Abstract:
An apparatus for wire bonding and a capillary tool thereof are provided. An exemplary embodiment of a capillary tool capable of a wire bonding comprises a body having a first internal channel of a first diameter for accommodating a flow of a conductive wire. A compressible head is connected to the body, having a second internal channel of a second diameter for accommodating the flow of the conductive wire, wherein the first diameter is fixed and the second diameter is variable, the second diameter is not more than the first diameter and a diameter the conductive wire flowed through the compressible head is adjustable. An integrated circuit (IC) package is also provided.

Description:
BACKGROUND 
       [0001]    The invention relates to semiconductor fabrication, and more particularly to an apparatus for wire bonding and an integrated circuit chip package formed thereby. 
         [0002]    Integrated circuit (IC) chip packages are typically formed by mounting an integrated circuit (IC) chip on a lead frame and coupling these two elements to form a package. The IC chip and lead frame may be encapsulated. The IC chip typically includes a plurality of bond pads which may be positioned about a perimeter of the chip according to a predetermined spacing therebetween. The lead frame typically includes a number of lead fingers about a perimeter thereof. 
         [0003]    In order to electrically couple the IC chip to the lead fingers of the lead frame, a wire bonding technique is often used. An apparatus for wire bonding may have a spool of bonding wire mounted on the machine. The bonding wire may be threaded through a capillary tool which is mounted to a horn of the apparatus. The horn may be manipulated to move the capillary tool both vertically and horizontally. 
         [0004]      FIG. 1  and  FIG. 2  are schematic diagrams showing a portion of an integrated circuit chip (IC) package  10  having an IC chip  12  mounted on a lead frame  14  for coupling to external circuitry.  FIG. 1  is a schematic top view and the lead frame now includes a paddle  16  to which the IC chip  12  is secured by epoxy resin, and a plurality of lead frame fingers  18  which extend from a dam portion  20  toward the paddle  16  to receive a conductive wire from the IC chip. The IC chip  12  is now formed with a number of bond pads  22  positioned around a perimeter of the chip according to a spacing  24  therebetween. The bond pads  22  are now illustrated as, for example, a square pad having a width  26 . Typically, the width  26  of the bond pads  22  is about 5˜100 μm and the spacing  24  therebetween is about 5˜100 μm. A conductive bond  40  is formed between one of the bond pads  22  and one of the lead frame fingers  18 , including a ball portion  30  formed over the bond pad  22 , a wedge bond portion  32  formed over the lead frame finger  18 , and a conductive wire  28  connected therebetween, thereby forming an electrical connection between the bond pad and the lead frame. 
         [0005]      FIG. 2  is a schematic cross section of an area  50  in  FIG. 1 , illustrating the conductive bond  40  connecting one of bond pads  22  of the IC chip  12  and one of the lead frame fingers  18  of the lead frame  14 . The conductive bond  40  bonded between an IC chip  12  and the lead frame finger  18  is generally accomplished by “ball/wedge” bonding. According to this technique, the conductive wire  28  is first held in a capillary tool  44  of an apparatus for wire bonding and is then projected beyond the end of the tool. The capillary tool  44  forms part of the apparatus for wire bonding in which the apparatus is appropriately mounted and positioned over the bond pad  22  of the IC chip  12  mounted on the paddle  16  and has an inner channel  46  of a uniform diameter. As shown in  FIG. 2 , the ball portion  30  is formed of same conductive material as that of the conductive wire  28  at one end of the conductive wire  28  by melting thereof by an energy such as a hydrogen gas flame torch or by electric arc discharge (both not shown). After rehardening the ball portion  30 , the ball end of the conductive wire  28  is brought into intimate contact with the bond pad  22  and the ball portion  30  of the conductive bond  40  is formed on the pad  22  by, for example, thermocompression bonding applying a specified force and temperature for a specified period of time. Metallic welding and diffusion combine to form this basic bond. Alternatively, ultrasonic bonding or other form of welding may be used. The capillary tools  44  are then moved relative to each other for bonding of the conductive wire  28  on the lead frame finger  18 . At this location, the wedge bond portion  32  between the conductive wire  32  and lead frame finger  18  is generally formed and the conductive wire  28  is severed below the bonding tool at the weld. The wedge bond portion  32  is formed by thermocompression or ultrasonic bonding with the edge of the capillary tool  30  bearing against the conductive wire  28  and lead frame finger  18 . In this manner, a conductive wire connection is established between the bond pads  22  of the IC chip  12  and the lead frame  14  for coupling to external circuitry. 
