Abstract:
An apparatus and method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame. The present invention includes the use of an individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding. If desired, the present invention also provides for the use of a conventional fixed clamp for the lead fingers during the wire bonding process in addition to the individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding. The present invention also contemplates the replacement of the fixed clamp with another, or second, independent clamp in addition to the first individual independent lead finger clamp during the wire bonding process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of application Ser. No. 09/955,561, filed Sep. 18, 2001, pending, which is a continuation of application Ser. No. 09/337,782, filed Jun. 22, 1999, now U.S. Pat. No. 6,290,116, issued Sep. 18, 2001, which is a divisional of application Ser. No. 08/865,911, filed May 30, 1997, now U.S. Pat. No. 6,000,599, issued Dec. 14, 1999, which is a continuation of application Ser. No. 08/597,616, filed Feb. 6, 1996, now U.S. Pat. No. 5,647,528, issued Jul. 15, 1997. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention is related to forming wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame.  
           [0004]    More specifically, the present invention is related to the apparatus and method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame using one or more independently actuated bondhead lead clamps during the bonding process.  
           [0005]    2. State of the Art  
           [0006]    Well known types of semiconductor chip devices are connected to a component known as lead frames and subsequently encapsulated in plastic for use in a wide variety of applications. The lead frame is typically formed from a single continuous sheet of metal, typically by metal stamping operations. The lead frame includes an outer supporting frame, a central semiconductor chip supporting pad and a plurality of lead fingers, each lead finger having, in turn, a terminal bonding portion near the central chip supporting pad. Ultimately, the outer supporting frame of the lead frame is removed after the wire bonds between the contact pads of the semiconductor chip device and the lead fingers are made.  
           [0007]    Since the lead frames are formed continuously using stamping operations, they are typically continuously rolled on a suitable reel and provided for use. Such reeling operations of the lead frames cause the lead frames to have induced deformations therein leading to lead frames exhibiting longitudinal curvature and transverse curvature. Such lead frame curvature and any attendant deformation of the lead frame cause problems in the formation of reliable wire bonds with the contact pads of semiconductor devices and the individual lead fingers of the lead frame, particularly, when the size of the semiconductor is decreased, the number of contacts pads on the semiconductor device is increased, and the number of lead fingers on the lead frame is increased.  
           [0008]    Typical apparatus and methods for forming the wire bonds between the contact pads on semiconductor devices and the lead fingers of lead frames are illustrated in U.S. Pat. Nos. 4,361,261, 4,527,730, 4,600,138, 4,653,681, 4,765,531, and 5,465,899. However, such apparatus and methods do not address the problem of deformed lead frames and their effect on the wire bonds.  
           [0009]    Typically, the deformation of the lead frames and its effect on the quality of wire bonds have been dealt with through the use of clamps on portions of the lead frames during the wire bonding operation. In U.S. Pat. No. 4,434,347, a circular fixed clamp is used to retain the lead fingers of the lead frame during the wire bonding operation. A spring loaded electrode is used to heat the end of the lead finger to help improve bonding of the wire.  
           [0010]    In U.S. Pat. No. 5,322,207, a fixed clamp is used to retain the lead frame during the automated wire bonding process for connecting the bond pads of a semiconductor device to lead fingers of a lead frame.  
           [0011]    In U.S. Pat. No. 5,307,978, a fixed clamp is illustrated for use in an apparatus and method for orienting bonding sites of a lead frame having a plurality of bonding sites.  
           [0012]    In U.S. Pat. No. 5,035,034, a hold-down clamp having a multi-fingered interchangeable insert for wire bonding semiconductor lead frames is illustrated. The clamp insert  21  includes a plurality of individual fingers  22  to be used to bias a lead finger of a lead frame in the wire bonding process to provide a better wire bond.  
           [0013]    In U.S. Pat. No. 3,685,137, jaws  26  and  28  of a lead frame clamp are used to force the lead fingers of a lead frame into a fixed position during the wire bonding process.  
