Abstract:
Method and apparatus for suction-holding a semiconductor pellet on a positioning stage of a bonding apparatus without causing the pellet to be misaligned after positioning thereof including a suction force control device. The suction force control device comprises a suction-switching electromagnetic valve, a suction force-adjusting electromagnetic valve, a vacuum source, a compressed air source and a throttle valve so that a semiconductor pellet is held on a positioning stage by a suction force that is weak enough that a positioning claw can move the semiconductor pellet for positioning; and upon completion of the positioning, the semiconductor pellet is held to the positioning stage by a suction force that is stronger than the weak suction force used for positioning.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a method and apparatus for positioning semiconductor pellet in a die bonding apparatus, tape bonding apparatus, bump bonding apparatus or the like. 
     2. Prior Art 
     In a die bonding apparatus, tape bonding apparatus, bump bonding apparatus or the like, a semiconductor pellet is removed from a tray or wafer and placed on a positioning stage, and once placed on this positioning stage, the semiconductor pellet is positioned by a positioning claw. After this, in a die bonding apparatus, the semiconductor pellet is bonded to a lead frame. In a tape bonding apparatus, the semiconductor pellet is bonded to a carrier tape. In a bump bonding apparatus, a bump is formed on an electrode of the semiconductor pellet. In other words, in these bonding apparatuses, the semiconductor pellet is positioned prior to bonding or the formation of a bump. 
     Operations in these bonding apparatuses will be described below in more detail. 
     As shown in FIG. 5, a die bonding apparatus has a positioning stage  51  for holding a semiconductor pellet  50  by means of a suction hole  51   a , a positioning claw  52  for positioning the semiconductor pellet  50  on the positioning stage  51 , a frame feeder  54  for conveying and positioning a lead frame  53 , and a bonding device  60  for bonding the semiconductor pellet  50  to the lead frame  53 . The positioning claw  52  is provided on an XY table  55  which is driven in the X and Y directions. In the bonding device  60 , a bonding head  62  is mounted on an XY table  61  that is driven in the X and Y directions, and a bonding arm  63  is provided on the bonding head  62  so as to be moved up and down. A bonding tool  64  is provided on the distal end of the bonding arm  63 . This bonding tool  64  is in the form of a suction nozzle that holds the semiconductor pellet  50  by suction. 
     This type of die bonding apparatus is disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) Nos. H4-61241 and H4-312936. 
     When the semiconductor pellet  50  is placed on the positioning stage  51 , it is held by suction on the positioning stage  51 . Then, the XY table  55  is driven to move the positioning claw  52  toward the semiconductor pellet  50 , and the semiconductor pellet  50  is positioned by the positioning claw  52 . Next, the XY table  61  of the bonding device  60  is moved in the Y direction so as to be above the semiconductor pellet  50  on the positioning stage  51 , and the bonding tool  64  is lowered to hold the semiconductor pellet  50 . The bonding tool  64  is then raised, moved to above the bonding position of the lead frame  53 , and then lowered, thus bonding the semiconductor pellet  50  to the lead frame  53 . 
     As to a tape bonding apparatus, and particularly an inner lead bonding apparatus, it is structured, as shown in FIG. 6, more or less the same as the die bonding apparatus shown in FIG.  5 . In this inner lead bonding apparatus of FIG. 6, however, the positioning claw  52  does not move; and instead the positioning stage  51  is mounted on the XY table  55 , and the positioning stage  51  is moved to beneath a carrier tape  65  by the XY table  55 . Also, the bonding tool  64  is not a suction nozzle and is shaped such that a lead provided on the carrier tape  65  will be pressed against the semiconductor pellet  50 . 
     Japanese Patent Application Laid-Open (Kokai) No. H2-244735 discloses this type of tape bonding apparatus. 
     When a semiconductor pellet  50  is placed on the positioning stage  51 , it is held by suction on the positioning stage  51 . The XY table  55  is driven to move the positioning stage  51  toward the semiconductor pellet  50 , and the semiconductor pellet  50  is positioned by the positioning claw  52 . The XY table  55  is then driven to move the positioning stage  51  to beneath the carrier tape  65 , after which the lead of the carrier tape  65  is pressed against and bonded to the semiconductor pellet  50  by the bonding tool  64  of the bonding device  60 . 
