Abstract:
A wire bonding method that connects a first bonding point and a second bonding point by a wire, the method including a step that press-bonds a ball formed on a tip end of a wire to a first bonding point, thus forming a press-bonded ball; a step that slightly raises a capillary, moves the capillary toward a second bonding point and then lowers the capillary by an amount that is smaller than an amount in which the capillary was raised, and a step that raises the capillary to allow the wire to be paid out of the capillary and moves the capillary toward a second bonding point, thus connecting the wire to the second bonding point.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a semiconductor device and a wire bonding method in which a first bonding point and second bonding point are connected by a wire and more particularly to a semiconductor device that has a low wire loop shape and to a method for manufacturing such a semiconductor device.  
         [0003]     2. Prior Art  
         [0004]     In wire bonding, when slack occurs in a wire that connects a first bonding point and a second bonding point, the wire contacts the die that causes short-circuiting. Conventionally, in order to prevent this, a press-bonded ball is first formed by press-bonding a ball to the first bonding point, then a neck height portion that extends upward is formed on the press-bonded ball, and a bent portion (kink) is formed at the upper end of this neck height portion. This method is disclosed in, for example, Japanese Patent Application Laid-Open (Kokai) No. H 10-189641.    
         [0005]     In methods of the prior art, since a neck height portion is formed on the press-bonded ball, the resulting wire loop is inevitably high. In recent years, though there are strong demands that semiconductor devices be made smaller and thinner, with prior art methods, such demands are not sufficiently satisfied.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, the object of the present invention is to provide a semiconductor device and a wire bonding method that form a low wire loop.  
         [0007]     The above object is accomplished by a unique structure of the present invention for a semiconductor device in which a first bonding point and a second bonding point are connected by a wire loop, and in the present invention, the wire loop is comprised of: 
        a circular arc portion that extends in a shape of a circular arc from the first bonding point,     an inclined portion that extends to the second bonding point from the circular arc portion, and     a bent portion formed between the circular arc portion and the inclined portion.        
 
         [0011]     The above object is accomplished by another unique structure of the present invention for a semiconductor device in which a first bonding point and a second bonding point are connected by a wire loop, and in the present invention, the wire loop is comprised of: 
        a circular arc portion that extends in a shape of a circular arc from the first bonding point,     a horizontal portion that extends horizontally from the circular arc portion,     an inclined portion that extends to the second bonding point from the horizontal portion, and     bent portions respectively formed between the circular arc portion and the horizontal portion and between the horizontal portion and the inclined portion.        
 
         [0016]     The above object is accomplished by a series of unique steps of the present invention for a wire bonding method that connects a first bonding point and a second bonding point by a wire, and in the present invention, the method comprises sequentially: 
        a step that press-bonds a ball formed on a tip end of a wire to a first bonding point, thus forming a press-bonded ball,     a step that slightly raises a capillary, moves the capillary toward a second bonding point, and then lowers the capillary by an amount that is smaller than an amount in which the capillary was raised, and     a step that raises the capillary to allow the wire to be paid out of the capillary and moves the capillary toward a second bonding point, thus connecting the wire to the second bonding point.        
 
         [0020]     The above object is accomplished by another series of unique steps of the present invention for a wire bonding method that connects a first bonding point and a second bonding point by a wire, and in the present invention, the method comprises sequentially: 
        a step that press-bonds a ball formed on a tip end of a wire to a first bonding point, thus forming a press-bonded ball,     a step that slightly raises a capillary, moves the capillary toward a second bonding point, and then lowers the capillary by an amount that is smaller than an amount in which the capillary was raised,     a step that raises the capillary and then performs at least once a reverse operation in which the capillary is moved in a direction opposite from the second bonding point, and     a step that raises the capillary to allow the wire to be paid out of the capillary and moves the capillary toward the second bonding point, thus connecting the wire to the second bonding point.        
