Abstract:
A method of making a semiconductor device comprises the steps of coating a first face of an insulative board ( 1 ) with a thermally plastic resin ( 2 ), bonding at least one semiconductor element ( 3 ) onto the thermally plastic resin ( 2 ), piercing the thermally plastic resin ( 2 ) and the insulative board ( 1 ) with at least one capillary that holds a metal wire ( 4 ), forming a metal ball ( 4   b ) and pulling out the capillary from the insulative board (1) and the thermally plastic resin ( 2 ), pressing the capillary onto an electrode ( 3   a ) of the semiconductor element ( 3 ) and cutting off an extra wire, and attaching at least one metal bump ( 6 ) to the second face of the insulative board ( 1 ) so as to be connected to the metal ball ( 4   a ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This is a divisional application No. 09/956,801, filed Sep. 21, 2001, now allowed.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to semiconductor devices and, particularly, to a semiconductor device package and a method of making the same.  
           [0004]    This application is a counterpart of Japanese application Serial Number 2000-347855, filed on Nov. 15, 2000, the subject matter of which is incorporated herein by reference.  
           [0005]    2. Description of the Related Art  
           [0006]    [0006]FIG. 10 shows a conventional ball grid array (BGA) type semiconductor device. The BGA type semiconductor device comprises an insulative board  51  and a plurality of metal bumps or solder balls  52  arranged on the lower face of the insulative board  51  as outer electrodes so that it makes miniaturization possible and stronger and easier to handle than the pin type package. Also, it comprises a plurality of conductive members or metal foils  53  and conductive members  54  and  55 . A solder resist  56  is provided on the lower face of the insulative board  51 . A semiconductor element  58  is bonded to the upper face of the insulative board  51  with a bonding agent  57 . The electrodes  59  of the semiconductor element  59  are connected to the conductive members  53  by metal wires  60 , which are covered by an insulative resin  61 .  
           [0007]    However, the BGA type semiconductor device has the solder resist  56  to coat the lower face of the insulative board  51  so that if the solder resist  56  has low adhesive powers, it could separate to lower the reliability of the semiconductor device. Since the insulative board  51  already has the conductive members  53 ,  54 , and  55 , the solder resist  56 , and the metal bumps  52 , the manufacturing cost is high.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, it is an object of the invention to provide a simple, inexpensive, and reliable semiconductor device having advantages of the BGA type semiconductor device, such as miniaturization, strength, and easiness to handle.  
           [0009]    According to one aspect of the invention there is provided a method of making a semiconductor device which comprises the steps of coating a first face of an insulative board with a thermally plastic resin; bonding a semiconductor element onto the thermally plastic resin; piercing the thermally plastic resin and the insulative board with at least one capillary that holds a metal wire, forming a metal ball at a front end of the metal wire on a side of a second face of the insulative board that is opposite to the first face of the insulative board and pulling out the capillary from the insulative board and the thermally plastic resin such that the metal ball is embedded in the insulative board; pressing the capillary onto an electrode of the semiconductor element to bond the metal wire to the electrode and cutting off an extra wire; and attaching at least one metal bump to the second face of the insulative board so as to be connected to the metal ball.  
           [0010]    According to another aspect of the invention there is provided a method of making a semiconductor device, comprising the steps of applying a coat of thermally plastic resin to a first face of an insulative board that is curable with ultraviolet rays; bonding a semiconductor element onto the thermally plastic resin; piercing the thermally plastic resin and the insulative board with at least one capillary that holds a metal wire, forming a metal ball at a front end of the metal wire on a side of a second face of the insulative board that is opposite to the first face of the insulative board and pulling out the capillary from the insulative board and the thermally plastic resin such that the metal ball is embedded in the insulative board; pressing the capillary onto an electrode of the semiconductor element to bond the metal wire to the electrode and cutting off an extra wire; irradiating the insulative board with the ultraviolet rays; and attaching at least one metal bump to the second face of the insulative board so as to be connected to the metal ball.  
           [0011]    According to still another aspect of the invention there is provided a method of making a semiconductor device, comprising the steps of coating a first face of an insulative board of nonwoven cotton fabric with a thermally plastic resin; bonding a semiconductor element onto the thermally plastic resin; piercing the thermally plastic resin and the insulative board with at least one capillary that holds a metal wire, forming a metal ball at a front end of the metal wire on a side of a second face of the insulative board that is opposite to the first face of the insulative board and pulling out the capillary from the insulative board and the thermally plastic resin such that the metal ball is embedded in the insulative board; pressing the capillary onto an electrode of the semiconductor element to bond the metal wire to the electrode and cutting off an extra wire; and attaching at least one metal bump to the second face of the insulative board so as to be connected to the metal ball.  
