Abstract:
Disclosed is an optical apparatus for locating a plurality of placement positions on a carrier object. The optical apparatus comprises: i) an imaging device having a plurality of imaging sensors, each imaging sensor being operative to capture an image of a part of a selected row of placement positions on the carrier object and the plurality of imaging sensors defining a combined field of view that includes all the selected row of placement positions; ii) a positioning device coupled to the imaging device, the positioning device being operative to position the imaging device relative to successive rows of placement positions on the carrier object; and iii) a processor connected to the imaging device and which is configured to receive the images captured by the plurality of imaging sensors for image processing in order to identify exact locations of the placement positions comprised in the selected row of placement positions. A method of locating a plurality of placement positions on a carrier object is also disclosed.

Description:
FIELD OF THE INVENTION 
     This invention relates to an optical apparatus particularly, but not exclusively, for locating a plurality of placement positions on a carrier object, such as a lead frame on which semiconductor dies may be bonded. The invention also relates to a method of locating a plurality of placement positions on a carrier object, such as a lead frame. 
     BACKGROUND OF THE INVENTION 
     Panning and zooming functions are usually provided in a conventional imaging system in order to capture a desired region of interest. Panning of the imaging system may involve moving the imaging system on an XY-plane in order to capture different parts of the desired region of interest. On the other hand, zooming of the imaging system may involve adjusting the internal mechanical assembly of the imaging system to vary a distance between the imaging system and the region of interest and/or the overall focal length of the imaging system, to thereby enlarge an image of the region of interest. 
     Invariably, the panning and zooming functions of the conventional imaging system require physical movement of either the whole or a part of the imaging system, or an object being inspected. However, the time required to move the whole of the imaging system also includes time for stabilising the imaging system or object at a resting positing, which may require tens of milliseconds, perhaps more. This might undesirably affect the overall throughput capacity among high-speed applications. Further, adjustment of the internal mechanical assembly of the imaging system may cause a shift of the optical centre of the imaging system, such that an allowable threshold—especially among high-accuracy applications—may be exceeded. In addition, the movement of the imaging system may also render the precise control of the imaging system&#39;s zooming capability hard to achieve among applications that require machine portability. 
     It is therefore an object of the present invention to seek to provide an apparatus that addresses, or at least ameliorates, some of the problems encountered by the conventional imaging system, and to provide the general public with a useful choice. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention is defined in claim  1 . In particular, each of the plurality of imaging sensors comprised in the imaging device is configured to capture an image of a part of a selected row of placement positions on the carrier object and the plurality of imaging sensors defining a combined field of view that includes all of the selected row of placement positions. By requiring the combined field of view of the plurality of imaging sensors to cover an entire row of placement positions on the carrier object, the entire row of placement positions can be imaged without moving the imaging sensors along the row of placement positions. Advantageously, the efficiency of placement operations of objects onto a carrier object can be increased. 
     A second aspect of the invention is defined in claim  13 . By using each imaging sensor to capture an image of a part of the selected row of placement positions on the carrier object, wherein the plurality of imaging sensor define a combined field of view that includes all the selected row of placement positions, the entire row of placement positions can be imaged without moving the imaging sensors along the row of placement positions. Advantageously, the efficiency of placement operations of objects onto a carrier object can be increased. 
     Some optional features/steps of the invention are defined in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which: 
         FIG. 1  shows an optical apparatus according to a preferred embodiment of the invention arranged in relation to a semiconductor die carrier for imaging respective rows of placement positions thereon; 
         FIGS. 2   a  to  2   c  show three modes of a zooming function of the optical apparatus of  FIG. 1 ; 
         FIGS. 3   a  and  3   b  show a stitching function of the optical apparatus of  FIG. 1 ; and 
         FIGS. 4   a  to  4   c  show a graphical user interface of the optical apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an optical apparatus  100  arranged with respect to a target object, which is shown as a semiconductor die carrier in the form of a lead frame  101  comprising a plurality of placement positions  101   a , each for receiving a semiconductor die (not shown). In particular, the placement positions  101   a  of the lead frame  101  are arranged in an array defining rows and columns in an ordered fashion. 
