Abstract:
An automatic wire bonder including a lead frame provided with N number of bonding sites, N being a positive integer; a window clamper for clamping the lead frame and for exposing M number of bonding sites, M being a positive integer; K number of cameras for obtaining images of dies and portions of the lead frame located in the exposed bonding sites, K being a positive integer; a microprocessor for calculating bonding points of the dies and the lead frame based on the obtained images; and a capillary for automatically wire bonding the chips based on the calculated bonding points. Each of the bonding sites has a die pad at a center portion thereof to attach a die and a number of leads at a peripheral portion of the bonding site. In the automatic wire bonder, the lead frame is fed into a space between the window clamp and the heater block by the M pitches at once in such a way that M numbers of bonding sites are aligned with the working areas.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an apparatus for assembling a semiconductor device and, more particularly, to an apparatus for automatically wire bonding a semiconductor device and a method for the implementation thereof.  
         DESCRIPTION OF THE PRIOR ART  
         [0002]    In general, an automatic wire bonder is used for electrically connecting a semiconductor chip to a lead frame. The automatic wire bonder can precisely move a bonding tool incorporated therein to a predetermined X-Y position where the lead frame is mechanically pre-positioned in a work holder. First, the automatic wire bonder recognizes a pattern of the chip and the lead frame to obtain bonding points. The bonding tool then connects the bonding points by using a gold wire.  
           [0003]    In FIG. 1, there is shown a conventional wire bonder  100  comprising a heater block  140 , a window clamp  120  provided with a window  124  for defining a working area, a bonding head  110  provided with a camera  112  and a transducer  114  having a capillary  115 . In the conventional wire bonder  100 , a lead frame  150  is fed into a space between the window clamp  120  and the heater block  140 . The window clamp  120  clamps the lead frame  150 , with the lead frame  150  being provided with a number of bonding sites  132 ,  134 ,  136 . Each of the bonding sites  132 ,  134 ,  136  includes a die pad at a center portion thereof and a plurality of leads at a peripheral portion thereof. The die pad is used for attaching a die thereto. The die pad includes a number of bonding pads at its peripheral portion. The die is electrically connected to the leads of the lead frame  150  by using a gold wire.  
           [0004]    After the window clamp  120  clamps the lead frame  150 , the camera  112  carries out a pattern recognition process for the working area to obtain an image thereof. The microprocessor (not shown) calculates bonding points by using the obtained image. Thereafter, the capillary  114  starts to bond the semiconductor chip in response to a control signal from the microprocessor. The control signal is generated based on the calculated bonding points.  
           [0005]    After one of the semiconductor chips located in the lead frame  150  is bonded, the lead frame  150  is moved a predetermined distance, e.g., a pitch of bonding sites. Again, the wire bonder  100  repeats the above processes to bond another semiconductor chip.  
           [0006]    One of the major shortcomings of the above-described wire bonder  100  is that it cannot implement a pattern recognition process for a next semiconductor chip to be bonded while the capillary  115  is carrying out a wire bonding.  
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, an object of the present invention to provide an apparatus for wire bonding semiconductor chips, which is capable of reducing an overall bonding time.  
           [0008]    It is another object of the present invention to provide a method for bonding semiconductor chips, which is capable of carrying out a pattern recognition process for a next semiconductor chip to be bonded while a capillary is bonding a semiconductor chip.  
           [0009]    In accordance with one aspect of the present invention, there is provided an apparatus for assembling a semiconductor device, comprising a lead frame provided with N number of bonding sites, each of which sites has a die pad at a center portion thereof to attach a die and a number of leads at a peripheral portion of the bonding site, the die having a number of bonding pads, with N being a positive integer; a window clamper for clamping the lead frame and for exposing M number of bonding sites, with M being a positive integer; K number of cameras for obtaining images of dies and portions of the lead frame located in the exposed bonding sites, with K being a positive integer; a microprocessor for calculating bonding points of the dies and the lead frame based on the obtained images; and a capillary for automatically wire bonding the chip based on the calculated bonding points.  
