JP2008153319A - Screen printing apparatus and bump forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in the method for filling a predetermined aperture with a solder ball by swaying or vibrating a mask in formation of a bump electrode that the aperture cannot be filled because particles are in close contact with each other due to reduction in diameter of solder ball particle and because a close contact force between particles becomes larger than the self-weight of particles in the case where the hole diameter of the mask is under 1.3 times the diameter of particle, and also to solve the similar problem on the occasion of filling the aperture with the solder ball by utilizing squeegee and parallel advancing motion of brushes or the like. <P>SOLUTION: A printer for filling of solder balls has been developed, on the basis of a low price and high precision screen printing technology used in the printing method, to achieve high-speed and highly accurate filling and printing of fine particles of solder balls for assuring stable height of bumps. Moreover, it has been achieved that the solder balls are used for filling and printing while the solder balls are held in the closed state in order to effectively use the fine particles of solder balls. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a screen printing apparatus, and more particularly to a bump forming method by solder ball printing.

  In ball bump formation (diameter 80 to 100 μm) with a pitch of 180 to 150 μm, there is a printing method in which a solder ball is formed by reflowing cream solder after printing using the above-described high-precision screen printing apparatus. As an example of a screen printing apparatus, a substrate carry-in conveyor, a substrate carry-out conveyor, a table unit provided with a lifting mechanism, a mask having a transfer pattern as an opening, a squeegee, a squeegee lifting mechanism, and a squeegee head equipped with a horizontal movement mechanism, A control device for controlling these mechanisms is provided. After the substrate is carried into the apparatus from the carry-in conveyor unit, the substrate is temporarily positioned and fixed to the printing table unit, and then both the marks on the substrate and the mask having the opening corresponding to the circuit pattern are recognized by the camera. After correcting the amount of misalignment and aligning the substrate with the mask, the print table is raised so that the substrate is in contact with the mask, and a paste such as cream solder is applied to the opening of the mask while the mask is in contact with the substrate with a squeegee In addition, the paste is transferred onto the substrate by lowering the table and separating the mask from the substrate, and then printing is performed by unloading the substrate from the apparatus.

  Also known is a ball transfer method in which solder balls are formed by transferring solder balls into jigs that have been drilled with high precision, aligning them at a predetermined pitch, transferring them directly onto the substrate, and reflowing after placement. ing. Furthermore, according to Japanese Patent Laid-Open No. 2000-49183, there is a method comprising a method of filling a predetermined opening with a solder ball by swinging or vibrating the mask, or a method of heating after filling by translational movement of a brush or the like.

JP 2000-49183 A

  The printing method using cream solder has an advantage that the equipment cost is low and a large amount of bumps can be formed at a time, so that the throughput is high and the manufacturing cost is kept low. However, in the printing method, it is difficult to ensure the uniformity of the transfer volume, and the process of smoothing the height by pressing the solder bump after reflow is performed by the fluttering process, and there is a problem that the number of processes is large and the equipment cost is high. . In addition, when the finer process progresses to a pitch of 150 to 120 μm as the density of the device increases, there is a point that the printing yield is poor and the productivity is not good. On the other hand, the ball transfer method can form bumps with a stable height by ensuring the classification accuracy of the solder balls, and is suitable for refinement. However, the solder balls are mounted by a robot using a high-precision solder ball suction jig. However, there are problems of increased tact when finer and increased bump formation cost due to increased jig / equipment prices.

  Further, in the method of swinging or vibrating a mask according to Japanese Patent Laid-Open No. 2000-49183 and filling a predetermined opening with a solder ball, an adhesion phenomenon between the particles occurs as the solder ball particle diameter is reduced. When the hole diameter is less than 1.3 times the particle diameter, there is a problem that the adhesion force between the particles is larger than the particle weight and the opening cannot be filled. Similarly, there is a similar problem in filling by squeegee or brush translation.

  The object of the present invention is to form a large amount of bumps as in the printing method, and to form a bump having a stable height as in the ball transfer method. It is an object of the present invention to provide a solder ball filling printing apparatus and a bump forming method which are inexpensive and capable of printing and filling efficiently at high speed and with high productivity.

  In order to achieve the above object, the following means are implemented in the present invention. First, based on the inexpensive and high-precision screen printing technology used in the printing method, we developed a solder ball filling printing device that can quickly and accurately fill and print solder ball fine particles with stable bump height. In addition, in order to use the solder ball fine particles efficiently, filling and printing was realized while holding the solder ball in a sealed state. Furthermore, we have developed a stable and high-quality bump formation method that suppresses solder ball filling defects.

