Abstract:
The present invention provides schemes which are associated with wire bonding process or wire bonding machine to detect the bonding status of a bonding wire of a package including at least a semiconductor unit. The schemes are very useful to a BGA (Ball Grid Array) package or similar types of packages, and provide significant advantages particularly for a package in which the resistance (such as the resistance resulting from an adhesion layer and a layer of Cupric Oxide for promoting adhesion) between a semiconductor unit and its carrier is not low enough. The present invention is characterized in that a preset connection between a semiconductor unit and a package-connection-area (such as the solder ball pad of a ball grid array package) is established in the beginning of a wire bonding process, and the package-connection-area is electrically connected with a press plate used by the wire bonding machine or the wire bonding process, so that a current loop can be formed via a bonding wire, the preset connection, the package-connection-area, and the press plate when the bonding wire is bonded to a semiconductor unit, and the bonding status between the bonding wire and the semiconductor unit can be indicated according to the current flowing through the current loop. The present invention is also applicable to the detection of bonding status between a bonding wire and a bonding finger electrically connected to a package-connection-area of the package.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to schemes for detecting bonding status of a bonding wire of a semiconductor package, particularly a package in which the resistance resulting from the adhesion layer and Cupric Oxide layer between the semiconductor unit (such as a chip or die) and its carrier is not low enough for forming a current loop.  
         BACKGROUND OF THE INVENTION  
         [0002]    The electrical connection status between a bonding wire and a semiconductor unit as well as that between the bonding wire and a solder ball pad in a package shall always be checked to see if it is good after wire bonding process. As shown in FIG. 1, after bonding wire  35  was bonded to a bonding pad  6  (or called wire bonding pad) of a semiconductor unit  1  to make an electrical connection between the bonding wire  35  and the semiconductor unit  1 , it is bonded to bonding finger  10 , which is followed by cutting off the bonding wire  35  at a proper position (such as the location slightly left to the point  18  in the figure), so that the capillary  24  of wire bonding machine may continue bonding another bonding wire to another wire bonding pad of semiconductor unit  1 . After capillary  24  completes bonding wire bonding pad  6  by bonding wire  35 , wire bonding machine applies an electrical potential difference between bonding wire  35  and a press plate  14 , thereby a current is expected to flow through bonding wire  35  (the part between capillary  24  and bonding pad  6 ), bonding pad  6 , semiconductor unit  1 , conductive adhesion layer  2 , heat dissipater  3 , and hot plate  14  back to the wire bonding machine to form a loop current (the direction shown by arrows  45 ,  46 , and  47  is a possible current flowing direction). In case the bonding status between bonding wire  35  and bonding pad  6  is not good, the loop current will be very small or negligible as a result of bad electrical connection between bonding wire  35  and wire bonding pad  6 . A normal loop current resulting from normal bonding status will thus be indicative of the good bonding status (good electrical connection) between bonding wire  35  and semiconductor unit  1 .  
           [0003]    Shown in FIG. 2 is a conventional art in which a layer  4  of Cupric Oxide is coated on a surface of heat dissipater  3  in order to enhance the adhesive force between heat dissipater  3  and semiconductor unit  1 , encapsulant body, as well as substrate  7 , resulting in the infeasibility of forming the loop current because the layer  4  of cupric oxide is nonconductive. This is why the current direction represented by arrow  47  of FIG. 1 does not exist in FIG. 2, leading to the extreme difficulty of detecting the bonding status (or called electrical connection status) between bonding wire and semiconductor unit in a package, particularly during wire bonding process.  
           [0004]    Although the arts disclosed by U.S. Pat. Nos. 5,712,570 and 5,893,508 are also used for detecting the bonding status of bonding wire in a semiconductor package, they are subject to a condition: chip and its carrier or some devices on its carrier form a conductive path for a current loop, therefore these arts cannot be applicable to the case illustrated in FIG. 2 where the layer  4  of Cupric Oxide or the adhesion layer  2  is not electrically conductive. The present invention is thus developed to resolve the problem resulting from either the nonconductive layer of Cupric Oxide or the nonconductive adhesion layer, and thereby to provide convenience for related industries to take advantage of the benefit of the layer of Cupric Oxide, while still be able to detect the bonding status of a bonding wire when packaging a Ball Grid Array package or similar types of packages, leading to more convenient, more systematic, and more flexible operation for detecting the bonding status of bonding wires in a semiconductor package, particularly during wire bonding process.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention is to provide a method associated with a wire bonding machine or a wire bonding process, for detecting bonding status of a bonding wire of a Ball Grid Array package or similar types of packages (such as those with solder ball pads thereof located on the same surface of a substrate as are semiconductor units thereof), the method achieving more convenient, more systematic, more flexible or less confined (allows the existence of insulation between semiconductor unit and its carrier, for example) schemes for detecting bonding status of a bonding wire, particularly for detecting abnormal bonding status during wire bonding process in order to make up it early enough.  
