Abstract:
An apparatus for lining up micro-balls in accordance with the present invention includes: ball carrying pallets having a plurality of pits for holding the micro-balls, respectively, on its surface, a pallet holder for holding the ball carrying pallets, a lining-up container defining a sealed chamber in association with the pallet holder hermetically fitted thereto, a storing tank for storing liquid carrier in which micro-balls are dispersed, and applying/collecting device for communicating the storing tank with the lining-up container via a passage to supply the micro-balls together with the liquid carrier from the storing tank to the sealed chamber and return the surplus micro-balls together with the liquid carrier from the sealed chamber to the storing tank.

Description:
This application is based on Japanese Patent Application No. 2000-15939 filed Jan. 25, 2000, the content of which is incorporated hereinto by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and an apparatus for holding micro-balls in a plurality of pits, respectively, opened on the surface of a ball carrying pallet. Particularly, the present invention is suitably applied to solder balls for forming electrode bumps on a circuit board or the like. 
     2. Description of the Related Art 
     When solder balls are placed on a bump-forming portion in a semiconductor chip or a circuit board coated in advance with flux, and molten to form electrode bumps, it is necessary to accurately position the solder balls of a micro size must be to the bump-forming portion in the semiconductor chip or the circuit board. For this purpose, a template or a ball carrying pallet is used, having a plurality of pits arranged thereon in the same pattern as that of the electrode bumps to be formed in the objective. That is, there has been known a method in which the solder balls placed in the pits of the ball carrying pallet are attractively held at once by a suction head with vacuum, and after the suction head has been located directly above the objective such as a semiconductor chip or a circuit board so that the lower end of the respective solder ball attractively held in the suction head is brought into contact with the flux on the bump-forming portion, the solder balls are released from the suction to transfer onto the flux in the bump-forming portion. Such a method is disclosed, for example, in Japanese Patent Application Laid-open No. 5-129374 (1993). 
     In this case, it is necessary for the solder balls to be held neither too much nor too less in the pits of the ball carrying pallet. In general, it is not so easy to hold the solder balls on the ball carrying pallet nether too much nor too less since the solder ball is extremely small in size. 
     To solve this problem, Japanese Patent Application Laid-open No. 11-8272 (1999) proposes a technology wherein a ball carrying pallet formed of silicon wafer is immersed in ethanol, and solder balls are made to drop onto ball carrying pallet through the ethanol, then rolled thereon to get into the individual pits. This method is advantageous in that the ball-carrying pallet can be quickly and easily dried due to the high volatility of ethanol, whereby the delay of subsequent process is avoidable. 
     On the other hand, a dry method for lining up the solder balls in air is problematic in that the solder balls are stuck to each other or to the surface of the ball carrying pallet due to static electricity or moisture, resulting in the difficulty in the stable lining-up operation. 
     Contrarily, an aforementioned wet method disclosed in Japanese Patent Application Laid-open No. 11-8272 (1999) is advantageous because it is possible to stably line up the solder balls in the pits of the ball carrying pallet while avoiding the adverse effect due to static electricity or moisture generated in air. It requires, however, the frequent replenishment of ethanol because of the high volatility of the latter. Further, a large amount of ethanol is necessary for continuing a stable operation. Also, since the ball-carrying pallet is in general small in thickness, the handling thereof in the immersed state in ethanol is considerably difficult. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method for lining up micro-balls, capable of suppressing the consumption of highly volatile liquid carrier used in a wet method as well as of easily holding the micro-balls in pits of a ball carrying pallet, and an apparatus for carrying the method. 
     A first aspect of the present invention is a method for lining up micro-balls in a plurality of pits, respectively, formed on surfaces of ball carrying pallets, comprising the steps of: 
     defining a first sealed chamber by attaching the ball carrying pallets to a lining-up container so that the surfaces of the ball carrying pallets abut on the chamber, 
     supplying the micro-balls dispersedly mixed with liquid carrier stored in a second sealed chamber to the first sealed chamber via a flexible duct so that the micro-balls are held in the pits of the ball carrying pallets, respectively, 
     returning the surplus solder balls together with the liquid carrier from the first sealed chamber to the second sealed chamber via the duct, and 
     removing the ball carrying pallets from the lining-up container. 
     The method for lining up micro-balls according to the first aspect of the present invention may further comprise the step for vibrating the ball carrying pallets while supplying the liquid carrier in which are dispersed the micro-balls to the first sealed chamber. 