         [0006]    Nevertheless, the continuing trend in semiconductor and integrated circuit industries is to develop and manufacture smaller components. This trend has resulted in integrated circuits and semiconductor devices having higher density due to an increased number of components coexisting in smaller physical areas. This downsizing has directly affected the location, number, and size of bond pads for electrical connections for these devices. Therefore, wire bonding techniques have been developed to accommodate smaller bond pad sizes as well as bond pad sizes with fine spacing therebetween through, for example, usage of conductive wires with reduced diameter, such as conductive wires having a diameter of about 0.8 mil or less. However, such reduction in conductive wire diameter results in poor IR performance thereof because electrical resistance of a conductive line increases when a diameter thereof is reduced. Reliability of diameter reduced conductive wire is thus affected. 
       SUMMARY 
       [0007]    Thus, a reliable wire bonding apparatus for providing wire bonds on bond pads with reduced spacing therebetween is desirable. An apparatus for wire bonding and a capillary tool used therein are provided. An integrated circuit (IC) package and a method for fabricating the same are provided. 
         [0008]    An exemplary embodiment of a capillary tool capable of a wire bonding comprises a body having a first internal channel of a first diameter for accommodating a flow of a conductive wire. A compressible head is connected to the body, having a second internal channel of a second diameter for accommodating the flow of the conductive wire, wherein the first diameter is fixed and the second diameter is variable, the second diameter is not more than the first diameter and a diameter the conductive wire flowing through the compressible head is adjustable. 
         [0009]    An exemplary embodiment of an apparatus for wire bonding comprises a capillary tool, an energy source, a control arm and a drive unit. The capillary tool comprises similar elements as described. The energy source is capable of providing energy to a tip of the capillary tool and the control arm is capable of moving the capillary tool in a bonding direction. The drive unit is capable of selectively moving the control arm. 
         [0010]    An exemplary embodiment of an integrated circuit (IC) package comprises a lead frame comprising at least one paddle and one frame finger. An integrated circuit chip is positioned over the paddle, wherein the IC chip comprises a plurality of pads thereover. A conductive wire electrically connects one of the pads and the frame finger, wherein the conductive wire comprises a ball portion with a first diameter, a line portion with a second diameter and a neck portion with a third diameter between the line portion and the ball portion, and the third diameter is smaller than the first and/or second diameter. 
         [0011]    An exemplary method for fabricating an integrated circuit package comprises providing a lead frame comprising at least one paddle and one frame finger. An integrated circuit chip is provided over the paddle, wherein the IC chip comprises a plurality of pads thereover. A conductive wire bond electrically connects one of the pad and the frame finger, wherein the conductive wire comprises a ball portion with a first diameter, a line portion with a second diameter and a neck portion with a third diameter between the line portion and the ball portion, and the third diameter is smaller than the first and/or second diameter. 
         [0012]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a schematic top view showing a part of a conventional integrated circuit chip (IC) package; 
           [0015]      FIG. 2  is a schematic cross section partially showing an area of the integrated circuit chip (IC) package illustrated in  FIG. 1 ; 
           [0016]      FIG. 3  is a schematic top view showing a part of an integrated circuit chip (IC) package according to an embodiment of the invention; 
           [0017]      FIG. 4  is a schematic cross section showing an area of the integrated circuit chip (IC) package illustrated in  FIG. 3 ; 
           [0018]      FIG. 5  is a schematic diagram showing an apparatus for wire bonding according to an embodiment of the invention; and 
           [0019]      FIGS. 6   a - 6   e  are schematic diagrams showing fabrication steps of a method for forming a wire bonding according to an embodiment of the invention, respectively. 
       
    
    
     DESCRIPTION 
       [0020]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0021]      FIG. 3  and  FIG. 4  are schematic diagrams showing a portion of an exemplary integrated circuit chip (IC) package  100  having an IC chip  102  mounted on a lead frame  104  for coupling to external circuitry (not shown).  FIG. 3  is a schematic top view and the lead frame  104  now includes a paddle  106  to which the IC chip  102  is secured by epoxy resin and a plurality of lead frame fingers  108  which extend from a dam portion  120  toward the paddle  106  to receive a conductive bond from the IC chip  102 . 
