Patent Abstract:
A device for arranging conductive particles in a preselected pattern for the connection of electric circuit boards or electric parts is disclosed. Particularly, a device capable of surely and efficiently transferring, e.g., solder bumps to the electrode pads of a semiconductor chip or the leads of a TAB (Tape Automated Bonding) tape and a conductive particle transferring method using the same are disclosed.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a Division of application Ser. No. 08/929,057, filed on Sep. 15, 1997, and now U.S. Pat. No. 6,063,701. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device for arranging conductive particles in a preselected pattern for the connection of electric circuit boards or electric parts. More particularly, the present invention is concerned with a device for surely and efficiently transferring solder bumps to the electrode pads of a semiconductor chip or the leads of a TAB (Tape Automated Bonding) tape, and a conductive particle transferring method using the same. 
     It is a common practice with, e.g., LSI (Large Scale Integration) circuits and LCDs (Liquid Crystal Displays) to connect electric circuit boards by using conductive particles. 
     After electric conduction has been set up between the circuit boards by the conductive particles, the circuit boards are fixed by an adhesive. Specifically, after the conductive particles have been arranged on either one of the circuit boards, an adhesive is applied and then set after the alignment of electrodes. To arrange the particles on the circuit board, they may be simply sprayed, as taught in, e.g., Japanese Patent Laid-Open Publication Nos. 2-23623 and 3-289070. 
     With the spraying scheme, however it is difficult to control the positions and the number of the particles on the electrodes. Particularly, when the electrodes are arranged at a fine pitch, the particles are apt to short the electrodes or to render the connection resistance irregular due to the irregular number thereof on the electrodes. Although the particles may be arranged on the electrodes while having their positions controlled, such an approach needs a sophisticated control system. 
     For the electrical connection of the electrode pads of a semiconductor chip and outside leads, a wire bonding system, a TAB system and a flip-chip bonding system are typical systems available at the present stage of development. The TAB system and flip-chip bonding system each uses conductive particles in the form of solder bumps (simply bumps hereinafter) for electrical connection. Specifically, in the TAB system, bumps intervene between the electrode pads of a semiconductor chip and the film-like leads of a TAB tape. In the flip-chip bonding system, bumps intervene between the electrode pads of a semiconductor chip and the leads of a circuit board. 
     Today, the following methods are extensively used to form bumps. In one method, the exposed portions of electrode pads provided on a semiconductor chip are covered with barrier metal. After a solder film pattern has been formed on the barrier metal, reflow and annealing are effected in order to cause the solder film to shrink on the barrier metal due to its own surface tension. In another method, bumps are formed on the electrode pads one by one by a wire bonder. Recently, a transfer bump method has been proposed which is advantageous over the above direct methods from the step and cost standpoint. The transfer bump method forms bumps on an exclusive transfer substrate by an electrolytic plating scheme. The bumps on the transfer substrate are aligned with the leads of a TAB tape in the TAB system or with the electrode pads of a semiconductor chip in the flip-chip bonding system. Then, the bumps are bonded by heat and transferred to the leads or the electrode pads. It is not too much to say that the the transfer bump method has broadened the applicable range of the TAB system. 
     However, the problem with the bumps formed by the electrolytic plating scheme is that they have flat surfaces and cannot be evenly transferred unless they have exactly the same height. In light of this, Japanese Patent Publication No. 7-27929 discloses a device capable of arranging spherical bumps on a transfer substrate. However, while the electrolytic plating scheme is capable of defining positions for forming the bumps beforehand, the spherical bumps are produced at random. Therefore, the key to the spherical bump scheme is how efficiently the bumps can be arranged in preselected positions. For the efficient arrangement of the bumps, the above document teaches that the diameter of the spherical bumps is strictly controlled. However, because the diameter of the bumps decreases with a decrease in the pitch of the electrode pads or that of the leads, it is extremely difficult to provide the bumps with the same diameter. As a result, the accuracy required of the flatness of the leads of a TAB tape, the flatness of a bonding tool and the parallelism of a transfer substrate and a TAB tape increases. The adjustment of such factors will become more difficult in the future in parallel with the progress of dense mounting. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a simple, low cost device capable of arranging conductive particles adequately. 
     It is another object of the present invention to provide a method capable of transferring conductive particles to a semiconductor chip, TAB tape or intermediate transfer member more surely and easily without increasing accuracy required of a device for practicing it. 
     In accordance with the present invention, a device for arranging conductive particles for connecting electric circuit boards includes a mask formed with openings in a preselected pattern for arranging the conductive particles. A squeegee is spaced from the mask by a preselected distance and movable over the mask in a preselected direction for filling the conductive particles in the openings of the mask. A stage is positioned below the mask for holding the conductive particles filled in the openings of the mask. A vacuum suction mechanism is positioned below the stage for sucking, via the stage, the conductive particles being moved on the mask by the squeegee into the openings of the mask. 