           [0010]    In accordance with another aspect of the present invention, there is provided a method for automatically wire-bonding a semiconductor device, the method comprising the steps of a) assigning identification (ID) numbers to all chips attached to a lead frame; b) clamping N number of working chips, selected from the total number of chips, to N number of working areas, each of the working chips being located at a corresponding working area, wherein N is a positive number; c) obtaining all images of working areas by using M number of cameras and calculating N sets of bonding points based on the images, wherein M is a positive integer; d) moving a capillary to one of the working areas to electrically connect a working chip to leads located therein; e) waiting a predetermined time until the bonding of the working chip is finished; f) moving the capillary to another working area to electrically connect a working chip to leads located therein based on a corresponding set of bonding points; g) repeating the steps d) to f) until all of the working chips are bonded; and h) repeating the steps b) to g) until all of the chips are bonded.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a perspective view setting forth a portion of a conventional wire bonder;  
         [0013]    [0013]FIG. 2 is a perspective view illustrating a portion of a wire bonder in accordance with a first preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 3 is a flow chart showing a method for implementing the first preferred embodiment of the present invention;  
         [0015]    [0015]FIG. 4 is a perspective view illustrating a portion of a wire bonder in accordance with a second preferred embodiment of the present invention;  
         [0016]    [0016]FIG. 5 is a flow chart setting forth a method for implementing the second preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 6 is a perspective view representing a portion of a wire bonder in accordance with a third preferred embodiment of the present invention;  
         [0018]    [0018]FIG. 7 is a flow chart showing a method for implementing the third preferred embodiment of the present invention;  
         [0019]    [0019]FIG. 8 is a perspective view depicting a portion of a wire bonder in accordance with a fourth preferred embodiment of the present invention; and  
         [0020]    [0020]FIG. 9 is a flow chart illustrating a method for implementing the fourth preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    There are provided in FIGS. 2, 4,  6  and  8  perspective views of automatic wire bonders and in FIGS. 3, 5,  7 , and  9  flow charts setting forth methods for implementing the respective automatic wire bonders in accordance with preferred embodiments of the present invention. It should be noted that like parts appearing in FIGS.  2  to  9  are represented by like reference numerals.  
         [0022]    In FIG. 2, there is provided a perspective view of a first preferred embodiment of the inventive automatic wire bonder  200  comprising a heater block  240 , a window clamp  220  provided with a pair of windows  221 ,  223  for defining two working areas  222 ,  224  and a bonding head  210  provided with a camera  212  and a transducer  214  with a capillary  215 .  
         [0023]    In the automatic wire bonder  200 , if a lead frame  250  is fed into a space between the window clamp  220  and the heater block  240 , the window clamp  220  clamps the lead frame  250 . The lead frame  250  is provided with a number of bonding sites. The windows  221 ,  223  are designed in such a way that a pitch A of the windows is equal to the pitch A′ of the bonding sites  232 ,  234 ,  236 . In the first preferred embodiment, the lead frame  250  is fed into the space such that both window pitches are aligned with bonding sites at once. Each of the bonding sites  232 ,  234 ,  236  includes a die pad at a center portion thereof and a plurality of leads at a peripheral portion thereof. The die pad is used for bonding a die thereto. The die includes a number of bonding pads at its peripheral portion. The die is electrically connected to the leads of the lead frame  250  by using a gold wire. The transducer  214  provides ultra sonic power to the capillary  215  while the capillary  215  presses the gold wire at a bonding point.  
         [0024]    [0024]FIG. 3 is a flow chart illustrating the operation of the automatic wire bonder  200  in accordance with the first preferred embodiment of the present invention. A microprocessor (not shown) of the automatic wire bonder  200  includes a wire bonding main processor and a pattern recognition system (PRS) main processor. In the automatic wire bonder  200 , the lead frame  250  is fed into the space between the window clamp  220  and the heater block  240  by the two pitches at once in such a way that two bonding sites  232 ,  234  are aligned with the working areas  222 ,  224 , respectively.  
