Abstract:
A conductive ball mounting apparatus for mounting conductive balls after an adhesive material was applied to individual electrodes formed in a predetermined array pattern on a mounting target adopts the following means is provided. Firstly, the conductive ball mounting apparatus comprises a stage for placing the mounting target, application means for applying the adhesive material to the electrodes of the mounting target placed on the stage, conductive ball mounting means for mounting the conductive balls at positions, to which the adhesive material has been applied, and transfer means for forming a transfer passage for passing the application means and the conductive ball mounting means. Secondly, the stage is disposed over the transfer means through moving means in a direction perpendicular to the transfer direction by the transfer means, and through turning means and vertically moving means.

Description:
[0001]     This application is based on Japanese Patent Application No. 2005-117805, which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an improvement in a conductive ball mounting apparatus and, more particularly, is developed mainly on drive means for a stage to mount a mounting target, in a conductive ball mounting apparatus for mounting conductive balls after an adhesive material was applied to individual electrodes formed in a predetermined array pattern on a mounting target.  
         [0004]     2. Description of the Related Art  
         [0005]     As the conductive ball mounting apparatus for mounting conductive balls after the adhesive material was applied to individual electrodes formed in a predetermined array pattern on the mounting target, there exists in the related art an apparatus for mounting the conductive balls, after sucked, arrayed and adsorbed by the ball mounting head having an array plate, on the individual electrodes on the mounting target, as disclosed in JP-A-2001-358451. However, as the mounting target product such as a wafer becomes larger, the number of solder balls to be mounted at one time exceeds one million. This makes it difficult at present to reduce the defects in the array of solder balls and the defects at the mounting time.  
         [0006]     As disclosed in JP-A-2002-538970, therefore, there has been provided an apparatus, in which an electronic substrate or a mounting target printed with flux is provided with an array mask and in which solder balls are directly dropped onto electrodes of the electronic substrate. In this apparatus, however, the flux printing device and the solder balls mounting device are individually required to have Y-axis moving means, Z-axis moving means and θ-axis moving means for the array mask.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention has an object to provide a conductive ball mounting apparatus for mounting conductive balls after an adhesive material was applied to individual electrodes formed in a predetermined array pattern on a mounting target. In this apparatus, a stage made movable on a transfer passage in an X-axis direction (or a transfer direction) for mounting a mounting target is equipped with Y-axis (a direction perpendicular to the transfer direction) moving means, Z-axis (a vertical direction) moving means and θ-axis (a turning direction) moving means. The Y-axis moving means, the Z-axis moving means and θ-axis moving means of an array mask needed in the related art individually for the flux printing apparatus and the conductive ball mounting apparatus are eliminated so that the number of component parts of the conductive ball mounting apparatus can be reduced to prevent the apparatus from being large-sized and to mount many conductive balls precisely.  
         [0008]     In order to solve the aforementioned problem, a first aspect of the invention adopts the following means in the conductive ball mounting apparatus for mounting conductive balls after an adhesive material was applied to individual electrodes formed in a predetermined array pattern on a mounting target:  
         [0009]     Firstly, the conductive ball mounting apparatus comprises a stage for placing the mounting target, application means for applying the adhesive material to the electrodes of the mounting target placed on the stage, conductive ball mounting means for mounting the conductive balls at positions, to which the adhesive material has been applied, and transfer means for forming a transfer passage for passing the application means and the conductive ball mounting means.  
         [0010]     Secondly, the stage is disposed over the transfer means through moving means in a direction perpendicular to the transfer direction by the transfer means, and through turning means and vertically moving means.  
         [0011]     According to a second aspect of the invention, the conductive ball mounting means mounts the conductive balls by arranging an array mask having through holes formed along with the predetermined array pattern of the electrode for receiving the conductive balls, over the mounting target, and by moving a ball reservoir housing a number of conductive balls, along the upper face of the array mask thereby to drop the conductive balls into the individual through holes.  
         [0012]     According to a third aspect of the invention, the conductive ball mounting means fixes and holds the array mask.  
         [0013]     According to a fourth aspect of the invention, the conductive ball mounting apparatus further comprises positioning means for positioning the array mask and the mounting target.  