     Further, in accordance with the present invention, a device for arranging conductive particles includes a feeding section for feeding the conductive particles. A stage is implemented as a porous flat plate having opposite major surface. One of the opposite major surfaces expected t o arrange the conductive particles is implemented as fine irregular surface for restricting the movement of the conductive particles. A mask is formed with openings in a preselected pattern for defining an arrangement of the conductive particles on the stage. A sucking mechanism sucks the conductive particles via the other major surface of the stage to thereby retain the conductive particles on the one major surface of the stage. A drive source is drivably connected to at least one of the stage and mask for selectively moving the one major surface of the stage and a major surface of the mask toward or away from each other. 
     Moreover, in accordance with the present invention, a method of transferring conductive particles includes the step of positioning a stage comprising a porous flat plate having one of opposite major surfaces thereof expected to arrange the conductive particles implemented as a fine irregular surface for restricting the movement of the conductive particles and a mask formed with openings in a preselected pattern for defining an arrangement of the conductive particles on the stage close to each other and parallel or substantially parallel to each other. In this condition, the conductive particles are from above the mask to thereby cause the openings of the mask to trap the conductive particles. Then, excess conductive particles other than the conductive particles trapped in the openings are removed from the mask. Subsequently, the mask and stage are separated from each other. Finally, the conductive particles arranged on the stage are transferred to another surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings in which: 
     FIG. 1 is a sectional side elevation showing a first embodiment of the conductive particle arranging device in accordance with the present invention; 
     FIGS. 2-7 are sectional side elevations each showing a particular modification of a squeegee included in the first embodiment; 
     FIG. 8 is a sectional side elevation showing a modification of a mask also included in the first embodiment; 
     FIG. 9 is a sectional side elevation showing a modification of a pedestal and stage further included in the first embodiment; 
     FIG. 10 is a section showing a conventional conductive particle arranging device; 
     FIG. 11 is a section showing Example 1 of a second embodiment of the present invention; 
     FIGS. 12-17 are sections each showing Example 2 of the second embodiment in a particular condition; 
     FIG. 18 is a section showing Example 3 of the second embodiment; 
     FIGS. 19 and 20 are sections each showing Example 4 of the second embodiment in a particular condition; 
     FIG. 21 is a section showing Example 5 of the second embodiment; 
     FIGS. 22 and 23 are sections each sowing Example 5 in a particular condition; 
     FIG. 24 is a section showing Example 6 of the second embodiment; 
     FIGS. 25-28 are sections each showing Example 6 in a particular condition; and 
     FIG. 29 is a section showing Example 7 of the second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will b e described hereinafter. 
     1st Embodiment 
     This embodiment relates to a conductive particle arranging device applicable to the bump forming step stated earlier. As shown in FIG. 1, the device, generally  10 , includes a base  12  on which a guide rail  14  is mounted. A slider  16  is slidably mounted on the guide rail  14  and moved in the right-and-left direction, as seen in FIG. 1, by an air cylinder, not shown. A stage  18  is mounted on the slider  14  and shiftable up and down over a distance of about 10 mm by being driven by, e.g., an air cylinder. 
     A pedestal  20  is mounted on the stage  18  and implemented as a box-like or hollow cylindrical top-open member. The pedestal  20  has a bore  20   a  fluidly communicated to a vacuum pump, not shown, via a passageway  20   b . A stage  22  is mounted on the pedestal  20 , closing the open top of the pedestal  20 . The stage  22  is implemented by a sintered ceramic body. The pedestal  20  carrying the stage  22  thereon has its bore  20   a  evacuated by the vacuum pump via the passageway  20   b.    
     A mask  24  is held on and in contact with the top of the stage  22 . The mask  24  is implemented as a metal mask by way of example and formed with openings, not shown, in a preselected pattern for arranging conductive particles. If conductive particles to be arranged by the device  10  have a diameter of, e.g., 40 μm, then the above openings each has a diameter of 50 μm and a depth of 40 μm. A frame  22   a  retains the peripheral portion of the mask  22  while a guide frame  26  guides and holds the peripheral portion of the mask  22 . The mask  24  with the openings is mounted on the stage  22  which is, in turn, mounted on the pedestal  20 , as stated above. Therefore, when the bore  20   a  of the pedestal  20  is evacuated, vacuum is developed in the openings of the mask  24  via the stage  22 . 
     A frame  30  is supported by posts  28  above the mask  24 . Sliders  32  and  34  are mounted on the frame  30  and driven horizontally by an air cylinder or a stepping motor, not shown, in directions perpendicular to each other. A pair of squeegees  38  and  40  are affixed to the slider  34  facing the mask  24  via a jig  36 . The jig  36  is made up of a Z axis stage implementing adjustment in the vertical direction (Z direction), as seen in FIG. 1, and a goniometer implementing the adjustment of the angles of the squeegees  38  and  40 , although not shown specifically. 