           [0006]    Another object of the present invention is to provide a system associated with a wire bonding machine or a wire bonding process, for detecting bonding status of a bonding wire of a Ball Grid Array package or similar types of packages (such as those with solder ball pads thereof located on the same surface of a substrate as are semiconductor units thereof), the system achieving more convenient, more systematic, more flexible or less confined (allows the existence of insulation between semiconductor unit and its carrier, for example) schemes for detecting bonding status of a bonding wire, particularly for detecting abnormal bonding status during wire bonding process in order to make up it early enough.  
           [0007]    A further object of the present invention is to provide the industries related to Ball Grid Array package or similar types of packages, with the convenience or flexibility of selecting, according to individual requirements or conditions, proper schemes for detecting the bonding status of bonding wires of a package. For example, it provides convenience or flexibility of selecting from among the three schemes: only detecting the bonding status between bonding wire and semiconductor unit, only detecting the electrical connection status between bonding wire and solder ball pad, and detecting both the above.  
           [0008]    The present invention may be represented by a system associated with a wire bonding process, for detecting bonding status of at least a bonding wire of a package including at least a semiconductor unit and at least a package-connection-means such as solder ball pad. The system primarily comprises: at least a carrier such as a substrate, a heat dissipater, or a piece of tape, or any object capable of supporting the semiconductor unit and/or package-connection-means; at least an electrical conduction means such as an object made of electrically conductive metal, or electrically conductive rubber, or anisotropically conductive film, or the combination of these material, the electrical conduction means contacting at least a selected one of the package-connection-means; at least a preset connection means such as an electrical connection system (an electric wire or a system composed of a trace, a bonding finger, and a bonding wire, for example) established in the beginning of the wire bonding process, for electrically connecting the selected one of the package-connection-means and the semiconductor unit; a voltage source which may be a direct or alternate source or a capacitor, for providing an electrical potential difference between the electrical conduction means and the bonding wire; and a detector such as a current meter, for measuring, when the bonding wire is so bonded (by the wire bonding process, for example) as to electrically connect at least one of the semiconductor unit and the package-connection-means, a current passing the voltage source, and for providing, according to the measured current, at least a status indicating signal reflecting the bonding status (or electrical connection status) between the bonding wire and the semiconductor unit, and/or the bonding status (or electrical connection status) between the bonding wire and a component which may be a bonding finger on the carrier supporting the package-connection-means, and which electrically connects the package-connection-means via the carrier (a trace on the carrier, for example) supporting the package-connection-means.  
           [0009]    The present invention may also be represented by a method associated with a wire bonding machine, for detecting bonding status of a bonding wire of a package including at least a semiconductor unit and at least a package-connection-means such as solder ball pad, wherein the semiconductor unit and the package-connection-means are supported by at least a carrier with the wire bonding pads of the semiconductor unit exposed. The method may comprise the steps of: selecting at least one of the package-connection-means such as sold ball pads to be contacted by an electrical conduction means such as an object made of electrically conductive metal, or electrically conductive rubber, or anisotropically conductive film, or the combination of these material; electrically connecting the semiconductor unit and the selected one of the package-connection-means; letting a press plate of the wire bonding machine contact the electrical conduction means; using a voltage source to provide an electrical potential difference which exists between the press plate and the bonding wire when the wire bonding machine completes bonding the bonding wire to the semiconductor unit; measuring a current passing the voltage source, and providing a status indicating signal according to the measured current to reflect the bonding status between the bonding wire and the semiconductor unit. An embodiment of the above step of electrically connecting the semiconductor unit and the selected one of the package-connection-means may be to bond a wire to the semiconductor unit and a bonding finger connecting the package-connection-means via a trace of the carrier supporting the package-connection-means.  