     The transfer of the micro-balls and the liquid carrier between the first and second chambers may be carried out by shifting the relative positions of both the sealed chambers in the vertical direction. 
     The liquid carrier may be electrically conductive. In this case, the liquid carrier may be alcohol. If the liquid carrier is electrically conductive, such as alcohol, the micro-balls can be more assuredly held in the individual pits, and further the ball-carrying pallet can be quickly dried while holding the micro-balls in the pits. 
     The micro-balls may be solder balls. 
     A second aspect of the present invention is an apparatus for lining up micro-balls, comprising 
     ball carrying pallets, each having a plurality of pits for holding the micro-balls, respectively, on its surface, 
     a pallet holder for holding the ball carrying pallets, 
     a lining-up container defining a sealed chamber in association with the pallet holder hermetically fitted thereto, 
     an storing tank for storing liquid carrier in which micro-balls are dispersed, and 
     applying/collecting means for communicating the storing tank with the lining-up container via a passage to supply the micro-balls together with the liquid carrier from the storing tank to the sealed chamber and return the surplus micro-balls together with the liquid carrier from the sealed chamber to the storing tank. 
     In the present invention, the pallet holder carrying the ball carrying pallets is hermetically fitted with the lining-up container to define the first sealed chamber. In this state, the micro-balls in the storing tank defining the second sealed chamber are fed by the pumping means to the first sealed chamber together with the liquid carrier so that the micro-balls get into the individual pits formed on the surface of the ball carrying pallets. Then, surplus micro-balls are returned from the first sealed chamber to the storing tank together with the liquid carrier by the pumping means, after which the pallet holder together with the ball carrying pallets carrying the solder balls in the respective pits is removed from the lining-up container defining the first sealed chamber now having no liquid carrier therein. 
     According to the present invention, it is possible to suppress the consumption of highly volatile liquid carrier and stably carry out the operation for lining up the solder balls in the pits of the ball carrying pallets because an amount of liquid carrier is maintained substantially constant. Also, since the ball carrying pallets are mounted to the pallet holder which in turn is detachably mounted to the lining-up container, the handling of the ball carrying pallets is extremely enhanced, whereby the lining-up operation can be automated to facilitate the working efficiency. 
     An apparatus for lining up micro-balls according to the second aspect of the present invention may further comprise vibration means for vibrating the pallet holder while the latter is fitted to the lining-up container. In this case, the micro-balls can be quickly and assuredly held in the respective pits. 
     The applying/collecting means may transport the liquid carrier by changing a position of the storing tank in the vertical direction relative to the lining up container fitted with the pallet holder. In this case, there is no need for using a pump having a high probability of blockage due to micro-balls. 
     The applying/collecting means may operate to incline, relative to the horizontal plane, the surfaces of the ball carrying pallets held by the pallet holder fitted with the lining-up container. In this case, an amount of liquid carrier remaining on the surface of the pallet can be limited as small as possible to minimize the consumption thereof. 
     The micro-balls may be solder balls. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view illustrating a schematic construction of one embodiment of an apparatus for lining up micro-balls according to the present invention; 
     FIG. 2 is a plan view of the embodiment shown in FIG. 1; 
     FIG. 3 is an enlarged sectional view of part of a lining-up container in the embodiment shown in FIG. 1; 
     FIG. 4 is a sectional view of a pallet holder used in the embodiment shown in FIG. 1; 
     FIG. 5 is a plan view of the pallet holder shown in FIG. 4; 
     FIG. 6 is a sectional view illustrating a schematic construction of part of a ball carrying pallet to be mounted to the pallet holder shown in FIG. 4; 
     FIG. 7 is a sectional view illustrating a schematic construction of part of a holder table in the embodiment shown in FIG. 1; 
     FIG. 8 is an enlarged sectional view of a storing tank in the embodiment shown in FIG. 1; 
     FIG. 9 is a schematic view of the operation for feeding micro-balls together with liquid carrier from the storing tank to the lining-up container; 
     FIG. 10 is a schematic view of the operation for returning the micro-balls together with the liquid carrier from the lining-up container to the storing tank; 
     FIG. 11 is a conceptual view of the operation of one step of exchanging the pallet holder; the remaining steps being illustrated in FIGS. 12 to  14 ; 
     FIG. 12 is a conceptual view of the operation of another step of exchanging the pallet holder; the remaining steps being illustrated in FIGS. 11,  13  and  14 ; 
     FIG. 13 is a conceptual view of the operation of a further step of exchanging the pallet holder; the remaining steps being illustrated in FIGS. 11,  12  and  14 ; and 
     FIG. 14 is a conceptual view of the operation of a still further step of exchanging the pallet holder; the remaining steps being illustrated in FIGS. 11 to  13 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in more detail below with reference to one embodiment of an apparatus for lining up micro-balls illustrated in FIGS. 1 to  14 , applied to solder balls for forming electrode bumps. The present invention, however, should not be limited to this embodiment but may be applied to other technologies to be included in the concept defined within a scope of claims appended to this specification. 