 
         [0025]     Since the portion of the wire that extends from the first bonding point is a circular arc portion, the height of this circular arc portion is lower than that of a conventional neck height portion. Accordingly, in the present invention, an extremely low wire loop is formed. Furthermore, since a bent portion is formed between the circular arc portion and the inclined portion, no slack occurs in the wire that is connected between the first bonding point and the second bonding point. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     FIGS.  1  ( a ) through  1  ( f ) show the steps of the first embodiment of the wire bonding method of the present invention; and  
         [0027]     FIGS.  2 ( a ) through  2 ( e ) show the steps of the second embodiment of the wire bonding method of the present invention, the step of  FIG. 2 ( a ) following the step of  FIG. 1 ( c ). 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     A first embodiment of the semiconductor device of the present invention will be described with reference to  FIG. 1 ( f ).  
         [0029]     The wire loop (or the wire loop shape) in which the first bonding point A and second bonding point B are connected by a wire  4  includes a circular arc portion  31 , which extends in the shape of a circular arc from the first bonding point A, and an inclined portion  33 , which extends from this circular arc portion  31  to the second bonding point B. A bent portion  21  is formed between the circular arc portion  31  and the inclined portion  33 .  
         [0030]     Since the portion of the wire that extends from the first bonding point A is thus a circular arc portion  31 , the height of the circular arc portion  31  is lower than that of a conventional neck height portion. Thus, the wire loop is extremely low. Since the bent portion  21  is formed between the circular arc portion  31  and the inclined portion  33 , no slack occurs in the wire  4  that is connected between the first bonding point A and second bonding point B.  
         [0031]     Next, a first embodiment of the wire bonding method of the present invention that is used to obtain a semiconductor device such as that shown in  FIG. 1 ( f ) will be described with reference to  FIG. 1 .  
         [0032]     As shown in  FIG. 1 ( f ), a die  3  on which an electrode pad  2  is formed is mounted on a circuit board  1  consisting of a lead frame or a board such as a ceramic substrate or printed board, etc. A first bonding point A on such an electrode pad  2  and second bonding point B such as wiring or a lead on the circuit board  1  are electrically connected by a wire  4 .  
         [0033]     First, as shown in  FIG. 1  ( a ), with a damper (not shown in the drawings) that holds the wire  4  in an open state, a capillary  5  is lowered so that a ball formed on the tip end of the wire  4  is bonded to the first bonding point A, thus forming a press-bonded ball  11 .  
         [0034]     The capillary  5  is then slightly raised to point C, and the wire  4  is paid out of the capillary  5 .  
         [0035]     Next, as shown in  FIG. 1  ( b ), the capillary  5  is moved horizontally to point D in the direction of the second bonding point B.  
         [0036]     Then, as shown in  FIG. 1 ( c ), the capillary is lowered to point E by an amount that is smaller than the amount of the above-described raising. As a result of the step shown in this  FIG. 1  ( c ), a strong bent portion  21  is formed in the portion of the wire that is located slightly above the press-bonded ball  11 .  
         [0037]     Next, as shown in  FIG. 1 ( d ), the capillary  5  is raised to point F by an amount that corresponds to the length of wire that is to be connected between the first bonding point A and the second bonding point B, and the wire  4  is paid out of the capillary  5 .  
         [0038]     Afterward, an operation that is the same as that performed in a conventional method is performed. More specifically, as shown in  FIG. 1 ( e ), the capillary  5  is caused to make a circular arc motion or is caused to make a circular arc motion and is then lowered, so that the capillary  5  is positioned at the second bonding point B, and the wire  4  is bonded to the second bonding point B.  
         [0039]     Next, the damper (not shown in the drawings) and the capillary  5  are both raised, and the damper is closed at an intermediate point during this raising movement, so that the wire  4  is cut from the root portion of the second bonding point B as shown in  FIG. 1  ( f ). As a result, the first bonding point A and second bonding point B are electrically connected.  
