Patent Publication Number: US-6337221-B1

Title: Die bonding method for manufacturing fine pitch ball grid array packages

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to die bonding equipment and methods for the fabrication of ball grid packages and more particularly to a die bonding method capable of detecting a failure of a land pattern on a mount tape before a chip transfer unit picks up a chip and capable of matching a good land pattern to a good semiconductor chip and a failed land pattern to a failed semiconductor chip. 
     2. Description of the Related Art 
     Recently, technologies for packaging semiconductor chips have rapidly developed with the development of thin film forming technologies. Ball grid array packages, currently in use, are a result of the application of such technologies. A ball grid array package uses a flexible tape in place of a lead frame. The flexible tape includes a conductive pattern formed thereon. One end of the conductive pattern is soldered to terminals of a printed circuit board by a solder ball interposed therebetween, and the other end is bonded to bonding pads that act as input and output terminals of a semiconductor chip. 
     In the fabrication of ball grid array packages, the process of attaching solder balls is the last step, which provides various advantages in carriage and handling of elements for a die attaching process and in mass production. Ball grid array packages also make unnecessary the trimming and forming processes that are indispensable in fabrication of more conventional packages. 
     Recently developed chip scale packages have a fine pitch in which the pitch of solder balls ranges from a few tens of microns to a few hundreds of microns and sizes of such packages approach about 120% of the chip sizes. 
     To form a fine pitch ball grid package, multiple land patterns are first formed on a rectangular, polyimide based tape. Throughholes are formed at selected portions of the polyimide based tape. The land patterns include solder ball pads, which are on a first surface of the polyimide based tape such that each of the pads covers a corresponding throughhole and has a circular plate shape. The land patterns also include conductive patterns that electrically connect to respective solder ball pads and extend to edges of the tape. 
     Beam leads, that is, the ends of the conductive patterns, are die-bonded to respective bonding pads of semiconductor chip. For such die bonding, rectangular openings or window,; are formed at edges of the polyimide based tape. After the die bonding, an electrical test determines whether or not the land patterns have open or short failures and from the electrical test, failed land patterns are marked. An elastomer is attached to a second surface of the polyimide based tape. 
     Continuously, the polyimide based tape on which the elastomer is attached is rolled, and the rolled tape is cut to length, for example, to include a number of land patterns. Hereinafter, a rolled tape having the above mentioned unit length is referred to as one base mount tape. A base mount tape&#39;s edge portions are attached to a square mount tape frame using an adhesive tape. 
     Semiconductor chips separated by sawing a wafer are transferred to corresponding base mount tapes, and a press head die bonds bonding pads of each of the semiconductor chips with beam leads exposed through open windows of base mount tape. 
     Afterwards, base mount tapes having semiconductor chips attached are subject to a solder ball attaching process. The solder ball attaching process attaches solder balls to solder ball pads through the throughholes in the base mount tape. The above solder ball attaching process prepares multiple ball grid array packages having a fine pitch. The multiple ball grid array packages are separated into individual ball grid array packages, and the individual ball grid array packages are tested. Thus, the above processes fabricate ball grid array packages. 
     FIG. 1 shows conventional die bonding equipment  100  for fabrication of ball grid array packages having a fine pitch. Referring to FIG. 1, die bonding equipment  100  generally includes a wafer mount frame stocker  5 , a base mount stocker  10 , a chip pickup table  15 , and a bonding unit  20  on a support plate  1 . A chip transfer unit  25  moves a semiconductor chip from the chip pickup table  15  to the bonding unit  20 , and a guide rail unit  40  guides a base mount tape frame  35  from the base mount tape stocker  10  to the bonding unit  20 . Multiple charge coupled device(CCD) cameras observe the operation of die bonding equipment  100 . 
     In FIG. 1, the chip pickup table  15  faces an opening  50  of the wafer mount frame stocker  5  so that a wafer mount frame  45  carrying multiple semiconductor chips can be loaded into or unloaded from the wafer mount frame stocker  5 . A square chip tray  55  that is attached to the chip pickup table  15  receives failed semiconductor chips. The chip tray  55  moves together with the chip pickup table  15  in an X-Y plane. 
