to the inverter module  300 , it includes a tray inverter apparatus  302 , a base plate  303 , and a front and a rear guide rail  508  and  511  mounted on the base plate  303 . Guide rails  508  and  511  define a bay area  306  therebetween. The outfeed transport assembly  502  operates to move trays into and out of the bay area  306 . The transport assembly  502  receives a tray near a left end  307  of the guide rails  508  and  511  (i.e., from a preceding inspection module) and transports the tray to the bay area  306  where the tray inverter  302  acts on the tray. When a tray is transported to the bay area  306 , the tray rests squarely between guide rails  508  and  511  and in a lip  516  of each guide rail  508  and  511 . A slide bar assembly  392 c on front rail  511  is actuated when the tray is in position and which pushes the tray against back rail  508 . 
     Inverter module  300  is adaptable to handle an industry-standard semiconductor inverted or noninverted device tray  12  such as tray  12  depicted in FIG.  2 . The tray  12  has a generally flat, rectangular frame  13  with top and bottom faces  16  and  18 , end walls  32  and  34 , and elongated side walls  28  and  30 . Within the frame  13 , the tray  12  provides a plurality of segregated pockets  14  designed to accommodate a device of particular dimensions. Each side wall  28  and  30  is equipped with a pair of lifting notches  36  formed along the bottom edge of the side walls  32  and  30  and near the ends. The lifting notches  36  on one side wall  28  are preferably disposed to transversely match the lifting notches  36  on the opposite side wall  30 . Thus, device tray  12  may be identified as being disposed in the upside-down position when all four lifting notches  36  are facing upward. Additionally, one corner  26  of the tray  12  is bevelled such that the bevelled corner  26  is preferably positioned in the rear left corner when the device tray  12  is in the upside-down position, as shown in FIG.  10 . 
     The tray inverter includes a fixed support frame  319 , a linearly movable frame  320 , and a rotatable tray holder  321 . The tray holder  321  provides means for selectively engaging and supporting one or two trays simultaneously. Linearly movable frame  320  supports rotatable tray holder  321  while also providing a means for rotating tray holder  321  about a center axis  322  and a means for moving the tray holder  321  in the vertical direction. Preferably, inverter module  300  inverts a tray by rotating it 180 degrees and in a position located vertically above linear path  42 . That is, the tray is not moved laterally with respect to the guide rails  508  and  511  and is maintained along and/or above the linear path  42  throughout the inverting operation. The fixed support frame  319  supports the linearly movable frame  320  and various other components of the tray inverter  302 . The tray inverter  302  also includes control components that are preferably mounted adjacent the guide rails  508  and  511  or other support locations in the inspection handling apparatus  10 . 
     Referring now to  FIGS. 5 and 6 , fixed support frame  319  extends vertically from behind the rear guide rail  508  and includes a pair of vertically extending side gussets  323  and a rectangular back plate  324  fastened between the side gussets  323 . Side gussets  323  are mounted onto a frame base plate  325  located below rear guide rail  508 . A top bearing plate  326  is fastened to the top ends of side gussets  323  and back plate  324 . The top bearing plate provides a mounting surface for several components of tray inverter  302 . 
     Forward of back plate  324  and in between the side gussets  323 , a vertical screw shaft  327  is rotatably mounted onto a bearing block  328  that is mounted to the frame base plate  325 . Screw shaft  327  extends upwardly from bearing block  328  and passes through a flanged bearing  329  mounted on the underside of top bearing plate  326 . Below top bearing plate  326 , an anti-backlash, self-lubricating nut  330  is movably mounted onto screw shaft  327 . A shaft pulley  331  is mounted onto a top end of screw shaft  327 . Behind back plate  324 , a stepper motor  332  is mounted to the underside of the bearing plate  326 . The stepper motor is operably connected to a horizontally disposed drive pulley  333  located above the top bearing plate  326 . A timing belt  334  is mounted around drive pulley  333  and shaft pulley  331 . Stepper motor  332  is operable to selectively drive screw shaft  327  in either a clockwise or the counterclockwise direction, and to drive nut  330  up or down on screw shaft  327 . 
     Linearly movable frame  320  includes a lift plate  335 , a back bar  336  mounted to the lift plate  335 , and a pair of stationary arms  337  and  338  attached to right and left ends of back bar  336 . Lift plate  335  is fastened directly to the front of the  330 , and moves up and down with the  330  upon operation of stepper motor  332 . Referring to the top view of  FIG. 7 , rectangular lift plate  335  is disposed between side gussets  323 . Vertical movement of lift plate  335  is guided by a vertical transport assembly  339  comprised of four grooved wheels  340  cooperable with two V-tracks  341 . 
     Referring to  FIGS. 8 and 9 , two wheels  340  on the right as view in the drawings, are mounted for adjustment on screw operated eccentric bushings  342  that are fastened to the back of lift plate  335 , near right corners of the lift plate  335 . The other two wheels (on the left) are mounted on fixed axes and are not adjustable. V-track  341  is formed from two upright bars that are each fastened to the front of side gussets  323 . One side of the bar is cut to form an angle or “V” (as viewed from the top). The two wheels  340  on each side of lift plate  335  ride up and down on the same “V-track”  341 . 
     It should be noted that the linearly movable frame  320  described herein is adaptable to being driven by alternative motor and transmission means. For example, in alternative embodiments, the linearly movable frame  320  may be moved up and down by a pneumatic cylinder or the like, or vertically transported on vertical rails or a collar-shaft assembly. 
     Referring back to  FIGS. 5 and 6 , the back bar  336  is an elongated plate that is mounted to the front of the lift plate  335 . The back bar  336  extends in the horizontal direction across the center of the lift plate  335  and to the right and left of the lift plate  335 . A stationary arm  337  and  338  is mounted to each end of the back bar  336 . Referring to the top view of  FIG. 25 , the stationary arms  337  and  338  extend forwardly from the back bar  336 , over the rear guide rail  508 , and over a longitudinal center line  343  of the bay area  306 . 