     The squeegees  38  and  40  are positioned above and at a preselected distance from the mask  24 . When the sliders  32  and  34  are moved in the horizontal direction, the slider  34  moves the squeegees  38  and  40  in the horizontal direction. Conductive particles are fed to the mask  24  via the gap between the squeegees  38  and  40 . 
     The device  10  having the above construction will be operated as follows. Initially, the squeegees  38  and  40  are located at their initial position or home position defined at the right-hand side or the left-hand side of the openings of the mask  24 . Conductive particles are present between the squeegees  38  and  40 . The stage  18  is held in its elevated position, maintaining the stage  22  in contact with the mask  24 . The bore  20   a  of the pedestal  20  is evacuated by the vacuum pump. 
     In the above condition, the squeegees  38  and  40  are moved over the openings of the mask  24  at the same time by the sliders  32  and  34 . As a result, the squeegees  38  and  40  move away from the home position while sequentially filling the openings of the mask  24  with the conductive particles. Because the bore  20   a  of the pedestal  20  is evacuated, air is sucked out of the openings of the mask  24  via the stage  22 . 
     Consequently, the particles fed to the mask  24  are surely introduced into and held in the openings of the mask  24 . 
     When the movement of the squeegees  38  and  40  ends, the evacuation of the bore  20   a  is interrupted while the stage  18  is lowered. As a result, the mask  24  and stage  22  are separated from each other. When the slider  16  is moved along the guide rail  14 , the conductive particles have been adequately arranged on the stage  22  in the desired pattern. 
     As shown in FIG. 2, the illustrative embodiment allows the distance between the mask  24  and the squeegees  38  and  40  to be smaller than the diameter of a conductive particle  42 . Specifically, in the illustrative embodiment, the mask  24  and squeegees  38  and  40  (only the squeegee  38  is shown) are spaced from the mask  24  by a distance a smaller than the diameter of the particle  42 . The distance a should preferably be one-half to one-fourth of the diameter of the particle  42 . In such a configuration, the particle  42  is prevented from escaping via the gap between the mask  24  and the squeegees  38  and  40 . This allows the particle  42  to be surely filled in the opening of the mask  24  and frees the mask  24  from wear or breakage. 
     As shown in FIG. 3, the thickness of the squeegees  38  and  40  (only the squeegee  38  is shown) may be reduced below the diameter of the particle  42 . Specifically, in the illustrative embodiment, each of the squeegees  38  and  40  has at least its lower edge provided with a thickness smaller than the diameter of the particle  42 . With this configuration, the squeegees  38  and  40  can move the particle  42  smoothly on and along the mask  24 . 
     More specifically, assume a squeegee  38 a shown in FIG.  4  and having a thickness greater than the diameter of the particle  42 . Then, it is likely that the particle  42  gets between the squeegee  38   a  and the mask  24  and cannot smoothly move on the mask  24 . By contrast, the squeegee  38  shown in FIG. 3 allows the particle  42  to easily slip away upward and smoothly move on the mask  24 . Therefore, even when the particle  42  is implemented as a resin particle plated with metal, it can smoothly move on the mask  24  and adequately enters the opening of the mask  24  without being damaged. 
     As shown in FIG. 5, the angle between each of the squeegees  38  and  40  (only the squeegee  38  is shown) and the mask  24  may be selected to be less than  30  degrees inclusive. The flat squeegee  38  is inclined relative to the mask  24  by an angle β of less than 30 degrees inclusive. This also allows the conductive particle  42  to easily slip away upward, i.e., prevents it from getting between the squeegee  38  and the mask  24  and being damaged thereby. Therefore, even when the particle  42  is implemented as a resin particle plated with metal, it can smoothly move on the mask  24  and adequately enter the opening of the mask  24  without being damaged. 
     As shown in FIGS. 6 and 7, projections  44  and  46  may be provided on the lower edge of each of the squeegees  38  and  40  (only the squeegee  38  is shown) facing the mask  24 , so that an adequate distance can be maintained between the squeegees and the mask  24 . In the illustrative embodiment, the projections  44  and  46  are positioned at opposite ends of the lower edge of each of the squeegees  38  and  40 . The projections  44  and  46  each has a height which is less than one-half of the diameter of the conductive particle  42  inclusive. Specifically, when the diameter of the particle  42  is 40 μm, resin beads whose diameter is 10 μm to 20 μm may be affixed to the above positions of the lower edge of the squeegee by, e.g., an adhesive. 
     When the squeegees  38  and  40  are moved above the mask  24  with their projections  48  and  40  contacting the mask  24 , a preselected distance is surely maintained between the squeegees  38  and  40  and the mask  24 . This is an economical, yet adequate, implementation for preventing the particle  42  from escaping and causing the mask  24  to wear. 