     FIG. 1 illustrates a schematic construction of an apparatus for lining up solder balls, and FIG. 2 illustrates a plan view thereof. The apparatus for lining up the solder balls according to the present invention includes a lining-up container  11 , a pallet holder  14  detachably fitted to an opening  12  provided in the bottom of the lining-up container  11  to define a sealed chamber  13  within the interior of the lining up container  11 , a manipulator  15  for holding the lining-up container  11  together with the pallet holder  14  and manipulating the former, a holder exchanging table  16  capable of detachably mounting the pallet holder  14 , and an storing tank  17  for storing ethanol C as a liquid carrier in which a number of small solder balls having a diameter of approximately 0.1 mm are dispersed (hereinafter merely referred to as a carrier). 
     FIG. 3 illustrates a schematic construction of the ball lining-up container  11  to which the pallet holder  14  is fitted. The ball lining-up container  11  having an opening  12  according to this embodiment has a connector  18  extending from the upper end thereof for mounting the container  11  in integral with the manipulator  15 . A pair of brackets  19  protrude from the outer periphery of the ball lining-up container  11  at positions apart 180 degree from each other, and a pair of lock arms  20  are pivoted at middle portions thereof to the brackets  19 , respectively, for preventing the pallet holder  14  fitted into the opening  12  from coming off therefrom. A tip end of each the lock arms  20  abuts to a conical surface  21  formed on the outer periphery of the lower end of the pallet holder  14  to generate a retaining force for urging the pallet holder  14  onto the ball lining-up container  11 . A tensile spring  22  is interposed between the upper portion of the respective lock arm  20  and the ball lining-up container  11  for biasing the tip end of the lock arm  20  away from the conical surface  21  of the pallet holder  14 . A communication hole  23  is provided in the ball lining-up container  11 , which opens into the lower end of the sealed chamber  13  defined by the ball lining-up container  11  and the pallet holder  14 . One end of a flexible duct  25  is connected to the communication hole  23  via a joint  24 . 
     The manipulator  15  in this embodiment is a multi-joint robot functioned as pumping means according to the present invention in association with the duct  25 . A chuck  26  is provided at a tip end of the manipulator  15 , for gripping the connector  18  of the ball lining up container  11 . A pair of locking cylinders  27 ,  27  are projected in the directions opposite to each other at a tip end of the manipulator  15  at positions apart 180 degrees from each other and abut to proximal ends of the lock arms  20 , respectively. By extending piston rods  28  of the locking cylinders  27  toward the lock arms  20 , respectively, the tip ends of the lock arms  20  abut to the conical surfaces  21  formed on the outer periphery of the lower end of the pallet holder  14  to urge the pallet holder  14  onto the ball lining-up container  11  and fixedly secured in integral therewith. 
     FIGS. 4 and 5 illustrate a sectional structure and a planar shape of the pallet holder  14  according to this embodiment, respectively, and FIG. 6 schematically illustrates a sectional structure of a ball carrying pallet  29  to be placed on the pallet holder  14 . On a smooth upper end surface  30  formed in the pallet holder  14 , a plurality of (nine in the illustrated embodiment) ball carrying pallets  29  are placed, each having conical pits  31  for accommodating solder balls W therein arranged at the lining-up state. The pit  31  formed in the ball carrying pallet  29  has a dimension so that the solder ball W is inserted therein by a somewhat deeper than a half thereof from the surface of the ball carrying pallet  29 . The pits  31  are accurately formed at a predetermined pattern if the ball-carrying pallet  29  is made of a silicon wafer and the pits  31  are formed by the anisotropic etching technology used for producing the semiconductor. 