     As to a bump bonding apparatus, it is also, as shown in FIG. 7, structured more or less the same as the die bonding apparatus shown in FIG.  5 . In this bump bonding apparatus, however, the positioning stage  51  doubles as a bonding stage, and a wire bonding device is used as the bonding device  60 . Therefore, a very fine (20 to 30 μm) wire of gold or solder (not shown) is passed through the bonding tool  64 . 
     When the semiconductor pellet  50  is placed on the positioning stage  51 , it is held by suction on the positioning stage  51 . The XY table  55  is driven to move the positioning claw  52  toward the semiconductor pellet  50 , and the semiconductor pellet  50  is positioned by the positioning claw  52  provided on the XY table  55 . A bump is then formed on an electrode of the semiconductor pellet  50  by the bonding device  60 . In this bump formation method, a ball formed at the distal end of the wire passing through the bonding tool  64  is pressed against the electrode of the semiconductor pellet, the wire is cut at the base of the ball, and a bump is formed on the electrode of the semiconductor pellet. 
     An example of this type of bump bonding apparatus can be found in Japanese Patent Application Laid-Open (Kokai) No. H7-86286. 
     In the above bonding apparatuses, the semiconductor pellet  50  is moved by the positioning claw  52  during the positioning process; accordingly, it is necessary that the positioning stage  51  holds the semiconductor pellet  50  with a weak suction force that allows the semiconductor pellet  50  to be moved. However, since the semiconductor pellet  50  is kept held by this weak suction force in the above bonding apparatuses, there is the danger that the semiconductor pellet  50  is misaligned due to vibration or other reasons as described below. 
     More specifically, in the die bonding apparatus shown in FIG. 5, the semiconductor pellet  50  positioned by the positioning claw  52  is moved over the lead frame  53  by being held by the bonding tool  64 ; accordingly, much of a problem would not occur. In the case of the tape bonding apparatus shown in FIG. 6, however, the positioning stage  51  and the semiconductor pellet  50  held thereon are moved to beneath the carrier tape  65 ; accordingly, the semiconductor pellet  50  is susceptible to misalignment during this movement. In addition, in the case of the bump bonding apparatus shown in FIG. 7, since the formation of the bump is performed by the bonding device  60  on the semiconductor pellet  50  held on the positioning stage  51 , the semiconductor pellet  50  is susceptible to misalignment during this bump formation. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention is to provide a semiconductor pellet positioning method and apparatus that prevent the misalignment of a semiconductor pellet once it has been positioned. 
     The method of the present invention for accomplishing the above object is a semiconductor pellet positioning method in which a positioning stage for holding a semiconductor pellet is moved relative to a positioning claw, and the semiconductor pellet is positioned by the positioning claw; and in the present invention during the positioning of the semiconductor pellet, the semiconductor pellet is held on the positioning stage by a suction force that is weak enough so that the positioning claw can move the semiconductor pellet, and upon completion of the positioning, the semiconductor pellet is held on the positioning stage by a suction force that is stronger than suction force used during the positioning. 
     The apparatus of the present invention for accomplishing the above object is a semiconductor pellet positioning apparatus that comprises a positioning stage for holding a semiconductor pellet and a positioning claw for positioning the semiconductor pellet by moving relative to this positioning stage; and in the present invention, a suction force control means is further provided so that the semiconductor pellet is held on the positioning stage during the positioning of the semiconductor pellet by a suction force that is weak enough so that the positioning claw can move the semiconductor pellet and that upon completion of the positioning the semiconductor pellet is held on the positioning stage by a suction force that is stronger than the suction force used during the positioning. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the structure of the suction force control means according to one embodiment of the semiconductor pellet positioning apparatus of the present invention, showing the control of the suction during the positioning of the semiconductor pellet; 
     FIG. 2 is a diagram showing the control of the suction upon completion of the positioning; 
     FIG. 3 is a diagram showing the control of the suction during the process of picking-up the semiconductor pellet; 
     FIG. 4 is a perspective view of an example of a bump bonding apparatus which uses an embodiment of the present invention; 
     FIG. 5 is a schematic top view of a die bonding apparatus; 
     FIG. 6 is a schematic top view of a tape bonding apparatus; and 
     FIG. 7 is a schematic top view of a bump bonding apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described with reference to FIGS. 1 to  4 . First, a bump bonding apparatus to which an embodiment of the present invention is applied will be described with reference to FIG.  4 . 
