JP4357580B2 - Conductive ball mounting method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for mounting conductive balls on a substrate, and more specifically, conductive balls are mounted on pads for external connection provided on a substrate (for example, a wiring substrate, a package substrate, a wafer, etc.). The present invention relates to a method and an apparatus.

  When forming solder bumps for connection with other electronic components on pads formed on a substrate such as a wiring board or wafer, conventionally, the solder paste is transferred onto the pads by printing and turned into hemispherical bumps by heating. It was. As the pitch of the pads becomes narrower with the increase in the density of electronic components, problems such as adjacent bumps being short-circuited by bridges have become apparent in this method. The bump formation by the printing method is limited to a bump pitch of about 200 μm.

  When forming bumps at a narrower pitch, a technique using solder balls formed in a spherical shape in advance is used. According to this technique, for example, as described in Patent Document 1, a metal mask having a through-hole into which one solder ball enters at a position corresponding to each pad of the substrate is aligned and superimposed on the substrate, and then on the mask. A large number of placed solder balls are dropped into the through-holes one by one, attached to the flux previously applied to the pad, and after removing the excess solder balls on the mask with a squeegee, the mask is removed to remove the solder balls on the board. Is installed.

  On the other hand, the inventors of the present application disclosed a container in which solder balls are placed under a substrate with a solder ball mounting surface facing down, in which a metal mask having a through hole into which one solder ball enters at a position corresponding to each pad. Place the solder ball that floats by blowing air from the hole drilled in the bottom of the container or by applying vibration to the container, and attach it to the flux applied in advance to the pad through the through hole of the mask, and then remove the mask Thus, a technology for mounting solder balls on a substrate was developed, and a patent application was filed for this (Patent Document 2).

JP-A-11-297886 Japanese Patent Application No. 2007-57785

  When mounting a conductive ball such as a solder ball for bump formation on a substrate with a pad with a narrow pitch of 200 μm or less, by the technique of dropping the balls one by one into the through hole of the metal mask described above, The placement of the ball on the pad and the removal of the ball remaining on the mask need to be performed in separate steps, and it is difficult to increase the time required for the mounting operation. In addition, when removing the ball remaining on the mask, the surface of the ball is easily scratched due to friction with the mask, which makes the ball easy to oxidize, which causes a problem in reusing the collected ball. There is also a problem.

  In the case of using a technique for floating a ball by blowing out air, if the momentum of the blown-out air is increased, the ball will fly out of the container, so that it is difficult to raise the ball at a high density all at once. Therefore, in this case, improvement of the ball mounting rate is required.

  When using the floating of the ball by vibration, the ball floats uniformly. However, when the pad pattern has a high density, there is a problem that the floated balls collide with each other and the ball cannot be supplied to a predetermined pad. Further, when the amount of balls in the container is increased, there is a problem that the balls do not float.

  As described above, the conventional technology in which conductive balls such as solder balls are mounted on a substrate having a narrow pitch pad requires a reduction in mounting time, an improvement in mounting rate, and a simple reuse of balls collected without mounting. Sex could not be satisfied at the same time.

  It is an object of the present invention to provide a method and apparatus that allows efficient mounting of conductive balls on a narrow pad pitch substrate that can meet these needs simultaneously.

The conductive ball mounting method of the present invention is a method of mounting a conductive ball on a substrate provided with a pad,
Placing a substrate having a pad to which an adhesive such as flux is applied, with the surface of the pad facing down, and containing a conductive ball;
By spike is moved at a predetermined stroke the container upwards, throwing upward collectively conductive balls in the container, depositing the adhesive agent applied to the pad,
Repeating the step of attaching the conductive ball by throwing out until the conductive ball adheres to the adhesive of all pads,
It is characterized by mounting a conductive ball.

  The moving stroke of the container can be 0.5 to 1000 mm, preferably 10 to 50 mm, and the conductive ball throwing cycle is 0.01 to 20 times per second, preferably 0.1 to 1 second. It can be 10 times.

  You may use the mask which has a through-hole into which one conductive ball enters in the position corresponding to each pad. When a mask is used, it is preferably used so as to overlap the surface of the substrate on which the conductive balls are mounted.

The conductive ball mounting device of the present invention is a device for mounting a conductive ball on a substrate having a pad,
A conductive ball container with an open top,
A substrate holding device for holding a substrate having a pad coated with an adhesive, with the surface of the pad facing downward, above the conductive ball container;
The conductive ball storage container is moved upward with a predetermined stroke and rapidly raised, so that the conductive balls in the container are collectively thrown upward and adhered to the adhesive applied to the pad of the substrate. Conductive ball throwing device,
It is characterized by comprising.

