Abstract:
A system for handling semiconductor workpieces, by aligning a movable pick and place device and a movable optical control device, is disclosed. The system and method provide for the formation of an imprint by the pick and place device. The optical control device can then be aligned to that imprint, creating alignment between the pick and place device and the optical control device. Once alignment is complete the imprinted material may be replaced with one or more semiconductor workpieces. The system provides precise, repeatable alignment between the pickup point for the pick and place device and the optical control device.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates generally to manufacturing systems that use pick and place equipment to handle small components. More specifically, the invention relates to an apparatus and method for aligning a camera to an imprint in a film layer which represents an attach position on a semiconductor workpiece, where a pick and place device picks up the semiconductor workpiece. 
     II. Description of the Related Art 
     In the assembly of semiconductor products, relatively small parts or components are picked up and accurately placed in another location. For example, in the assembly of optoelectronic systems, it may be necessary to accurately orient and align optical components, such as semiconductor lasers. In a known pick and place system, an operator manually aligns a vacuum collet with respect to an optical camera. These two devices working together are used to move a workpiece in the manufacturing process. The workpiece may be a chip, a bar, a wafer, etc. 
     In the known system, a test piece is located below the downward looking camera. Crosshairs, viewed on a monitor, are used to align the camera with an attach position on the test piece, which will be the actual attach position on a semiconductor workpiece in the manufacturing process. The attach position may be near the center of the test piece, which in turn would represent the center of a workpiece, for example. The vacuum collet is then moved over the test piece and lowered until it is slightly above the test piece, near the attach position. The operator then adjusts the position of the collet using x and y coordinates until it appears that it is aligned to what the camera perceives as the attach position. Lastly, the test piece is replaced with an actual semiconductor workpiece. 
     This manual alignment is performed at an angle and by human eye, thus making the process cumbersome, potentially inaccurate and unrepeatable. Inaccuracy in the procedure will result in the collet being placed some distance from where it was intended to be placed. The margin of error may be defined as the difference between the actual attach position, where the vacuum collet picks up a workpiece, and where the optical collection device perceives the attach position to be. 
     There exists a need for a pick and place system that provides precise, repeatable and efficient alignment between the pick and place equipment and the camera, such that what is seen by the camera as the attach position is aligned to the actual attach position, where the vacuum collet picks up the workpiece. Such precision will help ensure that the workpiece is ultimately placed in the correct location. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a system for handling a semiconductor workpiece, such as a semiconductor chip, laser bar, wafer and the like. The system includes a pick and place device for accurately moving the semiconductor workpiece. The pick and place device is arranged to form an imprint on a film layer to align an optical device. In addition, the system has a control device for moving the pick and place device to a remote location away from the imprint, and an optical device for viewing the imprint while the pick and place device is at the remote location. 
     According to one aspect of the invention, a device may be provided for aligning the optical device with respect to the imprint on the film layer while the pick and place device is in the remote location. 
     According to another aspect of the invention, the movement of the pick and place device is controlled in response to the location of the imprint on the film layer. 
     In a preferred embodiment of the invention, the optical device may be a vision camera with suitable vision control software. The present invention should not be limited, however, to the preferred embodiments described and shown in detail herein. 
     If desired, the pick and place device may have a source of vacuum and a vacuum collet. In a preferred embodiment of the invention, the pick and place device has an annular tip for forming the imprint on the film layer. 
     According to another aspect of the invention, the imprint is formed in a film layer provided on a film support. The film layer may be formed, for example, of adhesive tape. 
     The present invention also relates to a system for aligning a camera, or other optical collection device, to an imprint of a vacuum pick and place device. Thus, the present invention may be used to align the camera to the actual attach position of the pick and place device in a precise, repeatable and efficient manner. 
     According to another aspect of the invention, the vacuum pick and place device is moved over the film layer to a first (x,y) position, predetermined to be the attach position&#39;s coordinates. Once locked into the first position, the vacuum pick and place device then descends on the attach position and makes an imprint of the head of the vacuum pick and place device on the film layer. The vacuum pick and place device then ascends from the film layer and is released from the first position and moved out of the way to a second position. 
     Then, the optical collection device is aligned to the imprint of the vacuum pick and place device on the film layer. By doing so the optical collection device becomes aligned to the vacuum pick and place device pick up point. This may be accomplished relatively easily by an operator viewing the imprint on a monitor and accurately aligning the crosshairs to the imprint of the vacuum pick and place device on the film layer. The pick and place device is then brought back in and locked into its first (x,y) position where imprinting occurred. Thus, the optical collection and reproduction device and the vacuum pick and place device pick up point are in alignment using the imprint as a reference point employing devices and a methodology which can be replicated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other advantages and features of the invention will become more apparent from the detailed description of preferred embodiments of the invention given below with reference to the accompanying drawings in which: 
     FIG. 1 is a side view of a pick and place system constructed in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a cross sectional view of the system of FIG. 1, at a subsequent stage of operation; 
     FIG. 3 is a cross sectional view of the system of FIG. 1, at yet another stage of operation; 
     FIG. 4 is a top view of a film layer for the system of FIG. 1; and 
     FIG. 5 is another top view of the film layer of FIG. 4, with alignment crosshairs moved to an aligned position. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, where like reference numerals designate like elements, there is shown in FIG. 1 a system  90  for moving a semiconductor workpiece (not illustrated). The system  90  includes a vacuum collet  106  for picking and placing the workpiece, and a vision camera  100  for displaying a magnified image of the attach position on a film layer  118 . The film layer  118  is supported on a support structure  92 . 
