Abstract:
There is provided a strap-bonding machine, including a metal ribbon tape storage portion configured to hold a metal ribbon tape, a metal ribbon tape-cutting portion configured to cut the metal ribbon tape fed from the metal ribbon tape storage portion to a metal strap having a predefined shape, a metal strap-carrying portion configured to feed the metal strap to a picking-position, a lead frame-carrying portion configured to carry a lead frame mounted a semiconductor chip on and having a lead terminal, and a bonding portion configured to pick up the metal strap at the picking-position, to carry the metal strap above the lead frame and to bond the metal strap to the semiconductor chip and the lead terminal.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. JP2004-213756, filed on Jul. 22, 2004; the entire contents of which are incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a strap bonding machine and a method of manufacturing a semiconductor device, and in particular, to a strap bonding machine and a strap bonding method electrically connecting between a semiconductor chip and a lead terminal using a metal strap formed by cutting out a metal ribbon tape.  
       DESCRIPTION OF THE BACKGROUND  
       [0003]     In recent MOSFET and IGBT for an application to a power semiconductor device, a strap conductor made of Al or Cu has been used for electrically connecting between a semiconductor chip and a lead terminal instead of a wire bonding technique using high cost materials such as Au. For example, a strap bonding technique is described in Japanese Patent Publication (Kokai) No. JP2002-314018, P20, FIG. 15. The strap bonding technique mentioned in the above reference can lead to reduction of a cost on the device, lowering resistance and preventing the conductor from disconnecting.  
         [0004]     As comparing with the conventional wire bonding in which an Au wire or an Al wire is bonded to a semiconductor chip, the strap bonding technique has a shortage such as a comparatively low speed operation. Therefore, the strap bonding technique has an issue on production efficiency. On the other hand, another issue on the strap bonding technique is to simplify a construction of a strap bonding machine.  
       SUMMARY OF THE INVENTION  
       [0005]     According to an aspect of the invention, there is provided a strap-bonding machine, including a metal ribbon tape storage portion configured to hold a metal ribbon tape, a metal ribbon tape-cutting portion configured to cut the metal ribbon tape fed from the metal ribbon tape storage portion to a metal strap having a predefined shape, a metal strap-carrying portion configured to feed the metal strap to a picking-position, a lead frame-carrying portion configured to carry a lead frame mounted a semiconductor chip on and having a lead terminal, and a bonding portion configured to pick up the metal strap at the picking-position, to carry the metal strap above the lead frame and to bond the metal strap to the semiconductor chip and the lead terminal.  
         [0006]     Further, according to another aspect of the invention, there is provided a strap bonding machine, including a metal ribbon tape storage portion configured to hold a metal ribbon tape, a metal ribbon tape-cutting portion configured to include a lead connection area and a chip connection area, to process a metal ribbon tape as a loop-like shape in height direction between the lead connection area and the chip connection area, to cut the metal ribbon tape to a metal strap having the loop-like shape, a metal strap-carrying portion configured to feed the metal strap to a picking-position, a lead frame-carrying portion configured to carry a lead frame mounted a semiconductor chip on and having a lead terminal, and a bonding portion configured to pick up the metal strap and to bond the metal strap to the semiconductor chip and the lead terminal.  
         [0007]     Further, according to another aspect of the invention, there is provided a method of manufacturing a semiconductor device, including cutting a metal ribbon tape to a metal strap having a predefined shape, carrying the metal strap to a picking-position, carrying a lead frame mounted a semiconductor chip on and having a lead terminal to a bonding portion, picking up the metal strap, carrying the metal strap to the bonding portion, and bonding the metal strap to the semiconductor chip and the lead terminal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a front view showing an Al strap bonding machine in a first embodiment of the present invention;  
         [0009]      FIG. 2  is a plan view showing a bonding portion in the first embodiment of the present invention;  
         [0010]      FIG. 3  is a schematic diagram showing a manufacturing process steps of a semiconductor device by using the Al strap bonding machine in the first embodiment of the present invention;  
         [0011]      FIG. 4  is a perspective view showing an Al strap in a second embodiment of the present invention; and  
         [0012]      FIG. 5  is a block diagram showing a motion of a strap-carrying portion in the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Embodiments of the present invention will be described hereinafter in detail with reference to the drawings mentioned above.  
         [0014]     First, according to a first embodiment of the present invention, a strap bonding machine and a strap bonding method are explained with reference to  FIGS. 1-3 .  FIG. 1  is a front view showing an Al strap bonding machine.  FIG. 2  is a plan view showing a bonding portion.  FIG. 3  is a schematic diagram showing a motion on the Al strap bonding machine.  
         [0015]     As shown in  FIG. 1 , an Al strap bonding machine  1  has a mount  2 , a base  3 , an operation panel portion  4 , a control portion  5 , an Al ribbon tape storage portion  6 , an Al ribbon tape-cutting portion  7 , an Al strap-carrying portion  8 , a bonding portion  9 , a lead frame-carrying portion  13  and image monitors  16   a ,  16   b . The Al strap bonding machine  1  electrically connects an Al strap  22  to electrodes of a power semiconductor chip  15  and lead terminals disposed on a lead frame  14 .  