     A capillary  2  is provided to one end of a bonding horn  3  so that a wire  1  passes therethrough, and the bonding horn  3  is attached to a lifter arm  4 . The lifter arm  4  is mounted to a bonding head  5  so as to be moved up and down or swing and is moved up and down or swung by a Z axis motor  6  that is fixed to the bonding head  5 . The bonding head  5  is mounted on an XY table  7 . 
     A bond loading linear motor  11  that provides a bonding load for pressing the ball  1   a  formed at the distal end of the wire  1  against an electrode of a semiconductor pellet  10  is fixed on its coil side to the lifter arm  4  and on its magnet side to the bottom of the bonding head  5 . A detection camera  12  for providing an image of the semiconductor pellet  10  is fixed to the bonding head  5 . This detection camera  12  is connected to one end of a horizontally disposed lens barrel  13 , and a detection component  14  that incorporates the image of the semiconductor pellet  10  is provided to the other end of the lens barrel  13 . The semiconductor pellet  10  is vacuum-held on a positioning stage  15  by a suction hole  15   a  opened in the positioning stage  15 . The positioning stage  15  is used as a bonding stage as well. The structure described above is known and will not be described further. 
     In the above bump bonding apparatus, a positioning claw  16  is fixed to the XY table  7 . The positioning element  16   a  of the positioning claw  16  extends beneath the bonding horn  3  and to the rear side of the capillary  2 , so that the lower surface of the positioning element  16   a  is located slightly above the upper surface of the positioning stage  15 . The positioning element  16   a  is shaped so as to accommodate the corner of the semiconductor pellet  10  placed on the positioning stage  15 . 
     The suction force control means of the embodiment of the present invention will now be described with reference to FIGS. 1 to  3 . 
     The positioning stage  15  that holds the semiconductor pellet  10  is switchably connected to a vacuum source  21  and a compressed air source  22  via a suction-switching electromagnetic valve  20 . In this embodiment, a three-port electromagnetic valve is used as the suction-switching electromagnetic valve  20 . Thus, the suction-switching electromagnetic valve  20  has ports P 1  and P 1 ′ and P 2  and P 2 ′ on its inlet side, and it further has ports P 3  and P 3 ′ on its outlet side. Among these ports, the ports P 1  and P 3  and ports P 2 ′ and P 3 ′ communicate with each other, but the ports P 2  and P 1 ′ are closed (thus not communicating with each other). 
     Thus, when the suction-switching electromagnetic valve  20  is on, as shown in FIGS. 1 and 2, the port P 3  is connected to and communicates with a pipe  23  that leads to the suction hole  15   a  of the positioning stage  15 , and the ports P 1  and P 2  are connected to pipes  24  and  25 , respectively, leading to the vacuum source  21  and compressed air source  22 . Thus, when the suction-switching electromagnetic valve  20  is off, as shown in FIG. 3, the port P 3 ′ is connected to the pipe  23 , and the ports P 1 ′ and P 2 ′ are connected to the pipes  24  and  25 , respectively. 
     Furthermore, a pipe  30  is connected to the pipe  24 , and the pipe  30  is connected to an atmospheric air inlet  33  via a suction force-adjusting electromagnetic valve  31  and a throttle valve  32 . In this embodiment, a two-port electromagnetic valve is used as the suction force-adjusting electromagnetic valve  31 . Thus, the suction force-adjusting electromagnetic valve  31  has ports P 4  and P 4 ′ on its inlet side, and it also has ports P 5  and P 5 ′ on its outlet side. Here, the ports P 4  and P 5  communicate with each other, and the ports P 4 ′ and P 5 ′ are closed (thus not communicating with each other) 
     When the suction force-adjusting electromagnetic valve  31  is on, as shown in FIG. 1, the port P 4  is connected to the pipe  30 , and the port P 5  is installed so as to connect to the throttle valve  32 . When, on the other hand, the suction force-adjusting electromagnetic valve  31  is off, as shown in FIGS. 2 and 3, the port P 4 ′ is connected to the pipe  30 , and the port P 5 ′ is connected to the throttle valve  32 . 
     Before describing the positioning of the semiconductor pellet  10 , the action of the suction-switching electromagnetic valve  20  and the suction force-adjusting electromagnetic valve  31  will be explained. 
