Abstract:
A ultrasonic horn attached to a bonding arm of a bonding apparatus via two horn supporting members. These horn supporting members, preferably made from a resin material, are separate components from the ultrasonic horn, and the ultrasonic horn and the two horn supporting members are provided so that their positional relationship in the axial direction of the ultrasonic horn can be adjusted.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wire bonding apparatus, and more particularly, to an ultrasonic horn supporting structure. 
     2. Prior Art 
     The ultrasonic horn supporting structure in a conventional wire bonding apparatus is shown in FIG.  3 . 
     In this structure, a capillary  2  through which a wire (not shown) passes is mounted to one end of the ultrasonic horn  1 , and an ultrasonic vibrator  3  is fastened to another end thereof. A flange  4  is formed on the ultrasonic horn  1  so as to positionally correspond to a node of the ultrasonic vibration, and this flange  4  is connected to a cylindrical horn supporter  5 . The horn supporter  5  is fastened to a bonding arm  6 , and the bonding arm  6  is fastened to a supporting shaft  7 . The supporting shaft  7  is rotatably supported on a bonding head (not shown), either directly or via a lifter arm. 
     Examples of wire bonding apparatuses of this type are described in Japanese Patent Application Laid-Open (Kokai) Nos. H5-34734, H6-196532 and H10-303240. 
     Generally, as the speed of the operation of a wire bonding apparatus increases, the mechanical vibration of the ultrasonic horn also increases. In particular, vibration of the ultrasonic horn during vertical movement is a problem. 
     In the prior art, the ultrasonic horn is supported at one place that corresponds to a node of the ultrasonic vibration. Accordingly, the strength of the horn supporter is insufficient; and vibration of the ultrasonic horn generated by an improved speed increase of bonding apparatuses cannot be suppressed. When such vibration occurs, an excessive force applies during bonding to the ball formed at the end of the wire, resulting in an unsatisfactory shape in the crushed ball. Especially for balls having diameters reduced as a result of the use of finer pitches in semiconductor devices, this problem is difficult to deal with. 
     Furthermore, the flange  4  in the above prior art is integral to the ultrasonic horn  1 . Since the frequency of the ultrasonic horn  1  differs from horn to horn for structural reasons, it is difficult to achieve strict alignment of the mechanically worked flange  4  with the frequency node. When a discrepancy occurs between the node position and the flange  4 , the flange  4  vibrates so that a loss of vibrational energy, i.e., a so-called “leak”, occurs, so that energy unrelated to the bonding conditions is consumed. As a result, the impedance increases, and oscillation that deviates from the optimal frequency occurs, thus causing a deterioration in the bonding quality. Furthermore, since unnecessary power must be injected, unnecessary ultrasonic energy continues to be applied after the completion of bonding, thus causing, for instance, an increase in unsatisfactory crushed ball shapes, stripping of balls and damage to the substrate. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a wire bonding apparatus which reduces the vibration of a ultrasonic horn during vertical movement of the capillary. 
     Another object of the present invention is to provide a wire bonding apparatus which reduces the leakage of ultrasonic waves from the horn supporters, and which makes it possible to adjust the position of the horn supporters in accordance with the frequency of the ultrasonic vibration, thus increasing the energy utilization efficiency. 
     The above objects are accomplished by a unique structure of the present invention for a wire bonding apparatus that is equipped with an ultrasonic horn, which has a capillary attached at one end thereof and an ultrasonic vibrator attached to another end thereof, and a bonding arm to which the ultrasonic horn is attached; and in the present invention, the ultrasonic horn is attached to the bonding arm via two horn supporting members that are separate components from the ultrasonic horn, and the ultrasonic horn and the horn supporting members are provided so that their relative positions in the axial direction of the ultrasonic horn can be adjusted. 
     In the above structure the horn supporting members are preferably made from a resin material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 ( a ) is a longitudinal sectional view of one embodiment of the wire bonding apparatus according to the present invention, FIG.  1 ( b ) is a sectional view taken along the line  1   b — 1   b , and FIG.  1 ( c ) is a sectional view taken along the line  1   c — 1   c;    
     FIG.  2 ( a ) is a longitudinal sectional view of another embodiment of the wire bonding apparatus according to the present invention, FIG.  2 ( b ) is a sectional view taken along the line  2   b — 2   b , and FIG.  2 ( c ) is a sectional view taken along the line  2   c — 2   c ; and 
     FIG. 3 is a longitudinal sectional view of a conventional wire bonding apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the present invention will be described with reference to FIGS.  1 ( a ) through  1 ( b ) 
     A capillary  11  through which a wire (not shown) passes is mounted to one end (tip end) of an ultrasonic horn  10 , and an ultrasonic vibrator  12  is fastened to the another end (root end) of the horn  10 . This structure is the same as in the prior art apparatus. 
     Two horn supporting members  20 A and  20 B which have the same structures are fastened to the ultrasonic horn  10 . The horn supporting members  20 A and  20 B are formed with horn holes  21 A and  21 B so that the ultrasonic horn  10  is inserted therein. Also, cut-outs  22 A and  22 B whose widths are narrower than the diameters of the horn holes  21 A and  21 B are formed at the bottoms of the horn holes  21 A and  21 B. Furthermore, longitudinal slits  24 A and  24 B are formed so that thin elastic sections  23 A and  23 B are respectively formed in one side of each of the horn holes  21 A and  21 B. The longitudinal slits  24 A and  24 B extend in the direction of the length of the horn  10  and also extend upward from the undersurfaces of the horn supporting members  20 A and  20 B. Accordingly, the ultrasonic horn  10  is inserted in the horn holes  21 A and  21 B and fastened to the horn supporting members  20 A and  20 B by the elastic deformation of the elastic sections  23 A and  23 B that is caused by fastening bolts  25 A and  25 B which are screwed into the areas located outside the longitudinal slits  24 A and  24 B. 