         [0016]     The base  3  and the operation panel portion  4  disposed on the mount  2 . The control portion  5  is put in the lower right portion of the mount  2 . Data operated in the operation panel portion  4  is addressed into the control portion  5 . The control portion  5  sends control signals to the Al ribbon tape storage portion  6 , the Al ribbon tape-cutting portion  7 , the Al strap carrying-portion  8 , the bonding portion  9  and the lead frame-carrying portion  13 . The control signals control behavior of those potions.  
         [0017]     The Al ribbon tape storage portion  6  has an Al ribbon tape  21  like reel and a motor  18   a . The motor  18   a  controlled by the signals addressed from the control portion  5  makes the Al ribbon tape  21  feed to the Al ribbon tape cutting portion  7 . The Al ribbon tape-cutting portion  7  cut out the Al ribbon tape  21  to a plurality of Al straps  22  with a predefined shape. The Al strap-carrying portion  8  has a motor  18   b  and a carrying stage  20   a . The motor  18   b  operated by signals addressed from the control portion  5  makes the Al strap  22  feed to the carrying stage  20   a.    
         [0018]     The bonding portion  9  has a bonding head  10 , an arm  11 , an absorption head  12 , a high frequency power supply  17 , a motor  18   c  and a head supporting portion  19 . The absorption head  12  picks up the Al strap  22  by the signals addressed from the control portion  5 . The Al strap  22  is disposed above the surface between electrodes of a power semiconductor chip  15  and a lead terminal and is connected to the electrode and the lead terminal.  
         [0019]     The lead frame-carrying portion  13  has a motor  18   d  and a carrying stage  20   b . The carrying stage  20   b  received signals from the control portion  5  feeds the lead frame  14  from outside the lead frame-carrying portion  13 . On the other hand, the carrying stage  20   a  of the Al strap carrying portion  8  adjusts X-axis and Y-axis directions so as to correct the position of the Al strap  22 . The carrying stage  20   b  of the lead frame-carrying portion  13  adjusts X-axis and Y-axis directions so as to correct the position of the semiconductor chip  15  disposed on the lead frame  14 . An X-Y stage  20   c  disposed on a connection head in the bonding portion  9  adjusts X-axis and Y-axis directions so as to correct an absorption position (picking-position) and a connection position of the Al strap  22 .  
         [0020]     The image monitor  16   a  monitors a motion of the Al strap carrying portion  8  and inspects the lead frame  14  and the power semiconductor chip  15 . The image monitor  16   b  monitors a motion of the bonding portion  9  and the lead frame carrying portion  13  and inspects the power semiconductor chip  15  and the Al strap  22 . In addition, the operation panel portion  4  can change and extend the monitor position monitored by using the image monitors  16   a ,  16   b.    
         [0021]     As shown in  FIG. 2 , the bonding portion  9  has four bonding heads  10 . Each of the bonding head  10  picks up the Al strap (not illustrated) at a bonding head position  10   a  and move the Al strap to a bonding head position  10   b . Moreover, the Al strap is connected to a power semiconductor chip (not illustrated). After finishing the connection, the bonding head  10  moves again to the bonding head position  10   a . About a bonding head number, the singular number or plural are available.  
         [0022]     A manufacturing process steps of a semiconductor device by using the Al strap bonding machine  1  is shown a in  FIG. 3 . First, the Al ribbon tape  21  fed from the Al ribbon tape storage portion (not illustrated) is cut in rectangles at the Al ribbon tape cutting portion  7 , so that the plurality of Al straps  22  is formed.  
         [0023]     The position of the Al strap  22  on the carrying stage  20   a  is corrected by using a holding portion  23 . For a position correction method, a camera et al. (not illustrated) recognizes the Al strap  22  for adjusting to an Al strap image predominantly memorized in the control portion as shown in  FIG. 1 .  
         [0024]     The Al strap  22  is descended down by the holding portion  23  and is carried at the predetermined position by movement to X-direction and Y-direction of a holding piece  24  and rotation of the holding piece  24 . A rubber or the like having less hardness than that of Al, may set on a part of the holding piece  24  contacting with the Al strap  22 . A material with higher hardness can be applied for the rubber, if necessary.  
         [0025]     Next, the Al strap  22  on the carrying stage  20   a  is picked up. A camera or the like (not illustrated) is employed for observation of Al strap  22  in picking process. The bonding head  10  is carried at the position just above the Al strap  22  by movement to X-direction and Y-direction of the absorption head  12  and rotation of the absorption head  12 .  
         [0026]     The Al strap  22  is descended down by the bonding head  10  and is picked up by the absorption head  12 . The bonding head  10  holding the Al strap is rotated. The Al strap  22  is disposed on the connection portion  27  of the lead frame  14 . Ultrasonic wave generated by the high frequency power supply  17  bonds the Al strap  22  to a lead terminal  25  and a head  26 , so as to electrically connect between the lead terminal  25  and the power semiconductor chip  15  on the head  26 .  