  According to the present invention, it is possible to mount conductive balls on a substrate in a short time and with an improved mounting rate. Also, when a mask is used for mounting the ball, even if the ball may remain attached to the mask, the ball is attached to the lower surface of the mask, so it can be easily removed and reused ( In the case of the conventional method in which the ball is mounted by dropping into the metal mask through-hole, the ball is collected by rubbing the upper surface of the mask, so that the surface is easily scratched and is easily oxidized at the scratched part. This is a factor that hinders the reuse of balls).

  In the present invention, a conductive ball is supplied by throwing up a conductive ball from below to a substrate disposed with a pad coated with an adhesive facing downward, and the conductive ball is attached to the adhesive, thereby providing the conductive ball on the substrate. Is installed. As the adhesive, a flux, an adhesive, a conductive paste, or the like can be used. In the following, the present invention will be described using flux as an example of an adhesive.

  The substrate on which the conductive ball is mounted may be various substrates that are connected to an external circuit using bumps formed from the mounted conductive ball. Examples of such a substrate include a wiring substrate, a package substrate, and a wafer. The package substrate also includes a ball grid array (BGA) package and the like.

  The substrate has a pad formed in a predetermined pattern, and flux is applied to the upper surface of the pad. Although the pitch of the pad pattern is not particularly limited, the present invention can cope with a narrow pitch of 200 μm or less. For example, conductive balls can be efficiently mounted on a substrate having a pad pitch of about 100 to 200 μm. A flux corresponding to the type of conductive ball to be mounted is used.

  FIG. 1 shows an example of a substrate on which conductive balls are mounted according to the present invention. The substrate in this figure is manufactured as an aggregate of a plurality (three in this figure) of individual substrates 10 to be separated later. The individual substrate 10 is separated by a broken line indicated by A in the figure after the conductive ball is mounted and heated (reflowed) according to the present invention. Each individual substrate 10 has an upper wiring 12 a and a lower wiring 12 b formed on the upper surface and the lower surface of the core substrate 11, respectively, and the upper wiring 12 a and the lower wiring 12 b are connected by vias 13 penetrating the core substrate 11. . The upper wiring 12a and the lower wiring 12b include pads 14a and 14b for external connection as a part thereof. Except for the pads 14a and 14b, the upper wiring 12a and the lower wiring 12b are covered with solder resist layers 15a and 15b. According to the present invention, the flux 18 is applied to the surface of the lower wiring pad 14b on which the conductive ball 20 is mounted.

  A representative example of the conductive ball mounted on the substrate is a solder ball. However, in the present invention, as other conductive balls, for example, a resin core material coated with a solder material can be used.

  Next, mounting of conductive balls on a substrate according to the present invention will be described with reference to the drawings. Here, an example will be described in which conductive balls are mounted on one side of a substrate on which wiring has been formed on both sides described above with reference to FIG. 1, but in the drawings referred to below, Only the wiring 12b formed on the mounting surface (lower surface), the pad 14b, the solder resist layer 15b, and the flux 18 on the pad 14b are shown, and the other members are not shown. In the drawings referred to in the following description, a substrate having two individual substrates to be separated after mounting the conductive ball is shown.

  As shown in FIG. 2A, a mask 21 having a through-hole 25 into which one conductive ball enters at a position corresponding to each pad 14b is positioned on a substrate to be processed in which two individual substrates 10 are combined. The substrates are held by the holding device 31 with the side on which the masks 21 are stacked facing down. The substrate holding device 31 can hold the substrate from above by suction or mechanical holding means (for example, a clamp).

  The substrate held by the holding device 31 is placed above the conductive ball receiving container 32 that contains the conductive balls 22 and is open at the top. The illustrated conductive ball container 32 is designed so that the open area of the upper portion corresponds to the area of one individual substrate 10, and the conductive balls are mounted on each individual substrate 10. It is also possible to design so that the balls are simultaneously mounted on a plurality of individual substrates or all the individual substrates of the assembly.

  The conductive ball container 32 is connected to a conductive ball throwing device 33 for throwing the ball 22 upward in order to supply the ball 22 so as to adhere to the flux 18 on the surface of the pad 12b of the individual substrate 10. ing.