FIG. 1 shows an example of a metal mask used for forming bump electrodes. FIG. 1A shows the state of the entire mask, and FIG. 1B shows an example of an opening pattern 20p corresponding to an electrode group printed on one device. That is, the mask 20 is attached to the plate frame 21. Hereinafter, the whole including the plate frame 21 is referred to as a mask 20. As an example of using this mask, the electrode pad portion has a diameter of 120 μm, a pitch of 150 μm, and a multi-chip substrate in which dozens of electrode pads are arranged with several thousands of pads of one CPU chip. On the other hand, it is used for bump formation by a printing method. The square shape in FIG. 1A shows one electrode pad group 20a. That is, a large number of mask openings 20c provided corresponding to one electrode pad group are opened with a diameter corresponding to the size of the electrode pads. Printing is performed using the mask 20, and after the printing is finished, the printing table 10 is lowered, and the substrate 5 fixed to the printing table 10 is lowered, thereby performing the plate separation operation and printing.

  FIG. 2 shows the configuration of the screen printing apparatus according to the present invention. FIG. 2A shows a configuration and a system configuration diagram as viewed from the front of the screen printing apparatus. Further, FIG. 2B shows a configuration of the screen printing apparatus viewed from the side. FIGS. 3A and 3B show a state during printing with a configuration in which the screen printing apparatus is viewed from the side.

  A plate frame receiver (not shown) is provided on the main body frame, and a mask 20 with a screen having a printing pattern as an opening is set on the plate frame receiver. A filling / printing head 2 is disposed above the mask 20, and the filling / printing head 2 is composed of a filling unit comprising a squeegee (in the present invention, a shib 45 and a scraper 3 are used instead of the squeegee). Is installed. The filling / printing head 2 is configured to be movable in the horizontal direction by a filling / printing head moving mechanism 6. The filling unit can be moved in the vertical direction by the filling unit lifting mechanism 4. A printing table 10 is provided below the mask 20 to place and hold the substrate 5 as a printing object so as to face the mask 20. This printing table 10 receives the substrate 5 from the carry-in conveyor 25 and moves the substrate 5 in the horizontal direction to align it with the mask, and brings the substrate 5 close to or in contact with the mask 20 surface. The table elevating mechanism 12 is provided. A substrate receiving conveyor 26 is provided on the upper surface of the printing table 10. The substrate 5 carried by the substrate carrying conveyor 25 is received on the printing table 10, and when printing is completed, the substrate 5 is discharged to the substrate carrying conveyor 27.

  The printing unit main body 1 has a function of automatically aligning the mask 20 and the substrate 5. That is, the CCD camera 15 images the alignment marks provided on each of the mask 20 and the substrate 5, performs image processing to obtain a positional deviation amount, and sets the XYθ table 11 so as to correct the deviation amount. It is driven and aligned.

  A printing machine control unit 30 that performs a printing control unit 36 for driving each unit, an image input unit 37 that processes an image signal from the CCD camera 15, and the like is provided inside the printer body frame, and includes control data A data input unit 50 for rewriting, changing printing conditions, and the like, and a display unit 40 for monitoring the printing status and captured recognition marks are arranged outside the printing press.

The printing press control unit 30 has a filling unit control unit 36 for controlling the filling unit, and an appropriate filling / printing mode can be easily selected depending on the pitch of the bump to be produced, the difference in the solder ball particle diameter, and the type of the metal mask to be used. Select setting is possible. In addition, a correlation value calculation unit 31 that calculates a correlation value according to an input image, a shape estimation unit 32 that calculates a shape based on the captured image and data from the dictionary 38, a position coordinate calculation unit 33 that calculates a position coordinate, dimensions A calculation unit 34 is provided, and based on the position recognition marks provided on the substrate and the mask from the data captured by the CCD camera 15, the positional deviation amount is obtained and the XYθ table is driven to perform alignment. .

  Next, the operation of the printing apparatus of the present invention will be described.

