Abstract:
A high-speed tray transfer system for trays of semiconductor devices for increasing the rate at which trays are delivered to, and advanced through, a pick and place that moves orthogonal to the tray movement, so as to increase the overall throughput speed of a semiconductor handling machine. The invention utilizes two or more platens that carry trays. The platens can pass over, under or otherwise around each other so that while one platen is under and servicing the pick and place, another platen is cycling around and preparing another tray of electronic devices for the pick and place.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 60/818,131 filed Jun. 30, 2006 by the present inventors. 
     
     FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       SEQUENCE LISTING OR PROGRAM 
       [0003]    Not Applicable. 
       BACKGROUND 
       [0004]    1. Field of the Invention 
         [0005]    The electronics industry routinely transports semiconductor devices in trays consisting of an array of pockets. These trays provide safe and convenient handling of the devices. Typically these trays are feed into a machine for inspecting or testing or otherwise processing the devices. The present invention relates generally to tray transfer systems and more specifically it relates to tray transfer or delivery systems for trays of semiconductor devices for increasing the rate at which trays are supplied to a linear pick and place so as to increase the overall throughput speed of a semiconductor handling machine. The invention additionally improves the accuracy of tray positioning for improved pick and place functioning. 
         [0006]    2. Prior Art 
         [0007]    Tray transfer systems have been used on semiconductor processing machines for years. Typically, tray transfer systems utilize a single platen (tray holder) with a single tray delivery mechanism. For example, U.S. Pat. No. 6,266,873 to Kitamura (2001) shows a single tray moving mechanism. 
         [0008]    Typical tray transfer systems position the tray under an orthogonally oriented linear pick and place which can then pick up each electronic device along one row of the tray. The tray is then indexed forward so that the pick and place can access the second row of devices. This continues until all rows are accessed by the pick and place. Then the tray transfer system removes the tray from the pick and place area, disposes of the tray, obtains a new tray and repeats the process. 
         [0009]    The main problem with conventional tray transfer systems is that they slow down the overall throughput speed of a semiconductor handling machine because they are unable to continuously deliver trays, and thus semiconductor devices, to a linear pick and place for processing. There is down-time while the tray delivery mechanism removes the processed tray from the pick and place area, places the tray in an output destination, returns to a stack of new trays, picks up a new tray and finally delivers the new tray to the pick and place area so that the pick and place can continue picking and placing devices. 
         [0010]    U.S. Pat. No. 6,941,647 to Cho (2005) discloses a two platen tray feeder in which each platen can alternately position successive trays in identical load and unload positions, but they cannot index row by row under a linear orthogonal pick and place. Additionally, even if the horizontal travel was increased to allow for such indexing, the tray platens do not travel in a circuit so that an index between the last row of one tray and the first row of a subsequent tray would not be as fast as an index from one row to the next row within a tray. But rather, substantial tray translation is required between the pick and place servicing the last row of one tray and then servicing the first row of the subsequent tray. This requires additional time and thus slows down the overall throughput of the machine. 
         [0011]    Another problem with conventional tray transfer systems are that they are less accurate in positioning trays, and thus devices, under the pick and place, particularly in the vertical axis because they justify tray position based on the bottom surface of the tray instead of the top surface of the tray which is typically manufactured to tighter tolerances. 
         [0012]    Another problem with conventional tray transfer systems is that trays are often bowed or warped and no accommodation is made for this. A warped tray can result in an unsuccessful pick up by the pick and place because some devices may be lower than others. 
         [0013]    Another problem with conventional tray transfer systems is that they further slow down the overall throughput speed of a machine because they engage and release a tray clamp mechanism every time a tray is indexed underneath the pick and place. This action consumes valuable time because it cannot be performed in parallel with tray indexing or with pick and place processing. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention provides a new high-speed tray transfer module for trays of semiconductor devices for increasing the rate at which trays are delivered to and advanced through a pick and place so as to increase the overall throughput speed of a semiconductor handling machine. In brief, the invention utilizes 2 independently operable platens that can pass over, under or otherwise around each other so that while one platen is under the pick and place, the other platen is cycling around and preparing another tray for the pick and place. 
         [0015]    The present invention generally comprises a tray loader, two independent horizontal tray mover assemblies, two independent vertical tray mover assemblies, a tray unloader, and an electronic controller for controlling the operation of each assembly. 
         [0016]    A primary object of the present invention is to provide a high-speed tray transfer system that can continuously deliver trays to a pick and place without interruption so as to increase the overall throughput speed of a semiconductor handling machine. A second object is to more quickly index a tray, row by row, underneath a pick and place by eliminating multiple tray clamping operations so as to increase the overall throughput speed of a semiconductor handling machine. A third object of the invention is to more accurately and repeatably position devices in trays vertically by justifying the tray position from the top of the tray for more reliable picking and placing. A fourth object is to flatten bowed trays as they are presented to a pick and place to increase the consistency of the vertical location of tray pockets so that the pick and place can more quickly and reliably pick and place devices into or out of trays. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an isometric view of the entire high speed tray transfer system. 
           [0018]      FIG. 2  is an isometric view of the tray loader. 
           [0019]      FIG. 3   a  is an isometric view showing the vertical tray mover. 
           [0020]      FIG. 3   b  is a different angle isometric view of  FIG. 3 . 