         [0025]    At step S 301 , the wire bonding main processor assigns serial numbers (e.g., 1, 2, 3, . . . N) to all of the chips in sequence upon entering the window clamp  220 . Next, at step S 302 , I is set to 1.  
         [0026]    At step S 303 , an Ith chip is moved to a main working area  222 . Next, at step S 304 , a camera  212  of bond head  210  is moved to a sub working area  224 . Meanwhile, in the PRS main processor, the camera obtains a chip image of the sub working area  224  and stores the obtained chip image in the PRS main processor, at step S 311 .  
         [0027]    At step S 305 , the camera  212  is moved to the main working area  222  to obtain a chip image of the main working area  222  in response to a first control signal from the PRS main processor. The chip image of the main working area  222  is stored into the PRS main processor, at step S 312 .  
         [0028]    At step S 313 , the PRS main processor calculates bonding points of the main working area  222  based on the chip image of the main working area  222 . The wire bonding main processor controls the bonding head  210  based on the calculated bonding points in such a way that bonding points of the main working area  222  are electrically bonded to leads of the lead frame  250  with a gold wire using a capillary  215  of the bonding head  210 .  
         [0029]    During the bonding of the main working area  222 , the PRS main processor calculates bonding points of the sub working area  224  based on the stored chip image of the sub working area  224 , at step S 314 . After the bonding of the main working area  222 , the wire bonding main processor controls the bonding head  210  in such a way that bonding points of the sub working area  224  are electrically bonded to leads of the lead frame  250 , at step S 307 .  
         [0030]    The process then moves to step S 309  where it is determined whether or not all of the chips in the lead frame  250  have been bonded. If not, the wire bonding main processor adds 2 to I at step S 308  and returns to the step S 303 . When all of the chips in the lead frame  250  have been bonded, the wire bonding main processor ends all of the processes.  
         [0031]    In FIG. 4, there is provided a perspective view of a second preferred embodiment of the inventive automatic wire bonder. The automatic wire bonder  400  of the second preferred embodiment of the present invention is similar to that of the first preferred embodiment shown in FIG. 2 except that a window clamp  420  is provided with three windows  421 ,  423 ,  425  for defining three working areas  422 ,  424 ,  426 , wherein a pitch A of the windows  421 ,  423 ,  425  is equal to a pitch A′ of bonding sites  432 ,  434 ,  436 . In the second preferred embodiment, the lead frame  450  is fed into a space between the window clamp  420  and the heater block  440  in such a way that the three bonding sites  432 ,  434 ,  446  are each aligned with a respective working area  422 ,  424 ,  426 .  
         [0032]    The operation of the automatic wire bonder  400  will be described in more detail with reference to FIG. 5. A microprocessor (not shown) of the automatic wire bonder  400  includes a wire bonding main processor and a pattern recognition system (PRS) main processor. In the automatic wire bonder  400 , the lead frame  450  is fed into the space between the window clamp  420  and the heater block  440  in such a way that each of the three bonding sites  432 ,  434 ,  436  is aligned with a respective working area  422 ,  424 ,  426  at the same time.  
         [0033]    Upon start up, at step S 501 , the wire bonding main processor assigns serial numbers (e.g., 1, 2, 3, . . . N) to all of the chips in sequence of entering the window clamp  420 . Next, at step S 502 , M, C and I are initialized. Specifically, M is the number of working areas, C is equal to M and I is equal to 1.  
         [0034]    At step S 503 , an Ith chip is moved to a first working area  422 . Next, at step S 504 , a camera  412  of bonding head  410  is moved to a Cth sub working area, e.g.,  424 . Meanwhile, in the PRS main processor, the camera  412  obtains a chip image of the sub working area  424  and stores the obtained chip image in the PRS main processor, at step S 511 . The process goes to step S 505  where it is determined whether or not C is equal to 0. If C is not equal to 0, the wire bonding main processor subtracts 1 from C at step S 521  and the process returns to the step S 504  to repeat the steps S 504  and S 511 . If C is equal to 0, the process goes to step S 506  to set C and B to 1.  