     Referring to  FIGS. 6 and 7 , a motor mounting plate  344  is mounted to the left side of left stationary arm  337  by a linear slide assembly  345  and a center point adjustment screw  346 . Thus, motor mounting plate  344  may be fixedly secured to left stationary arm  337  by tightening center point adjustment screw  346 . Conversely, the position of motor mounting plate  344  relative to the left stationary arm  337  may be adjusted by loosening center adjustment screw  346  and sliding motor mounting plate  344  across linear slide  345 . Guided by linear slide  345 , the motor mounting plate  344  may be moved in a direction forward or rearward of the back bar  336 . 
     Referring to the side view of FIG.  6  and the top view of  FIG. 7 , the motor mounting plate  344  extends downwardly and forwardly from the back bar  336 . A horizontally disposed gear motor  347  is mounted to an upper portion of motor mounting plate  344  and operably connected to a drive pulley  348  rotatably mounted on the left side of the motor mounting plate  344  (see FIG.  6 ). Further, a left pivot bearing block  349  is fastened to a lower flange  350  of motor mounting plate  344 . The left pivot bearing block  349  rotatably supports a horizontally disposed shaft  351 . A rotate adapter  352 , a disk with a central bore, is fixedly mounted to shaft  351  on the right of left pivot bearing block  349  and a timing pulley  353  is mounted to the shaft  351  on the left of motor mounting plate  344 . The timing pulley  353  is operably connected to drive pulley  348  by a timing belt  354 . Thus, gear motor  347  is operable to rotate the rotate adapter  352  and any member securely fastened to the rotate adapter  352 , i.e., the tray holder  321 . 
     A side mounting plate  355  is similarly mounted to right stationary arm  338  by a right linear slide assembly  356  and a right center point adjustment screw  357 . A right pivot bearing block  358  is securely fastened to a lower flange  359  of the right side mounting plate  355 . Whereas left pivot bearing block  349  supports a shaft  351  with a rotate adapter  352  mounted thereon, right pivot bearing block  358  fixedly supports a horizontally disposed fixed pivot pin  360 . By utilizing linear slide assemblies  345  and  356 , the rotational axes of the rotate adapter  352  and fixed pivot pin  360  may be aligned, and the rotational axis of the tray holder  321  may be adjusted to accommodate trays of different widths. Such an adjustment of the rotational axis is typically made in conjunction with adjustment of the front guide rail  511  to modify the width and centerline  343  of the bay area  306 . In this way, the rotational axis of the tray holder will always be located directly above the linear path  42 . 
     Referring to  FIG. 10 , rotate adapter  352  and fixed pivot pin  360  are engageable with the tray holder  321  to support tray holder  321  between right and left stationary arms  337  and  338 , and directly above guide rails  508  and  511 . Generally rectangular in shape, tray holder  321  comprises four link members that bound an open inside area or tray area  361  therebetween. The four link members consists of a left side bar  362 , a right side bar  363 , a front cover plate assembly  364 , and a rear cover plate assembly  365 . At a location midway on the left side bar  362 , a dowel  366  is embedded in left side bar  362  projects horizontally outward from a cutout section  367  on the outside of left side bar  362 . Rotate adapter  352  mates with cutout section  367  and engages dowel  366 . 
     Directly across the tray area  361  from the dowel  366 , a horizontally disposed plunger  368  is seated inside the right side bar  363  and projects outward from the right side bar  363 . Fixed pivot pin  360  engages a bore of plunger  368  such that the plunger  368  is rotatable about fixed pivot pin  360  when tray holder  321  is rotated. A spring  369  attached around plunger  368  biases plunger  368  in the direction of fixed pivot pin  360 , thereby forcing tray holder  321  toward the left and ensuring a tight fit. Plunger spring  369  also facilitates removal of tray holder  321  from engagement with rotate adapter  352  and linearly movable frame  320 . 
     As illustrated in  FIG. 6 , linearly movable frame  320  is adapted to maintain tray holder  321  substantially horizontal between stationary arms  337  and  338  as linearly movable frame  320  is moved vertically over bay area  306 . Moreover, gear motor  347  is operable to rotate tray holder  321  through 360° while supported between stationary arms  337  and  338  and while supported over bay area  306 . In alternative embodiments, the rotate adapter-dowel connection and/or the fixed pivot pin-plunger connections may be replaced with other connector elements, e.g., quick lock fittings, a shaft and a sleeve secured together by a set screw, or a squared shaft and groove. 
     It should also be noted that in alternative embodiments, linearly movable frame  320  may be configured such that the rotational axis of tray holder  321  is disposed perpendicular to guide rails  508  and  511 . In this embodiment, stationary arms  337  and  338  may be replaced by a frame including rear and front support beams, e.g., a box frame, wherein rotate adapter  352  and pivot pin  360  are mounted on rear and front support beams, respectively. 
     Referring to  FIG. 10 , a vertical home photo sensor  370 , for example, a U-type photoelectric sensor, is preferably mounted on side gussets  323  facing back bar  336 . A vertical home flag  371  mounted on back bar  336  cooperates with the home photo sensor  370  to indicate when the back bar  336  is at its high or vertical home position. A similar photo sensor, referred to as a rotate home photo sensor  372 , is preferably mounted on a lower left portion of the back bar  336 . The rotate home photo sensor  372  cooperates with a vertical home flag  373  mounted on a designated corner of the tray holder  321  to determine a home rotate position for tray holder  321 . Accordingly, rotate home photo sensor  372  indicates whether a tray(s) supported within the tray holder  321  are in the upright or upside-down position. 