         [0014]     In the first aspect of the invention, the stage for mounting the mounting target is disposed over the transfer means through moving means in a direction perpendicular to the transfer direction by the transfer means, and through turning means and vertically moving means. Therefore, the application means for applying the adhesive material and the ball mounting means do not need any of the Y-axis moving means, the Z-axis moving means and the θ-axis moving means additionally so that the conductive ball mounting apparatus can be prevented from being large-sized.  
         [0015]     In the second aspect of the invention, the conductive ball mounting means mounts the conductive balls by arranging an array mask having through holes formed in the predetermined array pattern of the electrode for receiving the conductive balls, and by moving a ball reservoir housing a number of conductive balls, along the upper face of the array mask thereby to drop the conductive balls into the individual through holes. It is, therefore, possible to mount such many conductive balls precisely as have accompanied the enlarged size of the mounting target product such as the wafer.  
         [0016]     In the third aspect of the invention, the conductive ball mounting means fixes and holds the array mask. In the fourth aspect of the invention, the conductive ball mounting apparatus further comprises positioning means for positioning the array mask and the mounting target. According to either of these aspects of the inventions, it is possible to improve the precision in the conductive ball mounting action. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a schematic top plan view showing the entirety of a solder ball mounting apparatus according to the embodiment;  
         [0018]      FIG. 2  is a schematic top plan view of the case, in which a wafer feeding unit and a wafer housing unit are disposed in the same direction;  
         [0019]      FIG. 3  is a partially sectional, explanatory side elevation showing a ball mounting unit;  
         [0020]      FIG. 4  is a top plan view of the ball mounting unit; and  
         [0021]      FIG. 5  is a front elevation showing the movement of a wafer transfer stage. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     An embodiment of the invention is described in the following with reference to the accompanying drawings. In the invention, a semiconductor wafer (as will be simplified into the wafer), an electronic circuit substrate or a ceramic substrate is exemplified as a target for mounting conductive balls, but a wafer  14  is used in the embodiment. Moreover, flux, solder paste or a conductive adhesive is used as an adhesive material.  
         [0023]      FIG. 1  is a schematic top plan view showing the entirety of a solder ball mounting apparatus  1 . This solder ball mounting apparatus  1  includes a carry-in wafer transfer unit  2 , a flux printing unit  3 , a ball mounting unit  4 , and a carry-out wafer transfer unit  5 . A wafer feeding unit  6 , a primary alignment unit  7  and a carry-in robot  8  exist at the pre-step of the solder ball mounting apparatus  1 , and an inversion unit  9 , a wafer housing unit  10  and a carry-out robot  11  exist at the post-step of the solder ball mounting apparatus  1 .  
         [0024]     The primary alignment unit  7  for the pre-step turns the wafer  14  in a horizontal plane to detect the position of an orientation flat or notch of the wafer  14  thereby to correct the position of the wafer  14  approximately and to direct the wafer  14  to be mounted on the wafer transfer unit  2 , in a predetermined direction. On the other hand, the inversion unit  9  for the post-step turns the wafer  14  in the horizontal direction so that the wafer  14  is turned to bring its orientation flat or notch to a predetermined position and is housed in a magazine  32 .  
         [0025]     The solder ball mounting apparatus  1  is equipped with a wafer transfer stage  12  and a transfer passage  13  for transferring the wafer  14  from the wafer transfer unit to the flux printing unit  3 , the ball mounting unit  4  and the wafer transfer unit  5 . The transfer passage  13  is equipped with an X-axis (longitudinal, as shown) feeding device of the transfer stage  12 .  
         [0026]     The flux printing unit  3  is equipped with a flux feeding device  16 , a printing mask  15  for printing flux or the adhesive material on the wafer  14 , and vertical observation cameras  31  for observing the alignment marks of the wafer  14  and the printing mask  15  thereby to register the wafer  14  and the printing mask  15 . The printing mask  15  has through holes formed along with the pattern of the electrodes on the wafer  14 . Two (not-shown) alignment marks are formed at two portions on the lower face of the printing mask  15  in a through hole forming area  36 . The printing mask  15  is applied to a molding box  17  and is held by a fixing unit such as a frame. The flux feeding device  16  moves the (not-shown) squeezee along the upper face of the printing mask  15  so that the flux is printed in the through holes of the printing mask  15  and fed onto the electrodes of the wafer  14 . Here, numeral  33  in the drawing designates a cleaning unit for cleaning off the flux adhered to the printing mask  15 .  