The substrate 5 on which the bumps are formed is supplied to the substrate receiving conveyor 26 by the substrate carry-in conveyor 25 and fixed at a predetermined position on the printing table 10. After fixing the substrate, the CCD camera 15 is moved to a substrate mark position registered and set in advance. Subsequently, the CCD camera 15 images a position recognition mark (not shown) provided on the substrate 5 and the mask 20 and transfers it to the printing press control unit 30. The image input unit 37 in the control unit obtains the amount of positional deviation between the mask 20 and the substrate 5 from the image data, and based on the result, the printing press control unit 30 operates the XYθ table 35 for moving the printing table 10 to operate the mask 20. The position of the substrate 5 with respect to is corrected and aligned. After the alignment operation is completed, the CCD camera 15 is retracted by a predetermined amount to a position where it does not interfere with the print table 10. After the CCD camera 15 is retracted, the printing table 10 is raised and the substrate 5 and the mask 20 are brought into contact with each other. After that, the filling unit lifting mechanism is operated to bring the shibbed body provided in the filling / printing head 2 into contact with the surface of the mask 20. Next, solder balls are supplied to the electrode portions of the substrate through the openings provided in the mask surface by moving the surface of the mask while vibrating the shibs.

  The filling / printing head 2 moves up after a certain distance stroke in the horizontal direction. Then, the printing table 10 is lowered, the mask 20 and the substrate 5 are separated, and the solder ball filled in the opening of the mask 20 is transferred to the substrate. And the board | substrate 5 with which the solder ball was printed is sent to the following process through the board | substrate carrying-out conveyor 27. FIG.

  The substrate 5 and the mask 20 are provided with two or more recognition positioning marks at relatively the same location, and both of these marks are respectively separated by a special CCD camera 15 having two vertical fields of view. The mark of the mask 20 is recognized from the bottom, the mark of the substrate 5 is recognized from the top, the position coordinates of all the marks provided at predetermined positions are read, the amount of displacement of the substrate 5 with respect to the mask 20 is calculated and corrected, The substrate 5 is aligned with the mask 20.

  Next, the print head of the present invention will be described.

  FIG. 4 shows a schematic diagram when the filling / printing head moves on the mask while filling the solder balls into the mask. FIG. 5 shows a cross-sectional view of the filling / printing head.

  As shown in FIG. 4, the filling / printing head 2 has a shib-like body 45 on which a solder ball is placed, a shib-like body fixing bracket 3a, a vibration means 47 that applies vertical or horizontal vibration to the shib-like body 45, a screen. And a scraper 3 which can be scraped off without leaving unfilled solder balls supplied on the surface. In FIG. 4, the scraper 3 is attached to the shib-like body. However, as shown in FIG. 5, the shib-like body may be attached to the shib-like body fixing bracket 3a, and the scraper 3 may be provided outside. Moreover, it is good also as a structure which provides a brush in the shibu-shaped body fixing metal fitting 3a, and abbreviate | omits the scraper 3. FIG. The shib-like body 45 is formed of a net-like opening 46 or a very thin metal plate having an opening 46 such as a continuous circle, ellipse, rectangle, or slit. The mesh-shaped opening 46 can be formed by integrally molding a metal plate by electroforming or the like. The solder ball 48 placed on the upper part of the shib-like body 45 causes the shib-like body 45 to vibrate in the vertical or horizontal direction, or a direction in which both are combined (direction of the arrow 42) by the vibration means 47, It is possible to reduce and diffuse the adhesion force between the solder balls and to apply a rotational force to the solder balls. Due to the rotational force generated on the solder ball 48, a force having a downward component in the vertical direction is generated on the solder ball 48. With this downward force, the solder ball 48 can be filled into a predetermined opening position of the mask 20 through the opening 46 of the shim-like body 45. That is, the filling / printing head 2 continuously fills the electrode portion 5p on the surface of the substrate 5 by vibrating the shib-like body 45 on the surface of the mask 20 and moving in the horizontal direction.・ Print.

  As shown in FIG. 5, the filling / printing head 2 forms a solder ball storage means that can hold the amount of solder balls 48 necessary for printing in a hermetically sealed state by the shibbed body 45. The filling / printing head 2 is configured to connect and vibrate the shibbed body 45 containing the solder balls 48 with the opposing scraper 3 during the printing operation. That is, a vibration means 47 for vibrating the shib-like body fixing metal 3a and the scraper 3 is provided so that the scraper 3 and the shib-like body 45 vibrate in synchronization.

  FIG. 6 shows a shib structure diagram having a coupled vibration action. As described above, the shib-like body 45 is composed of an extremely thin metal plate, and has a mesh-like opening 46 provided on the bottom surface thereof. Then, both end portions are bent according to the inclination of the shib-shaped body fixing bracket 3a, and the bent portion is attached to the surface of the shib-shaped body fixing bracket 3a. Since the shib-like body 45 can be easily stretched and deformed, its shape characteristics are utilized. When the solder ball diameter> opening size + stretch deformation size, the solder ball 48 cannot pass and the solder ball 48 can be held. It becomes. On the other hand, when solder ball diameter <opening size + stretchable deformation size, a gap through which the solder ball 48 can pass is secured, and the solder ball can be filled. The expansion and contraction of the shibu-shaped body 45 can be generated by exciting the shibu-shaped body 45 or by an external force such as a magnetic force.