     As shown in FIG. 1, when the suction-switching electromagnetic valve  20  and the suction force-adjusting electromagnetic valve  31  are both on, the suction force of the suction hole  15   a  of the positioning stage  15  is as follows: When the suction-switching electromagnetic valve  20  is on, the port P 1  is connected to the pipe  24 , and the port P 3  is connected to the pipe  23 . Therefore, the suction hole  15   a  of the positioning stage  15  creates a suction at the level of vacuum pressure of the vacuum source  21 . However, since the suction force-adjusting electromagnetic valve  31  is on, the port P 4  is connected to the pipe  30 , and the port P 5  is connected to the throttle valve  32 ; thus the atmospheric air from the atmospheric air inlet  33  is supplied from the pipe  30  to the pipe  24  through the throttle valve  32  and the suction force-adjusting electromagnetic valve  31 . As a result, the vacuum pressure in the pipe  24  produced by the vacuum source  21  is reduced by the atmospheric air adjusted by the throttle valve  32 , and this reduced pressure suction force creates a suction from the suction hole  15   a  of the positioning stage  15  so as to hold the semiconductor pellet  10 . 
     On the other hand, as shown in FIG. 2, when the suction-switching electromagnetic valve  20  is on and the suction force-adjusting electromagnetic valve  31  is off, the suction force of the suction hole  15   a  of the positioning stage  15  is as follows: When the suction-switching electromagnetic valve  20  is on, as described for the case of FIG. 1, suction is created in the suction hole  15   a  of the positioning stage  15  at the level of vacuum pressure of the vacuum source  21 . However, since the suction force-adjusting electromagnetic valve  31  is off, the port P 4 ′ is connected to the pipe  30 , and the port P 5 ′ is connected to the throttle valve  32 . In other words, since the atmospheric air of the atmospheric air inlet  33  is not supplied to the pipe  30 , the vacuum pressure of the vacuum source  21  is unchanged (or not reduced), so that suction of the vacuum source  21  is created as is at the suction hole  15   a  of the positioning stage  15 . In other words, the semiconductor pellet  10  is held on the positioning stage  15  by a stronger suction force than that of the semiconductor pellet positioning process described above. 
     Furthermore, as shown FIG. 3, when the suction-switching electromagnetic valve  20  and the suction force-adjusting electromagnetic valve  31  are both off, the suction force of the suction hole  15   a  of the positioning stage  15  is as follows: When the suction-switching electromagnetic valve  20  is off, the port P 2 ′ is connected to the pipe  25 , and the port P 3 ′ is connected to the pipe  23 . Therefore, the compressed air of the compressed air source  22  is supplied to the suction hole  15   a  of the positioning stage  15 . In this case, since the pipe  24  is not connected to the pipe  23 , whether the suction force-adjusting electromagnetic valve  31  is on or off has no effect whatsoever on the compressed air supplied from the compressed air source  22  to the suction hole  15   a  of the positioning stage  15 . In FIG. 3, since the suction force-adjusting electromagnetic valve  31  is off, as described for FIG. 2, the atmospheric air of the atmospheric air inlet  33  is not supplied to the pipe  30 . 
     With the above-described structure, the vacuum pressure of the vacuum source  21  can be set at, for instance, approximately 500 to 650 mmHg; and the throttle valve  32  can be adjusted before hand so that the vacuum pressure at the suction hole  15   a  of the positioning stage  15  is approximately 200 to 350 mmHg, which is a reduced vacuum pressure level effected by the atmospheric air supplied from the atmospheric air inlet  33  as in FIG.  1 . This reduced, weak vacuum pressure is a suction force that allows the semiconductor pellet  10  to be moved by the positioning claw  16  (described below) but will not damage the semiconductor pellet  10 . 
     The positioning of the semiconductor pellet  10  performed after the above setting will now be described. 
     First, a semiconductor pellet  10  is picked up by a pick-up and conveyance means (not shown) from a tray or wafer (not shown) and conveyed to and placed on the positioning stage  15 . Once the conveyance of the semiconductor pellet  10  to the positioning stage  15  begins, the suction-switching electromagnetic valve  20  and the suction force-adjusting electromagnetic valve  31  are both turned on as shown in FIG.  1 . When the suction-switching electromagnetic valve  20  and the suction force-adjusting electromagnetic valve  31  are both on, this results in a suction state produced by a weak vacuum pressure at the suction hole  15   a  of the positioning stage  15  as discussed above. 