     The front and rear cover plate assemblies  364  and  365  of tray holder  321  are substantially identical in structure and function. Referring now only to front cover plate assembly  364 , as depicted in  FIGS. 5 through 12 , the front cover plate assembly  364  comprises a top cover plate  374  and a bottom cover plate  375 . Both cover plates  374  and  375  are equipped with two identical squared cutouts  376  that face tray area  361  (see FIG.  10 ). The squared cutouts  376  on the top cover plate  374  are vertically aligned with the squared cutouts  376  on bottom cover plate  375 . Referring to  FIG. 10 , a pair of block assemblies  382  is mounted between the top and bottom cover plates  374  and  375 , near each cutout  376 . Each block assembly  382  includes two pairs of matching lower and upper blocks  377  and  378 , or shims, that are horizontally spaced equidistantly from a vertical centerline of the cutouts  376 . A horizontally disposed middle plate  379  extends between each pair of lower and upper blocks  377  and  378 , so as to divide the space between the block assemblies  382  into a lower sleeve  380  and an upper sleeve  381 . The lower sleeve  380  is disposed below upper sleeve  381  when tray holder  321  is oriented in the home rotate position as illustrated in  FIGS. 10 and 11 . 
     Each of the four lower sleeves  380  of the tray holder  321  accommodates a lower pawl  382 , while each of the four upper sleeves  381  accommodates an upper pawl  383 . This provides four sets of clamp members C, each having two vertically spaced clamp arrangements as will be described in more detail. Referring to  FIG. 28 , each pawl  382  and  383  includes a generally flat body  382 a and  382 b that extends through the sleeve  380  and  381 . A clamp  384  and  385  is attached to the pawl body  382 a and  382 b and occupies a portion of the area defined by the cutout  376 . Each clamp  384  and  385  preferably has a leading edge or lip  384 a and  384 b that is bent in a direction away from the middle plate  379 . Each lip  384 a and  384 b facilitates engagement and disengagement with the trays. Lower pawls  382  further include a leading edge of pawl body  382 a that acts as a second clamp or inside clamp  386 . 
     Referring to  FIG. 12 , inside clamp  386  is disposed between single clamp  385  of upper pawl  383  and outside clamp  384  of lower pawls  382 . Further, two latch springs  387  disposed inside each sleeve  380  and  381  and operatively engaged with the pawl body, bias the pawl  382  and  383  inwardly such that the clamp(s) normally project into the tray area. 
     Referring to  FIGS. 10 and 31 , each pawl  382  and  383  further includes a pawl flange  388  that extends outwardly from the sleeve  380  and  381  and connects to an end of two horizontally disposed cross bar  389  and  390 . The tray holder  321  is equipped with a total of four cross bars; a pair of lower and upper cross bars  389  and  390  on the front and a second substantially identical pair of lower and upper cross bars  389  and  390  on the rear. The upper cross bars  390  are fastened to the flanges  388  of the upper pawls  383 , and the lower cross bars  389  are fastened to the flanges  388  of the lower pawls  382 . The upper cross bars  390  are disposed directly above and parallel to the lower cross bars  389 . Both cross bars  389  and  390  are disposed substantially parallel to the cover plate assembly  364 . A vertical gap is provided between upper and lower cross bars  389  and  390  (see FIG.  13 ). A horizontal gap is provided between cross bars  389  and  390  and outside of cover plate assemblies  364 . 
       FIGS. 10 and 12  illustrate the upper and lower pawls  382  and  383  engaging two trays  309  and  309 a to secure the trays  309  and  309 a within the tray holder  321 . The trays  309  and  309 a are disposed in the upside-down position, as indicated by the bevelled corner  26  of the trays  309  and  309 a being located in the rear left corner. The lifting notches  36  on each tray  309  and  309 a are facing up. The clamps  385  of upper pawls  383  engage lifting notches  36  on the top tray  309 . For lower pawls  382 , inside clamps  386  engage the lifting notches  36  of the bottom tray  309 a while outside clamps  385  engage the bottom edge of the bottom tray  309 a. 
     Proper fit of trays  309  and  309 a is also facilitated by edge guides  391  that are fastened on the inside of each side bar  362  and  363  (see FIG.  10 ). 
     Once trays  309  and  309 a are secured by respective ones the pawls  382  and  383  of the four sets of clamps, the edge guides  391  prevent lengthwise tray movement. Each edge guide  391  provides a vertically disposed face upon which end walls  32  and  34  of trays  309  and  309 a abut. 
     The edge guides  391  are preferably mounted on the side bars  362  and  363  such that the blocks face each other, as shown in  FIG. 28. A  horizontal flange portion of each guide  391  is fastened to side bar  362  and  363  by a bolt and lock washer or equivalent fastening means. Thus, guides  391  may be adjusted to accommodate a change to trays of shorter or longer lengths. 
     Referring to  FIG. 10 , a front lever  392  and a rear lever  392  are mounted to the front guide rail  511  and rear guide rail  508 , respectively. The rear and front levers  392  and associated components mounted adjacent to the rear and front guide rails  508  and  511  that respond to or impact levers  392 , are generally identical in structure and function. Accordingly, only the components associated with front lever  392  and front guide rail  511  are discussed herein. 
     Referring to  FIGS. 14 through 14 , the front lever  392  comprises a vertical section  392 a and a horizontal base  392 b that extends forward of the vertical section (in a direction away from front guide rail  511 ). A horizontally disposed slide bar  392 c is attached to the back of lever  392 , opposite horizontal base  392 b. The slide bar  392 c extends into a channel across the top of the front guide rail  511 . The slide bar  392 c is movable in the channel via a linear slide assembly  392 d interfacing the bottom of slide bar assembly  392 c and the channel. Slide bar assembly  392 c is also used to locate the tray against the back rail after the tray enters an inverted position. Further, a generally bar-shaped linear cam  393  is disposed beneath the horizontal base  392 b. The cam  393  is driveable by a pneumatic cylinder  399  along the linear path  42  generally perpendicular to the linear path of the slide bar  392 c. The cam surface of the cam  393  consists of a horizontal slot  393 a that extends diagonally with respect to the linear path of the cam  393 . A follower bearing  394  attached to the horizontal base  392 b engages the slot  393 a such that movement of the cam  393  imparts motion to the lever  392 . When the cam  393  is forced leftward by the pneumatic cylinder  399 , the cam  393  forces the lever  392  to slide away from the front guide rail  511 . When the cam  393  is retracted, the lever  392  is forced to slide forward, toward the front guide rail  511 . 
