Abstract:
A wire bonding machine is disclosed for bonding a wire to a semiconductor device. The wire bonding machine includes a wire bonding head having a bonding tool mounted to it. The bonding tool is adapted to attach a wire end to a semiconductor device. At least a portion of the bonding head is pivotable about a first horizontal axis so as to provide vertical displacement of the bonding tool. The bonding head is also rotatably mounted to the bonding machine so as to permit rotation of the bonding tool about a vertically oriented rotational axis. The machine also includes a work table for supporting at least one semiconductor device to be wire bonded. A conveyance system is used to translate the work table in a direction relative to the bonding head and in a substantially orthogonal direction to the horizontal pivot axis of the bonding head.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to and claims priority from co-pending U.S. Provisional Patent Application Ser. No. 60/427,788, filed Nov. 19, 2002, incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of wire bonding equipment and, more particularly, to an improved wire bonder which uses linear and rotation movement of the bonding head for providing high speed bonding. 
     BACKGROUND OF THE INVENTION 
     Wire bonding processes and machines are used extensively as a practical and expedient method to bond wires to semiconductors. One example of the use of wire bonders in a semiconductor manufacturing process is for attaching a semiconductor dies directly to a circuit board substrate. The substrate includes numerous traces which terminate in pads that are positioned adjacent to the place where the die is to be mounted. The package itself includes numerous die pads that are to be electrically connected to the pads on the circuit board. A wire bonder is used to attach a conductive wire, typically having a diameter of between 0.00051 to 0.030 inches, to each die pad and then to the pads on the circuit board. The configuration of the die and the location of the pads require that the wire bonds be formed at varying X, Y and Z locations. 
     Automatic wire bonders have been developed which utilize stored position data for each wire bond. The wire bonders use the position data to control the bonding operation. The most common bonder uses a vertically or rotary (Z direction) displaceable wire bonding head along with a translatable (in the X, Y direction) semiconductor work table. Three high speed motors (one associated with each direction of movement) are used to position the semiconductor device and bonding tool at the appropriate locations. 
     Generally, the speed of a bonding machine is measured by the number of units that are completed per hour (or, alternatively, the number of wires bonded per hour.) One way to reduce the costs associated with the manufacture of a semiconductor product is to increase the speed of the bonding machine to increase the number of units produced per hour. The high speeds of current machines require the bonding head and the table to move at accelerations of between 10 and 12 g&#39;s. Increasing the accelerations above this range has been difficult due to the large mass and inertia that is involved in moving the various components of the bonding machines. 
     A need, therefore, exists for an improved wire bonding machine which provides high speed bonding. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a wire bonding machine for bonding a wire to a semiconductor device. The wire bonding machine includes a wire bonding head having a bonding tool mounted to it. The bonding tool is adapted to attach a wire end to a semiconductor device. At least a portion of the bonding head is pivotable about, or slides perpendicular to, a first horizontal axis so as to provide vertical displacement of the bonding tool. The bonding head is also rotatably mounted to the bonding machine so as to permit rotation of the bonding tool about a vertically oriented rotational axis. 
     The wire bonding machine also includes a work table for supporting at least one semiconductor device to be wire bonded. A conveyance system is incorporated to translate the work table in a direction relative to the bonding head and in a substantially orthogonal direction to the horizontal pivot axis of the bonding head. 
     The foregoing and other features of the invention and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments, as illustrated in the accompanying figures. As will be realized, the invention is capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating the invention, the drawings show a form of the invention which is presently preferred. However, it should be understood that this invention is not limited to the precise arrangements and instrumentalities shown in the drawings. 
         FIG. 1  is a side perspective view of a portion of a wire bonding machine according to the present invention illustrating a bonding head, a work table and a portion of a conveyance system. 
         FIG. 2  is a front perspective view of the bonding head and work table of  FIG. 1 . 
         FIG. 3  is a top plan view of the wire bonding head and work table of  FIG. 1  illustrating the position of several workpieces relative to the head at one stage of the bonding operation. 
         FIG. 4  is a side perspective view of the bonding head and work table of  FIG. 1  illustrating the position of the workpieces relative to the head at another stage of the bonding operation. 
         FIG. 5  is a top plan view of the wire bonding head and work table of  FIG. 4 . 
         FIGS. 6A and 6B  are top views of the bonding head and work table of  FIG. 1  illustrating the position of the workpiece relative to the head along the X-direction at two different stages of the bonding operation. 
         FIG. 7  is a top view of a second embodiment of the present invention which uses two bonding heads for attaching wire bonds on a single work table. 