         [0027]     As mentioned in the first embodiment of the strap bonding machine and the method of manufacturing the semiconductor device, the Al ribbon tape  21  like a reel is cut out a plurality of the Al straps  22  as predefined. A plurality of Al straps  22  are serially picked up by a plurality of bonding heads  10 . The ultrasonic wave technique electrically connects between electrodes of the power semiconductor chip  15  and the lead terminal. Therefore, the bonding operation has higher speed as comparing with cutting the Al ribbon tape  21  at the bonding head.  
         [0028]     Furthermore, as the cutting apparatus on the Al ribbon tape  21  is separated from the picking mechanism on the bonding head  10  and ultrasonic wave mechanism, the bonding head becomes simply and lightly. This means that the machine operation having higher speed can be realized without generation of troubles and failures in this embodiment. As a result, high efficient bonding technique can be obtained.  
         [0029]     In this embodiment, the Al strap  22  is connected between electrodes of the power semiconductor chip  15  and the lead terminal  25  by ultrasonic wave technique, however, the Al strap  22  may be welded by using lump heating technique.  
         [0030]     As mentioned above, this embodiment can provide a strap bonding machine having simplified structure and a strap bonding method with high speed operation.  
         [0031]     Next, according to a second embodiment of the present invention, a strap bonding machine and a method of manufacturing a semiconductor device are explained with reference to  FIG. 4-5 .  FIG. 4  is a perspective view showing an Al strap.  FIG. 5  is a block diagram showing a motion of a strap-carrying portion.  
         [0032]     In the second embodiment, a portion of a same composition as the first embodiment is attached the same number and explanation of the portion of the same composition is omitted.  
         [0033]     As shown in  FIG. 4 , an Al strap  22   a  has a loop-like shape. This leads improvement of adhesion between a molding resin and the Al strap  22   a  in subsequent processes, so that reliability of a resin-molded semiconductor device is increased.  
         [0034]      FIG. 5  shows a motion of an Al strap-carrying portion  8   a . First, the Al ribbon tape  21  (not illustrated) fed from the Al ribbon tape storage portion (not illustrated) is cut out at the Al ribbon tape cutting portion  7 , so as to be formed a plurality of Al straps  22   a  as described in the first embodiment.  
         [0035]     A position and shape detect portion  31  set up such as a TV camera detects position data and shape data on the Al strap  22   a . The data are addressed to a cognition portion  32 . The cognition portion  32  recognizes and memorizes the data. The calculation portion  33  comparatively calculates position data and shape data of the Al strap  22   a  memorized in the cognition portion  32 . Furthermore, position data and shape data of a standard sample of an Al strap preliminarily memorized also in the cognition portion  32 . On the basis of the position data comparatively calculated at the calculation portion  33 , an absorption head  12   a  of a position-adjusting portion  34  is moved to X-direction and Y-direction and is rotated. After the position-adjusting portion  34  is descended down, the absorption head  12   a  picks up the Al strap  22   a.    
         [0036]     When the shape of the Al strap  22   a  is not preliminarily determined the position-adjusting portion  34  received signals from the calculation portion  33  picks up the Al strap  22   a . Moreover, the position-adjusting portion  34  carries the Al strap  22   a  out of the carrying stage  20   a . A shape of an absorption head  12   a  may have a slope like the Al strap  22   a , the slope makes the absorption head  12   a  easily pick up the Al strap  22   a.    
         [0037]     The Al strap  22   a  is set on a carrier tray (not illustrated) disposed on the carrying stage  20   a . Here, a shape of the carrier tray may have a slope like the Al strap  22   a.    
         [0038]     Finally, the Al strap  22   a  on the carrier tray is picked up and is connected to a lead terminal and a power semiconductor by using ultrasonic wave technique. Here, a shape of the absorption head  12  may have a slope like the Al strap  22   a.    
         [0039]     As mentioned above, the Al strap  22   a  is picked up at the prescribed position and is connected by ultrasonic wave technique in the strap bonding machine and the method of manufacturing the semiconductor device in the second embodiment. Therefore, the Al strap carrying portion  8   a  has the position and shape detect portion  31 , the cognition portion  32 , the calculation portion  33  and the position adjust portion  34 . A bonding process using the Al strap  22   a  with a complicated shape also has advantages same as the first embodiment has.  
         [0040]     The second embodiment on bonding a metal strap to a semiconductor chip can provide a strap bonding machine having a simple configuration and a method of manufacturing a semiconductor device including a high speed operation.  
         [0041]     Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and example embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the claims that follow. The invention can be carried out by being variously modified within a range not deviated from the gist of the invention.  
         [0042]     For example, the method in the embodiments is applied to the strap bonding machine using an Al-strap, however, the method can be also applied to a strap bonding machine using a Cu-strap or an Au-strap.  
         [0043]     Moreover, the method and the machine can be also applied to series of lead frames. The height of a lead connection area may have different height against a chip connection area.