FIG. 7 is an explanatory diagram of a solder ball filling / printing mechanism by a filling / printing head through a shim-like body 45 (not shown). In the figure, the shim-like body fixing bracket 3a has an attack angle θ set to about 60 degrees. The filling / printing head 2 is moved in the direction of the arrow 41 while vibrating the shib-shaped body fixing bracket 3a in an oblique direction (attack angle direction) using a vibration means 47 (not shown). This vibration is transmitted to the shib-like body 45 via the shib-like body fixing bracket 3a. When this vibration is transmitted to the solder ball 48 housed on the bottom surface of the shib-like body 45, a rotational force in the direction of the arrow 41r is generated in the solder ball 48. This rotation generates a force in the direction of arrow 41 (horizontal direction) and a force in the direction of arrow 41a (vertical direction) on the solder ball 48. That is, a downward force is generated on the solder ball 48 by the rotational force. In this state, the shib-like body 45 repeatedly expands and contracts, and when the shib-like body 45 is in a stretched state, the opening provided in the bottom surface portion is greatly opened, from which the solder ball falls and moves to the mask surface. The solder balls that have fallen into the opening of the mask are pushed into the mask opening by the bent corners or scrapers of the shibbed body. Solder balls that have fallen outside the opening on the mask surface are scraped off by the bent corners of the shibbed body 45 or by the scraper 3 or the like.

  In the above description, the scraper is provided to scrape off the solder balls remaining on the mask surface. However, the brush is provided at the lower part of the shib-like body fixing metal fitting 3a without contacting the mask surface. The solder balls may be swept away with a brush. In the above description, the brush body is provided on the brush body, but a scraper or brush may be attached separately from the shib body. In this case, a vibration mechanism that vibrates the shib-like body and a vibration mechanism that vibrates a scraper or a brush are required.

  Next, FIG. 8 shows an example of a situation in which solder balls are filled in the mask openings used in the present invention. FIG. 9 shows the arrangement of suction channels provided in the resin layer portion below the mask. FIG. 10 shows an enlarged view of the mask opening.

  As shown in FIG. 8, the mask 20 has a two-layered mask shape in which a resin layer 20n is provided under a metal layer 20s made of a magnetic material. In addition, although 20n was used as the resin layer in order to give adhesiveness and flexibility, it can also be realized by forming it with a thin metal such as nickel in view of durability. A flux 5f (paste) for increasing the adhesion of the solder balls is supplied to the upper part of the electrode pad 5p. A plurality of magnet pads 10 b are fixed on the substrate receiving surface side of the printing table 10 so as to be the same surface as the printing table 10 surface. By attracting the metal layer 20s of the mask with the magnetic force of the magnet pad 10b, the adhesion between the mask 20 and the respective surfaces of the substrate 5 is increased.

  Further, in this embodiment, as shown in FIG. 9, the resin layer 20n below the metal layer 20s is provided with grooves for sucking an air flow from an opening provided on the mask surface in a substantially grid pattern. It is. This groove serves as an exhaust passage 52 for discharging air when a mask is placed on the substrate. The exhaust passage 52 is formed so as to connect an exhaust groove 51 constituted by a groove provided so as to surround the electrode group. Although not shown, a pump for sucking air is arranged, and a pipe for connecting the pump and the exhaust passage 52 is provided. In the above description, air is sucked from the mask opening via the exhaust flow path 52 using a pump. However, a pressurized air supply means for blowing air to the mask surface is provided on the printing / filling head side. Then, after the solder ball is printed, the solder ball may be pushed into the electrode pad portion from the mask opening by blowing the compressed air onto the mask surface. Also in this case, by providing an exhaust passage in the resin layer constituting the mask so that air can escape from the periphery of the mask, the solder balls can be easily supplied to the mask opening.