     As shown in FIG. 8, the mask  24  may be provided with a thickness smaller than the diameter of the particle  42 , but greater than one-half of the same. Specifically, the mask  24  is formed with a plurality of openings  24   a . In the illustrative embodiment, the thickness of the mask  24  is selected to be smaller than the diameter of the particle  42 , but greater than one-half of the same. Therefore, when such particles  42  are introduced into the openings  24   a  of the mask  24  laid on the stage  22 , the particles  42  rest on the top of the stage  22 . In this condition, less than one-half of each particle  42  protrudes from the top of the mask  24 . The particles  42  received in the openings  24   a  of the mask  24  are delivered to the next step. In the next step, a transfer head, not shown, is lowered onto the mask  24  with the result that the particles  42  each protruding from the top of the mask  24  are transferred to the head. 
     With the configuration shown in FIG. 8, it is possible to deliver the mask  24  and stage  22  to the next step together, i.e., without lowering the stage  18  in order to separate the mask  24  and stage  22 . This reduces the number of steps of the device  10  and thereby promotes smooth and adequate arrangement of conductive particles. 
     FIG. 9 shows an alternative configuration of the pedestal  20 . As shown, the box-like or hollow cylindrical pedestal, labeled  48 , has a center bore  48   a  and a peripheral bore  48   b  surrounding the center bore  38   a , i.e., a double bore structure. The pedestal  48  is formed with a passageway  48   c  communicated to the peripheral bore  48   b  and a passageway, not shown, communicated to the center bore. The passageway  48   c  and the other passageway, not shown, each is fuidly communicated to a respective vacuum pump, not shown, and evacuated thereby. 
     The stage  22  implemented as a sintered ceramic body is mounted on the top of the pedestal  48 , closing the center bore  48   b  and peripheral bore  48   b . The mask  24  with the openings  24   a  is mounted on the stage  22 , although not shown specifically. The conductive particles  42  are received in the openings  24   a  of the mask  24  positioned above the center bore  48   a.    
     The center bore  48   a  and peripheral bore  48   b  of the pedestal  48  each is evacuated by the respective vacuum pump, as stated above. When the mask  24  having the particles  42  in its openings and the stage  22  are separated from each other, the pump communicated to the center bore  48   a  above which the particles  42  are arranged is turned on while the other pump communicated to the peripheral bore  48   b  is turned off. As a result, the particles  42  are prevented from being displaced. This can be done with miniature vacuum pumps at a low cost. 
     While the mask  24  has been shown and described a s comprising a metal mask, it may alternatively be implemented by, e.g., a polyimide film or similar resin film. With a polyimide film, it is possible to form the openings  24   a  and therefore to arrange the particles  42  more accurately than with a metal mask when use is made of an excimer laser. It is to be noted that the openings  24   a  formed by an excimer laser are tapered. From the accuracy standpoint, therefore, the particles  42  should preferably be directly transferred to a transfer head without the mask  24  being separated. 
     As stated above, the first embodiment achieves the following advantages. 
     (1) The device is capable of arranging conductive particles adequately with a simple, low cost structure. 
     (2) The particles are prevented from escaping via a gap between squeegees and a mask and causing the mask to wear or break. 
     (3) The particles are prevented from getting between the squeegees and the mask. Therefore, even when the particles are implemented as resin particles plated with metal, they are free from breakage. 
     (4) The squeegees are constantly spaced from the mask by a preselected distance during movement. 
     (5) The particles received in the openings of the mask can be directly transferred to a transfer head, so that the number of steps is reduced. 
     (6) When the stage is separated from the mask, only the portion around the particles is evacuated in order to prevent the particles from being displaced. 
     (7) The openings of the mask can be formed more accurately than the openings of a metal mask. 
     2nd Embodiment 
     To better understand this embodiment, reference will be made to FIG. 10 showing the conventional arrangement taught in Japanese Patent Publication No. 7-27929 mentioned earlier. The arrangement to be described addresses irregular transfer particular to the transfer bump method which forms conductive particles, i.e., bumps on an exclusive transfer substrate by electrolytic plating, and then transfers the bumps to the electrode pads of a semiconductor chip or the leads of a TAB tape. As shown in FIG. 10, a transfer substrate  50  is formed with through holes  53 . The holes  53  each has a smaller diameter than a bump bp at its bottom, but has a greater diameter than the bump bp at its top. With this configuration, the substrate  50  itself plays the role of a jig for positioning the bumps bp. The bottom side of the substrate  50  is depressurized in order to retain the bumps bp in the holes  53  by suction. Specifically, a bore  57  formed between the substrate  50  and a holder  56  supporting it is evacuated via an tubing  58 . 