     The XY table  7  is then driven such that the positioning element  16   a  of the positioning claw  16  pushes on the corner of the semiconductor pellet  10 . 
     When the positioning element  16   a  of the positioning claw  16  has pushed the semiconductor pellet  10  to a predetermined position, the suction-switching electromagnetic valve  20  stays on and the suction force-adjusting electromagnetic valve  31  is turned off as shown in FIG.  2 . As a result, suction is created in the suction hole  15   a  of the positioning stage  15  at the vacuum pressure of the vacuum source  21  as described above. In other words, the weak vacuum is switched to a strong vacuum, and the semiconductor pellet  10  is firmly held to the positioning stage  15 . 
     The XY table  7  is then driven such that the detection component  14  of the lens barrel  13  is positioned above the semiconductor pellet  10 . As a result, the positioning claw  16  retracts from above the positioning stage  15 . 
     After this, an image of the electrode on the semiconductor pellet  10 , which is the bonding location, is taken by the detection camera  12  via the detection component  14  and the lens barrel  13 , the ball  1   a  formed at the distal end of the wire  1  is bonded at the bonding location on the electrode of the semiconductor pellet  10 , and after this bonding the wire  1  is cut at the base of the ball  1   a . Thus, a bump is formed on the electrode of the semiconductor pellet  10 . 
     Once the formation of the bump on the semiconductor pellet  10  is complete, the semiconductor pellet  10  is taken out from the positioning stage  15 . This operation involves moving the suction nozzle (not shown) to above the positioning stage  15 , then lowering it and moving it to a position approximately 0.03 to 0.1 mm over the semiconductor pellet  10 . The suction force-adjusting electromagnetic valve  31  is kept off and the suction-switching electromagnetic valve  20  is turned off as shown in FIG.  3 . When the suction-switching electromagnetic valve  20  is turned off, a small amount of compressed air is supplied from the compressed air source  22  to the suction hole  15   a  of the positioning stage  15 , and the suction nozzle picks up and holds the semiconductor pellet  10 . The suction nozzle then moves the semiconductor pellet  10  to the specified place. 
     The above embodiment is described with reference to a bump bonding apparatus, and the positioning claw  16  is provided on the XY table  7 . However, the suction force control means of the present invention can be applied to the positioning stage  51  of the bump bonding apparatus shown in FIG. 7 in which the positioning claw  52  is provided on the XY table which is independent from the bonding head  62 . 
     It should go without saying that the suction force control means can also be applied to the positioning stage  51  of the die bonding apparatus shown in FIG.  5  and that of the tape bonding apparatus shown in FIG.  6 . 
     As seen from the above, during the positioning of the semiconductor pellet  10 , the semiconductor pellet  10  is held to the positioning stage  15  at a suction force weak enough that the semiconductor pellet  10  can be moved by the positioning claw  16 ; but upon completion of the positioning, the semiconductor pellet  10  is held to the positioning stage  15  at a suction force that is stronger than the above-described weak suction force. As a result, misalignment of the semiconductor pellet  10  after it has been positioned is prevented. 
     Also, there is no need for a positioning stage to have a bulky construction since the positioning claw  16  is provided on the XY table  7 . Furthermore, since the positioning claw  16  is driven by the XY table  7 , which is a part of the bonding apparatus itself, there is no need for the drive means of the positioning claw  16  to have a bulky construction, either. The apparatus is therefore simpler and less expensive. Though the positioning claw  16  is provided on the XY table  7 , it may instead be provided on the bonding head  5  mounted on the XY table  7  or on any member fixed to the bonding head  5 . 
     As seen from the above, according to the present invention, during the positioning of the semiconductor pellet, the semiconductor pellet is held on the positioning stage by suction that is weak but enough for the semiconductor pellet to be moved by the positioning claw; but once the positioning by the positioning claw is completed, the semiconductor pellet is held on the positioning stage by suction that is strong enough for semiconductor pellet to be immovable, so that misalignment of the semiconductor pellet after it has been positioned is prevented. 
     Also, when the positioning claw for positioning a semiconductor pellet on the positioning stage is provided on the bonding head or on the XY table on which the bonding head is mounted, the semiconductor pellet positioning stage and positioning claw, the positioning drive means for the positioning stage, and so on do not have a bulky construction; and the cost of the apparatus can be reduced.