         [0027]     The ball mounting unit  4  is equipped with a solder ball feeding device  20 , a ball array mask  19  having through holes  18  formed along with the pattern of the electrodes on the wafer  14 , and vertical observation cameras  34  for observing the alignment marks of the wafer  14  and the ball array mask  19  thereby to register them.  
         [0028]     The ball array mask  19  has a thickness substantially equal to the diameter of solder balls  21  to be fed, and the through holes  18  have a diameter slightly larger than that of the solder balls. Like the printing mask  15 , the ball array mask  19  has the (not-shown) alignment marks formed at two portions on the lower face of the through hole forming area  36 . The ball array mask  19  is adhered to a molding box  37  and is held by a fixing unit such as the frame.  
         [0029]     The solder ball feeding device  20  is equipped with a ball hopper  22  for reserving a number of solder balls  21 , a ball cup  23  for dropping the solder balls  21  into the ball array mask  19 , a mask height detecting sensor  27 , and a carriage unit  24  not only for moving the ball cups  23  along an X-axis guide  25  and a Y-axis guide  26  but also for displacing the same in a Z-axis direction. Here, the ball hopper  22  is exchanged according to the size and material of the solder balls  21 . Inside of and in the lower portion of the inner wall face of the ball cup  23 , there is formed a recess  35  for causing the solder balls  21  housed therein to circulate, as indicated by an arrow in the ball cup  23  in  FIG. 3 .  
         [0030]     The mask height detecting sensor  27  may be of either the contact type or the non-contact type. Specifically, a laser sensor or an electrostatic capacity sensor is used as the mask height detecting sensor  27 . The mask height detection is made by bringing the molding box  37  of the ball array mask  19 , when exchanged at an initial setting time or at a mold exchanging time, into abutment against a stopper or the like, and by positioning and fixing the molding box  37  by means of a clamp. Specifically, after the ball array mask  19  was fixed, the ball cup  23  empty of the solder balls  21  is moved sequentially on a plurality of height detection points preset outside of the through hole forming area  36 , and the height of the upper face of the ball array mask  19  is measured.  
         [0031]     On the other hand, the height of the upper face of the ball array mask  19  in the through hole forming area  36  is determined by calculations. Moreover, the heights at the individual positions are calculated by considering the weight which is applied when the solder balls  21  are housed in the ball cup  23 . At the ball mounting time, the ball cup  23  is so moved on the basis of the determined height, while being controlled by the moving unit  24 , that the clearance between the upper face of the ball array mask  19  and the lower face of the ball cup  23  may not exceed a predetermined distance.  
         [0032]     The wafer transfer stage  12  is a stage for placing the wafer  14  thereon and is so mounted on the transfer passage  13  that it can move in the X-axis direction. The wafer transfer stage  12  is equipped with a Y-axis drive mechanism  28  acting as moving means in the direction (i.e. the Y-axis direction) perpendicular to the transfer direction of the wafer  14 , a θ-axis drive mechanism  29  acting as turning means, and a Z-axis drive mechanism  30  acting as vertically moving means.  
         [0033]     The actions of the solder ball mounting apparatus  1  of the embodiment are described. At first, the wafer  14  to have the solder balls  21  mounted thereon is housed in the magazine  32  of the wafer feeding unit  6 . Then, one wafer  14  is extracted from the magazine  32  of the wafer feeding unit  6  and carried in the primary alignment unit  7 . In this primary alignment unit  7 , the wafer  14  is turned to detect the position of the orientation flat or notch thereby to correct the position of the wafer  14  approximately and to set the orientation flat or notch at a predetermined position. Subsequently, the wafer  14  is carried by the carry-in robot  8  from the primary alignment unit  7  to the wafer transfer stage  12  on standby at the wafer transfer unit  2 .  