     Specifically, the optical apparatus  100  comprises: i) an imaging device  102 ; ii) a light box  104  attached to the imaging device  102 ; iii) a positioning device (shown as a Y-arm  106 ) to which the imaging device  102  and the light box  104  are connected; and iv) a processor  108  for processing the images taken by the imaging device  102  and for controlling the imaging device  102 , the light box  104 , and the Y-arm  106 . 
     The imaging device  102  and the light box  104  both define a common longitudinal axis  105 , which extends perpendicularly with respect to an XY-plane on which the lead frame  101  is located. The imaging device  102  and the light box  104  are actuated by the Y-arm  106  to capture different regions of interest at the top of the lead frame  101 . Moreover, the imaging device  102  comprises a plurality of imaging sensors  102   a —in particular four imaging sensors  102   a  as shown in the embodiment illustrated in FIG.  1 —to capture images of respective rows of placement positions  101   a  on the lead frame  101 . More specifically, the imaging sensors  102   a  are aligned on the imaging device  102  such that the imaging sensors  102   a  defines a combined field of view that includes all of a selected row of the placement positions  101   a . When the light box  104  is activated, light is directed towards the respective regions of interest to increase their brightness before the imaging sensors  102   a  are activated to capture the images. Preferably, each of the imaging sensors  102   a  has a resolution of at least 4.9 megapixels. This means that the imaging sensors  102   a  are capable of capturing images with an exemplary resolution of at least 2560 pixels by 1920 pixels (i.e. 2560×1920≈4.9 megapixels). Nevertheless, it should be appreciated that other imaging sensors having different resolutions (e.g. 1.9 megapixels or 7.2 megapixels) may also be used for the optical apparatus  100 . 
     During operation, the processor  108  controls the Y-arm  106  to position the imaging device  102  such that the imaging sensors  102   a  are arranged to view an entire first row of placement positions  101   a  on the lead frame  101  for imaging. In particular, the imaging sensors  102   a  are arranged directly above the first row of placement positions  101   a . After imaging of the first row of placement positions  101   a  on the lead frame  101  is completed, the Y-arm  106  is actuated to index the imaging device  102  and the light box  104  such that the imaging sensors  102   a  are positioned to view an entire second row of placement positions  101   a  on the lead frame  101 —which is immediately adjacent to the first row of placement positions  101   a -before the imaging sensors  102   a  are activated to image the second row of placement positions  101   a . Similarly, the imaging sensors  102   a  are arranged directly above the second row of placement positions  101   a  for imaging. At the same time, the processor  108  is operative to process images that are captured by the imaging sensors  102   a  to locate the corresponding placement positions  101   a  on the lead frame  101  using known pattern recognition techniques. This continues until each successive row of placement positions  101   a  of the lead frame  101  has been imaged by the imaging device  102 , and all the placement positions  101   a  have been accordingly located by the processor  108 . 
     Preferably, some or all of the imaging sensors  102   a  are simultaneously activated when imaging respective rows of the placement positions  101   a  on the lead frame  101 . Nevertheless, the imaging sensors  102   a  may also be sequentially activated when imaging respective rows of the placement positions  101   a.    
     It should be appreciated that by arranging the plurality of imaging sensors  102   a  to view respective rows of placement positions  101   a  of the lead frame  101 , entire rows of the placement positions  101   a  can be imaged without moving of the imaging device  102  and the light box  104  along the X-axis, besides the Y-axis. In contrast, movement of a conventional imaging system with respect to the lead frame  101  along the X-axis—in addition to the Y-axis—will be necessary in order to capture images of an entire row of the placement positions  101   a , which undesirably reduces the throughput capacity of bonding operations of semiconductor dies due to increased motion and settling time. 
     It should also be appreciated that although it has been shown that the imaging device  102  comprises four imaging sensors  102   a , the imaging device  102  may include any number of imaging sensors  102   a . Preferably, the imaging device  102  comprises between 1 and 25 imaging sensors  102   a . Further, the imaging device  102  may comprise an array arrangement of imaging sensors  102   a  arranged in rows and columns within the imaging device  102 , instead of only a single row of imaging sensors  102   a , as shown in  FIG. 1 . For instance, in the case whereby the imaging device  102  comprises 25 imaging sensors  102   a , the imaging sensors  102   a  may be arranged in a 5×5 format. 