           [0014]    In U.S. Pat. No. 4,821,945, a method and apparatus for the single lead automated clamping and bonding of lead fingers of lead frames are illustrated. However, such apparatus and method are used to replace the fixed clamp during such wire bonding. Additionally, the individual clamp is concentrically located with respect to the wire bonding apparatus and must rotate therearound during wire bonding operations.  
           [0015]    While such prior art apparatus and methods have been directed in attempting to solve the problems of forming reliable wire bonds between the contact pads of semiconductor devices and lead fingers of lead frames, they have not been as successful as envisioned.  
           [0016]    The present invention is directed to an improved wire bonding apparatus and method for forming such wire bonds.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention is related to the apparatus and method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame. The present invention includes the use of an individual independent lead finger clamp during the wire bonding process to provide increased stability of the individual lead finger for improved bonding. If desired, the present invention also provides for the use of a conventional fixed clamp for the lead fingers during the wire bonding process in addition to the individual independent lead finger clamp to provide increased stability of the individual lead finger for improved bonding. The present invention also contemplates the replacement of the fixed clamp with another, or second, independent clamp in addition to the first individual independent lead finger clamp during the wire bonding process. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]    The present invention will be better understood when the description of the invention is taken in conjunction with the drawings wherein:  
         [0019]    [0019]FIG. 1 is a perspective view of the present invention used in a wire bonding process.  
         [0020]    [0020]FIG. 2 is a perspective view of a lead-over-chip semiconductor device having the bond pads thereof connected to the lead fingers of a lead frame.  
         [0021]    [0021]FIG. 3 is a side view of the present invention used in the wire bonding of a semiconductor chip arrangement.  
         [0022]    [0022]FIG. 4 is a perspective view of a second alternative type of independent lead clamp of the present invention.  
         [0023]    [0023]FIG. 5 is a perspective view of a third alternative type of independent lead clamp of the present invention.  
         [0024]    [0024]FIG. 6 is a perspective view of the use of two independent lead clamps of the present invention in a wire bonding operation with a lead finger of a lead frame. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Referring to drawing FIG. 1, a semiconductor chip (die)  10  is shown being supported by the paddle  12  of a lead frame. A heat block  20  is used to heat the paddle  12 , die  10 , and lead fingers  14  during the wire bonding process. As shown, a suitable wire  16  has one end thereof  17  bonded to a bond pad of the die  10 . The wire  16  may be of any suitable type for connection and bonding purposes, such as gold, gold alloy, aluminum, aluminum alloy, etc. The other end  18  of the wire  16  is shown being bonded to the end  15  of a lead finger  14  of the lead frame by a suitable bonding apparatus  26 . The bonding apparatus  26  may be of any suitable type well known in the bonding area, such as a tailless thermosonic or ultrasonic capillary type bonding apparatus which dispenses wire during the bonding process. As previously stated, the lead finger  14  is in contact with the heat block  20  to heat the lead finger  14  to a suitable temperature for the bonding operation to help insure a satisfactory wire bond. If desired, in the wire bonding operation, further shown in contact with lead finger  14  is a portion of a conventional fixed clamp  22  used to clamp portions of the lead frame during such bonding operations. The conventional fixed clamp  22  may be of any well known suitable type, such as those described hereinbefore, and is generic in shape. Further shown in drawing FIG. 1 is independently actuated lead clamp  24  used in place of or in addition to the conventional fixed clamp  22  to maintain the lead finger  14  in position during the bonding process. The independent actuated lead clamp  24  helps insure that the lead finger is in contact with the heat block  20  during the bonding process and helps minimize any deflection of the end  15  of the lead finger  14  so that the bonding apparatus  26  accurately, precisely contacts the end  15  to provide the desired wire bond. The action of independent actuated lead clamp  24 , and if desired the additional use of fixed clamp  22 , provides improved clamping of a lead finger  14  during the wire bonding process as well as insures that the lead finger  14  is in intimate contact with the heat block  20  for effectiveness.  