         [0035]    At step S 512 , the PRS main processor calculates bonding points of the Cth working area based on the stored Cth chip image. The process goes to step S 513  where it is determined whether or not C is larger than M. If C is not larger than M, the PRS main processor adds 1 to C at step S 514  and the process returns to the step S 512  to repeat the steps S 512  and S 513 . If C is larger than M, the processor stops these processes.  
         [0036]    After the step S 506 , the process goes to step S 507  where the bonding head  410  waits for the recognition of bonding points in the Bth working area. Then, the bonding head  410  bonds the chip in the Bth working area, at step S 508 . The process goes to step S 509  where it is determined whether or not B is larger than M. If B is not larger than M, the wire bonding main processor adds 1 to B at step S 523  and the process returns to the step S 507  to repeat the steps S 507 , S 508  and S 509 . If B is larger than M, the process goes to step S 510  where it is determined whether or not all of the chips in the lead frame  450  have been bonded. If all of the chips have not been bonded, the wire bonding main processor sets C to M and I to I+M at step S 522  and returns to the step S 503 . If all the chips have been bonded, the wire bonding main processor stops all these processes.  
         [0037]    In FIG. 6, there is provided a perspective view of a third preferred embodiment of the inventive automatic wire bonder. The automatic wire bonder  600  of the third preferred embodiment of the present invention is similar to that of the first preferred embodiment shown in FIG. 2 except that the bonding head  610  is provided with two cameras  612 ,  616 , wherein a pitch A of the windows  621 ,  623  is equal to a pitch A′ of the bonding sites  632 ,  634 ,  636 . In the third preferred embodiment, in order to reduce the pattern recognition time, two cameras  612 ,  616  are installed into the bonding head  610 . It should be noted that a pitch A″ of cameras  612 ,  616  is equal to the pitch A of the windows  621 ,  623 . The lead frame  650  is fed into a space between the window clamp  620  and the heater block  640  in such a way that each of two bonding sites  632 ,  634  is aligned with a respective working area  622 ,  624  at the same time.  
         [0038]    [0038]FIG. 7 is a flow chart illustrating the operation of the automatic wire bonder  600  in accordance with the third preferred embodiment of the present invention. A microprocessor (not shown) of the automatic wire bonder  600  includes a wire bonding main processor and a pattern recognition system (PRS) main processor. In the automatic wire bonder  600 , the lead frame  650  is fed into a space between the window clamp  620  and the heater block  640  in such a way that two bonding sites  632 ,  634  are aligned with the working areas  622 ,  624  at the same time.  
         [0039]    At step S 701 , the wire bonding main processor assigns serial numbers (e.g., 1, 2, 3, . . . N) to all of the chips in sequence of entering the window clamp  620 . Next, at step S 702 , I is set to 1.  
         [0040]    At step S 703 , an Ith chip is moved to a main working area  622 . Next, at step S 704 , a first camera  612  of bond head  610  is moved to a sub working area  624 . Meanwhile, in the PRS main processor, the first camera  612  obtains a chip image of the main working area  622  and the second camera  616  obtains a chip image of the sub working area  624  to store the obtained chip images in the PRS main processor, at step S 711 .  
         [0041]    At step S 712 , the PRS main processor recognizes bonding points of the obtained chip image in the main working area  622 . The process goes to step S 705  to bond the chip in the main working area  622  by using the capillary  614 .  
         [0042]    During the bonding of the main working area  622 , at step S 713 , the PRS main processor calculates bonding points of the obtained chip image in the sub working area  624 . At step S 706 , the wire bonding main processor waits until the chip in the main working area  622  is bonded. After the bonding of the chip in the main working area  622 , the process goes to the step S 707  for bonding a chip in the sub working area  624  based on the bonding points calculated at the step S 713 .  