     Meanwhile, an alignment table  65 , which includes a mount head  60 , is spaced apart from the chip pickup table  15 . The mount head  60  receives a semiconductor chip from the chip pickup table  15 , moves the received semiconductor chip to the bonding unit  20 , and aligns the semiconductor chip for die bonding. To align the semiconductor chip, the alignment table  65  can freely move along X-Y coordinate axes as does the chip pickup table  15 , and when the semiconductor chip is skewed from the required orientation for bonding of the chip, the alignment table  65  rotates the skewed semiconductor chip for the required alignment. The alignment table  65  can also move along the Z coordinate axis direction. 
     Here, the chip transfer unit  25 , which reciprocates between the chip pickup table  15  and the alignment table  65 , transfers semiconductor chips from the wafer mount frame  45  of the chip pickup table  15 . The chip transfer unit  25  includes: a collet  70  (hereinafter referred to as the first collet) for holding good semiconductor chips with a vacuum; a collet  75  (hereinafter referred to as the second collet) for holding failed semiconductor chips; and a moving block  80  including a collet selection unit (not shown) that selects the first or second collet  70  or  75  for use. The chip transfer unit  25  also includes a straight line reciprocating unit (not shown) for transferring the moving block  80 . 
     The described base mount tape stocker  10  is spaced away from the wafer mount frame stocker  5 . The guide rail unit  40  extends from an opening  85  of the base mount tape stocker  10 , and a base mount tape frame  35  received at the base mount tape stocker  10  is unloaded through the opening  85 . The guide rail unit  40  includes a pair of guide rails  42  and  44  that guide the base mount tape frame  35 . 
     A bonding unit  20  is over the guide rails  42  and  44  and distant from the base mount tape stocker  10 . The bonding unit  20  includes a press head  22 , which moves up and down, and a bonding unit CCD camera  24 , which moves together with the press head  22 . The press head  22  is over the base mount tape frame  35 , and the mount head  60  is below the base mount tape frame  35  so that the press head  22  faces the mount head  60 . The bonding unit CCD camera  24  checks the position of the base mount tape frame  35  as it moves and simultaneously checks for a failed mark formed during the production of the base mount tape. 
     In addition to the bonding unit CCD camera  24 , the conventional die bonding equipment typically includes two other CCD cameras. A chip pickup table CCD camera  17  is for determining a position of a failed semiconductor chip or a good semiconductor chip among the chips sawed from a wafer, and an alignment table CCD camera  62  is for checking the alignment of a semiconductor chip on the mount head  60  of the alignment table  65 . 
     Hereinafter, the operation of the conventional die bonding equipment is described with reference to FIG.  1 . 
     First, prior to starting the die bonding process, an operator discriminates failed semiconductor chips from a sawed wafer mounted on the wafer mount frame  45  and manually loads the discriminated failed semiconductor chips into the failed semiconductor chip tray  55 . This avoids an increase in the loading time for loading of failed semiconductor chips. Such increases in the loading time occur when another wafer is loaded to start a process after processing of a wafer is completed, a corresponding land pattern to be bonded among base mount tapes is failed, and there are no failed semiconductor chips on the wafer mount frame  45 . 
     The operator loads all failed semiconductor chips in the failed semiconductor chip tray  55 , and then an unloading unit unloads one sheet of wafer mount frame  45  from the wafer mount frame stocker  5  and fixes the sheet to the chip pickup table  15 . 
     The chip pickup table CCD camera  17  continuously images semiconductor chips on the chip pickup table  15  to discriminate between good semiconductor chips and defective semiconductor chips. 
     An X-Y table moves the chip pickup table  15  so that a good semiconductor chip is below the first collet  70  of the chip transfer unit  25 . To shorten the bonding time, the first collet  70  picks up and stands by with a good semiconductor chip. 
     Concurrently with the stand by of the first collet  70 , the mount tape frame  35  is unloaded from the mount tape stocker  10  and moves to the bonding unit  20  along the guide rail unit  40 . At this time, the bonding unit CCD camera  24  of the press head  22  photographs a first land pattern that is being processed first, to thereby discriminate whether the first land pattern is good or defective. 