  Next, as shown in FIG. 2B, the throwing device 33 is operated to raise the container 32 rapidly. When the upper end of the throwing stroke is reached, the ball 22 is thrown upward from the container 32. A part of the thrown ball 22 enters the through hole 25 of the mask 21 and adheres to the flux 18. When the throwing device 33 shifts to the lowering operation, the container 32 moves downward, and the ball 22 that did not adhere to the flux 18 falls back into the container 32. This operation is repeated until the ball 22 enters all the through holes 25 and adheres to the flux 18. Subsequently, with respect to another individual substrate 10, the ball is repeatedly thrown until the ball 22 enters all the through holes 25 and adheres to the flux 18.

The conductive ball 22 is mounted at a temperature equal to or lower than the melting point of the conductive ball 22 (usually normal temperature).
The ball mounting device including the substrate holding device 31, the conductive ball container 32, and the conductive ball throwing device 33 can be placed in the atmosphere. The ball mounting device may be placed under reduced pressure or in an atmosphere filled with an inert gas, thereby preventing dust from adhering to the substrate and oxidation of the pad or the conductive ball.

The holding device 31 holding the substrate may be moved up and down in accordance with the throwing-up operation of the ball 22 by the throwing device 33 so as to reduce the impact when the ball 22 hits the substrate 10. Thereby, damage to the substrate 10 or the conductive ball 22 can be prevented.
Although only one throwing device 33 is shown in FIGS. 2 (a) and 2 (b), a plurality of ball throwing devices 33 are provided for one substrate 10 on which a ball is mounted, and the throwing operations are alternately performed. May be performed. Thereby, production efficiency can be improved.

  In the process of mounting the conductive ball by throwing up, the ball 22 that did not adhere to the flux 18 falls and returns to the container 32, but some of the balls 22 remain on the mask 21 as shown in FIG. There is. In some cases, the ball 22 may remain attached to the substrate 10. The balls 22 remaining on the mask 21 and the substrate 10 can be collectively removed after the mounting of the balls on all the individual substrates 10 is completed. For this purpose, a method of blowing the air on the mask or the substrate by blowing air, removing it by suction with a suction head, or removing it with a brush can be used. Alternatively, the holding device 31 (FIGS. 2A and 2B), the substrate 10, and the mask 21 may be impacted and removed by dropping excess balls attached to the mask 21 or the substrate 10. .

  The conductive ball throwing device 33 that allows the conductive ball to be thrown up by moving the container 32 up and down with a predetermined stroke, used in the present invention, for example, enables a cam mechanism and a piston movement. The ball can be thrown up by using a cylinder. If the stroke of the throwing device 33 for moving the container 32 for throwing the ball is long, the operation time becomes long and the production efficiency is lowered. If the stroke is short, the ball does not rise to a sufficient height. Therefore, the stroke of the throwing device 33 can be generally 0.5 to 1000 mm, preferably 10 to 50 mm. If the cycle of the throwing operation by the throwing device 33 is long, the operation time becomes long and the production efficiency is lowered. If the cycle is short, the load (power) of the device becomes large. Therefore, the cycle of the throwing operation by the throwing device 33 is generally 0.01 to 20 times per second (0.01 to 20 Hz), preferably 0.1 to 10 times per second (0.1 to 10 Hz). ). By such a throwing-up operation, the balls 22 in the container 32 can be collectively supplied upward toward the substrate. For this reason, even if it is a board | substrate which formed the pad with the high-density pattern, a conductive ball can be mounted in a short time.

  On the other hand, when a ball is mounted on a substrate by applying vibration to the container in which the ball is placed and floating the ball as described in Patent Document 2, the vibration period is generally about 100 to 150 Hz and the amplitude is less than 150 μm. It is. The balls move randomly and rise evenly, but the raised balls collide with each other. Therefore, when the pad pattern has a high density, it is difficult to supply the balls to predetermined pads. Further, if the amount of balls in the container is increased, the balls cannot be levitated.

  In the example described above, for the purpose of ensuring that the thrown ball 22 adheres to the flux 18 of each pad 14b, the through hole 25 into which one conductive ball enters the position corresponding to each pad 14b is provided. The mask 21 having it was used by being aligned with the substrate. The mask 21 may be placed away from the substrate 10. In this case, the mask 21 is fixed to the substrate 10 or the holding device 31 (FIGS. 2A and 2B) so that the relative position with respect to the substrate 10 does not shift. In some cases, such a mask can be provided on the conductive ball container 32 side. An example in which conductive balls are mounted on the substrate 10 using the conductive ball storage container 32 provided with the mask 21 is shown in FIGS. It is also possible to omit the use of a mask.