         [0026]    During the wire bonding process, it is desirable for the heat block to be heated to substantially 230 degrees Centigrade. Although the heat block may be any suitable temperature during the bonding operation, the heat block  20  temperature should not exceed 300 degrees Centigrade to prevent thermal damage to the die  10 . It is further preferred that the bond of the end  18  of the wire  16  made to the end  15  of the lead finger  14  be made at a temperature of substantially 190 degrees Centigrade for bonding effectiveness. It is also preferred that the bonding apparatus  26  exert a bonding force of substantially 50 to 100 grams when bonding the end  18  of the wire  16  to the end  15  of lead finger  14  for effective bond formation of the wire  16  to lead finger  14 .  
         [0027]    The independent actuated lead clamp  24  may be of any suitable shape for use in independently clamping the lead finger  14 , in place of the use of conventional fixed clamp  22 , such as square, semicircular, rectangular, arcuate, etc. Also, as shown, the independent actuated lead clamp  24  may be resiliently mounted through the use of a shoulder  50  thereon abutting a spring  52  to control the amount of the force exerted on any lead finger  14  during the wire bonding operation. If desired, the independent actuated lead clamp  24  may include insulation or cushioning  25  on the end thereof. The independent actuated lead clamp  24  is actuated independently of bonding apparatus  26  and has the capability of independent movement along the x-axis, y-axis and z-axis with respect to the bonding apparatus  26 . The independent actuated lead clamp  24  is also free to move about the bonding apparatus  26  and the central axis of the die  10  so that any lead finger  14  that is to be connected to bond pads on the die  10 , regardless of location, may be accommodated. The independent actuated lead clamp  24  does not need to be, and preferably is not, concentrically centered about the bonding apparatus  26  so that it will not interfere with the operation thereof. Any desired number of independent actuated lead clamps  24  may be used about the bonding apparatus  26  to minimize the amount of movement of the independent actuated lead clamp  24  between wire bonding operations. The independent actuated lead clamps  24  may be located in quadrants about the die  10 , or in any manner as desired.  
         [0028]    Referring to drawing FIG. 2, a lead over chip configuration using the present invention is shown. The lead fingers  14  are located over the chip (die)  10  for wire bonding thereto. In such a configuration, the lead fingers  14  are secured to the die  10  by insulating adhesive strips  30 . During the bond operation, one or more of the independent actuated lead clamp  24  clamps the end  15  of lead finger  14  prior to the bonding of a wire  16  thereto by one or more of the bonding apparatus  26 . The independent actuated lead clamp  24  applies sufficient pressure to the end  15  of the lead finger  14  to compress the insulating adhesive strips  30  to insure a satisfactory bond between the end of any wire  16  and the end  15  of the lead finger  14 .  
         [0029]    Referring to drawing FIG. 3, a die  10  is shown having a plurality of wires  16  bonded thereto. As shown, one or more of the independent actuated lead clamps  24  contacts the end  15  of lead finger  14  aft of the area of the wire end  18  to the lead finger  14 . The bonds of the wire end  18  to the end  15  of the lead finger  14  are typically a wedge type wire bond, although a ball bond may be made if desired. As shown, the heat block  20  is in contact with the paddle  12  of the lead frame and the lead fingers  14 .  
         [0030]    Referring to drawing FIG. 4, a portion of a lead finger  14  is shown in conjunction with a bonding apparatus  26  and modified independent lead clamp  22 ′. The independent lead clamp  22 ′ is formed having a modified end or foot  23  thereon to provide a larger clamping area of the independent lead clamp  22 ′ on the end  15  of the lead finger  14  during bonding operations. The modified end or foot  23  is substantially the same width as the lead finger  14  and may be mounted to have articulated movement about the end of the independent lead clamp  22 ′, such as using a pin  125  extending through suitable apertures in a pair of ears  27  attached to the foot  23  and the end of the modified independent lead clamp  22 ′ for illustration purposes.  