     Here, when the first land pattern is good, the good semiconductor chip held by the first collet  70  is moved onto the mount head  60  of the chip alignment table  65  and is then aligned. Thereafter, the aligned good semiconductor chip is transferred onto a corresponding good land pattern of the base mount tape  30  by the movement of the mount head  60 . After the transfer of the good chip, the press head  22  moves downward and the mount head  60  moves upward, so that bonding pads of the good semiconductor chip are bonded to beam leads of the good land pattern. 
     Meanwhile, when the first land pattern as discriminated is defective, the good semiconductor chip held by the first collet  70  returns to an original position. Then, the second collet  75  instead of the first collet  70  picks up the defective semiconductor chip and moves the defective chip onto the mount head  60 . Thereafter, the defective chip is transferred to a corresponding defective land pattern of the base mount tape  30  by the movement of the mount head  60  without a specific alignment. After the transfer of the defective chip, the press head  22  moves downward and the mount head  60  moves upward, so that bonding pads of the defective semiconductor chip are bonded to beam leads of the defective land pattern. 
     First, when a land pattern of the base mount tape to be die bonded is determined to be defective, the first collet  70  of the chip transfer unit  25  holds the good semiconductor chip. Therefore, the first collet  70  returns the good semiconductor chip to an original position. Instead of the first collet  70 , the second collet  75  holds a defective semiconductor chip on the mount head Accordingly, a delay occurs. 
     Second, the bonding unit CCD camera determines whether the land pattern of the base mount tape is good or not during the die bonding time. Accordingly, much time is spent in determining the status of the semiconductor chip. 
     Third, an operator must manually pick up a defective semiconductor chip from the wafer mount frame and then load the defective semiconductor chip in tray  55 . As a result, loading times lengthen. 
     Fourth, when a use of a defective semiconductor chip that is received in the defective semiconductor tray is required, X-Y table has to move the semiconductor chip tray below the second collet  75 . As a result, the time spent in picking up the received defective semiconductor chips increases. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to decrease the die bonding time of a ball grid array package having a fine pitch by determining whether a corresponding land pattern of the base mount tape on which a semiconductor chip is being die-bonded, is good or not before a chip transfer unit picks up a semiconductor chip and thereby allowing the chip transfer unit to pick up a semiconductor chip matching the land pattern. 
     It is another object of the present invention to shorten a time taken in determining whether a land pattern of a base mount tape is good by performing such a determination only once during the loading of the mount tape. 
     It is yet another object of the present invention to decrease a time taken in picking up defective semiconductor chips by establishing the defective semiconductor chip tray at the lower face of the collet of the semiconductor chip transfer unit along the trace of the collet and thereby allowing the wafer extend table not to be moved in order to pick up a defective semiconductor chip. 
     It is yet another object of the present invention to shorten the time taken in loading defective semiconductor chips into the defective semiconductor chip tray by allowing the collet of semiconductor chip transfer to perform the work for loading defective semiconductor chips into the defective semiconductor chip tray. 
     Other objects and advantages of the present invention will be more apparent in view of the description that follows. 
     One embodiment of the present invention is a die bonding method for a fine pitch ball grid array package. The die bonding method includes inspecting the status and position of a semiconductor chip which is on a mount frame and the status and position of a land pattern of a mount tape, wherein the land pattern is on one surface of the mount tape and the other surface of the mount tape is attached to a surface of the mount frame. Thereafter, the status data and the position data corresponding to the semiconductor chip and the land pattern inspected are stored. After repeating the inspection of one or more semiconductor chips, a semiconductor chip is selected using the stored status data and the position data of the semiconductor chip and the land pattern. The selected semiconductor chip has a status matching to the status of the land pattern at a bonding region for the die bonding. The selected chip is transferred to an alignment region for an operation corresponding to the status of the transferred chip. 