     More specifically, the substrate  50  is implemented as a laminate of two flat sheets  51  and  52 . The sheets  51  and  52  are respectively formed with openings  54  having a diameter d 1  smaller than the diameter of the bumps bp, and openings  55  having a diameter d 2  greater than the same. The openings  54  and  55  are aligned with each other, constituting the through holes  53 . The holes  53  each has such a depth that less than one-half of the the bump bp, inclusive, introduced therein protrudes from the top of the substrate  50 . In practice, the thicknesses t 1  and t 2  of the sheets  51  and  52 , respectively, are optimized. The bumps bp arranged on the substrate  50  are transferred to, e.g., the leads of a TAB tape. Subsequently, the TAB tape is bonded to a semiconductor chip. 
     The bumps bp each is assigned to one electrode pad or one lead. Therefore, if the transfer of the bump to even one of several tens to a hundred and tens of electrodes or leads fails, the semiconductor chip is rejected. The conventional device transfers the bumps bp while retaining them in the holes  53 , so that the amount of protuberance of the bumps bp necessary for transfer is not achievable without resorting to strict control over the diameter of the bumps bp. However, the bumps decrease in diameter with a decrease in the pitch between nearby electrode pads or leads, making it more difficult to evenly control the diameter of the bumps bp. 
     The embodiment to be described realizes easy and sure transfer of bumps or conductive particles to a semiconductor chip or a TAB tape. 
     Basically, in this embodiment, the support for the conductive particles and the definition of a particle arrangement each is assigned to one of two independent members. The two members are moved toward each other for particle arrangement and then moved away from each other for particle transfer, so that the particles can be transferred in their fully exposed position. Assume that the particles are bumps. Then, this embodiment is capable of surely transferring the bumps with a high throughput without resorting to strict control over the height of the bumps, the flatness of the leads of a TAB tape, and the flatness of a bonding tool. 
     A conductive particle arranging device embodying the above concept needs a stage for laying conductive particles, a mask for defining a particle arrangement, and drive means drivably connected to at least one of the stage and mask. For the simplest construction and control, the drive means may be connected only to the stage in order to move the stage up and down relative to the mask fixed in place. 
     The particles can be fixed in place on the stage to a certain degree if the stage is implemented as a flat porous plate, and if suction is applied to the rear of the stage. In this embodiment, the stage is additionally provided with an irregular surface for arranging the particles, so that the particles can be prevented from being displaced when the stage and mask are separated from each other. The irregular surface may be implemented by fine lugs formed on the above surface or by a mesh whose mesh size is smaller than the diameter of the particles. 
     The fine lugs may be formed in either one of a regular pattern and an irregular or random pattern. A simple method for forming the irregular pattern consists in spraying a solution of thermosetting resin or that of ultraviolet (UV) curable resin onto the particle arranging surface of the stage, and curing the resulting fine drops by use of heat or UV rays. On the other hand, to form the regular pattern most simply, use may be made of the patterning of photoresist. With the patterning scheme, it is possible to freely select even the relation between the pitch of the fine lugs and that of the particles. If the pitch of the lugs is greater than the pitch of the particles, each particle will be trapped between two nearby lugs. If the former is smaller than the latter, each particle will be caught by a plurality of adjoining lugs. 
     The fine lugs or the mesh may at least partly be provided with tackiness to act on the particles. For this purpose, the lugs themselves may be formed of an adhesive material, or an adhesive material may be applied to the mesh. The adhesive material may be implemented by a silicone resin or an acryl resin. If desired, the mesh may be selectively provided with tackiness in its region corresponding to the region of the mask adjoining the openings, but not provided with it in the peripheral regions of the stage. This protects the mask from needless contamination. 
     In the illustrative embodiment, the drive means may include a tilting mechanism for causing the major surface of the stage and that of the mask to tilt by a small angle from their parallel position. When the stage and mask are separated from each other after the arrangement of the particles, the tilting mechanism reduces the sharp inflow of air and thereby prevents the particles from being displaced or flying about. 
     A bump arranging device with high practicability is achievable if the openings of the mask each is so sized as to trap a single particle, and if the particle is implemented as a conductive particle for forming a solder bump. 
     In the illustrative embodiment, two different particle arranging methods are available for the transfer of the particles to another surface, depending on the operating timing of the above tilting mechanism. A first method is t o slightly lower the degree of parallelism of the stage and mask at the time of arrangement of the particles. A second method is to arrange the particles while maintaining the stage and mask parallel to each other, slightly lower the degree of parallelism at least in the initial stage of separation of the stage and mask, and then restore the original parallelism when the danger of the sharp inflow of air has decreased. In any case, when the drive means is connected to the stage, the stage will be caused to tilt relative to the horizontal mask. 