     When the tray holder  321  is brought down to engage the guide rails  508  and  511 , both levers  392  extend upwardly into the horizontal gap between the lower cross bar  389  and the lower cover plate  364 , if the tray holder  321  is in the home rotate position as in  FIG. 28 , or between the upper cross bar  390  and the upper cover plate  364  of the tray holder  321  is disposed 180° from the home rotate position. When the cam  393  is actuated, the levers  392  push the cross bars  389  outward against the resistant force of the latch springs  387  and cause the lower pawls  382  to disengage from the bottom tray. When the pneumatic cylinder  399  deactuates the cam  393 , the latch springs  387  force the lower pawls  382  and the cross bars  389  to return to their normal positions. 
     Referring to  FIGS. 5 and 10 , a sensor mounting wall  396  is disposed forward of the lever  392  and cam  393 . An upper photo sensor  397  and a lower photo sensor  398  are mounted on the sensor mounting wall  396  at different elevations, but both pointing in a horizontal direction over the front guide rail  511 . When the tray holder  321  is disposed in the low position, engaging the guide rails  508  and  511 , the lower photo sensor  398  senses the bottom tray  309 a in the tray holder  321  and the upper photo sensor  397  senses the top tray  309  in the tray holder  321 . 
     In operation, the inverter module  300  receives a filled device tray that is in the upside-down position and that supports devices, such as semiconductor devices in the dead bug position. Provided below is one example of a programmed series of stages of the inverter operation which results in the semiconductor devices being inverted, so as, for example to be supported in the live bug position. 
     Stage 1. The lift plate  335  is positioned in the vertical home position with the vertical home flag  373  engaging the vertical home photo sensor  370  and the tray holder  321  is oriented in the home rotate position with the rotate home flag  371  engaging the rotate home photo sensor  372 . The tray holder  321  engages a single empty tray by the lower pawls  382 . This is a prepositioned empty tray which awaits the arrival of a filled or carrier tray. The prepositioned tray is in the upside down position with the lifting notches  36  facing up. A second, carrier tray has been transported from the left side of the guide rails  508  and  511  to the bay area  306  and is then pushed to the back rail  508  to properly orient the tray. The filled carrier tray is also in the upside-down position, but supports semiconductor devices in the dead bug position. The lower photo sensor  398  senses that tray is disposed in the bay area  306 . 
     Stage 2. The stepper motor  332  is operated to drive the screw shaft  327  so as to lower the tray holder  321  until the prepositioned tray engages the carrier tray. The upper photo sensor  397  senses one tray above the other. The pneumatic cylinders  399  actuates the cams  393  and the levers  392  push the lower cross members  389  outward, thereby releasing the lower pawls  382  from prepositioned tray. 
     Stage 3. The tray holder  321  is lowered further to its low position, while the lower cross member  389  remain pushed outward by the levers  392 . The upper pawls  383  come to rest on the lifting notches  36  on the prepositioned tray. Then, the cams  393  are deactuated and the lower cross member  389  are released by the levers  392 . Accordingly, the lower pawls  382  spring back to engage the carrier tray, wherein the inside clamps  386  of the lower pawls  382  simultaneously engage the lifting notches  36  of the carrier tray and the bottom of the prepositioned tray. 
     Stage 4. The tray holder  321 , now securing both the prepositioned tray and the carrier tray in the upside-down positions, is raised vertically. When the vertical home flag  373  engages the vertical home photo sensor  370 , operation of the stepper motor  332  is ceased. The lift plate  335  is now in the vertical home position. 
     Stage 5. The gear motor  347  is operated to rotate the tray holder  321  through 180°, with both trays secured therein. This results in both trays being disposed in the upright position, and with the prepositioned tray disposed below the carrier tray. The tray holder  321  is no longer in the home rotate position. The semiconductor devices are now supported by the prepositioned tray and are in the live bug position. 
     Stage 6. The tray holder  321  is lowered until the prepositioned tray (now below the prior carrier tray) engages the guide rails  508  and  511 . The upper photo sensor  397  senses the upper tray. The levers  392  are actuated to push the upper cross bars  390  outward (which are now below the lower cross bars), thereby releasing the prepositioned tray. Having been previously rotated through 180°, the prepositioned tray is now disposed in the upright position and supports the semiconductor devices in the live bug position and becomes a carrier tray to move through the downstream modules. 
     Stage 7. Supporting only the empty tray by the lower pawls  382  which are now disposed above the upper pawls  383 , the tray holder  321  is raised vertically to its vertical home position. The cams  393  and the levers  392  are deactuated. Meanwhile, the new carrier tray is transported by the outfeed transport assembly  502  from the bay area  306  to the PVI module  400 . The emptied carrier tray  2  is now in the upright position and the lower pawls  382  are above the upper pawls  383 . 
     Stage 8. The gear motor  347  is operated to rotate the empties carrier tray through 180°. This results in that tray being disposed in the upside down position again and it now becomes the prepositioned tray. A subsequent, filed carrier tray is transported to the bay area  306  from the left side of the inverter module  300 . This begins a second series of stages that are identical to the first, except different trays are acted upon. 
     The above described operation describes only one application of the inverting method and apparatus of the taper module  300 . Other sequences of steps may be employed to accomplish the inversion of the devices. 
     An alternative embodiment of the holder for the tray in the inversion module is illustrated in  FIGS. 17-26 . Some of the description of that alternative will be repetitious of the previously described embodiments in order that the common features of the two will be evident. Also it will make it apparent as to how some of the features of the alternative are applicable to the previously described embodiment. 