       FIGS. 2   a - c  show three modes of the zooming function of the optical apparatus  100  of  FIG. 1 . For these three operation modes, instead of transferring entire images—each having a resolution of 2560×1920 pixels—as taken by each of the imaging sensors  102   a  to the processor  108  for image processing, sampled image portions each having a fixed data packet size that measures 640×480 pixels are selected and received by the processor  108  from the respective imaging sensors  102   a  for image processing. Thus, the processing speed of the optical apparatus  100  can be advantageously increased. It should, of course, be appreciated that other data packet sizes of each sample image portion may also be transmitted from the imaging sensors  102   a  to the processor  108  depending on the resolution requirements of the particular application. 
       FIG. 2   a  shows the optical apparatus  100  in a 4× zoom mode, to provide the best zoomed-in capability with the highest image resolution. Image resolution refers to the clarity or sharpness of a sampled image. In this 4× zoom mode, an inspected area  201  measuring 640×480 pixels of a captured image is first identified by the processor  108  before it samples every pixel along each row of the inspected area  201 . In other words, there is no downsampling of the inspected area  201  (i.e. the sampled image portion) or the downsampling factor is 0. 
       FIG. 2   b  shows the optical apparatus  100  in a 2× zoom mode, to provide the second best zoomed-in capability with the next highest image resolution. In this 2× zoom mode, an inspected area  203  measuring 1280×960 pixels from the captured image is first identified by the processor  108 . In particular, each row of the inspected area  203  comprised sampled pixels  203   a  (which are sampled by the processor  108 ) and skipped pixels  203   b  (which are skipped by the processor  108 ). Specifically, for every sampled pixel  203   a  along each row of the inspected area  203  that is sampled by the processor  108 , the next immediate pixel constitutes a skipped pixel  203   b  that is not sampled by the processor  108 . This means that the processor  108  downsamples (or subsamples) the inspected area  203  (i.e. the sampled image portion) of the captured image by a factor of 2. Consequently, the inspected area  203  in the 2× zoom mode is larger than the inspected area  201  in the 4× zoom mode. This also means that the processor  108  samples data of a fixed data packet size measuring 640×480 pixels, notwithstanding the inspected area  203  having an area that is twice larger than the inspected area  201  in the 4-× zoom mode. 
       FIG. 2   c  shows the optical apparatus  100  in a 1× zoom mode, to provide a zoomed-out capability with the lowest image resolution. In this 1× zoom mode, an inspected area  205  that is identified by the processor  108  actually constitutes the entire captured image that measures 2560×1920 pixels. Similarly, each row of the inspected area  205  comprised sampled pixels  205   a  (which are sampled by the processor  108 ) and skipped pixels  205   b  (which are skipped by the processor  108 ). Specifically, for every sampled pixel  205   a  along each row of the inspected area  205  that is sampled by the processor  108 , the next three immediate pixels constitute skipped pixels  205   b  that are not sampled by the processor  108 . This means that the processor  108  downsamples (or subsamples) the entire image by a factor of 4. Since the inspected area  205  covers the area of the entire image as captured by the imaging sensors  102   a , the inspected area  205  is thus twice larger than the inspected area  203  in the 2× zoom mode and four times larger than the inspected area  201  in the 4× zoom mode. Again, the processor  108  samples data of a fixed data packet size measuring 640×480 pixels, despite the inspected area  205  being larger than the inspected areas  201 ,  203  in the 4× and 2× zoom modes respectively. 
     It should therefore be noted that the areas and image resolutions of the respective inspected areas  201 ,  203 ,  205  have an inverse relation, in order to maintain a consistent rate of data transfer from the imaging device  102  to the processor  108 . In other words, the larger the area  201 ,  203 ,  205  that is inspected, the lower will be the image resolution of the image that is transmitted to the processor  108 . In particular, the processor  108  is configured to sample the inspected areas  201 ,  203 ,  205  at a pixel sampling rate that decreases with an increase in the size of the same. It should also be noted that although three modes of the zooming function have been described, it should be appreciated that the optical apparatus  100  may comprise any number of modes depending on the application requirements. 
       FIGS. 3   a  and  3   b  show a stitching function of the optical apparatus  100  of  FIG. 1 . 