           [0012]    According to yet another embodiment of the invention, the capillary piercing step is performed while the thermally plastic resin is heated on a heat stage.  
           [0013]    According to another embodiment of the invention, the metal ball of the metal wire is formed by a spark produced between the metal wire and an electric torch. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the invention;  
         [0015]    [0015]FIG. 2( a ) is a plan view of a tape of insulative boards;  
         [0016]    [0016]FIG. 2( b ) is a sectional view taken along line S 2 -S 2  of FIG. 2( a );  
         [0017]    [0017]FIG. 3( a ) is a plan view of the tape of insulative boards on which semiconductor elements are bonded;  
         [0018]    [0018]FIG. 3( b ) is a sectional view taken along line S 3 -S 3  of FIG. 3( a );  
         [0019]    [0019]FIG. 4( a ) is a plan view of the tape of insulative boards to which metal wires are attached;  
         [0020]    [0020]FIG. 4( b ) is a sectional view taken along line S 4 -S 4  of FIG. 4.( a );  
         [0021]    [0021]FIG. 5( a ) is a plan view of the tape of insulative boards on which enveloping resins are applied;  
         [0022]    [0022]FIG. 5( b ) is a sectional view taken along line S 5 -S 5  of FIG. 5( a );  
         [0023]    [0023]FIG. 6( a ) is a plan view of the lower face of the tape of insulative boards to which metal bumps are attached;  
         [0024]    [0024]FIG. 6( b ) is a sectional view taken along line S 6 -S 6  of FIG. 6( a );  
         [0025]    FIGS.  7 ( a )-( f ) are diagrams showing the steps of making the metal wires of FIG. 4( a );  
         [0026]    [0026]FIG. 8 is a sectional view of a semiconductor device according to the second embodiment of the invention;  
         [0027]    [0027]FIG. 9 is a sectional view of a semiconductor device according to the third embodiment of the invention; and  
         [0028]    [0028]FIG. 10 is a sectional view of a conventional semiconductor device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0029]    In FIG. 1, a semiconductor device comprises an insulative board or sheet  1 , a thermally plastic resin  2  coated on the insulative sheet  1 , a semiconductor element  3  secured to the insulative sheet  1  by the thermally plastic resin  2 , and a plurality of metal wires  4  that are made of gold or the like. An end  4   a  of each metal wire  4  is connected to the electrode  3   a  of the semiconductor element  3  while the other end forms a metal ball  4   b  that is embedded in the insulative board  1  on the side of the lower face or the face opposite to the face where the semiconductor element  3  is mounted. The semiconductor device also comprises an enveloping resin  5  that is made of an insulative material to envelope the metal wires  4  on the side of the semiconductor element  3 , and a plurality of metal bumps or outer electrodes  6  that are connected to the metal balls  4   b . The metal bumps  6  are made of solder balls for example.  
         [0030]    The semiconductor device is made as follows.  
         [0031]    In FIGS.  2 ( a ) and  2 ( b ), a tape of the insulative board  1  is unreeled and the thermally plastic resin  2  is coated on the tape.  
         [0032]    In FIGS.  3 ( a ) and  3 ( b ), a plurality of semiconductor elements  3  are bonded under heat and pressure onto the thermally plastic resin  2 .  
         [0033]    In FIGS.  4 ( a ) and  4 ( b ), the metal wires  4  are attached while the thermally plastic resin  2  is softened on a heat stage  12 . This step comprises the following substeps.  
         [0034]    A capillary  11  that holds the metal wire  4  as shown in FIG. 7( a ) is put through the thermally plastic resin  2  and the insulative board  1  as shown in FIG. 7( b ). Then, a metal ball  4   b  is formed at the front end of the metal wire  4  by the spark between an electric torch  13  and the metal wire  4  as shown in FIG. 7( c ). Then, the capillary  11  is pulled out of the insulative board  1  and the thermally plastic resin  2  such that the metal ball  4   b  is embedded in the insulative board  1  as shown in FIG. 7( d ). Then, the capillary  11  is press-bonded against the electrode  3   a  of the semiconductor element  3  to bond the metal wire  4  to the electrode  3   a  and cut as shown in FIGS.  7 ( e ) and  7 ( f ), respectively.  