     Another embodiment of the invention is a die bonding equipment for fine pitch ball grid array packages. The die bonding equipment includes: a semiconductor chip pickup stage for inspecting the status and position of a loaded semiconductor chip, wherein a wafer mount frame is unloaded from a wafer mount frame stocker and the wafer mount frame is loaded on the semiconductor chip pickup stage; an alignment stage spaced apart from the semiconductor chip pickup stage; a chip transfer unit for transferring the semiconductor chip from the semiconductor chip pickup stage to the alignment stage; a guide rail for a mount tape frame having a mount tape on which at least one land pattern is formed, the mount tape frame being transferred from a mount tape frame stocker in which the mount tape frame is received to a die bonding position adjacent to the alignment stage; an inspection system disposed over the guide rail, for inspecting a status and a position of the land pattern on the mount tape frame; and a bonding unit for bonding the land pattern to the semiconductor chip that is mounted on the mount head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and other advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 is a perspective view of a conventional die bonding equipment; 
     FIG. 2 is a perspective view of a die bonding equipment according to an embodiment of the present invention; 
     FIG. 3 is a partial perspective view of portions of a transfer unit and a chip pickup stage in the equipment of FIG. 2; 
     FIG. 4 is a perspective view of a portion of the equipment of FIG. 2 that removes the transfer unit body from the transfer unit; 
     FIG. 5 is a schematic diagram showing the positions of CCD cameras in the equipment of FIG. 2; 
     FIGS. 6A,  6 B, and  6 C together are a flow chart for a die bonding method for a fine pitch ball grid array package; 
     FIG. 7 is a plan view of a wafer fixed on a wafer mount frame; 
     FIG. 8 is a plan view of a base mount tape fixed on a base mount frame; and 
     FIG. 9 is a schematic view of a memory table or data structure storing status and position information for the land pattern of the base mount tape. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Die bonding equipment for ball grid array packages having fine pitch according to the present invention is described more fully hereinafter with reference to the accompanying drawings. 
     FIG. 2 is a perspective view of die bonding equipment  200  used for the fabrication of ball grid array package having fine pitch according to one embodiment of the present invention. As major components, die bonding equipment  200  includes a support plate  201 , a wafer mount frame supplying unit (stocker)  210 , a chip pickup stage  220 , a bonding unit  260 , a chip transfer unit  230 , a chip alignment stage  240 , a base mount tape supplying unit  250 , a mount tape frame loader  290 , a control module (not shown), and multiple charge coupled device (CCD) cameras. 
     Although not shown in the drawings, the control module includes a control unit such as a microprocessor and a memory unit for storing data. Here, the memory unit permits data input and output and can be, for example, a hard disk driver (HDD) or a random access memory (RAM). The memory unit stores status information indicating whether semiconductor chips are good or defective and position data for the good or defective semiconductor chips. The memory unit also stores status information indicating whether land patterns of a base mount tape  251  are good or defective and position data for the land patterns. 
     The wafer mount supplying unit  210  is disposed on the support plate  201  and includes a wafer mount frame stocker  214  and a mount frame moving unit  216 . The wafer mount frame stocker  214 , which typically has a hexagonal shape, receives and stores a stack of wafer mount frames. The mount frame moving unit  216  loads or unloads a wafer mount frame  212  from the wafer mount frame stocker  214 . The mount frame moving unit  216  includes a pneumatic cylinder and a gripper  216 a coupled to an end of the cylinder. The wafer mount supplying unit  210  has one open face  218  such that movement of the mount frame moving unit  216  can load or unload the wafer mount frame  212  via the open face  218 . The chip pickup stage  220  is at a position corresponding to the open face  218  of the wafer mount supplying unit  210 . 
     The chip pickup stage  220  includes a ring shaped stage  222  and an X-Y table  224 . The X-Y table freely moves the ring shaped stage  222  in an X-Y plane. A chip pickup stage CCD camera  226  is over the chip pickup stage  220  and allows an operator to acquire position data for good or defective semiconductor chips among the semiconductor chips in pickup stage  220 . 
     A guide rail  219  between the chip pickup stage  220  and the wafer mount frame stocker  214  precisely guides the wafer mount frame  212  from the wafer mount frame stocker  214  to the chip pickup stage  220  and allows the wafer mount frame  212 , which is being guided, to be aligned with the ring shaped stage  222 . 