  The substrate on which the ball is mounted is taken out from the ball mounting device, and the ball is reflowed. By heating by the reflow process, the ball is melted and fixed to the pad.

  The following examples further illustrate the invention.

[Comparative example]
Using the method described in Patent Document 2, the ball is levitated and mounted on a circuit board provided with 4000 pads (applied with a flux) having a diameter of 90 μm at a pitch of 150 μm and mounted on the board. Three types of Sn / Ag solder balls of 80 μm and 100 μm were mounted. At the time of mounting, masks having opening diameters of 80 μm, 100 μm, and 120 μm were used in an overlapping manner on the mounting surface of the substrate according to each diameter of the solder balls. After mounting the ball on the substrate by vibrating the container containing the solder ball for 10 seconds at an amplitude of 100 Hz and 100 μm, the number of pads on which the ball was not mounted (the ball did not adhere to the flux) was examined.

〔Example〕
The same experiment as the comparative example was repeated, except that the solder ball was thrown upward according to the present invention and mounted on the substrate. The solder balls were thrown up at a cycle of 2 times per second (2 Hz) and a stroke of 20 mm. The throwing time was 10 seconds as in the comparative example.

  Table 1 shows the results of the comparative example and the example.

  As is apparent from this result, according to the present invention, the conductive ball can be reliably mounted on the substrate in a short time.

It is a schematic diagram explaining the example of the board | substrate which mounts an electroconductive ball. It is a figure explaining the example of the electroconductive ball mounting to the board | substrate by this invention. It is a figure explaining the ball | bowl which remained on the mask after electroconductive ball mounting. It is a figure explaining another example of electroconductive ball mounting to the board | substrate by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 Core substrate 12a Upper wiring 12b Lower wiring 13 Via 14a, 14b Pad 15a, 15b Solder resist layer 18 Flux (adhesive)
20, 22 Conductive ball 21 Mask 25 Mask through-hole 32 Conductive ball container 33 Conductive ball throwing device

Claims (11)

A method of mounting a conductive ball on a substrate having a pad,
A step of placing a substrate having a pad coated with an adhesive with the surface of the pad facing down and containing a conductive ball, above an open container;
The process of moving the container upward at a predetermined stroke and rapidly raising it, throwing out the conductive balls in the container all at once, and attaching it to the adhesive applied to the pad,
Repeating the step of attaching the conductive ball by throwing out until the conductive ball adheres to the adhesive of all pads,
A conductive ball mounting method comprising mounting a conductive ball by the method described above.   The conductive ball mounting method according to claim 1, wherein a movement stroke of the container is 0.5 to 1000 mm.   The method for mounting a conductive ball according to claim 1 or 2, wherein a pitching cycle of the conductive ball is 0.01 to 20 times per second.   The method for mounting a conductive ball according to any one of claims 1 to 3, wherein a mask having a through-hole into which one conductive ball enters at a position corresponding to each pad is used.   The conductive ball mounting method according to claim 4, wherein the mask is used while being overlapped on a surface of the substrate on which the conductive ball is mounted.   The method for mounting a conductive ball according to claim 1, wherein each of the steps is performed under reduced pressure or in an atmosphere filled with an inert gas.   The method for mounting a conductive ball according to any one of claims 1 to 6, wherein the substrate is moved up and down in accordance with a throwing-up operation of the conductive ball. The conductive balls remaining on the substrate after the mounting of the conductive balls on the substrate are removed by blowing air onto the substrate, suction by a suction head, or brushing off by a brush. The conductive ball mounting method according to any one of Items 1 to 7. A device for mounting a conductive ball on a substrate having a pad,
A conductive ball container with an open top,
A substrate holding device for holding a substrate having a pad coated with an adhesive, with the surface of the pad facing downward, above the conductive ball container;
The conductive ball storage container is moved upward with a predetermined stroke and rapidly raised, so that the conductive balls in the container are collectively thrown upward and adhered to the adhesive applied to the pad of the substrate. Conductive ball throwing device,
A conductive ball mounting apparatus comprising: The conductive ball mounting device according to claim 9 , wherein the conductive ball throwing device moves the container with a stroke of 0.5 to 1000 mm. The conductive ball mounting device according to claim 9 or 10 , wherein the conductive ball throwing device moves the container at a cycle of 0.01 to 20 times per second.

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