JP5948633B2 - Solder ball mounting method - Google Patents

Description

  The present invention relates to a solder ball mounting method for mounting a solder ball on a semiconductor element connection pad in a wiring board for mounting a semiconductor element.

  2. Description of the Related Art Conventionally, for example, a wiring board for mounting a semiconductor element by flip-chip connection has a mounting portion on which the semiconductor element is mounted at the center of the upper surface. A large number of semiconductor element connection pads to which the electrode terminals of the semiconductor element are connected via solder are formed on the mounting portion. By connecting the semiconductor element connection pads and the electrode terminals of the semiconductor element via solder, A semiconductor element is mounted on the wiring board. The semiconductor element connection pads are formed from, for example, a copper plating layer having a thickness of several to several tens of μm, and several tens to several thousands of the pads are exposed to a circular shape having a diameter of about 50 to 100 μm. Are arranged on the mounting portion in a grid pattern with a pitch of.

  In such a wiring board, a solder bump having a diameter of about 50 to 100 μm is formed on the semiconductor element connection pad in order to easily and surely connect the semiconductor element connection pad and the electrode terminal of the semiconductor element via solder. Generally, it is welded in advance. As a method for welding a solder bump on a semiconductor element connection pad, a method is often used in which a small solder ball corresponding to the volume of the solder bump is mounted on the semiconductor element connection pad and the solder ball is welded by heating and melting. Has been.

  As a method for mounting the solder ball on the semiconductor element connection pad of the wiring board, a method using a solder ball mounting mask is generally used. The mask is generally made of a thin flat plate made of stainless steel, and has an opening that can accommodate one solder ball at a position corresponding to the semiconductor element connection pad. Then, the mask is positioned and placed on the wiring board so that the opening of the mask is positioned on the semiconductor element connection pad of the wiring board, and solder balls are supplied onto the mask by, for example, spraying or the like. Then, the solder balls are mounted on the semiconductor element connection pads by removing the remaining solder balls from the mask.

  However, it is difficult to mount the solder balls on all the semiconductor element connection pads only by supplying the solder balls on the mask by spraying or the like. This is because the number of semiconductor element connection pads on the wiring board ranges from several hundred to several thousand, and is densely arranged at a narrow pitch of several tens to several hundreds μm. Therefore, it is difficult in terms of probability to drop the solder balls into all the openings of the mask corresponding to the semiconductor element connection pads arranged in large numbers at these narrow pitches. Furthermore, the case where the solder ball is stuck in the opening of the mask due to the influence of static electricity and does not fall on the semiconductor element connection pad of the wiring board may occur.

  In Japanese Patent Application Laid-Open No. 2009-272529, after spraying solder balls on the mask, the remaining solder balls are removed from the mask with a rotating brush, and then the solder balls in the opening of the mask are connected to the wiring board with a pressing brush. A method of pressing to the side has been proposed. However, according to this method, the remaining solder balls on the mask are removed by the rotating brush. Therefore, when the solder balls in the mask opening are pressed by the pressing brush, the solder balls are not accommodated in the opening. There is no opportunity for solder balls to enter. Further, when the solder ball is not projected from the upper surface of the mask and is caught in the middle of the opening, the solder ball cannot be sufficiently pressed by the pressing brush and the solder ball is placed on the semiconductor element connection pad. It may not be installed.

JP 2009-272529 A

  An object of the present invention is to provide a solder ball mounting method capable of mounting solder balls on a semiconductor element connection pad of a wiring board at a high mounting rate.