     The chip alignment stage  240  is on the support plate  201  and spaced apart from the chip pickup stage  220 . The chip alignment stage  240  receives a semiconductor chip from the chip pickup stage  220  and moves and/or rotates the semiconductor chip in the X-Y plane, to thereby align the semiconductor chip for bonding. The chip alignment stage  240  operates according to a control signal of the control module and includes an X-Y table  246 , a stage  248  on the upper surface of the X-Y table  246 , and a mount head  244 . An alignment stage CCD camera  242  is over the chip alignment stage  240 . The alignment stage CCD camera  242  confirms the alignment status of the semiconductor chip that is supported and fixed on the mount head  244 . 
     The chip transfer unit  230  transfers semiconductor chips from the chip pickup stage  220  to the alignment stage  240 . FIGS. 3 and 4 illustrate features of an embodiment of the chip transfer unit  230 , which is disposed between the chip pickup stage  220  and the chip alignment stage  240 . As shown in FIG. 3, the chip transfer unit  230  includes a transfer unit body  232 , a collet unit  234 , and a defective semiconductor chip tray  236 . The transfer unit body  232  has a length greater than the interval L between the central portion of the chip pickup stage and the mount head  244  of the alignment stage  240 . 
     As shown in FIG. 4, a pair of pulleys  237   a  and  237   b  are at opposite ends of the inner portion of the transfer unit body  232 . A tension wire  238  is around pulleys  237   a  and  237   b  and moves when pulleys  237   a  and  237   b  rotate. A servo motor  239  attached to a rotational axis  239   a  of pulley  237   a  controls the rotation of pulley  27   a  and thereby controls the direction and distance that the tension wire  238  moves. 
     The collet unit  234  includes a guide block  234   a  coupled to the tension wire  238  and a guide bar, a collet support body  234   b  coupled to the guide block  234   a , a collet  234   c  coupled to the collet support body  234   b , and a collet displacement generating unit (not shown) for moving the collet  234   c.    
     The defective semiconductor chip tray  236  is below the transfer unit body  232 . The defective semiconductor chip tray  236  is along the transfer path of the collet unit  234 , which allows the collet unit  234  to load a defective semiconductor chip from the chip pickup stage  220  and unload the defective semiconductor chip in a single row to the semiconductor chip tray  236 . 
     Returning to FIG. 2, a long guide rail  253  for transferring the base mount frame  251  is adjacent to the chip alignment stage  240 . The guide rail  253  has a guide groove (not shown) that couples to and guides the base mount frame  251  during movement along the guide rail  253 . At the guide groove, there are provided multiple driving rollers (not shown) for movement of the base mount frame  251  back and forth along the guide rail  253 . A mount tape frame stocker  255 , which holds a stack of the base mount tape frames  251 , is at one end of the guide rail  253 , and the mount tape frame loader  290 , which holds a stack of base mount tape frames  251  when the die bonding process is complete, is at the other end of the guide rail  253 . 
     The bonding unit  260 , which performs the die bonding process, is at a central portion of the guide rail  253 , and a CCD camera  257  for inspecting the land patterns is between the bonding unit  260  and the mount tape frame stocker  255 . The CCD camera  257  photographs the land patterns of the base mount frame  251  for determination of status information indicating whether the land patterns are good or defective. A conventional pattern recognition system (not shown) can determine whether the land patterns are good or defective and store status information to indicate the results. The collet  234  picks up a good or defective semiconductor chip according to whether the status information indicates a corresponding land pattern is good or defective. 
     The bonding unit  260  further includes: an X-Y table (not shown) which the control module operates; a movable press head  262  coupled to the X-Y table; and a bonding unit CCD camera  264  fixed to the press head  262 . The bonding unit CCD camera  264  is for confirming alignment of the land pattern of the mount tape and the transferred semiconductor chip and correcting deviations from the required alignment. 
     FIG. 5 schematically shows a top view of the equipment  200  of FIG.  2  and illustrates the positions of the CCD cameras  226 ,  257 ,  242 , and  264  in a camera frame  270 . In FIG. 5, symbol C 1  represents the chip pickup stage CCD camera  226  which is over the chip pickup stage  220 , C 2  represents the CCD camera  257  for determining whether the land patterns are good or defective, C 3  represents the alignment stage CCD camera  242 , and C 4  represents the bonding unit CCD camera  264 . 
     The die bonding equipment  200  of FIG. 2 can perform a die bonding process illustrated in FIGS. 6A,  6 B, and  6 C. Prior to the die bonding, a wafer on which processes for the fabrication of a plurality of semiconductor chips have been completed, is prepared and is mounted on one of the wafer mount frames  212 . The wafer mount frame  212  has a diameter greater than that of the wafer. At this time, the backside of the wafer is attached to the wafer mount frame  212 . The wafer is then sawed along the scribe lines to separated individual chips. The wafer mount frames  212 , each having multiple separated semiconductor chips, are loaded into the mount frame stocker  214 . 
     In an initial step ST 10  of the die bonding process, the mount frame moving unit  216  unloads one of the wafer mount frames  212  that contains separated semiconductor chips from the mount frame stocker  214  and then loads the mount frame  212  onto the ring shaped stage  222  of the chip) pickup stage  220 . 
     Meanwhile, a step ST 30  unloads from the mount tape frame stocker  255  a base mount tape frame  251  having a base mount tape to which a semiconductor chip will be die-bonded. A step ST 40 , which is during the unloading of the base mount tape frame  251  from the mount tape frame stocker  255  and the transfer to the bonding unit  260 , includes a visual inspection of the base mount tape using CCD camera  257  to determine whether the land patterns on the base mount tape  251  ire good or defective. The status information indicating the results of the determination are then stored in the memory device. 
     FIG. 8 shows a base mount tape  251 , and FIG. 9 shows a data structure  500  that includes,; the status data corresponding to the base mount tape  251 . For step ST 40 , the CCD camera  257  photographs land patterns C 11 , C 12 , and C 13  first and determines whether the photographed land patterns are good or defective. The determined status information for the land patterns C 11 , C 12 , and C 13  are stored at addresses corresponding to entries T 11 , T 12 , and T 13  in data structure  500  of FIG. 9 
     In the example of FIGS. 8 and 9, the land patterns C 11  and C 13  did not fail the inspection and are determined to be good land patterns. Accordingly, corresponding entries T 11  and T 13  of the data structure  500  store a value G. In this example, the land pattern C 12  failed the visual inspection and is determined to be defective. Accordingly, the corresponding entry T 12  stores a symbol F. Visual inspection similarly determines the status information for all land patterns. For example, the  30  land patterns of the base mount tape attached on the base mount tape frame  251  of FIG.  8  and their determined status data are stored in corresponding addresses of the data structure  500 . 
     A step ST 50  transfers the base mount tape frame  251  to the bonding unit  260  while visual inspection continues. After the visual inspection is completed and the inspection data of land patterns are stored, a step ST 60  determines from the status information in the data structure  500  whether a first land pattern for a die bonding process is good or defective. 
     When the first land pattern is good, the process transfers from step ST 60  to a step ST 70 . Step ST 70  uses the status information stored in the memory device for the semiconductor chips and determines whether a semiconductor chip currently positioned for transfer for the die bonding process is good or not. 
     From step ST 70 , when the inspected semiconductor chip proves to be defective, step ST 75  stores the defective semiconductor chip in the defective semiconductor chip tray  236 . Thereafter, step ST 77  visually inspects another semiconductor chip on the chip pickup stage  220  before the process returns to step ST 70 . A matrix such as the one illustrated in FIG. 7 can store the status information for the semiconductor chips from the chip pickup stage  220 . Each semiconductor chip from the chip pickup stage  220  has a corresponding matrix element, and the value of the corresponding matrix element indicates whether the chip is good or defective. In the example of FIG. 7, dots mark the defective chips. For example, a matrix element corresponding to a semiconductor chip in row  2  and column  3  and matrix element corresponding to a semiconductor chip in row  2  and column  4  indicate that the corresponding chips are defective. 