       FIG. 3   a  shows two separate images—Image A and Image B—which are taken by two different imaging sensors  102   a  and are subsequently sent to the processor  108  for image processing. Before the processor  108  begins image analysis, it performs image stitching of Images A and B to combine them into a single image  302 . Although  FIG. 3   a  only shows image stitching of two images, it should again be appreciated that the processor  108  may perform image stitching of any number of images, particularly depending on the number of imaging sensors  102   a  in the imaging device  102  as well as the required field of view in order to image the target object. For instance, if there are four imaging sensors  102   a , the processor  108  may image stitching of four separate images that have been captured by the respective imaging sensors  102   a  to form a single image. 
     More preferably, the processor  108  may be capable of identifying and selecting a region of interest from each of Images A and B before performing image stitching of the corresponding regions of interest. Referring to  FIG. 3   b , corresponding regions of interest  303   a ,  303   b  are identified and selected from Images A and B respectively, before these selected regions of interest  303   a ,  303   b  are stitched together to form a single image  303 . In this case, it is seen that only the relevant portions of Images A and B are identified by the processor  108  and sent thereto to shorten the time taken for data transfer between the imaging sensors  102   a  and the processor  108 . It should be also appreciated that the regions of interests  303   a ,  303   b  may be derived from any one of the zooming operation modes as described above with reference to  FIGS. 2   a - 2   c.    
     With the plurality of imaging sensors  102   a  and the stitching function, the optical apparatus  100  is capable of capturing images having a larger field of view without the need for panning which typically requires physical movement of the imaging device  102 . Consequently, additional motion and settling time for the imaging device  102  can be eliminated. This desirably improves the overall throughput for the bonding operations of semiconductor dies. 
     With the zooming and stitching functions as described above, the images as captured by the imaging sensors  102   a  and processed by the processor  108  can be displayed to a user through a graphical user interface (GUI)  400  of the optical apparatus  100 , as shown in  FIGS. 4   a  to  4   c.    
     Specifically,  FIG. 4   a  shows the GUI  400  when the optical apparatus  100  is in the 1× zoom mode, wherein the zoomed-out image is displayed on a display area  402  of the GUI  400 . 
     As the size of the zoomed-out image is larger than the display area  402 , a vertical scroll bar  404  is provided on the right of the display area  402  to allow the user to adjust the position of the zoomed-out image within the display area  402 . The vertical scroll bar  404  is controllable by a cursor of a computer mouse, but it should be appreciated that the GUI  400  may also be displayed on a touch screen that allows the user to control the vertical scroll bar  404  using finger touch. 
     Additionally, the GUI  400  includes a ‘+’ zoom icon  406  for zooming into a specified portion of the zoomed-out image through an enhanced resolution when displayed on the display area  402 . When the user clicks on the ‘+’ zoom icon  406  with the computer mouse&#39;s cursor, the optical apparatus  100  transits into the 2× zoom mode such that a zoomed-in image having an enhanced image resolution is displayed on the display area  402  of the GUI  400 , as shown in  FIG. 4   b . If the user further clicks on the ‘+’ zoom icon  406  with the computer mouse&#39;s cursor, the optical apparatus  100  accordingly transits into the 4× zoom mode such that a further zoomed-in image of the specified image portion having a more enhanced image resolution is displayed on the display area  402  of the GUI  400 , as shown in  FIG. 4   c . On the contrary, if the user clicks on a ‘−’ zoom icon  408  on the GUI  400  as shown in  FIG. 4   b , the optical apparatus  100  transits back to the 1× zoom mode, such that the original zoomed-out image (as shown in  FIG. 4   a ) is displayed on the display area  402  of the GUI  400 . Likewise, if the user clicks on the ‘−’ zoom icon  408  on the GUI  400  as shown in  FIG. 4   c , the apparatus  100  transits from the 4× zoom mode back to the 2× zoom mode as shown in  FIG. 4   b.    
     Having fully described the invention, it should be apparent to one of ordinary skill in the art that many modifications can be made thereto without departing from the scope as claimed. For instance, a die bonder for bonding semiconductor dies to the lead frame  101  may include the optical apparatus  100 . Although the use of the optical apparatus  100  with respect to the lead frame  101  has been described, it should be appreciated that the optical apparatus  100  may also be used for other technologies. One example is in the area of surface mount technology (SMT) placement of electronic packages onto a printed circuit board (PCB), wherein the PCB is another configuration of the carrier object with a plurality of placement positions for receiving the electronic packages.