         [0043]    The process then moves to step S 708  where it is determined whether or not all of the chips in the lead frame  650  have been bonded. If all the chips have not been bonded, the wire bonding main processor adds 2 to I at step S 709  and returns to the step S 703 . If all the chips have been bonded, the wire bonding main processor ends all of the processes.  
         [0044]    In FIG. 8, there is provided a perspective view of a fourth preferred embodiment of the inventive automatic wire bonder. The automatic wire bonder  800  of the fourth preferred embodiment of the present invention is similar to that of the second preferred embodiment shown in FIG. 4 except that a bonding head  810  is provided with three cameras  812 ,  814 ,  818 , wherein a pitch A of windows  821 ,  823 ,  825  is equal to a pitch A′ of bonding sites  832 ,  834 ,  836 . In the third preferred embodiment, by utilizing three cameras  812 ,  814 ,  818 , the automatic wire bonder  800  can drastically reduce the bonding time of chips in comparison with the prior art wire bonder  100 . It should be noted that a pitch A″ of cameras  812 ,  814  is equal to the pitch A of windows  821 ,  823 . The lead frame  850  is fed into a space between the window clamp  820  and the heater block  840  in such a way that each of the three bonding sites  832 ,  834 ,  836  is aligned with a respective working area  822 ,  824 ,  826  at the same time.  
         [0045]    It should also be understood that the present invention is not limited to the number of cameras and the number of windows of the window clamp, provided that the automatic wire bonder is made to implement PRS in parallel.  
         [0046]    The operation of an automatic wire bonder  800  will be described in more detail with reference to FIG. 9. A microprocessor (not shown) of the automatic wire bonder  800  includes a wire bonding main processor and a pattern recognition system (PRS) main processor. In the automatic wire bonder  800 , the lead frame  850  is fed into a space between the window clamp  820  and the heater block  840  in such a way that the three bonding sites  832 ,  834 ,  836  are aligned with the working areas  822 ,  824 ,  826  at the same time.  
         [0047]    Upon start up, as step S 901 , the wire bonding main processor assigns serial numbers (e.g., 1, 2, 3, . . . N) to all of the chips in sequence of entering the window clamp  820 . Next, at step S 902 , M and I are initialized. Specifically, M is the number of working areas and I is equal to 1.  
         [0048]    At step S 903 , an Ith chip is moved to a first working area  822 . Meanwhile, in the PRS main processor, each of the cameras  812 ,  814 ,  818  of bonding head  810  are moved to a corresponding working area, respectively. Each of the cameras  812 ,  814 ,  818  obtains a corresponding chip image of the sub working areas  822 ,  824 ,  826  and stores the obtained chip images in the PRS main processor, at step S 913 . The process goes to steps S 905  and S 914  to set each of B and C equal to 1.  
         [0049]    After the step S 914 , the process goes to step S 915  to recognize bonding points based on the Cth stored chip image. The process then goes to step S 917  where it is determined whether or not C is larger than M. If C is not larger than M, the wire bonding main processor adds 1 to C at step S 916  and the process returns to the step S 915  to repeat the steps S 915  and S 917 . If C is larger than M, the process stops.  
         [0050]    On the other hand, after the step S 905 , the wire bonding main processor waits until the recognition of the chip in the Bth working area is finished, at step S 906 . When the recognition of bonding points in the Bth working area is ended, the process goes to step S 907  to bond the chip in the Bth working area. Then, the process goes to step S 908  where it is determined whether or not B is larger than M. If B is not larger than M, the wire bonding main processor adds 1 to B at step S 910  and the process returns to the step S 906 . If B is larger than M, the process goes to step S 909  to determine whether or not all of the chips have been bonded. If all of the chips have not been bonded, the wire bonding main processor adds M to I at step S 912  and the process returns to the step S 903 . If all of the chips have been bonded, the wire bonding main processor stops all of the processes.  
         [0051]    In comparison with the prior art, the present invention can drastically reduce the bonding time of chips by utilizing a number of cameras. This is achieved by designing a window clamp in such a way that the lead frame can be fed into a space between the window clamp and the heater block by the M pitches at once.  
         [0052]    While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.