     Referring to  FIG. 17 , a tray inverter assembly  12  embodying the invention is shown. The assembly  12  is used in conjunction with a tray inverter mechanism for inverting devices semi-constrained in compartmented trays. The assembly  12  can be used with various types of compartmented trays. 
     A typical tray  14 , similar to that previously described, for use with the assembly  12  is shown in  FIGS. 24 and 25 . The tray  14  is generally rectangular although the tray can be of varying shapes. The tray  14  has a first or top face  16  having therein a plurality of pockets  18 . The tray  14  has a second or bottom face  20  having therein a plurality of pockets  22 . The pockets  18  and  22  are preferably arranged in multiple columns and rows on their respective faces  16  and  20 . The devices can be housed in the pockets  18  or in the pockets  22 . The tray  14  includes a side edge  24 , a side edge  26 , an end edge  28 , an end edge  30 , a corner  32 , a corner  34 , a corner  36  and a corner  38 . Preferably, the corner  38  is bevelled and is used to determine the orientation of the tray  14 . As best shown in  FIG. 26 , each side edge  24  an  26  has therein two recesses or notches  40 . The tray  14  nest together with the bevelled corners  38  adjacent one another when stacked one upon another. 
     Referring back to  FIG. 1 , the assembly  12  functions to releasably secure one or two trays  14  at a time within the assembly  12  while the trays are being inverted, i.e. rotated through 180 degrees. Preferably, the assembly  12  is designed to accommodate one width of tray, i.e. the distance between the side edge  24  and the side edge  26 . However, the assembly  12  can also be constructed to be adjustable and thus enable one assembly  12  to accommodate varying widths of trays  14 . 
     With reference to  FIG. 17 , the assembly  12  has a pair of ends  42  and  44  and a pair of sides  46  and  48  and further includes a pair of generally rectangular, spaced cover plates  50  and  52  (plate  52  best shown in FIG.  19 ). The cover plates  50  and  52  defines a tray bay  54  which is an area in which one or two trays  14  are held. As shown in  FIG. 1 , the bay  54  is filled with a tray  14 . A pair of stiffener bars  56  and  58  are positioned between the cover plates  50  and  52 , with one bar  56  positioned adjacent to and generally parallel with the side  46  of the assembly  12  and the other bar  58  positioned adjacent to and generally parallel with the side  48  of the assembly  12 . Each bar  56  and  58  includes a central elongate portion  60  bounded by a pair of generally rectangular end portions  62  and  64 . 
     Four upper pawl assemblies  66 a,  66 b,  66 c and  66 d are housed between the cover plates  50  and  52 , with the two assemblies  66 a and  66 b being adjacent the bar  56  and the other two assemblies  66 c and  66 d being adjacent the bar  58 . Preferably, the four upper pawl assemblies  66 a-d are identical. The upper pawl assembly  66 a is axially aligned across the bay  54  with the upper pawl assembly  66 d and the upper pawl assembly  66 b is axially aligned across the bay  54  with the upper pawl assembly  66 c, so that the two sets of aligned upper pawl assemblies  66 a/ 66 d and  66 b/ 66 c are generally parallel to each other. 
     Likewise, two lower pawl assemblies  70 a and  70 b are housed between the bar  56  and the cover plate  52  and two lower pawl assemblies  70 c and  70 d are housed between the bar  58  and the cover plate  52 . The four lower pawl assemblies  70 a-d are partially hidden from view by the upper pawl assemblies  66 a-d in FIG.  1 . Preferably, the four lower pawl assemblies  70 a-d are identical and the lower pawl assembly  70 a is axially aligned across the bay  54  with the lower pawl assembly  70 d and the lower pawl assembly  70 b is axially aligned across the bay  54  with the lower pawl assembly  70 c, so that the two sets of aligned lower pawl assemblies  70 a/ 70 d and  70 b/ 70 c are generally parallel to each other. 
     The four lower pawl assemblies  70 a-d are oriented between the cover plates  50  and  52  so as to be vertically axially aligned with a corresponding upper pawl assembly  66 a-d, respectively. Accordingly, a pair of aligned upper and lower pawl assemblies  66 a/ 70 a,  66 b/ 70 b,  66 c/ 70 c or  66 d/ 70 d which are separated by either the bar  56  or  58  are positioned between the cover plates  50  and  52  in four locations. 
     Referring now to  FIG. 18 , one of the upper pawl assemblies  66 a is shown in enlarged detail. Since the four upper pawl assemblies  66 a-d are preferably identical, only the upper pawl assembly  66 a will be described hereafter. The upper pawl assembly  66 a includes an outer pawl  72 , an inner pawl  74 , a pair of mounting blocks  76  and  78 , a pair of outer springs  80  and  82  and an inner spring  84 . As will be explained below, the outer pawl  72  and inner pawl  74  are selectively moveable as a unit with respect to the cover plates  50  and  52  and the inner pawl  74  is selectively moveable with respect to the outer pawl  72 . Preferably, the outer springs  80  and  82  have a higher spring rate than does the inner spring  84 . 
     The mounting blocks  76  and  78  are spaced relative to each other and are positioned one block adjacent each end of the end portion  62  or  64  of the bar  56 . Each mounting block  76  and  78  has a body  86  and a flange  88 . The blocks  76  and  78  are oriented so that the flange portions  88  extend toward one another. Fasteners  90 a and  90 b extends through the cover plate  50 , through a block  76  or  78  respectively, through the bar  56 , through the mounting block  76  of the vertically adjacent lower pawl assembly  70 a, and through the cover plate  52  to hold the mounting blocks  76  and  78  and the bar  56  in a fixed position. As such, the mounting blocks  76  and  78  and bar  56  are not moveable with respect to the cover plates  50  and  52  or each other. 
     As best shown in  FIGS. 4 and 5 , the outer pawl  72  is generally U-shaped and includes a central passageway  92 , a recess  94  axially aligned with the passageway  92 , a pair of outwardly extending flanges  96  and  98 , a pair of elongate axially aligned channels  100  and  102 , an upwardly extending wall  104 , and an outwardly extending mounting tab  106 . 