     The upper surface  30  of the pallet holder  14  is adapted to be flush with a bottom surface  32  of the ball lining-up container  11  when correctly fitted to the ball lining-up container  11 . An engagement surface  33  of the pallet holder  14  opposite to the opening  12  of the ball lining-up container  12  is machined so that a gap between the same and the inner wall of the opening  12  of the ball lining-up container  12  is as small as possible to prevent the solder ball W from entering the gap. For the purpose of assuredly preventing the carrier C supplied into the sealed chamber  13  from leaking outside through the gap, a seal ring such as an O-ring may preferably be incorporated onto a stepped surface  34  of the ball lining-up container  11  in contact with the lower end surface. 
     A conical surface  36  is formed in a recess  35  provided in a central zone of the lower portion of the pallet holder  14 , for fixedly securing the pallet holder  14  to the holder exchanging table  16 . 
     FIG. 7 illustrates a partially broken view of the holder-exchanging table  16 . The holder-exchanging table according to this embodiment is movable in reciprocation left ward and rightward on a bed  37  as viewed in FIG. 7. A pair of holder receivers  38  is attached onto the holder-exchanging table  16  along the moving direction thereof. A pair of clamp arms  39  engageable with the recess  35  of the pallet holder  14  is pivoted to the respective holder receiver  38  on which the pallet holder  14  is placed, at positions apart 180 degrees from each other. The pair of clamp arms  39  are connected to each other by a tensile spring  40  so that tip ends of the clamp arms are pressed onto the engagement surface  36 . A clamp-releasing cylinder  42  is incorporated in the interior of the holder exchanging table  16 , for releasing the pallet holder  14  from being fixed to the holder receiver  38  by pushing the proximal ends of the pair of clamp arms  39  away from each other against the elastic force of the tensile spring  40  to separate the tip ends of the clamp arms  39  from the engagement surface  36 . 
     In FIG. 1, while the lining-up operation for the solder balls W is being carried out on the ball carrying pallets  29  placed on the pallet holder  14  mounted to one holder receiver  38  located left-hand in FIG. 1, the solder balls W already lined up on the ball carrying pallets  29  placed on the other holder receiver  38  located right-hand in FIG. 1 are sucked by using a suction head of a transferring device not shown and transferred to a bump-forming portion in an objective such as a semiconductor chip or a circuit board. These operations are alternately carried out on the left and right holder receivers  38 . To carry out the attachment/detachment operation of the pallet holder  14  relative to the holder receiver  38  and the transferring operation by the transferring device always at the predetermined positions, the holder exchanging table  16  moves to locate the holder receiver  38  holding the desired pallet holder  14  therein at the desired position. 
     FIG. 8 illustrates a main part of the storing tank  17  in the enlarged manner. The storing tank  17  is connected via a joint  43  by a flexible duct  25  to the ball lining-up device  11 , and held at the upper end of a stand  44  to be swingable about a pin  45 . An opening  46  is provided in a central region of a top wall of the storing tank  17 , for replenishing the solder balls W and the carrier C if necessary. The interior of the storing tank  17  is sealed by a lid member  47  detachably mounted to the opening  46 . The storing tank  17  is disposed at a lower level than the pallet holder  14  placed on the holder receiver  38  as seen in the vertical direction. 
     Accordingly, there is neither solder balls W nor carrier C immediately after the sealed chamber  13  has been formed by fitting the fresh pallet holder  14  placed on the holder receiver  38  to the ball lining-up container  11 . Thus, the pallet holder  14  is lifted up from the holder receiver  38  and laterally shifted to a position not interfering with the holder exchanging table  16 , after which the manipulator  15  operates to bring the sealed chamber  13  to a lower level than the storing tank  17  as shown in FIG. 9 as seen in the vertical direction. Thereby, the solder balls W contained in the storing tank  17  flow into the sealed chamber  13  together with the carrier C through the duct  25 . In this case, care must be taken to operate the manipulator  15  to incline the ball lining-up container  11  so that the joint  24  of the ball lining-up container  11  is directed upward while the joint  43  of the storing tank  17  is directed downward via the duct  25  to ensure all the solder balls W and the carrier C smoothly flowing. 