           [0021]      FIG. 4  is an isometric view of the two vertical tray movers attached to their respective horizontal tray movers. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  illustrates the invention. It comprises a tray loader  1 , two independent horizontal mover assemblies  2 , two independent vertical tray mover assemblies  3  with platens  31 , a tray unloader (not shown), and an electronic controller for controlling the operation of each assembly (not shown). 
         [0023]    The tray loader  1  can hold a stack of trays, and lower the bottom tray onto a platen one at a time. The stack of trays are placed within four vertical bars  10  that are positioned to capture the corners of the trays. The stack of trays are supported on the bottom by four tray holder fingers  11 . 
         [0024]      FIG. 2  shows elevator assembly  12  which can lift the stack of trays by raising or lowering the elevator plates  13  that are connected on the bottom via a horizontal plate  17 . These elevator plates straddle other components (see  FIG. 1 ). These plates can move up or down via an electric motor  14  connected to a screw drive  15 . The elevator plates are each attached to linear bearings  16 . In operation, the elevator plates  13  are moved upward until they contact the bottom of the stack of trays. From this position the elevator plates move slightly higher and thus slightly raise the entire stack of trays. The tray holder fingers  11  are now retracted. Next the elevator plates  13  are moved downward by a distance approximately equal to the thickness of a tray. The tray holder fingers  11  are then extended between the lowest and second lowest tray. As the elevator plates move further down, the tray that was second from the bottom of the stack comes to rest on the tray holder fingers. In this way a single tray is removed from the bottom of the stack of trays. Then the elevator plates  11  continue to lower the tray until it rests on a platen  31  (a flat plate that a tray can rest on). 
         [0025]    Each platen  31  is connected to a vertical tray mover assembly  3  as seen in  FIGS. 3   a  and  3   b . Once a tray is resting on the platen it is clamped in place. The tray clamps are mechanisms on the platens that hold a tray in place on the platen. In a preferred embodiment they consist of two stationary pins  32  on one end of the platen and a movable pin  33  on the other end. This movable pin is activated on demand by a solenoid  34  ( FIG. 3   b ) or other actuator and can move toward and away from the stationary pins. The vertical tray mover is a mechanism that can move the platen, and thus the tray, vertically. It employs an electric motor  35 , connected to a screw drive  36  via a pair of bevel gears to achieve the up and down motion. Linear bearings  37  guide the vertical movement. 
         [0026]    The horizontal tray mover  2  is a mechanism that horizontally moves a vertical tray mover  3  as seen in  FIG. 4 . In a preferred embodiment this consists of a high-speed electric motor  31  driven screw drive  32  and linear bearing  33  with structural members that support the vertical tray mover. Activating the motor and thus turning the screw causes the horizontal tray mover to move horizontally. Bearing  33  guides the horizontal motion and bears the weight of the attached assemblies. Various alternate actuators could be used for the horizontal tray mover. The horizontal tray mover is attached to the housing of the high-speed transfer system. There are two of these assemblies in the housing; a left hand version and a right hand version. They are oriented 180 degrees rotated from each other so that the platens of each unit can pass above or below each other as they cycle through the same path in a clockwise or counter-clockwise fashion. 
         [0027]    Precise positional information about of each horizontal tray mover is provided by encoder  34 . Likewise, feedback regarding the location of each vertical tray mover is provided by encoder  38  ( FIG. 3   b ). The elevator positional information is provided by encoder  17  ( FIG. 2 ). These encoders allow the electronic controller to precisely position these movers. These are optical rotary encoders connected to the motor shafts. Alternatively, linear encoders could be used. Non-optical encoders could be used also. 
         [0028]    During operation, once a tray has been placed on a platen, the horizontal mover moves the tray away from the tray loader. The tray is thus feed between horizontal rails  42  and  43  (see  FIG. 1 ). Rail  43  is spring loaded so as to apply pressure to push the tray against rail  42 . In this way the tray is laterally justified against rail  42 . When the tray has moved far enough to be clear of the loader mechanisms, the vertical tray mover moves the tray upward until the top surface of the tray contacts the vertical tray limit rails  41 . The servomotor on the vertical tray mover can change from position mode to torque mode. Thus the motor moves the platen vertically until it experiences a specific force against it. In this way the force exerted upon the tray can be used to flatten warped trays. Additionally, the tray location is thus justified from the top of the tray for greatest vertical positional accuracy of devices. Now the tray can be horizontally indexed underneath the pick and place by means of the horizontal tray mover. The method of tray clamping does not require any additional clamping or unclamping while this platen is providing devices to the pick and place. Therefore the index time is minimized. Meanwhile, the other platen delivers its tray to the end of the tray transfer system where a tray unloader can process it. One embodiment utilizes another instance of the tray delivery system operated in reverse and thus stacks up used trays. This now empty platen can move downward via the vertical tray mover, until it is lower than the platen that is currently servicing the pick and place. Then the platen moves back to the tray delivery system by passing underneath the other platen. The platen obtains a new tray of devices and is queued behind the platen servicing the pick and place, so that as soon as the pick and place is finished with the current tray, a tray full of new devices can be immediately delivered. 
         [0029]    By having these mechanisms cycle around in a somewhat circular fashion, this high-speed tray transfer system is able to continuously feed trays to the pick and place without any interruption. It should be obvious that various actuators could be used and still remain within the scope of this invention. Various alternative structures could produce the same effect of having two or more platens that can pass each other. For example, if the platens tilted or pivoted they could pass each other also.