     When step ST 70  determines the semiconductor chip is good, the chip transfer unit  230  picks up the good semiconductor chip in a step ST 80 . 
     In a step ST 90  (FIG.  6 B), the chip transfer unit  230  transfers the good semiconductor chip to the mount head  244  of the chip alignment stage  240 . The chip alignment stage  240  precisely aligns the chip in the die bonding position in a step ST 100 , subsequent to transferring of the semiconductor chip to the bonding unit  260  in a step ST 110 . More specifically, in step ST 100 , the alignment stage CCD camera  242  photographs the good semiconductor chip when transferred onto the chip alignment stage  240 . When photographing indicates an alignment failure, the mount head  244  having the good semiconductor chip thereon rotates or moves up or down to align the good semiconductor chip. After the alignment is complete, the mount head  244  loads the good semiconductor chip onto the bonding unit  260  in step ST 110 . 
     At this time, the base mount tape frame  251  has been loaded on the bonding unit  260  and awaits the bonding process. When both of the good semiconductor chip and the base mount tape frame  251  are loaded onto the bonding unit  260 , the bonding unit CCD camera  264  inspects whether the beam leads of the land patterns formed on the base mount tape of the base mount tape frame  251  are precisely aligned with bonding pads of the good semiconductor chip. A step ST 120  aligns the base mount tape and the good semiconductor chip for beam lead bonding. After step ST 120 , a step ST 130  is the beam lead bonding that the bonding unit  260  performs. 
     After a certain time elapses, a step ST  140  determines whether or not another land pattern for die bonding still remains. If a land pattern for die bonding does not remain, the die bonding process is complete. If a land pattern for die bonding still remains, the process returns to step ST 20 , which determines whether the semiconductor chip that is being die bonded to the land pattern is good or bad. The visual inspection classifies the semiconductor chip as good or defective, and the classification result is stored. In addition, inspection step ST 60  again determines from the stored status data whether a land pattern that is being die-bonded is good or defective. If in step ST 60  the land pattern proves not to be good, the process proceeds to a step ST 150 , which determines whether or not there is a defective semiconductor chip in the fail semiconductor chip tray  236 . When no defective semiconductor chips remain in the semiconductor chip tray  236 , the collet  234  picks up a defective semiconductor chip that is identified from the position data that was stored in step ST 75 . Otherwise, when the semiconductor chip tray  236  contains a defective semiconductor chip, the collet  234  picks up a defective semiconductor chip from the semiconductor chip tray  236 . In a step ST 170 , the chip transfer unit  230  transfers the defective semiconductor chip as picked up to the mount head  244  of the chip alignment stage  240 . 
     For a defective semiconductor chip transferred to the chip alignment stage  240  through steps ST 150  to ST 170 , a step ST 180  transfers the defective semiconductor chip directly to the bonding unit  260  without an alignment process. The bonding unit  260 , in a step ST 190 , performs the die bonding for such defective semiconductor chips and defective land patterns. 
     After step ST 190 , a step ST 200  determines whether or not a land pattern remains for die bonding and whether another die bonding is needed. If a land pattern for die bonding remains, tie process returns to the step ST 20  and repeatedly performs the steps from ST 20  to ST 200 . When no land pattern remains for further die bonding, a step ST 210  determines whether the semiconductor chip tray  236  has room for another defective semiconductor chip. When there is a vacant site in the semiconductor chip tray  236 , the chip transfer unit  230 , in a step ST 220 , loads a defective semiconductor chip from the wafer mount frame  212  onto the semiconductor chip tray  236 . 
     As described previously, the present invention prevents a mismatched bonding such as die bonding a good semiconductor chip to a defective land pattern or die bonding a defective semiconductor chip to a good land pattern. In particular, visual inspection determines whether a land pattern that is being die-bonded to a selected semiconductor chip is good or defective prior to the picking up of the semiconductor chip. Moreover, the invention enhances productivity during the die bonding process by automatically transferring the defective semiconductor chips into the semiconductor chip tray using the bonding unit. 
     The present invention is not limited to the above-described embodiments. Various changes and modifications may be effected and remain within the scope of the invention, as defined by the appended claims.