         [0035]    Then, as shown in FIGS.  5 ( a ) and  5 ( b ), the metal At wires  4  are enveloped by the enveloping resin  5  of an insulative material that is provided on the side of the semiconductor element  3 . As shown in FIGS.  6 ( a ) and  6 ( b ), a plurality of metal bumps  6  connected to the metal balls  4   b  are attached to the lower face of the insulative board  1 . Then, a plurality of the semiconductor elements on the insulative board  11  are divided by individual cut to provide a semiconductor device such as shown in FIG. 1.  
         [0036]    As has been described above, according to the first embodiment of the invention, the metal bumps  6  are provided on the lower face of the insulative board  1  as outer electrodes so that further miniaturization is possible and, since the metal bumps  6  do not have a pin-shaped form, the semiconductor device is strong and easy to handle. Also, it is simpler than the BGA type semiconductor device, thus making it possible to reduce the manufacturing cost. In addition, no solder resist coating is used so that there is no solder resist separation, eliminating the reliability problem resulting therefrom. Furthermore, the enveloping resin  5  has high reflow resistance.  
         [0037]    The method of making the semiconductor device according to the first embodiment of the invention is applicable to the semiconductor elements  3  of any chip-size that can be mounted within the tape of the insulative board  1 . In addition, a variety of semiconductor element chips can be mounted on the same insulative board  1 . Furthermore, the steps of drawing a tape of the insulative board  1  from a reel, installation of the semiconductor elements  3 , formation of the metal wires  4 , enveloping of the resin  5 , and formation of the metal bumps  6  by solder printing can be streamlined to minimize the number of process steps. Moreover, the electrodes are provided on the lower face of the insulative board  1  so that a great number of metal bumps  6  can be made readily to provide a multiple pin semiconductor device.  
       Second Embodiment  
       [0038]    In FIG. 8, a semiconductor device according to the second embodiment of the invention is the same as that of the first embodiment except that an insulative board  21  is cured by ultraviolet radiation. The method of making the semiconductor device according to the second embodiment comprises the step of irradiating ultraviolet rays to the insulative board  21  following the step of piercing or putting the capillary through the insulative board  21 . This irradiating step prevents the insulative board  21  from being torn by the capillary piercing. The other features and functions of the second embodiment are the same as those of the first embodiment.  
       Third Embodiment  
       [0039]    In FIG. 9, a semiconductor device according to the third embodiment of the invention is the same as that of the first embodiment except that the insulative board is replaced by an insulative board  22  that is made of nonwoven cotton fabric that is impregnated with the thermally plastic resin  2  to form such an integral layer as shown. A preferred example of the nonwoven cotton fabric is Benleaze (trademark) of Asahi Kasei Co., Ltd. It has a carbonization temperature from 260 to 300 degrees C., which is substantially higher than 180 degrees C. or the molding temperature of the thermally plastic resin. By heating the insulative board  22  it is possible to prevent the insulative board  22  from being torn in the capillary piercing step. The use of the nonwoven cotton fabric reduces the manufacturing cost. The other features and functions of the third embodiment are the same as those of the first embodiment.  
         [0040]    As has been described above, according to the invention, the metal bumps are provided on the lower face of an insulative board so that further miniaturization is possible. Since the metal bumps do not have a pin-shaped form, they are strong and easy to handle. The semiconductor device is simpler than the BGA type semiconductor device so that it is possible to cut the manufacturing cost. Since no solder resist coating is used, there is no solder resist separation that reduces the reliability of the semiconductor device. Finally, the enveloping resin applied to the semiconductor device has an excellent reflow resistance.  
         [0041]    According to another aspect of the invention, the manufacturing method is useful for semiconductor elements of any size that is mountable within the insulative board. In addition, the same insulative board is useful for any type of semiconductor chip. It is possible to streamline the steps of drawing a tape of insulative board from a reel, bonding the semiconductor element, forming the metal wires, enveloping with the resin, and forming metal bumps by solder printing so that it is possible to reduce the number of process steps. Furthermore, a great number of bumps can be formed, making it easy to provide a multiple-pin semiconductor device.  
         [0042]    Following the step of piercing the insulative board with the capillary, the step of irradiating the insulative board with ultraviolet rays is provided to prevent the insulative board from being torn in the capillary piercing step.  
         [0043]    The employment of the nonwoven cotton fabric for the insulative board reduces the manufacturing cost.