         [0022]    With the trend in the semiconductor and integrated circuit industries of developing and manufacturing smaller components, the IC chip  100  is now formed with semiconductor devices (not shown) having higher density and the location, number, and size of bond pads for electrical connections for these devices are provided in a greater number and a finer spacing compared with those of the conventional IC chip illustrated in  FIG. 1 . The IC chip  102  is now formed with a greater number of bond pads  122  positioned around a perimeter of the chip according to a finer spacing  124  therebetween. The bond pads  122  are now illustrated as, for example, a square pad having a width  126 . The width  126  of the bond pads  22  is now reduced to about 5˜50 μm and the spacing  124  therebetween is also reduced to about 5˜50 μm, thereby allowing formation of greater number of bond pads  122  over the IC chip  102 . As shown in  FIG. 3 , a conductive bond  140  can be formed between one of the bond pads  122  and one of the lead frame fingers  108 , having a ball portion  130  formed over the bond pad  122 , a wedge bond portion  132  formed over the lead frame finger  108  and a conductive wire  128  connecting the ball portion  130  and the wedge bond portion  132 . 
         [0023]      FIG. 4  is a schematic cross section of an area  200  in  FIG. 1 , illustrating the conductive bond  140  connecting the bond pad  122  and the lead frame finger  108 . The conductive bond  140  is now formed with a conductive wire  128  electrically connecting the IC chip  102  and the lead frame finger  108  as a wire of non-uniform diameter. The conductive wire  128  includes a main portion  128   b  of a greater diameter and a neck portion  128   a  of a smaller diameter. Formation of the conductive bond  140  can be accomplished by, for example, “ball/wedge” bonding. According to this technique, the main portion  128   b  of the conductive wire  128  is first held in a capillary tool  150  of an apparatus for wire bonding (see  FIG. 5 ) projecting beyond the end of the tool. The capillary tool  150  forms part of the apparatus for wire bonding in which the apparatus is appropriately mounted and positioned over the bond pad  122  of the IC chip  102  mounted on the paddle  106 . As shown in  FIG. 4 , the capillary tool  150  is formed of a main body  152  and a compressible head  154 , having an inner channel of a uniform diameter  160  for accommodating the main portion  128   b  of the conductive wire  128  and a reduced diameter (not shown) for accommodating the reduced portion  128   a  of the conductive wire  128 . The compressible head  154  first compress a portion of the main portion  128  of the conductive wire  128  to thereby form the neck portion  128   a  of a reduced diameter. The neck portion  128   a  protrudes slightly from an opening adjacent the compressible head  154 . Next, the ball portion  130  is formed at one end of the neck portion  128   a  of the conductive wire  128  by an energy source such as a hydrogen gas flame torch or by electric arc discharge (both not shown), thereby forming a ball (not shown) of reduced diameter for the bond pad  122 . After rehardening the ball portion  130 , the ball end of the wire (not shown) is brought into close contact with the pad  122  and the ball portion  130  of the conductive bond  140  is formed on the conductive pad  122  by, for example, thermocompression bonding applying a specified force and temperature for a specified period of time. Metallic welding and diffusion combine to form this basic bond. Alternatively, ultrasonic bonding or another form of welding may be used. Next, the compressible head  154  maintains at a uncompress position and the capillary tool  150  is then moved relative to each other for bonding of the main portion  128   b  of the conductive wire  128  on the lead frame finger  108 . At this location, the wedge bond portion  132  between the main portion  128   b  of the conductive wire  128  and lead frame finger  108  is formed and the main portion of the conductive wire  128  is severed below the bonding tool at the weld. The wedge bond portion  132  is formed by thermocompression or ultrasonic bonding with the edge of the capillary tool  150  bearing against the conductive wire  128  and the lead frame finger  108 . In this manner, a conductive wire connection is established between one of the bond pads  122  of the IC chip  102  and the lead frame  104  for coupling to external circuitry. 
         [0024]      FIG. 5  shows a schematic diagram of an exemplary apparatus.  200  for wire bonding. As shown in  FIG. 5 , the apparatus  200  includes a wire bonding device  210 , such as the capillary tool  150  illustrated in  FIG. 4 , which is controllably positioned relative to an integrated circuit chip  220  and a lead frame  230  positioned over a package substrate  240 . The bonding device  210  is capable of forming wire bonds at a plurality of bonding positions on the IC chip  220 . The apparatus  200  further comprises a drive unit  250 , such as a motor, for selectively moving a control arm  260  which in turn moves the bonding device  210  in any direction represented by multiple arrows  270 . The apparatus  200  may also comprise a measuring device  280  for measuring movements of the wire bonding device  210 , and a controller  290  for controlling the drive unit  250 . 