According to the solder ball mounting method of the present invention, one solder ball is disposed on the upper surface of the wiring board having a plurality of semiconductor element connection pads to which the electrodes of the semiconductor element are connected, each at a position corresponding to the semiconductor element connection pad. A first step of placing a flat solder ball mounting mask having an opening capable of accommodating a solder ball and placing a large number of solder balls close to one end on the mask; The rotating squeegee that moves while sweeping the solder ball by rotating the solder ball forward in the direction from the one end side toward the other end side in a direction that sweeps the solder ball forward about a rotation axis parallel to the upper surface of the mask. a second step of leaving a portion of the remainder of the solder balls with on drop in the opening of the solder balls in a state of being dispersed on the mask, the upper mask the solder balls are dispersed Rotation that moves from the other end side toward the one end side while rotating the solder balls forward in the direction of sweeping the solder balls forward about a rotation axis parallel to the upper surface of the mask. A third step of dropping the solder ball into the opening by a squeegee and leaving a part of the remaining solder ball in a dispersed state on the mask; and the other end on the mask in which the solder ball is dispersed And a fourth step of scraping the remaining solder balls toward the one end side by a recovery squeegee that moves while pushing the solder balls on the mask from the side toward the one end side. .

According to the solder ball mounting method of the present invention, in the second step, the solder ball placed close to one end on the mask is directed from one end to the other end of the mask and parallel to the upper surface of the mask. A rotating squeegee that moves while sweeping and rolling the solder balls forward about the rotation axis drops them into the mask opening and leaves a part of the remaining solder balls dispersed on the mask. Then, in the third step, the solder ball dispersed on the mask is directed from the other end side to the one end side, and the dispersed solder ball is rotated forward about the rotation axis parallel to the upper surface of the mask. The solder ball is dropped into the opening by a rotating squeegee that moves while pressing the solder ball, and a part of the remaining solder ball is left dispersed on the mask. In fourth step, the solder balls can scrape the solder balls remaining on the one end side of the mask by the collecting squeegee moving while forces the solder balls on the mask toward the upper mask dispersed from the other end side to one end side Thus, not only in the second step, but also in the third and fourth steps, an opportunity is given for the solder ball to enter the opening in which the solder ball is not accommodated. Therefore, the solder balls are accommodated in the openings of the mask with a very high probability. Even if the solder ball is caught in the middle of the opening of the mask, the remaining solder ball dispersed on the mask moves the solder ball in the opening by the movement of the recovery squeegee in the fourth step. By pressing downward from above, the solder balls caught in the middle of the opening can be reliably dropped onto the semiconductor element connection pads of the wiring board. Therefore, it is possible to mount the solder balls on the semiconductor element connection pads of the wiring board at an extremely high mounting rate.

1A to 1E are schematic cross-sectional views for each process for explaining an example of an embodiment of a solder ball mounting method of the present invention. FIGS. 2A and 2B are schematic views showing a squeegee unit of a rotating squeegee and a recovery squeegee used in an example of an embodiment of the solder ball mounting method of the present invention.

  Next, an example of an embodiment of the solder ball mounting method of the present invention will be described with reference to the accompanying drawings. FIG. 1A to FIG. 1E are schematic cross-sectional views for each process for explaining an example of an embodiment of the solder ball mounting method of the present invention. In FIG. 1, 1 is a wiring board, 2 is a mask, 7 is a rotating squeegee, and 8 is a recovery squeegee. FIG. 2 is a schematic diagram of a squeegee unit U used for the rotary squeegee 7 and the recovery squeegee 8.

  First, as shown in FIG. 1A, a wiring board 1 and a solder ball mounting mask 2 are prepared. The wiring substrate 1 is formed by, for example, a well-known build-up method, and has a large number of semiconductor element connection pads 3 at the center of the upper surface thereof. The semiconductor element connection pads 3 have a circular shape with a diameter of about 50 to 100 μm, and several tens to several thousand pieces are arranged in a grid-like arrangement at a pitch of 100 to 200 μm. The mask 2 is made of a stainless steel flat plate having a thickness of 50 to 120 μm, and is attached to the lower surface of the stainless steel frame 5. In the mask 2, a large number of openings 4 having a diameter of about 70 to 140 μm are formed at positions corresponding to the semiconductor element connection pads 3 of the wiring substrate 1, and the lower surface of the region facing the semiconductor element connection pads 3 is formed on the mask 2. It is laid down to a depth of 30-50 μm. In this example, only one wiring board 1 is shown for simplicity, but in reality, a plurality of wiring boards 1 are integrally formed vertically and horizontally in a panel for the wiring board. It is prepared in the form of a single-piece wiring board.