     As best shown in  FIGS. 18 and 19 , the inner pawl  74  includes a shaft  108  having a first end  110 , a second end  112  and a notch or window  114  therein. A pawl extension  116  is secured to the end  110  of the shaft  108 . The extension  116  is generally rectangular, dimensioned so as to be moveable within the passageway  92 , and preferably terminates in a chamfered or sloped edge  118 . The inner pawl  74  is movably positioned within the outer pawl  72  such that the extension  116  is housed in the passageway  92  and the shaft  108  is partially housed in the recess  94  so that the end  112  of the shaft  108  is adjacent the wall  104  of the outer pawl  72 . 
     The inner pawl  74  is moveable relative to the outer pawl  72  between a first position wherein the window  114  in the shaft  108  does not align with both of the channels  100  and  102  in the outer pawl  72  so as to allow the channels  100  and  102  to communicate and a second position wherein the window  114  in the shaft  108  is aligned with the channels  100  and  102  so as to allow communication between the channels  100  and  102  across the recess  94 . 
     The inner spring  84  surrounds the shaft  108 . The inner spring  84  normally biases the inner pawl  74  so that the extension  116  extends outwardly from the passageway  92  in a direction away from the tab  106  of the outer pawl  72 . A tray guide bracket  120  is secured to the outer pawl  72  with fasteners to retain the inner pawl  74  within the passageway  92 . A pair of plates  124  are secured to the outer pawl  72  over each channel  100  and  102 . 
     Referring now to  FIG. 18 , the outer pawl  72  is positioned between the mounting blocks  76  and  78  so that the mounting tab  106  extends outwardly from the cover plates  50  and  52  in a direction away from the bay  54 . In this orientation, the flanges  88  of the blocks  76  and  78  align with a respective flange  96  or  98  on the outer pawl  72  and one of the outer springs  80  or  82  is positioned between the flange  88  of that blocks  76  or  78  and the flange  96  or  98  of that outer pawls  72 . In this position, the outer pawl  72  is moveable relative to the cover plates  50  and  52  along a path defined by the cover plate  50 , the bar  56  and the mounting blocks  76  and  78 . The outer springs  80  and  82  bias the outer pawl  72  such that the bracket  120  extends outwardly from and above the cover plate  50 . 
     As shown in  FIGS. 19 ,  22  and  23 , the four lower pawl assemblies  70 a-d are substantially identical to the upper pawl assemblies  66 a-d, however, with the following differences. The outer pawl  72  of the lower pawl assemblies  70 a-d further includes a middle bracket  126  extending outwardly from the outer pawl  72 . With respect to the inner pawl  74  of the lower pawl assemblies  70 a-d, the inner pawl  74  includes a pawl extension  116  that terminates in a rectangular end portion  130  (FIG.  3 ). 
     Referring back to  FIG. 17 , the tabs  106  of the pair of upper pawl assemblies  66 a and  66 b on the side  46  of assembly  12  are connected with a cross bar  132  that is secured to each tab  106  with a fastener. The tabs  106  of the pair of lower pawl assemblies  70 a and  70 b on the side  46  of the assembly  12  are connected with a cross bar  134  that is secured to each tab  106  with a fastener. 
     Likewise on the side  48  of the assembly  12 , the tabs  106  of the pair of upper pawl assemblies  66 c and  66 d are connected with a cross bar  136  that is secured to each tab  106  with a fastener and the tabs  106  of the pair of lower pawl assemblies  70 c and  70 d are connected with a cross bar  138  that is secured to each tab  106  with a fastener. 
     The cross bars  132 ,  134 ,  136  and  138  are adapted to be moved away from the bay  54  in the same manner as cross bars  389  and  390  are activated in the previously described embodiment to actuate movement of each outer pawl  72 /inner pawl  74  unit relative to the cover plates  50  and  52  and in a direction away from the bay  54 . Preferably, the cross bar  132  and the cross bar  134  are individually movable by a first mechanism such as an air cylinder and cam and the cross bar  136  and the cross bar  138  are individually moveable by a second mechanism such as an air cylinder and cam. It should be noted that other methods to actuate movement of the cross bars  132 ,  134 ,  136  and  138  can be utilized. 
     Continuing to refer to  FIG. 17 , the assembly  12  includes a plunger  144  between and extending outwardly from the cover plates  50  and  52  on the end  42  of the assembly  12 . A dowel  146  extends outwardly from the cover plates  50  and  52  on the end  44  of the assembly  12 . The dowel  146  and plunger  144  are axially aligned along a center pivot axis  148 . A pair of edge guides  150  extends inwardly into the bay  54 . The edge guides  150  are moveable and function to enable the assembly  12  to accommodate variations in lengths of trays  14  in the bay  54 . A mounting plate  152 a-d is mounted adjacent each of the four pairs of aligned upper and lower pawl assemblies  66 a/ 70 a,  66 b/ 70 b,  66 c/ 70 c, and  66 d/ 70 d, respectively. 
     The function of the tray inverter assembly  12  is to releasably hold one or two trays  14  at a time in the bay  54 . To accomplish this, the upper and lower pawl assemblies  66  and  70  are selectively moved so that the extensions  116  of the inner pawls  74  can be retractably housed within the notches  40  of the trays  14 . When the extensions  116  of the upper or lower pawl assemblies  66  and  70 , respectively are within the notches  40  of a tray  14 , the tray  14  can be raised, lowered or rotated with the assembly  12  without falling from the assembly  12 . 
     The tray inverter assembly  12  can be utilized in conjunction with tray inverter mechanism  302 . The assembly  12  is mounted in the tray inverter mechanism using the plunger  144  and dowel  146 . To start the cycle, the assembly  12  has secured in the bay  54  a first tray  14 . A second tray  14  is supported by a supporting surface such as guide rails and has devices in the pockets  18  of the top surface  16 . When the devices in the second tray  14  need to be flipped over, the assembly  12  with the first tray  14  secured within the bay  54  is moved (such as downwardly) by the lift/lower mechanism until the first tray  14  contacts and nests with the second tray  14  (FIG.  10 ). The extensions  116  (preferably of the lower pawl assemblies  70 a-d) that hold the first tray  14  within the assembly  12  are retracted from the four notches  40  of the first tray  14  by retracting the cross bars  134  and  138 . 