  As shown in FIG. 10, the mask 20 is formed such that the opening on the resin layer 20n side is larger than the opening on the metal layer 20s side. Thus, by providing the resin layer on the side of the mask that comes into contact with the substrate, adhesion of the mask to the substrate is increased, damage to the substrate is prevented, and solder balls can be reliably supplied to the electrode portions of the substrate. It is a thing. The distance (pitch) L between the openings of the mask, the diameter Rs of the opening on the metal layer 20s side, the diameter Rr (= 1.1Rs) of the opening on the resin layer 20n side, and the width Rl (about 0.4 Rr) of the exhaust groove 52 are set. . The opening diameter of the mask is determined by the diameter of the solder ball to be supplied.

  As described above, according to the present invention, it is possible to form a large number of solder bumps with stable solder bump height accuracy at a low cost at a high speed. In addition, the apparatus has a simple configuration, and the equipment cost can be kept low.

It is a figure which shows an example of a metal mask. It is a figure which shows an example of a screen printing apparatus. It is a figure for demonstrating the outline of the printing operation of a screen printing apparatus. It is a figure which shows the example of the solder ball filling of a filling and a printing head. It is a figure which shows the cross section of an example of a filling and a printing head. It is a figure which shows an example of the storage-type shib shape of a filling and printing head. It is a figure which shows a filling and printing mechanism. It is a structure conceptual diagram of a metal mask. It is a figure which shows the example of the exhaust flow path of a metal mask. It is a figure which shows the outline of the opening part of a metal mask, and an exhaust flow path.

Explanation of symbols

1 Print Unit Body 2 Filling / Print Head 3 Scraper 5 Substrate 10 Print Table 11 XYθ Table 15 Camera 20 Mask 45 Shiv

Claims (8)

  In a bump forming method using solder balls, a screen having an opening for filling and transferring solder balls in a predetermined pattern, a screen fixing means for placing and fixing the screen, and a substrate for bump formation are carried in and fixed to a predetermined A substrate fixing means for carrying out after completion of printing / transfer, a recognition positioning means for performing image processing on the reference marks of the screen and the substrate and aligning the screen and the substrate, a contact means for bringing the substrate into close contact with the screen, Printing means for filling solder balls in a predetermined position through the screen, flat movement means for moving the printing means in parallel with the screen surface, and solder balls filled in the screen openings are fixed on the substrate and transferred by releasing the plate. And a transfer device for transferring, and the printing means includes a shib-like body on which a solder ball is placed; Bump forming method and a vibration means for imparting vertical or horizontal vibrations in Shiv-shaped body.   A solder ball storage means capable of holding in a sealed state a quantity of solder balls necessary for printing is provided on the shib-like body, and the shib-like body containing the solder balls is vibrated during a printing operation. 1 is a bump forming method.   2. A printing apparatus and a bump according to claim 1, wherein said printing means is provided with a brush-like body or scraper means which is provided with or independent of a shib-like body, and vibrates the scrap-like body or scraper means during a printing operation. Forming method.   A step in which a step is integrally formed of a resin material around the pattern opening on the back side of the screen, the total thickness being 1 to 1.2 times the solder ball diameter, and the step being ½ or less of the solder ball diameter; 2. The bump forming method according to claim 1, further comprising: a suction path formed when a slit is provided in the stepped portion of the screen and brought into close contact with the substrate; and a screen suction means.   2. The bump forming method according to claim 1, wherein the printing means includes solder ball pressurizing means for applying a pressing force downward from the upper part of the screen by utilizing the flexibility of the screen after the solder ball filling operation. In a screen printing apparatus that supplies and prints solder balls using a printing means through a mask to electrodes formed on a substrate,
The printing means includes a shib-like body having a metal surface having a plurality of openings, and a vibration means for applying vibration to the shib-like body, and the shib-like body is vibrated by the vibration means. A screen printing apparatus characterized in that an opening is widened and a solder ball accommodated on the shib-like body is supplied to an electrode on a substrate through the mask. In a screen printing apparatus that supplies and prints solder balls using a printing means through a mask to electrodes formed on a substrate,
The printing means includes a shib-like body having a metal surface having a plurality of openings, a vibration means for applying vibration to the shib-like body, and a substrate holding means for supporting and fixing the substrate. Has a built-in magnet, and when the printing means moves in parallel on the mask surface, a magnetic force is applied to the metal mask and the metal shib through the substrate to widen the shib opening, and the solder ball stored on the shib-like body is transferred to the mask. A screen printing apparatus characterized in that it is configured to be supplied to an electrode on a substrate via   8. A screen printing apparatus according to claim 6 or 7, wherein said filling unit is provided with a shim-like body or a scraper means independently of said shib-like body, and the shading body is vibrated during a printing operation. A screen printing apparatus comprising a vibration means.

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