  Next, as shown in FIG. 1B, the mask 2 is placed on the wiring substrate 1 so that the semiconductor element connection pads 3 and the corresponding openings 4 overlap each other when viewed from above. A large number of 10 to 20 million solder balls 6 are arranged close to one end of the upper surface of 2. The solder balls 6 have a diameter of about 50 to 120 μm and have a substantially uniform diameter so that each of the solder balls 6 is accommodated in the opening 4. In addition, it is preferable to apply a viscous flux on the semiconductor element connection pad 3 before mounting the mask 2.

  Next, as shown in FIG. 1 (c), the solder ball 6 is moved into the opening 4 by a rotating squeegee 7 that moves while pressing the solder ball 6 on the mask 2 from one end side to the other end side. Drop it. At this time, a part of the remaining solder balls 6 remains in a dispersed state on the mask 2 behind the rotating squeegee 7. As a result, the solder balls 6 are accommodated in most of the openings 4. Then, as shown in FIG. 1D, the same operation is performed from the other end side on the mask 2 toward the one end side. As a result, the accommodation rate of the solder balls in the opening 4 is further improved, and a part of the remaining solder balls 6 remains dispersed on the mask 2.

  The rotary squeegee 7 has a structure in which a plurality of squeegee units U are mounted around a rotation axis parallel to the upper surface of the mask 2, and moves while rotating in the direction of sweeping the solder ball 6 forward around the rotation axis. To do. As shown in FIG. 2A, the squeegee unit U constituting the rotary squeegee 7 is constructed by attaching a stainless steel squeegee wire W to a stainless steel support block B so as to have a semi-cylindrical arrangement. As shown in FIG. 2B, the squeegee wire W has a width of about 40 mm and a number of wires having a width of about 0.1 mm by etching a thin stainless steel ribbon having a thickness of about 0.1 mm. Are arranged obliquely at intervals of 0.1 to 0.2 mm so as to have an angle of about 10 degrees with respect to the long side direction of the ribbon. The angle of the squeegee wire W with respect to the long side direction of the ribbon is arranged so that the adjacent squeegee units U are opposite to each other. The rotating squeegee 7 can adjust the sweeping condition of the solder balls 6 according to the number of rotations. Specifically, when the rotational speed of the rotary squeegee 7 is increased, the solder balls 6 can be swept out so that no solder balls 6 remain behind. On the contrary, when the rotational speed is decreased, the solder balls 6 are dispersed behind the rotational squeegees 7. It can be swept out to remain.

  Next, as shown in FIG. 1 (e), the solder balls 6 on the mask 2 are pushed from the other end side of the mask 2 toward the one end side over the mask 2 where the solder balls 6 are dispersed and left. The remaining solder ball 6 is scraped toward one end of the mask 2 by the moving recovery squeegee 8. The recovery squeegee 8 is formed by arranging a plurality of squeegee units U similar to the rotary squeegee 7 in a row. At this time, if there is an opening 4 in which the solder ball 6 is not accommodated, the movement of the recovery squeegee 8 gives an opportunity for the solder ball 6 on the mask 2 to enter the opening 4. Therefore, the solder ball 6 is accommodated in the opening 4 of the mask 2 with a very high probability by this operation. Further, even if the solder ball 6 accommodated in the opening 4 due to the movement of the rotating squeegee 7 is caught in the middle of the opening 4 due to the influence of static electricity or the like, one end of the mask 2 is moved by the movement of the recovery squeegee 8. Since the remaining solder ball 6 pushed to the side presses the solder ball 6 caught in the opening 4 downward from above, the solder ball 6 caught in the middle of the opening 4 is placed on the semiconductor element connection pad 3 of the wiring board 1. Can be reliably dropped. Therefore, according to the solder ball mounting method of the present invention, it is possible to mount the solder balls 6 on the semiconductor element connection pads 3 of the wiring board 1 at an extremely high mounting rate. Also in the recovery squeegee 8, the angle of the squeegee wire W with respect to the long side direction of the ribbon is arranged so that the adjacent squeegee units U are opposite to each other.