           [0010]    The present invention may further be represented by a second method also associated with a wire bonding machine, for detecting bonding status of a bonding wire of a package including at least a semiconductor unit and at least a package-connection-means such as solder ball pad, wherein the semiconductor unit and the package-connection-means are supported by at least a carrier with the wire bonding pads of the semiconductor unit exposed. The second method may comprise the steps of: contacting all of the package-connection-means by an electrical conduction means such as an object made of electrically conductive metal, or electrically conductive rubber, or anisotropically conductive film, or the combination of these material; selecting at least one of the package-connection-means to electrically connect the semiconductor unit; letting a press plate of the wire bonding machine contact the electrical conduction means; using a voltage source to provide an electrical potential difference which exists between the press plate and the bonding wire when the wire bonding machine completes bonding the bonding wire to the semiconductor unit, and also exists when the wire bonding machine completes bonding the bonding wire to a component (a bonding finger of the carrier supporting the package-connection-means, for example) electrically connecting the package-connection-means; and measuring twice the current passing the voltage source, and providing a first status indicating signal according to the current measured at the first time to reflect the bonding status between the bonding wire and the semiconductor unit, then providing a second status indicating signal according to the current measured at the second time to reflect the electrical connection status between the bonding wire and the package-connection-means, or the bonding status between the bonding wire and the component electrically connecting the package-connection-means. 
       
    
    
       [0011]    The present invention may best be understood through the following description with reference to the accompanying drawings, in which:  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 and FIG. 2 show conventional arts for detecting bonding status of bonding wires during a wire bonding process for packaging a chip.  
         [0013]    [0013]FIG. 3, FIG. 4, and FIG. 5 show some embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    A first embodiment of the present invention is shown in FIGS. 3, 4, and  5 . The first embodiment is configured to associate with a wire bonding process or wire bonding machine, for detecting bonding status of a bonding wire of a Ball Grid Array package or similar types of packages including at least a semiconductor unit and at least a solder ball pad (also called package-connection-means in this disclosure). According to the first embodiment, the bonding status of a bonding wire between a semiconductor unit  1  (a chip or die) and a solder ball pad  8  can be detected in spite of the existence of an layer  4  of Cupric Oxide between semiconductor unit  1  and carrier  3 . The system embodiment comprises: p 1  at least a carrier such as a heat dissipater  3  and substrate  7  for supporting the semiconductor unit  1  and the solder ball pads  8  (only one solder ball pad  8  is shown in FIGS. 3 and 4 while a plurality of solder ball pads  8  can be seen in FIG. 5); at least an electrical conduction means  19  (an electrically conductive rubber, for example) contacting at least a selected one of the solder ball pads  8 ;  
         [0015]    at least a preset connection means  5  for electrically connecting (via a bonding finger  10  and a trace  7  of the carrier  7 , for example) the selected one of the solder ball pads  8  and a point of the semiconductor unit  1  such as a wire bonding pad  6  corresponding to the selected one of the solder ball pads  8 ;  
         [0016]    a voltage source  21  enclosed in or independent of a wire bonding machine used for the wire bonding process, for providing an electrical potential difference between the electrical conduction means  19  and a bonding wire  17  (via a press plate  11  used by the wire bonding process, a conductor  26 , a bonding wire  25 , and the bonding wire remaining in the capillary  24  of the wire bonding machine, for example); and  
         [0017]    a detector  22  enclosed in or independent of the wire bonding machine used for the wire bonding process, for measuring, a current passing the voltage source, and for providing, according to the measured current, at least a status indicating signal reflecting the bonding status of bonding wire  17 , i.e., the bonding status between the bonding wire  17  and semiconductor unit  1 .  
         [0018]    In the first embodiment for detecting bonding status of a bonding wire of a Ball Grid Array package or similar types of packages, the carrier such as  3  or  7  in FIG. 3 may be a substrate, a tape, or a heat dissipater, or their combination, the carrier  3  supporting semiconductor unit  1  is a heat dissipater to which semiconductor unit  1  is attached via adhesion layer  2  and a layer  4  of Cupric Oxide, the preset connection means  5  may include a bonding finger  10  which is on the carrier  7  (a substrate, for example) supporting the solder ball pads  8  and electrically connects the selected one of the solder ball pads  8 , thereby the preset connection means  5  electrically connects the selected one of the solder ball pads  8  via bonding finger  10 , with part of it being a bonding wire so bonded by the wire bonding process as to electrically connect semiconductor unit  1  and bonding finger  10  (i.e., connected to a wire bonding pad  6  of semiconductor unit  1  and to bonding finger  10 , for example), the preset connection means  5  may further include a trace (not shown in figures) lying on carrier  7  and electrically connecting both bonding finger  10  and the selected one of the solder ball pads  8 . The voltage source  21  provides an electrical potential difference between the electrical conduction means  19  and bonding wire  25  (still including bonding wire  17 ) by electrically connecting (via a conductor  26 , for example) a bonding wire provider  28  used by the wire bonding process, and the bonding wire  25  contained in capillary  24  used by the wire bonding process, and by electrically connecting (via a conductor  27 , for example) a press plate  11  used by the wire bonding process.  