         [0025]      FIGS. 6   a - 6   e  are schematic diagrams showing individual fabrication steps of a method for forming a wire bonding according to an embodiment of the invention. As shown in  FIG. 6   a,  a bonding device such as a capillary tool  500  for wire bonding device  200  of the apparatus shown in  FIG. 5  is provided. The capillary tool  500  is similar to that illustrated in  FIG. 4  and has an internal channel  502  for accommodating a conductive wire  504 , and an opening  506  to introduce the conductive wire  504  to an intended surface, such as a top surface of a bond pad  600  and/or a lead frame  700 . The capillary tool  500  is formed with a main body  508  and a compressible head  510 . At least one side of the compressible head  510  is removable toward another side thereof, thereby reducing the diameter of the conductive wire  504 . 
         [0026]    As shown in  FIG. 6   b,  during a wire bonding process, the conductive wire  504  is fed through the inner channel  502  and out of the opening  506 . The conductive wire  506  is preferably a gold wire, however, any suitable conductive material such as aluminum wire, lead wire, or iron wire can be substituted. Prior to feeding the conductive wire  504  out of the opening  506 , the portion of the conductive wire  504  adjacent to the opening  506  is first compressed by the compressible head  510  to thereby form a portion thereof in a reduced diameter and partially protruding over the opening  506 , titled as  504   a.  The above compression can be achieved by movement of at least one side or both sides of the compressible head  510 . As shown in  FIG. 6   b,  the conductive wire  504  is now formed with a reduced portion at an end thereof adjacent to the compressible head  510  of the capillary tool  500  and the reduced portion  504   a  is now off-axial with the conductive layer  504  but is not limited thereto. Once the conductive wire  504  is compressed through movements of both sides of compressible head  510 , the reduced portion  504   a  of the conductive wire  504  may be co-axial with the other portion of the conductive wire  504  and is not illustrated here, for simplicity. 
         [0027]    As shown in  FIG. 6   c,  a ball  512  is formed at the tip of the protrusion of the reduced portion  504   a  of the conductive wire  504  by an energy source  800  such as an electric discharge of a torch electrode, or by heating the tip of the capillary tool  500 . Other methods of forming the ball  512  can also be utilized. The size of the ball  512  can be controlled by varying hardware and software of the apparatus for wire bonding and is formed with a reduced diameter. After the ball  22  is formed, the capillary tool  500  is positioned above a desired location on a top surface of the bond pad  600 , as shown in  FIG. 6   d.  The ball  512  is then forced downward to the surface by downward movement of the capillary tool  500 , thereby causing the ball  512  to deform into a mass. The downward force of the capillary tool  500  can be combined with, for example, ultrasonic energy to create a bond between the ball  512  and the top surface of the bond pad  600 . Thereafter, as shown in  FIG. 6   e,  the capillary tool  500  is moved away from the top surface of the bond pad  600  causing the conductive wire  504  to continually feed through the inter channel  502  thereof and move to a bonding site on the lead frame  700 . The lead frame  700  is heated to a temperature of about 150-350° C. and the conductive wire  504  is pressed against the lead frame  700  to alloy the conductive wire with lead frame  700 , thereby bonding the conductive wire  504  to the lead frame  700  and forming an wedge portion  514  thereon. It is noted that the conductive wire  504  is formed with a reduced portion  504   a  having a diameter smaller than that thereof and the ball  512  is thus formed with a reduced diameter compared with conventional conductive ball formed in conventional wire bonding. The conductive wire  504  can be provided in a diameter of about 0.1˜1.0 mil and the reduced portion  504   a  is about 90% less than the diameter of the conductive wire  504 . For example, the diameter of the reduced portion is less than 0.9 mil and preferably less than 0.7 mil. The diameter of the conductive wire  504  flows through the compressible head  510  is adjustable between 10 E −6 ˜1 mm. Since only portions of the conductive wire  504  is previously and partially size-reduced, therefore providing a conductive wire capable formed on a size-reduced bond pad, having a diameter substantially not reduced. Thus, IR performance of such conductive wires with partially reduced diameter is ensured and electrical resistances thereof will not be increased since an overall diameter thereof is not significantly reduced. 
         [0028]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.