     In the FIG. 1 position, the vision camera  100  is positioned above the vacuum collet  106  and the support structure  92 . The vision camera  100 , which is capable of imaging an imprint, is connected to a vision control system  104  by a signal line  102  and an operative arm  138 . The vision control system  104  controls the operative arm  138  and receives signals from the camera  100  via the signal line  102 . The vision control system  104  may be controlled by suitable vision software. The operative arm  138 , controlled by the control system  104 , may be used to support the camera  100  in the desired position, and to move the camera  100  as desired. The present invention should not be limited to the system shown and described in detail herein. In an alternative embodiment, for example, another suitable vision or sensing device may be used in place of the vision camera  100 . 
     The vacuum collet  106  is connected to an operative arm  140  and a vacuum tube  112 . The operative arm  140  and vacuum conduit  112  are connected to a pick and place control system  114 . The pick and place control system  114  controls the operative arm  140  and provides a source of vacuum for the vacuum conduit  112 . The vacuum collet  106  has an internal vacuum tube  110 . The vacuum conduit  112  is operatively connected to the internal vacuum tube  110 . The internal vacuum tube  110  is coaxially aligned within the outer surface  108  of the vacuum coliet  106 . The internal vacuum tube  110  and the outer surface  108  of the vacuum collet  106  form a cylindrical tip  116 . The tip  116  provides a discrete pick up point where the device  106  is attached by vacuum to the workpiece. 
     The invention should not be limited to the pick and place equipment  114 ,  112 ,  140 ,  106  described in detail above. In an alternative embodiment of the invention, the pick and place device may have a rectangular configuration, for example. 
     The illustrated film layer  118  may be affixed to the support structure  92 . The film layer  118  may be tape, or another material which is capable of maintaining an imprint. Preferably the film layer  118  is adhesively connected to the support structure  92 . In a preferred embodiment of the invention, the support structure  92  may include a flexible sheet for supporting the workpiece. The top of the film layer  118  faces the vacuum collet  106  and the vision camera  100 . In the illustrated embodiment, the iris  96  of the vision camera  100  and the tip  116  of the pick and place collet  106  are both pointed downward toward the film layer  118 . 
     In operation, the operative arm  140  moves the vacuum collet  106  under the vision camera  100  and above the film layer  118  to the position shown in FIG.  1 . In the FIG. 1 position, the vacuum collet  106  is located directly above the desired attach position  94  (FIG.  4 ). The attach position  94  may be, for example, at the center of the film layer  118 . The vacuum collet  106  is then lowered by the pick and place control system  114  onto the film layer  118  to the position shown in FIG.  2 . 
     Preferably, the collet  106  is moved with sufficient pressure to make a direct imprint  134  (FIG. 3) of the cylindrical tip  116  of the vacuum collet  106  in the film layer  118 , at the attach position  94 . In the FIG. 2 position, the tip  116  of the vacuum collet  106  is slightly above the top surface  142  of the film support  92 . 
     FIG. 3 illustrates the system  90  after the vacuum collet  106  has made the imprint  134  and after the pick and place control system  114 ,  140  has lifted the collet  106  from the film layer  118 . As shown in. FIG. 4, the imprint  134  has concentric imprinted sides  148 ,  142  and an imprinted bottom  146 . The bottom  146  resides at a different plane than the nominal top surface  82  of the film layer  118 . The film layer  118  at this point has a cavity  80  (FIG. 3) at its otherwise planar surface  82  where the imprint  134  is located. Next, the operative arm  140  moves the vacuum collet  106  out from between the camera  100  and the film layer  118  to a remote position (not illustrated). This leaves the vision camera  100  alone focusing down on the imprinted film layer  118  with no visual obstructions. The camera  100  can view the imprint  134  directly without being obstructed by the collet  106 . 
     The vision camera  100  is then aligned to the actual attach position by aligning itself to the imprint of the vacuum collet  134  using visual crosshairs  130 . FIG. 5 depicts the crosshairs  130  after the vision camera  100  has been aligned with the imprint  134 . When the center  132  of the crosshairs  130  is at the center of the imprint  134 , then the vision camera  100  and the imprint  134  are aligned. The vision control system  104  may utilize vision software to control the vision camera  100  in this alignment process. Alternatively, the alignment may be performed manually. 
     Subsequently, the vacuum collet  106  is swung back into its first position using the pick and place control system  114  together with the operative arm  140 . This places the vacuum collet  106  between the vision camera  100  and the support structure  92  at the imprint position  134 . 
     At this point, the vision camera  100  and the vacuum collet  106  are aligned. After alignment is complete, the film layer  118  may be replaced with the semiconductor workpiece (not illustrated). The workpiece may be supported on the illustrated support structure  92  or on another support structure. In a preferred embodiment of the invention, the workpiece may be located on a movable film or sheet. In manufacturing operations, the vacuum collet  106  attaches to the workpiece precisely at the point where the imprint  134  was made previously, thus allowing a user to pick up the workpiece with confidence that the visual depiction generated by the vision camera  100  represents the actual pick and place location  134  of the vacuum collet tip  116  on the workpiece. The workpiece then may be placed in a desired location by referring to the image generated by the vision camera  100 . If desired, numerous workpieces may be handled by the pick and place equipment  106  based on a single alignment of the camera  100  with respect to the pick and place equipment  106 . 
     The invention may be practiced with a variety of workpieces, including semiconductor chips, laser bars, and semiconductor wafer products and preforms, including products with integrated circuits formed therein. 
     The scope of the present invention is not to be considered as limited by the specifics of the particular structures which have been described and illustrated, but is only limited by the scope of the appended claims.