     The assembly  12  is further moved downwardly (approximately the width of one tray) such that the extensions  116  of the upper pawl assemblies  66 a-d are aligned with the four notches  40  of the first tray  14  and the extensions  116  of the lower pawl assemblies  70 a-d are aligned with the four notches  40  of the second tray  14 . The cross bars  132 ,  134 ,  136  and  138  are then released by the mechanisms such that the extensions  116  of the upper pawl assemblies  66 a-d are housed within the notches  40  of the first tray  14  and the extensions  116  of the lower pawl assemblies  70 a-d are housed within the notches  40  of the second tray  14 . The extensions  116  along with the brackets  120  and  126  will maintain the orientation of the first tray  14  relative to the second tray  14 . 
     The two nested trays  14  are then raised upwardly by the lift/lower mechanism. The rotation mechanism is then actuated to rotate the nested trays  14  through 180 degrees about the pivot axis  148 . During the rotation, the devices are transferred from the pockets  18  on the top surface  16  of the second tray  14  to the pockets  22  on the bottom surface  20  of the first tray  14 . In other words, the devices are flipped over such that the device surface that used to abut the second tray  14  is now visible and can be inspected. The rotated trays  14  are then lowered to the supporting surface by the lift/lower mechanism until the first tray  14  contacts the supporting surface. The cross bars  132  and  136  of the upper pawl assemblies  66 a-d are retracted thus releasing the first tray  14  (which now contains the devices) from the assembly  12 . 
     The assembly  12  with the second tray  14  held by the extensions  116  of the lower pawl assemblies  70 a-d is raised upwardly by the lift/lower mechanism and then rotated through 180 degrees about the pivot axis  148  by the rotation mechanism. The combination of the extensions  116 , the guide brackets  120  and the bracket  126  maintain the positioning of the second tray  14  within the bay  54  of the assembly  54  throughout the rotation. The second tray  14  must be rotated by itself to maintain the proper orientation of the assembly  12  for the next inversion cycle. The first tray  14  can then by transported to an inspection station. The process can then begin again in that the assembly  12  and second tray  12  can be lowered to contact a third tray  14  having devices therein that are to be inverted. 
     When the extensions  116  of the upper and lower pawl assemblies  66 a-d and  70 a-d, respectively are moved into the notches  40  of a tray  14 , it is important that a sensor arrangement make sure that the extensions  116  are positioned properly within the notches  40  before the tray  14  is inverted. If the tray  14  is not properly oriented and secured in the correct orientation in the bay  54  of the assembly  12 , the devices will not be transferred properly from a pocket of one tray  14  to a corresponding adjacent pocket of the nested tray  14  and may even dislodge entirely from the trays  14 . 
     With specific reference to  FIG. 17 , the tray inverter queue assembly  12  utilizes a photo-optic sensor arrangement for this purpose. It should be noted, however, that a switch arrangement or other like arrangements could also be employed in place of the photo-optics. The photo optic sensor arrangement uses light circuits to determine the positioning of the extensions. Specifically, there are four light circuits  154 a-d of which only the two light circuits  154 a and  154 b associated with the upper pawl assemblies  66 a-d are visible in FIG.  17 . 
       FIG. 17  illustrates two of the light circuits  154 a and  154 b. The first light circuit  154 a is constructed as follows. A first segment  156  of an optic conductor, such as 1 mm monofilament cable, extends from an anchoring station  158  on the mounting plate  152 a, through the channel  100  and terminates adjacent the recess  94  of the upper pawl assembly  66 a. A second segment  160  extends in the channel  102  from a point adjacent the recess  94 , along the bar  56 , through the channel  100  and terminates adjacent the recess  94  of the upper pawl assembly  66 b. A third segment  162  extends from a point adjacent the recess  94  of the upper pawl assembly  66 b, through the channel  102  and terminates in an anchoring station  164  on the mounting plate  152 b. 
     Light, preferably red modulated light, is sent into the first segment  156  by a light source  168  such as, for example, model FS-MO available from Keyence Inc. of New Jersey. A sensor  170 , preferably fixed near the supporting surface, measures the amount of light that has traveled along the light circuit  154 a from the first segment  156 , across the recess  94  of the upper pawl assembly  66 a, along the second segment  160 , across the recess  94  of the upper pawl assembly  66 b, and along the third segment  162  to the terminal end  172  of the third segment  162 . If the inner pawls  74  of either upper pawl assembly  66 a or  66 b are in their first positions (wherein the window  114  in the shaft  108  does not align with the channels  100  and  102  in the outer pawl  72 ), the sensor  170  adjacent the terminal end  172  of the third segment  162  will not detect any light because the light cannot pass across recesses  94  when the inner pawls are in their first position (thereby blocking the path of travel of the light across the recess  94 ). 
     If both of the inner pawls  74  of the upper pawl assemblies  66 a and  66 b are in their second positions (wherein the windows  114  in the shaft  108  aligns with the channels  100  and  102  in the outer pawl  72 ), the sensor  170  will detect received light at the terminal end  172  of the third segment  162  because light can travel across the recesses  94  of both upper pawl assemblies  66 a and  66 b through the windows  114  in the shafts  108  of the inner pawls  72  to complete the light circuit  154 a. 
     The second light circuit  154 b is shown in  FIG. 17  between the upper pawl assemblies  66 c and  66 d on the side  48  of the assembly  12 . The third and fourth light circuits  154 c and  154 d respectively are also similar to the first light circuit  154 a, however, they extend between the pairs of lower pawl assemblies  70 a/ 70 b and  70 c/ 70 d, respectively. 