         [0019]    As shown in FIGS. 4 and 5, when the wire bonding process completes the bonding of bonding wire  17  (still being part of bonding wire  25 ) to another wire bonding pad  16  of semiconductor unit  1 , a current loop is constituted by conductor  26 , bonding wire  25  (still including bonding wire  17 ), semiconductor unit  1 , the preset connection means  5  (may be deemed to include bonding finger  10  and a trace of carrier  7 ), the selected one of the solder ball pads  8 , electrical conduction means  19 , press plate  11 , conductor  27 , and voltage source  21  to form a current passing the voltage source  21 ; the current shall be small if the bonding status between bonding wire  17  and the wire bonding pad  16  of semiconductor unit  1  is poor, while will be large if the bonding status between bonding wire  17  and the pad  16  of semiconductor unit  1  is good. The detector  22  measures the current passing voltage source  21  to provide a status indicating signal  23  reflecting the magnitude of the current, thereby reflecting the bonding status of bonding wire  17 , i.e., reflecting the bonding status between bonding wire  17  and semiconductor unit  1 .  
         [0020]    A second embodiment of the present invention may also be illustrated by FIGS. 3, 4, and  5  where electrical conduction means  19  contacts all of solder ball pads  8  instead of only the selected one of the solder ball pads  8 , the carrier  7  supporting the solder ball pads  8  includes more than one bonding finger  10  each connecting one of the solder ball pads  8 . In the second embodiment, voltage source  21  also provides an electrical potential difference between the electrical conduction means  19  and bonding wire  17  by electrically connecting (via a conductor  26 , for example) a bonding wire provider  28  used by the wire bonding process, and the bonding wire  25  contained in capillary  24  used by the wire bonding process, and by electrically connecting (via a conductor  27 , for example) a press plate  11  used in the wire bonding process. When the wire bonding process completes the bonding of bonding wire  17  (still being part of bonding wire  25 ) to wire bonding pad  16  of semiconductor unit  1 , a current loop is constituted by conductor  26 , bonding wire  25  (still including bonding wire  17 ), semiconductor unit  1 , preset connection means  5  (may include bonding finger  10  and a trace of carrier  7 ), the selected one of the solder ball pads  8 , electrical conduction means  19 , press plate  11 , conductor  27 , and voltage source  21  to form a first current passing the voltage source  21  and having its magnitude reflecting the good or poor bonding status of the bonding wire  17 , i.e., the good or poor bonding status between bonding wire  17  and semiconductor unit  1  (specifically the wire bonding pad  16  of semiconductor unit  1 ). Detector  22  measures the first current to provide a first status indicating signal reflecting the magnitude of the first current, thereby reflecting the bonding status between bonding wire  17  and semiconductor unit  1 . When the wire bonding process completes the bonding of bonding wire  17  to bonding finger  10 , a current loop is constituted by conductor  26 , bonding wire  25  (still including bonding wire  17 ), the bonding finger  10 , the solder ball pads  8  which electrically connects the bonding finger  10  directly or via a trace of carrier  7 , electrical conduction means  19 , press plate  11 , conductor  27 , and voltage source  21  to form a second current passing voltage source  21  and having its magnitude reflecting the good or poor bonding status between bonding wire  17  and the bonding finger  10 . Detector  22  also measures the second current to provide a second status indicating signal reflecting the magnitude of the second current, thereby reflecting the good or poor bonding status between bonding wire  17  and the bonding finger  10 . The second current will always be larger than the first current because the second current does not flow through semiconductor unit  1  (semiconductor unit is electrically semiconductive). Based on these facts, the bonding status between bonding wire  17  and semiconductor unit  1  as well as that between bonding wire  17  and the bonding finger  10  can be respectively detected.  