     It is to be noted that “another surface” to which the particles are to be transferred refers to a TAB tape having leads, a semiconductor chip having bare pad electrodes, or a n intermediate transfer member preceding the TAB tape or the semiconductor chip. 
     Examples of the second embodiment are as follows. 
     EXAMPLE 1 
     FIG. 11 shows a conductive particle arranging device including a stage having fine lugs formed by spraying and then curing a UV curable resin. As shown, the device, generally  60 , includes a movable stage  62  and a fixed mask  72 . The stage  62  is movable along a guide rail  64 . A bump arranging section  60 A and a bump transferring section  60 B are respectively arranged at one end (right-hand side as seen in FIG. 11) and the other end (left-hand-side as seen in FIG. 11) of the guide rail  64 . Drive means, not shown, moves the stage  62  back and forth between the two sections  60 A and  60 B in a direction indicated by an arrow C. As a result, the arrangement of bumps Bp on the stage  62  and the transfer of the bumps Bp to a transfer head  66  are effected alternately. 
     The bump arranging section  60 A is surrounded by a frame  68  whose one end is open in the form of a gate  68   a  for the ingress and egress of the stage  62 . The mask  72  is supported by a mask holder  70  which is, in turn, supported by the frame  68 . The bumps Bp are fed from above the mask  72  via a piping  74 . A squeegee  76  collects the bumps Bp not arranged on the mask  72 , i.e., excess bumps Bp. A guide rail  78  allows the squeegee  76  to move therealong only in a direction indicated by an arrow A. The squeegee  76  is driven by drive means, not shown. 
     The mask  72  is implemented as an about 40 μm thick nickel sheet and formed with openings  72   a  each being so sized as to trap a single bump Bp. The bumps Bp had a mean diameter of about 40 μm while the openings  72   a  had a diameter of about 50 μm. In Example 1, the mask  72  is fixed in its horizontal position. 
     The gap between the squeegee  76  and the mask  72  is selected to be less than one-half of the diameter of the bumps Bp inclusive, i.e., less than 20 μm inclusive, so that the squeegee  76  can collect all the excess bumps Bp. 
     In the bump transferring section  60 B, the transfer head  66  includes optics  80  for exposure. A quartz window  82  coated with an adhesive paint is provided on the surface of the head  66  which will face the stage  62 . The optics  80  fixes the bumps Bp to the electrode pads of an LSI chip, not shown, by using a UV curable adhesive. For this purpose, the optics  80  includes a light source for feeding optical energy for the curing reaction of the adhesive, and an optical fiber for evenly guiding light issuing from the light source to the quartz window  82 . 
     The head  66  is movable up and down in a direction indicated by an arrow D in order to adhere the bumps Bp of the stage  62  to the quartz window  82  and then transfer the bumps Bp to the LSI chip, not shown, at another place. The stage  62  is formed of ceramics or similar porous material. A great number of fine lugs  84  each being about 10 μm high are formed on the surface of the stage  62 . The lugs  84  not only restrict the movement of the bumps Bp on the particle arranging surface of the stage  62 , but also prevent the particle arranging surface and mask  72  from closely contacting each other. The above specific height of the lugs  84  was selected in order to prevent two or more bumps Bp from gathering at a single position. In Example 1, the lugs  84  were formed by spraying a UV curable resin dissolved in a suitable solvent onto the stage  62 , and then curing the drops of the solution by UV radiation. 
     The stage  62  is supported by the stage holder  86  along its edges. A chamber  90  is formed between the rear of the stage  62  and the stage holder  86  and fluidly communicated to an evacuating unit  88 . In this configuration, the bumps Bp each being trapped in one opening  72   a  of the mask  72  are restricted in position on or between the lugs  84 , and additionally restricted by suction acting from the rear of the stage  62 . 
     The stage holder  86  is fixed to an elevatable base  91  engaged with the guide rail  64  stated earlier. The base  90  is moved in the direction C while carrying the stage  62  thereon. 
     The base  91  is extendable in a direction indicated by an arrow B and allows the distance between the stage  62  and the mask  72  to be adjusted when they are conveyed to the bump arranging section  60 A. The amount of extension in the direction B does not have to be uniform over the entire stage  62 . For example, an actuator may be used to cause the base  91  to extend more at one end of the stage  62  than at the other end of the stage  62 . This allows the particle arranging surface of the state  62  to slightly tilt from horizontal in a direction E when the bumps Bp are arranged on the stage  62  or when the stage  62  carrying the bumps Bp is moved away from the mask  72 . 
     In the above configuration, the transfer of the bumps Bp is effected without regard to the mask  72 . Therefore, all the bumps Bp arranged on the stage  62  can be transferred to another surface without resorting to sophisticated control over the height of the bumps Bp, as measured from the surface of a substrate, and bump diameter. 