         [0034]     The wafer transfer stage  12  having the wafer  14  mounted thereon moves along the transfer passage  13  to the flux printing unit  3  and stops at a predetermined position. Here, the alignment marks of the wafer  14  and the printing mask  15  are individually observed by the vertical observation cameras  31  so that the wafer transfer stage  12  is positioned in the X-axis direction by the X-axis drive mechanism of the transfer passage  13 , in the Y-axis direction by the Y-axis drive mechanism  28  and in the θ-axis direction by the θ-axis drive mechanism  29 . After positioned, the wafer transfer stage  12  is raised by the Z-axis drive mechanism  30  so that it is stopped at a predetermined height position with respect to the printing mask  15  having been prepared with the flux. In this state, the printing mask  15  is fed with the flux at its one end portion in the Y-axis direction, and the squeezee is moved toward the other end portion to print the flux on the electrodes of the wafer  14  from the through holes of the printing mask  15 .  
         [0035]     After the flux-printing, the wafer transfer stage  12  is moved downward by the Z-axis drive mechanism  30  and is moved to the ball mounting unit  4  by the transfer passage  13  so that it is stopped at a predetermined position. Here, the alignment marks of the wafer  14  and the ball array mask  19  are also individually observed by the vertical observation cameras  34 , and the wafer transfer stage  12  is positioned in the X-axis direction by the X-axis drive mechanism of the transfer passage  13 , and in the Y-axis direction and in the θ-axis direction by the Y-axis drive mechanism  28  and the θ-axis drive mechanism  29 , respectively. After this, the wafer transfer stage  12  is moved upward by the Z-axis drive mechanism  30  so that it is stopped while leaving the predetermined clearance from the ball array mask  19 .  
         [0036]     As shown in  FIG. 3 , the ball cup  23  moves over the ball array mask  19  to drop the solder balls  21  into the through holes  18  of the ball array mask  19  so that the solder balls  21  are mounted on the wafer  14 . After this ball dropping operation, the ball array mask  19  is finely moved horizontally (in the X-axis direction and in the Y-axis direction) with respect to the wafer transfer stage  12  thereby to correct the positions of the solder balls  21  in the through holes  18 .  
         [0037]     After the solder balls mounting operation, the wafer transfer stage  12  is moved downward by the Z-axis drive mechanism  30  so that it is moved to stop at the carry-out wafer transfer unit. In the wafer housing unit  10 , the wafer  14  is transferred from the wafer transfer stage  12  to the inversion unit  9  by the carry-out robot  11 , and the wafer  14  is turned to bring the orientation flat or notch to the predetermined position. The wafer  14  is further transferred by the carry-out robot  11  from the inversion unit  9  to the magazine  32  of the wafer housing unit  10 . When the carry-out robot  11  takes out the wafer  14  from the wafer transfer stage  12 , the wafer transfer stage  12  returns to the original position or the wafer transfer unit  2 , thus completing one step. The present apparatus repeats the actions thus far described.  
         [0038]     In the embodiment shown in  FIG. 1 , the wafer feeding unit  6  is disposed in front of the solder ball mounting apparatus  1 , and the wafer housing unit  10  is disposed at the back. Since the wafer transfer stage  12  returns to the original position, as described above, the wafer feeding unit  6  and the wafer housing unit  10  may also be disposed on one side, as shown in  FIG. 2 .  
         [0039]     With the structure thus made, the carry-out robot  11  can be replaced by the carry-in robot  8 , and the wafer  14  is held and housed in the same direction as that of the wafer  14  being carried in, so that the inversion unit  9  can be omitted. Moreover, one of the wafer transfer units  2  and  5  can also be omitted so that the number of structural components can be reduced. Moreover, this embodiment employs the vertical observation cameras  31  and  34  for photographing the alignment marks of the wafer  14  and the printing mask  15  or the ball array mask  19  simultaneously at the stop time of the wafer transfer stage  12 , as the means for positioning the printing mask  15  and the ball array mask  19 , and the wafer  14 . However, the invention should not be limited thereto but can be conceived to have various structures.