     The detailed operation of the sensor arrangement of the tray inverter queue assembly  12  is as follows. When the assembly  12  is not supporting any trays  14 , the outer pawls  72  of the upper and lower pawl assemblies  66 a-d and  70 a-d are in their normal biased position and the inner pawls  74  are in their first position. Accordingly, the sensors  170  of the four light circuits  154 a-d cannot detect any light at the respective terminal ends  172  of the third segments  162  and the light circuits  154 a-d are said to be blocked. 
     When any of the cross bars  132 - 138  are moved outwardly in a direction away from the bay  54 , the outer pawls  72  attached to the particular cross bar  132 - 138  also move outwardly against the force of the springs  80  and  82 . When the outer pawls  72  are so moved, the inner pawls  74  passively move along with the outer pawls  72  as one unit. Accordingly, the inner pawls  74  remain in their first position such that none of the sensors  170  detected any received light at the terminal end  172  of the third segment  162 . When the cross bars  132 - 138  are released, the springs  80  and  82  return the outer pawls  72  to their normal biased position. Since the inner pawls  74  have not moved relative to their respective outer pawls  72 , the sensors  170  will still not detect any transmitted light at the terminal end  172  of the third segment  162  and the light circuits  154  remains blocked. 
     If there is a tray  14  positioned in the bay  54 , for example aligned with the upper pawl assemblies  66 a-d, when the cross bars  132  and  136  are released, the four outer pawls/inner pawls units of the upper pawl assemblies  66 a-d travel toward the tray  14  because of the bias of the outer springs  80  and  82 . Before the outer pawls  72  terminate their travel and reach their normal biased position at a point that is not in contact with the tray  14 , the extensions  116  of the inner pawls  74  travel into the notches  40  of the tray  14  and contact the tray  14 . When the extensions  116  contact the tray  14 , because of the lower spring rate of the inner spring  84  as compared to the outer springs  80  and  82 , the inner pawls  74  move an incremental distance relative to the respective outer pawls  72 , in a direction toward the respective cross bar  132  and  136 . As the inner pawls  74  move this incremental distance, the inner pawls  74  move into their second position such that the windows  114  in the shafts  108  align with the respective channels  100  and  102  and allow communication between then channels  100  and  102  of the outer pawls  72 . When the windows  114  align with the channels  100  and  102 , light on one side of the recess  94  of the outer pawls  72  is able to cross the recess  94 . 
     If both inner pawls  94  have contacted the tray  14  within the notches  40  and moved into their second position, the first and second light circuits  154 a and  154 b will be completed such that the sensors  170  will receive transmitted light at the terminal end  172  of the third segment  162 . 
     If a tray  14  is to be held in position by the upper pawl assemblies  66 a-d, only if the first and second light circuits  154 a and  154 b are completed (sensors  170  detecting light at the terminal ends  172  of the third segments  162 ) is it certain that the upper pawl assemblies  66 a and  66 b have a secure hold on the tray  14 . Likewise, if a tray  14  is to be held in position by the lower pawl assemblies  70 a-d, only if the third and fourth light circuits  154 c and  154 d are completed is it certain that the lower pawl assemblies  70 a-d have a secure hold on the tray  14 . 
     Accordingly, before the pair of nested trays  14  are inverted, all four light circuits  154 a-d should be checked to make sure light is detected by all four respective sensors  170 , thus ensuring that the assembly  12  has a secured hold on both trays  14  to avoid any misplacement or dislodging of devices during the inversion of the nested trays  14 . 
     With reference to  FIG. 1 , the inspection handler apparatus  10  includes a suitably programmed computer system  850  to control the operation and function of the apparatus as described above. Preferably, an Intel 860x86 or Pentium computer system is utilized. The computer system  850  includes an operator interface  851  which is utilized to select program commands and features and to enter information into program files. 
     Trays are processed in the inspection handler apparatus  10  as follows. It should be noted that the following description will follow one tray from the infeed module  100  to the outfeed module  500 . However, in operation, the inspection and handler apparatus  10  preferably processes a plurality of trays at one time, with the trays being processed simultaneously in each of the various modules. 
     Before processing, the various tray holding mechanisms are adjusted to accommodate the dimensions of the trays to be processed. The computer system  850  communicates the spacing between rows of devices on one tray and the spacing between sequential trays to the scanner and PVI modules and the PNP module  450 . 
     The trays, having devices contained therein, that are to be processed are stacked in the infeed module  100 . One tray is then indexed onto the linear path  42  into the scanner module  200 . In the scanner module  200 , the tray is transported in the scanner module along the linear path  42  where the devices on the tray are inspected by the laser scanner. The results of the laser inspection for each device on the tray are communicated to the computer system  850 . While another tray on the other bed is being scanned, the tray is transported along the linear path  42  to the inverter module  300 . 
     After the devices on the tray are inverted above the linear path  42 , the resulting tray is transported along the linear path to the PVI module  400 . The camera in the PVI module inspects the devices on the tray and reports the results of the inspection of each device to the computer system  850 . As the devices on part of the tray are being inspected by the camera  401 , the PNP module  450  will be moving devices, on the other end of the tray that have already been scanned by the camera, to their destinations. The computer system  850  communicates the results of the various inspections for each device on the tray to the PNP module  450  so that each device can be transported to its proper destination. 
     If the destination of the “good” devices, those that have passed all of the inspections, is carrier tape, the PNP module  450  transports the good devices from the tray, one at a time, to the taper module  900 . Any “reject” devices, those that have not passed the inspections, are transported by the PNP module  450  to a tray in tray module  700 . 
     If the good devices are to remain in the tray, the PNP module  450  removes the reject devices to the tray module  700 . The resulting empty pockets of the tray are filled with good devices that are transported by the PNP module  450  from a tray in the tray module  700  to the empty pocket(s) of the tray. In this mode of operation, before processing starts, a tray of good devices is loaded into one of the bays of the tray module  700 .