         FIGS. 8A and 8B  are isometric views of additional embodiments of the present invention which incorporate a camera. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals illustrate corresponding or similar elements throughout the several views,  FIG. 1  is a perspective view of a portion of a wire bonding machine  10  according to one preferred embodiment of the present invention. The wire bonding machine includes a wire bonding head  12  which has a bonding tool  14  attached to it for dispensing and/or channeling a wire to a workpiece. Many of the detailed features of the wire bonding head  12  are conventional in the art and are not necessary for an understanding of the present invention. As such, no discussion is provided in this application. Similarly, many of the aspects of the wire bonding machine are conventional and, therefore, are also not described herein. Those skilled in the art are familiar with the general construction and arrangement of such components, and would be readily capable of applying the teachings provided herein to such machines. 
     The bonding head  12  is positioned above a high speed conveyance system  16 , which, in the illustrated embodiment, may include a conventional set of guide rails  18  and a motor drive (not shown), for translating the workpiece  20  (e.g., a semiconductor device) relative to the bonding head  12 . Any conventional wire bonding conveyance system may be used in the present invention. More particularly, the workpiece  20  is mounted on a work table  22  that includes a fixture  24  which holds one or more workpieces  20 . The fixture  24  (or magazine) may be supplied to the high speed conveyance system  16  by a magazine handler  30  as shown in  FIG. 1 . 
     One difference between the present invention and current systems is that the conveyance system  16  provide translation of the work table  22  in one direction, e.g., the X-axis direction, for purposes of positioning the workpiece  20  and to provide the high speed bonding motion relative to the bonding tool  14 . Contrary to conventional bonding machines which use the conveyance system to position the workpiece and control the X and Y position of the bonding tool  14  relative to the workpiece, the present invention uses the positional control of the bonding head  12  to control the Y and Z position of the bonding tool  14  relative to the workpiece  20 . The bonding tool  14  is controllable along both the Y-axis and Z-axis for positioning the bonding tool  14  relative to the workpiece. As a consequence, the Y-axis positional control is split from the X-axis positional control and from the work table  22  entirely. 
     More particularly, the bonding head  12 , in addition to controlling the vertical location (i.e., in the Z direction) of the bonding tool  14 , also is rotatable in the X-Y plane, i.e., rotatable about a vertical rotational or pivot axis  26 . This allows the bonding head  12  to provide control over the Y-axis position of the bonding tool  14  relative to the worktable  22  and, thus, the workpiece  20 . A pivotal or rotational mount  28 , such as a pin and/or bearing, attaches the bonding head  12  to the bonding machine so as to permit angular (rotational) movement of at least the bonding tool portion of the bonding head  12 . 
     Referring to  FIGS. 1-5 , the rotation of the bonding head  12  along the X-Y plane (horizontal plane) can be seen more clearly.  FIGS. 1-3  illustrate a first position of the bonding head  12 , and in particular the bonding tool  14 , with respect to a workpiece  20 . The rotational connection between the bonding head  12  and the bonding machine  10  permits the bonding head  12  to be rotated about a vertical axis  26 , thus providing positioning of the bonding tool  14  along the Y-axis.  FIGS. 4 and 5  show a second position in the X-Y plane of the bonding head  12  and tool  14  relative to the workpiece  20 . The workpiece  20  and work table  22  have not been moved. Only the bonding head  12  has changed position. As illustrated, the pivoting of the bonding head  12  permits the bonding tool  14  to rotate along an arcuate path through an angle ox relative to the workpiece  20 . The amount of angular rotation cc that is provided by the bonding head  12  would be determined based on the amount of movement in the Y direction that would be required for the anticipated semiconductors, and where the rotational axis  26  of the bonding head  12  is located relative to the bonding tool  14 . 
     It should also be apparent that the angular movement of the bonding head  12  provides, in addition to positional change in the Y-direction, some positional change in the X-direction too. Thus, the programming which controls the movement of the bonding tool  14  and worktable  12  to properly position the tool  14  for bonding, must take into account both the rotation of the bonding head  12  and translation of the worktable  22  when determining the position of the worktable  22  in the X-direction for achieving a bond. 
     The bonding head  12  is mounted to the bonding machine  10  through a conventional attachment which permits the bonding tool  14  to move vertically (i.e., in the Z-direction) relative to the work piece  20 . U.S. Pat. No. 4,266,710, the disclosure of which is incorporated herein by reference in its entirety, describes one type of mounting arrangement that could be used in the present invention. The mounting arrangement may include a pivot or hinge mount which permits the bonding tool  14  to move up and down in the Z-direction (toward and away from the workpiece) so as to permit the bonding of the wires to the semiconductor device at various vertical positions. Those skilled in the art are familiar with such mounting arrangements as well as other mechanisms for vertical positioning of a bonding tool and, therefore, no further discussion is needed. The present invention can be readily incorporated into many conventional wire bonders, such as Kulicke &amp; Soffa&#39;s 8028 Ball Bonder or Maxμm IC Ball Bonder. 