         [0040]     Conventionally, a bent portion is formed by performing a reverse operation on a portion of the wire  4  located above the press-bonded ball  11 . Accordingly, a neck height portion that rises upward from the press-bonded ball  11  is formed. However, in the shown embodiment, the capillary  5  is moved toward the second bonding point B as shown in  Fig. 1 ( b ), and the capillary  5  is then lowered so that a bent portion  21  is formed as shown in  FIG. 1 ( c ). Accordingly, the bending direction of the bent portion  21  is the opposite of that in a conventional method. Consequently, when the capillary  5  is moved to a point above the second bonding point B as shown in FIGS.  1 ( d ) through  1 ( e ), the portion of the wire between the press-bonded ball  11  and the bent portion  21  forms a circular arc portion  31 , and the height of this circular arc portion is lower than that of a conventional neck height portion, and the wire loop is extremely low. Furthermore, since the bent portion  21  is formed by lowering the capillary  5  as shown in  FIG. 1 ( c ), a strong bent portion  21  is formed, and no slack occurs in the wire  4  that is connected between the first bonding point A and second bonding point B.  
         [0041]     A second embodiment of the semiconductor device of the present invention will be described with reference to  FIG. 2 ( e ).  
         [0042]     Here, the wire loop (or the shape of the wire loop) in which the first bonding point A and second bonding point B are connected by a wire  4  includes a circular arc portion  31  that extends from the first bonding point A, a horizontal portion  32  that extends horizontally from this circular arc portion  31 , and an inclined portion that extends to the second bonding point B from this horizontal portion  32 . Bent portions  21  and  22  are respectively formed between the circular arc portion  31  and the horizontal portion  32  and between the horizontal portion  32  and the inclined portion  33 .  
         [0043]     In addition to the advantages of the above-described embodiment, the second embodiment also provides advantages. Especially, since the bent portion  22  is formed at an intermediate point of the wire loop, the portion of the wire between the bent portion  21  and the bent portion  22  is a substantially horizontal to be a horizontal portion  32 . As a result of the existence of this horizontal portion  32 , contact of the wire  4  with the die  3  is prevented even if, for example, the die  3  should extend as indicated by the two-dot chain line so that the distance between the first bonding point A and the end portion of the die  3  is long; Furthermore, sagging of the wire loop is reduced even in cases where the distance between the first bonding point A and the second bonding point B is long. Accordingly, such a horizontal portion  32  is effective.  
         [0044]     Next, a second embodiment of the wire bonding method of the present invention that produces a semiconductor device such as that shown in  FIG. 2 ( e ) will be described with reference to FIGS.  2 ( a ) through  2 ( e ). The same reference numerals are assigned to members or portions that are the same as in FIGS.  1 ( a ) through  1 ( f ) or that correspond to members or portions in FIGS.  1  ( a ) through  1  ( f ), and a detailed description of such members or portions is omitted. In this embodiment, as seen from  FIG. 2 ( e ), a bent portion  22  is formed at an intermediate point on the wire  4 .  
         [0045]     First, a bent portion  21  is formed at a point located slightly above the press-bonded ball  11  by the steps shown in FIGS.  1 ( a ) through  1 ( c ).  
         [0046]     Next, as shown in  FIG. 2 ( a ), the capillary  5  is raised to point G by an amount that corresponds to the length of the horizontal portion  32  shown in  FIG. 2 ( e ).  
         [0047]     Then, as shown in  FIG. 2 ( b ), a reverse operation is performed in which the capillary  5  is moved in a circular arc to point H in the opposite direction from the second bonding point B and is lowered. As a result, the wire  4  is placed in an inclined state, and a bent portion  22  is formed.  
         [0048]     Next, as shown in  FIG. 2 ( c ), the capillary  5  is raised to point I by an amount that corresponds to the length of the inclined portion  33  shown in  FIG. 2 ( e ). Subsequently, the same operations as those shown in FIGS.  1 ( e ) and  1 ( f ) are performed, so that the wire  4  is bonded to the second bonding point B as shown in FIGS.  2 ( d ) and  2 ( e ).  
         [0049]     In the above embodiment shown in  FIG. 2 , a single bent portion  22  is formed in the portion of the wire  4  located between the bent portion  21  and the second bonding point B. However, it is also possible to perform two or more reverse operations so that two or more bent portions are formed.