     EXAMPLE 2 
     In Example 2, the particle arranging device  60  was used to actually transfer the bumps Bp to the electrode pads of an LSI chip. The transfer will be described with reference to FIGS. 12-17. 
     First, as shown in FIG. 12, the mask  72  and stage  62  are positioned close to each other, and each is held in its horizontal position. The bumps Bp each is received in one of the openings  72   a . The bumps Bp are implemented as resin beads plated with Ni (nickel) and Au (gold) in a laminate structure. The excess bumps Bp not received in the openings  72   a  are collected by the squeegee  76  moving back and forth in the direction A. 
     Subsequently, as shown in FIG. 13, the elevatable base  91  is operated to move the stage  62  away from the mask  72 . In the initial stage of the separation, the tilting movement stated earlier may be effected in order to prevent air from sharply flowing into the gap between the mask  72  and the stage  62 . This maintains the accurate arrangement of the bumps Bp. Thereafter, the stage  62  is lowered in the direction B to a level at which the stage  62  can be conveyed out of the bump arranging section  60 A. It is to be noted that the stage  62  can be restored to its horizontal position at the time when the influence of the stream of air has become negligible. 
     FIG. 14 shows a condition wherein the stage  62  is fully separated from the mask  72 , and the bumps Bp are arranged on the stage  62 . Because the fine lugs  84  are irregularly arranged on the stage  62 , some bumps Bp are trapped between nearby lugs  84  while the other bumps B rest on a plurality of nearby lugs  84 . Although the height above the stage surface slightly differs from one bump Bp to another bump Bp, the difference is only less than 10 μm. 
     Subsequently, the base  91  is moved in the direction C in order to convey the stage  62  out of the bump arranging section  60 B. Then, as shown in FIG. 15, the transfer head  66  was lowered in the direction D until the bumps Bp adhered to the surface of the quartz window  82  applied with the adhesive material. In Example 2, the bumps Bp existed on the stage  62  in their bare state. This, coupled with the fact that the adhesive material absorbed the difference in height between the bumps Bp and sufficiently contacted all the bumps Bp, allowed the bumps Bp to be shifted to the head  66  without exception. 
     As shown in FIG. 16, the head  66  was moved to a position above an LSI chip  92  in order to align the bumps Bp with the electrode pads  94  of the chip  92 . Then, the head  66  was lowered in the direction  66 . The surfaces of the electrode pads  94  are covered with UV curable adhesive layers  96  beforehand. After the bumps Bp on the head  66  contacted the adhesive layers  96 , UV rays hv were radiated from the optics  80 . The UV rays hv caused the adhesive layers  96  to set via the quartz window  82 . As a result, the bumps Bp were fixed to the electrode pads  94  as shown in FIG.  17 . 
     Finally, the head  66  is raised away from the chip  92 . 
     This is the end of the bump transfer procedure of Example 2. 
     EXAMPLE 3 
     In Example  3 , the stage  62  is slightly tilted from the horizontal at the time of arrangement of the bumps Bp thereon in order to protect the arrangement of the bumps Bp from a stream of air. Specifically, as shown in FIG. 18, the bumps Bp were arranged on the stage  62  inclined by an angle of θ from the horizontal via the base  91 . The angle θ is free to choose so long as the bumps Bp do not escape from the openings  72   a  of the mask  72 . After the arrangement of the bumps Bp, the stage  62  and mask  72  may be separated from each other by the method described in relation to Example 2. 
     EXAMPLE 4 
     As shown in FIGS. 19 and 20, in this example, the fine lugs  84  on the stage  62  are replaced with fine lugs  84   a  formed in a regular pattern by photolithography. Specifically, the lugs  84   a  are implemented as a resist pattern formed by the selective exposure and development of a photoresist film provided on the stage  62 . 
     As shown in FIG. 19, when the pitch P 2b  of the lugs  84   a  is sufficiently smaller than the pitch P B  of the bump Bp, the bumps Bp rest on the lugs  84   a  without contacting the particle arranging surface of the stage  62 . As shown in FIG. 20, when the pitch P 2b  is sufficiently greater than the pitch P B , the bumps Bp contact the particle arranging surface of the stage  62  between the adjacent lugs  84   b.    
     EXAMPLE 5 
     In this example, the fine lugs on the stage  62  are provided with tackiness. As shown in FIG. 21, the fine lugs are constituted by an adhesive resin buried layer  98  which may be formed by use of a silicone resin. A method of forming the layer  98  will be described with reference to FIGS. 22 and 23. 
     First, as shown in FIG. 22, conventional resist patterning was effected on the stage  62  in order to form a resist pattern  100 . Then, as shown in FIG. 23, the adhesive resin buried layer  98  was formed such that a silicone resin filled the spaces of the resist pattern  100 . After the setting of the silicone resin, the resist pattern  100  was removed by a peeling liquid. As a result, only the layer  98  was left on the stage  62 , as shown in FIG.  21 . 