     After all the solder balls W and the carrier C has flowed into the sealed chamber  13 , the manipulator  15  is operated to rock and rotate the ball lining-up container  11  so that the solder balls W are uniformly dispersed throughout the carrier C, whereby the lining-up operation is carried out wherein the solder balls W fall into the pits  31  of the ball carrying pallet  29 . According to this embodiment, since the manipulator  15  is adopted, it is possible to easily realize the motion of the ball lining-up container  11  suitable for smoothly lining up the solder balls W in alignment with all the pits  31 . Also, since the solder balls W are mixed with the carrier C, the adverse effect of static electricity and/or moisture is avoidable to achieve the stable lining-up operation. 
     After the lining-up operation has been completed in such a manner, the surplus solder balls W are returned together with the carrier C to the storing tank  17 . For this purpose, the ball lining-up container  11  is raised higher in the vertical direction than the storing tank  17  as shown in FIG. 10, and inclined so that the joint  24  of the ball lining-up container  11  is directed downward, while inclining the storing tank  17  about the pin  45  to direct the joint  43  of the storing tank  17  upward by using the elastic deformation of the duct  25 , whereby the surplus solder balls W in the sealed chamber  13  are returned together with the carrier C to the storing tank  17 . In this regard, care must be taken so that no solder balls W held in the pits  31  come off therefrom. 
     Thereafter, as shown in FIG. 12, the pallet holder  14  is returned to the waiting vacant holder receiver  38  shown in FIG. 11, and the operation of the clamp-releasing cylinder  42  is interrupted to engage the tip ends of the clamp arms  39  with the engagement surface  36  of the pallet holder  14  due to the elastic force of the tensile spring  40 , whereby the pallet holder  14  is secured to the holder receiver  38 . Then, the operation of the pair of locking cylinders  27  is interrupted to retreat the tip ends of the lock arms  20  from the conical surface  21  of the pallet holder  14  due to the elastic force of the tensile springs  22 , whereby the ball lining-up container  11  is released from the pallet holder  14 . Next, the manipulator  15  is operated to move the ball lining-up container  11  upward and disengage and separate the pallet holder  14  from the ball lining-up container  11 . Thereafter, as illustrated in FIG. 13, the holder exchanging table  16  is operated to move the fresh pallet holder  14  held by the other holder receiver  38  adjacent to the former to a position directly beneath the ball lining-up container  11 . Then, as shown in FIG. 14, the manipulator  15  is operated to lower the ball lining-up container  11  again and engage the same with the pallet holder  14  held by the other holder receiver  38 , after which the locking cylinders  27  are operated to fixedly secure the pallet holder  14  to the ball lining-up container  11 . Further, the clamp-releasing cylinder  42  is operated to disengage the pallet holder  14  from the holder receiver  38 , after which the pallet holder  14  is lifted up from the holder receiver  38 . Next, the manipulator  15  is operated to laterally shift this pallet holder  14  to a position at which the pallet holder  14  does not interfere with the holder exchanging table  16  and the sealed chamber  13  is located lower than the storing tank  17  as shown in FIG.  9 . The above-mentioned steps are repeated to line up the solder balls W to the fresh pallet holder  14 . 
     In the meanwhile, the solder balls W are sucked from the ball carrying pallets  29  on the pallet holder  14  held by the one holder receiver  39  by using the transferring device not shown, and transferred to the objective such as a semiconductor chip or a circuit board. The pallet holder  14  attractively holding the solder balls W is in a waiting state for the next lining-up operation. In such a manner, the lining-up operation for the solder balls W is alternately carried out on the pallet holders  14  held by the two holder receivers  38 . In this regard, when the solder balls W has expired or the carrier C has evaporated in association with the above operation, the lid member  47  may be removed from the storing tank  17  to replenish the solder balls W or the carrier C if necessary. 
     According to this embodiment, since the highly volatile carrier C is stored in the sealed storing tank  17  and movable between the same and the sealed chamber  13  defined by the ball lining-up container  11  and the pallet holder  14  through the duct  25 , it is possible to restrict the reduction of the carrier C due to the vaporization as small as possible. 
     While the solder balls W and the carrier C are transferred between the ball lining-up container  11  and the storing tank  17  by shifting the relative positions thereof in the vertical direction by using the manipulator  15  in the above embodiment, the solder balls W and the carrier C may be forcibly transferred by using a pump or the like. Also, while the storing tank  17  is inclined about the pin  45  by using the elastic deformation of the flexible duct  25  in the above embodiment, the inclination may be switched by using a positive power. 
     The present invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the invention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention.