Abstract:
A method and apparatus electrically coupling input/output bond pads that are disposed proximate to one another on a microelectronic device. The apparatus includes a microelectronic device having at least two conductive input/output bond pads electrically coupled to an integrated circuit of the microelectronic device and first and second conductive stud balls bonded to first and second input/output pads, respectively, and a third conductive stud ball bonded to the first and second conductive stud balls. A wire bonding tool in “stud ball” mode is utilized to bond the conductive stud balls.

Description:
TECHNICAL FIELD 
   The present invention relates to methods for electrically coupling and electrically coupled input/output bond pads of a microelectronic device. 
   BACKGROUND ART 
   Integrated circuit devices typically comprise a group of circuits, each of which is formed of interconnected elements fabricated on a semiconductor substrate. Certain circuits on an integrated circuit device are designed to be electrically separate so that they may be customized after the wafer-fabrication process. These integrated circuit devices can be customized by electrically connecting the separate circuits. Because gaps disposed between typical integrated circuits are relatively small, it can be difficult to make typical wire bond connections with a wire bonding tool known in the art. Typical wire bond connections include ball and wedge bonds having a ball and tail. The following patents illustrate different types of methods for electrically connecting separate circuits and apparatuses having electrical connections. 
   U.S. Pat. No. 4,298,856 to Schuchardt discloses establishing short circuit connections between different pairs of the bonding pads of a resistor by use of a simple glob of solder. Thus, the bonding pads must likely be solderable. 
   U.S. Pat. No. 6,262,434 to Kalb describes an integrated circuit including a first circuit structure, a first conductive bonding pad coupled to the first circuit structure, a second circuit structure, and a second conductive bonding pad coupled to the second circuit structure. The first conductive bonding pad is arranged to be separated from the second conductive bonding pad by a gap having a gap dimension. The gap dimension is configured to be bridged by a wire bond formed by a wire bonding tool, thereby electrically coupling the first conductive bonding pad to the second conductive bonding pad. It is possible to bridge the two bonding pads with a single bonding wire because the gap is bigger than that of the gap formed by a conventional semiconductor processing technique. 
   U.S. Pat. No. 6,169,331 to Manning et al. describes electronically coupling bond pads of a microelectronic device to each other. A first conductive member extends between the two bond pads and a second conductive member extends from one of the pads to a position external to the device. A combination of ball and wedge wire bonds, each having a ball and tail, is used to electrically connect the bond pads of the device. Where a conductive link already exists between the bond pads, the link between the two bond pads can be used to supplement the internal circuitry of the microelectronic device. Where a conductive link does not exist between the bond pads, the link between the two bond pads can be used to modify or repair the electronic device after it has been manufactured. The spacing between the bond pads of one device and the bond pads of another device may be large enough to allow for typical wire bonds. 
   It is an object of the present invention to provide a method for electrically connecting input/output bond pads of a microelectronic device. 
   It is another object of the present invention to provide an apparatus having electrically connected input/output bond pads on a microelectronic device. 
   It is another object of the present invention to provide a method for customizing an integrated circuit device. 
   SUMMARY OF THE INVENTION 
   The above and other objects have been achieved by a method including bonding first and second conductive stud balls to respective first and second conductive input/output bond pads of a microelectronic device and bonding a third conductive stud ball to the first and second conductive stud balls with a wire bonding tool in a “stud ball” mode or other tool capable of bonding stud balls. A wire bonding tool in stud ball mode bonds only a stud ball to the desired surface, instead of both a ball and tail. The stud ball bonding may occur at the packaging assembly level and is easily integrated into the standard automatic wire bonding process. 
   The microelectronic device of the present invention includes a semiconductor substrate having an integrated circuit with circuitry electrically connected to conductive input/output bond pads. Each input/output bond pad of at least one pair of the input/output pads has a bonded conductive stud ball. An additional third conductive stud ball is bonded to the stud balls on the bond pad pairs. The input/output bond pads are disposed proximate to one another and may be separated by a standard distance utilized in the art. In one example, the conductive stud ball is a gold stud ball and the input/output bond pads are aluminum. 
   A user may customize the integrated circuit by selecting, from a plurality of input/output bond pads, a particular pair of input/output bond pads on a microelectronic device corresponding to circuitry to be electrically connected. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of an integrated circuit chip and associated leads and pins. 
       FIG. 2A  is a partial side view of the integrated circuit chip of  FIG. 1  having a first stud ball bonded to a first input/output bond pad. 
       FIG. 2B  is a partial side view of the integrated circuit chip of  FIG. 2A  having a second stud ball bonded to a second input/output bond pad. 
       FIG. 2C  is a partial side view of the integrated circuit chip of  FIG. 2B  having a third stud ball bonded to the first and second stud balls. 
       FIG. 2D  is a partial top view of the integrated circuit chip of  FIG. 2C . 
       FIG. 2E  is a partial perspective view of the integrated circuit chip of  FIG. 2D . 
       FIG. 3  is a partial side view of a wire bonding tool. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , stud ball bond arrangement  12  of the present invention is seen. An integrated circuit device such as integrated circuit chip  10 , including a plurality of input/output bond pads  14 , has for example, three stud ball bond arrangements  12  of the present invention. In the example shown in  FIG. 1 , three pairs  16   a ,  16   b , and  16   c  of conductive input/output bond pads  14  disposed on a surface  30  of the integrated circuit chip  10  are electrically connected by the stud ball bond arrangements  12   a ,  12   b , and  12   c  of the present invention. Any desired number of pairs  16  of input/output bond pads may be electrically connected with a corresponding number of stud ball bond arrangements  12  of the present invention. If desired, the stud ball bond arrangement  12  of the present invention may be formed post wafer fabrication and at stages before or after package level assembly. When conductive stud balls are bonded in accord with the present invention, select input/output bond pads and the circuitry connected to the select input/output bond pads are electrically connected. 