     The fine lugs formed by the above procedure have tackiness themselves and retain the bumps Bp more positively than the fine lugs implemented by the previously stated UV curable resin. Therefore, even when a flow of air occurs at the time of separation of the stage  62  and mask  72 , the disturbance to the arrangement of the bumps Bp can be minimized. In addition, to obviate the flow of air, the tilting angle of the stage  62  can be increased. 
     EXAMPLE 6 
     In this example, the fine lugs with tackiness are not formed over the entire particle arranging surface of the stage  62 , but formed only in the region of the stage  62  adjoining the openings  72   a  of the mask  72 . Specifically, as shown in FIG. 24, the fine lugs are constituted by an adhesive resin buried layer  98   b  and a resist pattern  100   c . The layer  98   b  is selectively formed in a region M adjoining the openings  72   a  of the mask  72 . For the layer  98   b , use may be made of a silicone resin. The resist pattern  100   c  surrounds the above region M and is formed of a conventional positive type photoresist material. With this configuration, it is possible to free the mask  72  from contamination when the mask  72  and stage  62  are brought into contact. 
     FIGS. 25-28 show a procedure for forming the fine lugs of this example by two consecutive photolithographic steps. First, as shown in FIG. 25, a positive type photoresist film  102  formed on the stage  62  was subjected to the first selective exposure via a photomask  104 . The photomask  104  is made up of a substrate  106  transparent for exposing light, and a Cr (chromium) film or similar light intercepting film pattern  108  formed on the substrate  106 . The pattern  108  defines a position for forming the layer  98   b  (FIG. 27) in the region M. While the exposure is shown as being proximity exposure in FIG. 25, it may be contact exposure or projection exposure, if desired. 
     Subsequently, the exposed region of the photoresist film  102  was removed by the first development in order to form a resist pattern  100   b  shown in FIG.  26 . Then, as shown in FIG. 27, the adhesive resin buried layer  98   b  was formed such that the spaces of the resist pattern  100   b  were filled with a silicone resin. 
     As shown in FIG. 28, after the setting of the above layer  98   b , the resist pattern  100   b  on the stage  62  was subjected to the second selective exposure via a photomask  110 . The photomask  110  is also made up of a substrate  112  transparent for exposing light, and a Cr film or similar light intercepting film pattern  114  formed on the substrate  112 . The pattern  114  causes a new resist pattern  100   c  shown in FIG. 28 to be formed in the peripheral region around the region M. At the same time, the pattern  114  defines an exposure area for causing the resist pattern  100   b  existing in the region M to be removed. 
     After the second selective exposure, the second development was effected so as to produce the stage  62  shown in FIG.  24 . As shown, the stage  62  has two different kinds of fine lugs each being confined in a respective region. 
     EXAMPLE 7 
     In this example, the fine lugs for retaining the bumps Bp are replaced with a mesh  116  laid on the stage  62 . As shown in FIG. 29, the mesh  116  is laid on the stage  62  such that the bumps Bp trapped in the openings  72   a  of the mask  72  are arranged on the mesh  116 . The mesh  116  is formed of, e.g., stainless steel. The mesh size of the mesh  116  is selected to be sufficiently smaller than the diameter of the bumps Bp, yet to surely retain the bumps Bp. In Example 7, the apertures of the mesh were about 20 μm. 
     The bumps Bp may be arranged on the stage  62  and then transferred by the previously stated procedure. 
     While this example maintains both the stage  62  and mask  72  horizontal at the time of arrangement of the bumps Bp, the stage  62  may be slightly tilted from the horizontal via the elevatable base  91  in the same manner as in Example 3. Further, when the stage  62  and mask  72  are separated from each other, the stage  62  may advantageously be lowered while being tilted, as in Example 1. 
     The illustrative embodiment is not limited to Examples 1-7 shown and described. For example, the bumps Bp arranged on the stage  62  and brought to the bump transferring section  60 B may be directly bonded to the leads of a TAB tape by a conventional bonding tool, i.e., without using the transfer head  66 . The kinds and sizes of the bumps Bp, the sizes of the openings of the mask and mesh, the dimension of the fine lugs, and the details of the particle arranging device shown and described are only illustrative. In addition, this embodiment is applicable not only to the bumps Bp but also to other various kinds of particles. 
     In summary, in the illustrative embodiment, bumps can be easily and surely arranged and transferred without resorting to strict control over the diameter of the bumps, the flatness of the leads of a TAB tape, the flatness of a bonding tool, and the parallelism of a stage and a TAB tape or an LSI chip. This successfully increases the yield of bonding using the TAB system or the flip-chip bonding system, and thereby enhances the productivity of semiconductor devices. 
     Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Technology Classification (CPC): 7