     Preferably, the pivotal or hinged mounting of the bonding tool  14  or head  12  (for Z-axis positioning) is located outboard of the rotational mounting location (i.e., outboard of the rotational axis  26 ). This reduces the mass of components and/or material that needs to be moved to raise and lower the bonding tool  14 . 
     In order to rotate the bonding head  12  about the rotational axis  26 , the present invention incorporates a motor drive assembly  28 . The motor drive assembly  28  is preferably mounted or engaged with the bonding head  12  on the opposite side of the rotational axis  26  from the bonding tool  12 . By mounting the motor drive assembly  28  on the opposite side of the rotational axis  26  from the bonding tool  12 , it is possible to reduce the force needed to rotate the bonding tool  14 . More particularly, it is desirable to substantially balance the mass of the components of the bonding head  12  on opposite sides of the rotational axis  26 . This balancing of the masses reduces dynamic vibration causes by the motion of the boning head, as well as reduces the braking force needed to overcome the momentum of the bonding head  12  when reciprocating the bonding head  12  back and forth. Thus, locating the bonding tool  14  and the motor drive assembly  28  on opposites sides of the rotational axis  26  greatly increases the rotational acceleration of the bonding head  12 . 
     Those skilled in the art would be readily capable of mounting the motor drive assembly  28  to the bonding head  12  so as to maximize the speed and capabilities of the bonding tool  14  and bonding head  12  in light of the teachings provided herein. 
     As described above, the present invention controls translation of the work table  22  (and, thus, the work piece  20 ) along the X-axis by translating the table along guide rails  18 . Referring to  FIGS. 6A and 6B , two positions of the work table  22  relative to the bonding head  12  are shown, illustrating the translation of the table  22  under the bonding head  12 . It is contemplated that the rails  18  would preferably extend completely under the bonding head  12  such that the travel of the work table would be along a linear path from the left side of the figures to the right side and out of the bonding machine  10 . This arrangement is different from conventional wire bonding machines where the feed direction of the work table is generally orthogonal to the longitudinal axis of the bonding head. The illustrated embodiment permits the footprint of the overall bonding machine  10  to be reduced considerably, thus taking up less factory space which provides a cost savings to customers. 
     Referring now to  FIG. 7 , a variation on the present invention is shown. In this embodiment of the invention, there are two bonding heads  12  mounted above the worktable  22 . Each bonding head includes a bonding tool  12  which is mounted so as to bond wires to the semiconductor device  20 . The two bonding heads  12  are both preferably mounted so as to be rotatable with respect to the work table  22 . This embodiment of the invention speeds up the manufacturing process by increasing the number of units that can be completed at a time in certain wiring configurations. It is further contemplated that multiple bonding heads can be used, and/or that multiple bonding tools could be mounted to a single bonding head to further accelerate the bonding process using the present invention. 
     Turning now to  FIGS. 8A and 8B , isometric views of another embodiment of the present invention is shown which incorporates a camera for recording/storing image data related to the workpiece  20 . Specifically, the camera stores position data, such as X-Y location and orientation, of the workpiece  20  and/or bonding locations on the workpiece  20 . The data is fed to a microprocessor or similar controller for use in controlling the head  12  and tool  14 . In  FIG. 8A , a fixed line scan camera  50  is used. The camera does not move but, instead, retrieves information related to the entire table on a line by line basis. In  FIG. 8B  the camera  50  is mounted to a conveyance system  52  which carries the camera  50  along the Y-axis. Thus, the camera  50  scans across the table in the Y-direction as the table moves the workpieces along the X-axis. 
     Alternatively, the camera may be mounted to the bonding head  12 , such that it reciprocates with the head. A further embodiment is contemplated wherein the camera  50  is mounted to a separate rotary head which permits the camera  50  to be rotated in the theta (θ) direction about a Z-axis. The camera would be mounted in much the same manner as the second bonding head in  FIG. 7 . 
     Conventional software is used to retrieve, store and extract position data for use by the bonding head. Accordingly, no further discussion is needed. 
     In an alternate embodiment (not shown), two bonding heads could be balanced on opposite sides of the rotational axis such that as the bonding tool on a first head is translated down the bonding tool on the opposite head would be raised up. Thus, two workpieces can be bonded at the same time. Separate cameras would be necessary for each bonding head and each workpiece should be mounted on a work table that can be independently controlled. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.