   The integrated circuit chip  10  is mounted on a substrate, such as a chip carrier  17 . The chip carrier  17  includes leads  18  and pins  20  which are typically electrically connected to input/output bond pads  14  of the plurality of input/output bond pads of the integrated circuit chip. Electrical connections to the leads  18  and pins  20  may occur at the package assembly level, though such electrical connections are not shown here. 
   Referring to  FIGS. 2A–2E  and  FIG. 3 , a method of forming the stud ball arrangement  12   a  with regard to bond pair  16   a  is shown. This method is applicable when forming additional stud ball arrangements  12  for other bond pairs  16  of an integrated circuit chip. A first input/output bond pad  14   a  is spaced apart from and proximate to a second input/output bond pad  14   b  to which it is paired. On a standard integrated circuit chip, the input/output bond pads are typically spaced about 60–65 microns apart, however, other spacing may be used in conjunction with the present invention. In one example, the input/output bond pads  14   a  and  14   b  have dimensions of 80 microns by 80 microns. The input/output bond pads  14   a  and  14   b  are in electrical communication with circuitry, for example circuits  26  and  28 , represented with the illustrated perforations, of integrated circuit chip  10 . 
   In each select input/output bond pad pair  16   a , a first conductive stud ball  32  is bonded to the first input/output bond pad  14   a , a second conductive stud ball  34  is bonded to the second input/output bond pad  14   b , and a third conductive stud ball  36  is bonded to both first and second conductive stud balls  32  and  34 , forming the stud ball arrangement  12   a . The stud balls desirably comprise a metal that can be formed into a fine wire for the standard ball bonding process. The metal used to form the stud balls should form a reliable bond with the integrated circuit chip&#39;s input/output bond pad. For example, gold alloys reliably bond with aluminum metal input/output bond pads on a typical integrated circuit chip, and thus may be used to form stud balls. Also, copper wire for standard ball bonding can be used to form the stud balls. Copper reliably bonds to copper input/output bond pads. In one example, the stud balls  32 ,  34 , and  36  are gold and the input/output bond pads  14   a  and  14   b  are aluminum. In another example, the stud balls  32 ,  34 , and  36  are copper and the input/output bond pads  14   a  and  14   b  are copper. 
   Stud balls are typically twice the diameter of the bond wire. In one example, the bond wire diameter is 1 mil and the stud ball has a diameter of 2 mils. In one example, the thickness of the stud ball is approximately 1.5 mils. 
   Referring back to  FIG. 1 , the input/output bond pads  14  provide means by which electrical signals are input or output from the underlying connected circuitry of the integrated circuit chip  10  to enable the operation of the underlying circuits. In one example, one input/output bond pad of the bond pad pair is utilized to input or output a int_osc_en_vdd signal utilized for internal oscillator enable power where the other input/output bond pad of the same bond pair is utilized to input or output a int_osc_en signal utilized for internal oscillator enable. Therefore, when the input/output bond pad pair  16  is connected with the stud ball bond arrangement  12 , electrical connecting of the circuitry associated with these signals occurs. 
   Other examples of input/output bond pad pairs on an integrated circuit electrically connected by means of the stud ball bond arrangement of the present invention are bond pad pairs utilized for the input or output of the following signals:
     int_osc_en and int_osc_en_vss for connecting the internal oscillator enable to ground;   den_cs 0  and den_cs 0 _vss for connecting the density chip select  0  to ground; and   den_cs 1  and den_cs 1 _vss for connecting the density chip select  1  to ground.   

   With reference to  FIG. 3 , a wire bonding tool  38 , known in the art, is seen. In one example, the wire bonding tool utilized in the present invention is a K&amp;S 8020 wire bonding tool. Other wire bonding tools and other tools capable of bonding stud balls may be utilized in the present invention. The wire bonding tool may be a type that bonds a stud ball to the select location using thermo-sonic, ultrasonic, or compression bonds. The resulting stud ball size and shape is determined by the bonding tool and the bonding tool settings. The bonding tool parameters and related equipment parameters affect the geometry of the stud ball. The stud ball need not be spherical and may take the shape of a bump, for example. 
   With reference to  FIGS. 2A and 3 , the wire bonding tool  38  is programmed to be or placed in stud ball bonding mode and the first conductive stud ball  32  is bonded to conductive input/output bond pad  14   a  of the integrated circuit device  10  with the wire bonding tool  38 . 
   With reference to  FIGS. 2B and 3 , the wire bonding tool  38  in stud ball bonding mode is used to bond a second conductive stud ball  34  to the conductive input/output bond pad  14   b  spaced apart from and disposed proximate to the input/output bond pad  14   a.    
   With reference to  FIGS. 2C ,  2 D and  3 , the wire bonding tool  38  in stud ball bonding mode is used to bond a third conductive stud ball  36  to the first and second conductive stud balls  32  and  34 , electrically connecting the underlying circuits. With the stud ball bond arrangement  12  of the present invention, the underlying circuits, in one example circuits  26  and  28 , are electrically connected customizing the integrated circuit chip. 
   After the desired number of stud ball bonding arrangements  12  of the present invention have been bonded to select input/output bond pad pairs, the wire bonding tool may be programmed to be or placed in a standard bonding mode to wedge or ball bond together desired structures with a typical ball and tail structure. In the standard bonding mode, the integrated circuit device may be electrically connected to the device carrier. 
   The present invention allows a user to select which circuits of an integrated circuit device he desires to electrically connect through select input/output bond pad pairs corresponding to the circuits to be electrically connected by means the stud ball bond arrangement of the present invention.