         [0021]    A first method embodiment of the invention which is associated with a wire bonding machine to detect bonding status of at least a bonding wire of a semiconductor package is illustrated hereinafter by referring to FIGS. 3, 4, and  5 . The wire bonding machine may include a press plate  11 , a capillary  24 , or may further include a hot plate  14 . The semiconductor package includes at least a semiconductor unit  1  and at least a package-connection-means such as solder ball pads  8 , the semiconductor unit  1  and the solder ball pads  8  being supported by at least a carrier such as heat dissipater  3  and substrate  7 , with wire bonding pad  6  and  16  of semiconductor unit  1  being exposed. The first method embodiment of the invention comprises the steps of:  
         [0022]    selecting at least one of the solder ball pads  8  to be contacted by an  
         [0023]    electrical conduction means  19 ;  
         [0024]    electrically connecting the semiconductor unit  1  and the selected one of the solder ball pads  8 ;  
         [0025]    letting a press plate  11  of the wire bonding machine contact the electrical conduction means  19 ;  
         [0026]    providing (using a voltage source, for example) an electrical potential difference which exists between the press plate  11  and the bonding wire  17  when the wire bonding machine completes bonding the bonding wire  17  to the semiconductor unit  1 ;  
         [0027]    measuring a current passing the voltage source (or the press plate  11  or bonding wire  17 ), and providing a status indicating signal according to the measured current to reflect the bonding status between the bonding wire  17  and the semiconductor unit  1 .  
         [0028]    The electrical conduction means  19  according to the invention may be made of at least one type of material selected from among electrically conductive metal, electrically conductive rubber, and anisotropically conductive film.  
         [0029]    According to the invention, the step of electrically connecting the selected one of the solder ball pads  8  and the semiconductor unit  1  comprises a step of electrically connecting the selected one of the solder ball pads  8  and an arbitrary point of the semiconductor unit  1  or a corresponding wire bonding pad which is a wire bonding pad  6  of the semiconductor unit  1  and which corresponds to the selected one of the solder ball pads  8 .  
         [0030]    For the first method embodiment of the invention, the carrier  7  supporting the selected one of the solder ball pads  8  may include at least a trace (not shown in the figures) and at least a bonding finger  10 , each of the solder ball pads  8  connects at least one of the bonding finger  10  via the trace; and the step of electrically connecting the selected one of the solder ball pads  8  and the semiconductor unit  1  includes the step of: bonding a preset connection means  5  by the wire bonding machine between the bonding finger  10  connected to the selected one of the solder ball pads  8 , and a corresponding wire bonding pad which is a wire bonding pad  6  of the semiconductor unit  1  and corresponds to the selected one of the solder ball pads  8 . The wire bonding machine may further include a voltage source  21  and a bonding wire provider  28 , the voltage source  21  providing the electrical potential difference between the press plate  11  and the bonding wire  17 , by electrically connecting bonding wire  17  via conductor  26 , bonding wire provider  28 , and bonding wire  25 , and by electrically connecting press plate  11  via conductor  27 .  
         [0031]    A second method embodiment of the invention which is also associated with a wire bonding machine to detect bonding status of at least a bonding wire of a semiconductor package is also illustrated hereinafter by referring to FIGS. 3, 4, and  5 . The second method embodiment of the invention comprises the steps of: contacting all (instead of only a selected one) of the solder ball pads  8  of the semiconductor package by an electrical conduction means  19 ; selecting at least one of the solder ball pads  8  to electrically connect the semiconductor unit  1 ;  
         [0032]    letting a press plate  11  of the wire bonding machine contact the electrical conduction means  19 ;  
         [0033]    providing an electrical potential difference which exists between the press plate  11  and the bonding wire  17  when the wire bonding machine completes bonding the bonding wire  17  to the semiconductor unit  1 ;  
         [0034]    measuring a current passing the press plate  11  or bonding wire  17 , and providing a status indicating signal according to the measured current to reflect the bonding status between the bonding wire  17  and the semiconductor unit  1 .  
         [0035]    According to the second method embodiment of the invention, obviously the same or different electrical potential difference may also be so provided to exist between press plate  11  and bonding wire  17  when the electrical connection between the bonding wire  17  and one of the solder ball pads  8  is completed by the wire bonding machine which has bonded the bonding wire  17  to a bonding finger  10  electrically connecting (via a trace of carrier  7 , for example) the one of the solder ball pads  8 . The current passing press plate  11  or bonding wire  17  are measured twice, one when the wire bonding machine completes the bonding of bonding wire  17  to semiconductor unit  1 , and another when the electrical connection between the bonding wire  17  and one of the solder ball pads  8  is completed, i.e., after bonding wire  17  is bonded by the wire bonding machine to the bonding finger  10  that electrically connects the one solder ball pad  8 . It can be understood that the status indicating signal may reflect the bonding status between bonding wire  17  and semiconductor unit  1 , as well as the electrical connection status between bonding wire  17  and the one of the solder ball pads  8 . The detection of electrical connection status between bonding wire  17  and the one of the solder ball pads  8  in such a case can be represented by the detection of the bonding status between bonding wire  17  and the bonding finger  10 , because the electrical connection between bonding finger  10  and the solder ball pads  8  is usually inherent in substrate  7 .