         [0031]    Referring to drawing FIG. 5, an independent conventional fixed clamp  22 ′ is shown having a modified end or foot  23 ′ located on the end thereof. The end or foot  23 ′ may be integrally attached to the conventional fixed clamp  22 ′ or may have an articulated mounting arrangement, such as shown in drawing FIG. 4. In this instance, the modified end or foot  23 ′ is generally semicircular, or arcuate, in configuration so as to engage a large portion of the end  15  of the lead finger  14  surrounding the bonding apparatus  26  during the wire bonding operation to hold the end  15  in position.  
         [0032]    Referring to drawing FIG. 6, the independent actuated lead clamp  24  is shown in relation to the bonding apparatus  26  on the end  15  of a lead finger  14  as well as further being shown in relation to a second independently actuated clamp  150  located thereon during wire bonding operations. The second independently actuated clamp  150  may be of any suitable type and structure such as described and illustrated hereinbefore. The actuated lead clamp  24  and second independently actuated clamp  150  may be actuated independently of each other and independently of the bonding apparatus  26  as described and illustrated hereinbefore.  
       Method of Bonding  
       [0033]    Referring to drawing FIGS. 1 through 3, in the method of the present invention, a die  10  is positioned within the bonding area of the bonding apparatus  26 . If desired, for use in addition to an individual independent actuated lead clamp  24 , a conventional fixed clamp  22  serves to help straighten the lead frame and position the lead fingers  14  during subsequent bonding operations. Next, the die  10  and the lead finger  14  are heated to the desired temperature before bonding operations by the heat block  20 . At this time, the independent actuated lead clamp  24  is engaged, moved to the appropriate lead finger  14  which is to have a wire bonded thereto, and the actuated lead clamp  24  actuated to clamp the end  15  of the lead finger  14  against the heat block  20  or the insulating adhesive strip  30 . The wire bonding apparatus  26  is then actuated to form a wire bond on end  17  of wire  16  to an appropriate bond pad on die  10 . After the formation of the bond of end  17  of wire  16  to the bond pad of die  10 , the bonding apparatus is moved to appropriate end  15  of lead finger  14  for the formation of a suitable wire bond thereto by end  18  of wire  16 . After the formation of the bond of the end  18  of wire  16  to the end  15  of lead finger  14 , the independent actuated lead clamp  24  and the bonding apparatus  26  are actuated to substantially simultaneously remove the independently actuated lead clamp  24  and the bonding apparatus  26  from the end  15  of the lead finger  14 . Alternately, the bonding apparatus  26  is actuated to remove the apparatus from the bond location at the end  15  of the lead finger  14  either prior to or after the removal of the independent actuated lead clamp  24  from a lead finger  14 . During the removal of the bonding apparatus  26  from the end  15  of the lead finger  14 , if used in addition to the independent actuated lead clamp  24 , a conventional fixed clamp  22 , if in contact with a lead finger  14 , supplies the necessary force to retain the finger  14  in position relative to other lead fingers located around die  10 , both bonded and unbonded. As previously stated, it is not necessary for the independent actuated lead clamp  24  to remain in contact with the end  15  of lead finger  14  during the removal of the bonding apparatus  26  therefrom. After the wire  16  has been bonded to the desired bond pad of die  10  and end  15  of lead finger  14 , the process is repeated until all desired wire bonds between lead fingers  14  and bond pads of die  10  are completed.  
         [0034]    If desired to have additional clamping of the lead finger  14 , either a fixed clamp  22  and/or a second independent actuated lead clamp  24  may be used with the bonding apparatus  26 . The second independent actuated lead clamp  24  may be actuated and moved from the lead finger  14  with, before or after the removal of the bonding apparatus  26  from the lead finger  14 .  
         [0035]    It will be understood that the present invention may have changes, additions, deletions, modifications, and sequence of operation which fall within the scope of the invention. For instance, the fixed clamp may be eliminated and a second independent actuated lead clamp used in its place.