     The horn supporting members  20 A and  20 B are fastened to a bonding arm  13  by attachment bolts  26 A and  26 B. The holes in the bonding arm  13  into which the attachment bolts  26 A are inserted are formed as slots (not shown) that extend in the axial direction of the ultrasonic horn  10 . As in the prior art apparatus, the bonding arm  13  is fastened to a supporting shaft  15 , and the supporting shaft  15  is rotatably supported on a bonding head (not shown), either directly or via a lifter arm. 
     In the above structure, since the ultrasonic horn  10  is supported in two places by two horn supporting members  20 A and  20 B, the rigidity of the horn supporters is high, and vibration occurring during vertical movement of the capillary  11  can be reduced. As a result of the vibration being reduced, no excessive force is applied to the ball at the end of the wire (not shown) during bonding, and a consistent crushed shape of the ball is obtained. 
     Furthermore, since the horn supporting members  20 A and  20 B are separate components from the ultrasonic horn  10 , the positions of the horn supporting members  20 A and  20 B can be adjusted to positions that corresponds to nodes of the ultrasonic vibration of the ultrasonic horn  10 . 
     This adjustment is performed in the following manner. First, the position of the ultrasonic horn  10  is adjusted relative to the horn supporting member  20 B. This adjustment is done so that the fastening bolt  25 B is loosened with the horn supporting member  20 B fastened to the bonding arm  13  by the attachment bolts  26 B; as a result, the elastic section  23 B deforms elastically toward the longitudinal slit  24 B, so that the position of the ultrasonic horn  10  in its axial direction can be changed relative to the horn supporting member  20 B. After an adjustment is made so that the horn supporting member  20 B is positioned at a vibrational node of the ultrasonic horn  10 , the fastening bolt  25 B is tightened back. As a result, a part of the ultrasonic horn  10  that corresponds to a vibrational node is fastened to the horn supporting member  20 B. 
     Next, the position of the horn supporting member  20 A in the axial direction relative to the ultrasonic horn  10  is adjusted. Since the ultrasonic horn  10  is fastened to the horn supporting member  20 B as described above, it is necessary to make this adjustment in regards to the horn supporting member  20 A by way of moving the horn supporting member  20 A. This is done by loosening the fastening bolt  25 A so that the elastic section  23 A of the horn supporting member  20 A deforms elastically toward the longitudinal slit  24 A, and further by loosening the attachment bolts  26 A so that the horn supporting member  20 A can be moved along the slots (not shown) formed in the bonding arm. After an adjustment is made so that the horn supporting member  20 A is positioned at a vibrational node of the ultrasonic horn  10 , the fastening bolt  25 A and the attachment bolt  26 A are tightened. As a result, the horn supporting member  20 A is fastened not only to the bonding arm  13  but also to a part of the ultrasonic horn  10  that corresponds to a vibrational node. 
     As seen from the above, the horn supporting members  20 A and  20 B are of separate members from the ultrasonic horn  10 . In addition, it is possible to adjust the relative positions of the horn supporting members  20 A and  20 B and ultrasonic horn  10 . Accordingly, the positions of the horn supporting members  20 A and  20 B can be aligned with the positions of the vibrational nodes of the ultrasonic horn  10 . As a result, the ultrasonic vibrational energy that leaks from the horn supporting members  20 A and  20 B can be reduced, and the ultrasonic horn  10  can be caused to oscillate at the optimal frequency, thus improving the bonding quality. Furthermore, since the horn supporting members  20 A and  20 B are separate components from the ultrasonic horn  10 , they can be made from a different material than the ultrasonic horn  10 . Thus, vibrational leakage can be further reduced by using a material such as an engineering plastic that tends not to lose ultrasonic vibrational energy. 
     FIGS.  2 ( a ) through  2 ( c ) illustrates another embodiment of the present invention. The embodiment of FIGS.  2 ( a ) through  2 ( c ) differs from the previous embodiment only in the structure for fastening the horn supporting members  20 A and  20 B to the ultrasonic horn  10 , and the remaining structure is the same. 
     In the horn supporting members  20 A and  20 B of the embodiment of FIGS.  2 ( a ) through  2 ( c ), the bottom surface portions that correspond to the horn holes  21 A and  21 B of the previous embodiment are covered with thin holding sections  30 A and  30 B that have an elasticity. Furthermore, lateral slits  31 A and  31 B are formed so as to extend into the horn holes  21 A and  21 B. Thus, by way of tightening fastening bolts  32 A and  32 B that pass through the holding sections  30 A and  30 B, the horn  10  is held in the horn supporting members  20 A and  20 B by the holding sections  30 A and  30 B. An effect substantially the same as that of the previous embodiment can be obtained using the structure of FIGS.  2 ( a ) through  2 ( c ). 
     As seen from the above, in the present invention which is for a wire bonding apparatus equipped with an ultrasonic horn which has a capillary at one end and an ultrasonic vibrator at another end and a bonding arm to which the ultrasonic horn is attached, the ultrasonic horn is attached to the bonding arm via two horn supporting members that are separate components from the ultrasonic horn, and the relative positions of the ultrasonic horn and the horn supporting members in the axial direction of the ultrasonic horn is adjustable. Accordingly, vibration of the ultrasonic horn during the vertical movement of the capillary can be reduced. Furthermore, the leakage of ultrasonic waves from the horn supporters can be reduced, and the positions of the horn supporters can be adjusted in accordance with the frequency of the ultrasonic vibration, thus increasing the energy utilization efficiency.