  Next, examples of the present invention will be described. First, a 23 mm square wiring substrate in which 1012 semiconductor element connection pads having a diameter of 85 μm are arranged in a staggered arrangement of 45 rows vertically and horizontally at a pitch of 128 μm at the center of the upper surface is 295 mm vertically and 245 mm horizontally. A multi-piece wiring board was prepared which was integrally formed in an array of 12 rows vertically and 10 rows horizontally in the panel for wiring board. In addition, a stainless steel mask having a circular opening having a diameter of 113 μm at a position corresponding to the semiconductor element connection pad of each wiring board in the multi-piece wiring board was prepared. The mask had a thickness of 87 μm, a length of 730 mm, and a width of 730 mm. In addition, the mask was provided with a counterbore with a depth of 42 μm on the lower surface of the multi-piece wiring board facing the region where the semiconductor element connection pads of each wiring board were formed.

  Next, these multi-cavity wiring boards and masks are set in a microball mounting machine HB-07SB manufactured by Hitachi Plant Technology Co., Ltd. so that the corresponding openings of the mask are positioned on the respective semiconductor element connection pads of the wiring board. did. This microball mounting machine HB-07SB includes a table for placing a multi-piece wiring board and a holding mechanism for holding a mask, and the rotating squeegee and the recovery squeegee described above as a short side of the mask. It is provided to extend in a parallel direction. These squeegees have dimensions that are larger than the width of the multi-piece wiring substrate in a direction parallel to the short side of the mask and narrower than the width of the mask, and move in a direction parallel to the long side of the mask. Note that a viscous flux was previously applied to a thickness of 20 μm on each semiconductor element connection pad of the multi-piece wiring board.

  Next, about 20 million solder balls having a diameter of 90 μm are formed on one end of the long side direction on the mask, and a mountain having a height of about 10 mm is formed in a slightly wider range in the short side direction of the mask than the squeegee size. So as to be arranged like a band.

  Next, the rotating squeegee is rotated at a rate of 35 mm / s while rotating the rotating squeegee at a rate of 20 revolutions per minute in the direction of sweeping out the solder balls. By moving the solder ball toward the side, the solder ball was dropped into the opening of the mask, and the solder ball was leveled so that a part of the remaining solder ball remained dispersed on the mask behind the rotating squeegee. Further, in the same operation, the rotary squeegee was moved and reciprocated once while pushing the solder balls from one end side to the other end side in the long side direction of the mask. Due to these operations, a part of the remaining solder balls remained substantially uniformly dispersed on the mask through which the rotating squeegee passed.

  Next, the recovery squeegee is moved at a speed of 100 mm per second so that the solder ball on the mask is pushed in the direction of travel from the other end side in the long side direction of the mask toward the one end side. The solder balls were mounted on each semiconductor element connection pad by scraping to one end side in the long side direction.

  Next, the multi-piece wiring board is taken out from the microball mounting machine, and whether or not the solder ball is placed on each semiconductor element connection pad is inspected by an automatic inspection using an image recognition device. The ratio of the semiconductor element connection pads not mounted with was determined.

  In addition, for comparison, the rotational speed of the rotating squeegee was rotated at a speed of 35 revolutions per minute while moving at a speed of 70 mm per second, and the soldering balls were smoothed so that no solder balls remained on the mask behind the rotating squeegee. Similarly, when the solder balls are mounted, the ratio of the semiconductor element connection pads on which the solder balls are not mounted is obtained.

  As a result, in the comparative method, the ratio of the semiconductor element connection pads on which the solder balls are not mounted was 94 ppm, whereas in the embodiment of the present invention, the ratio was significantly improved to 7 ppm. It was confirmed that it was possible to mount solder balls on the connection pads at an extremely high mounting rate.

DESCRIPTION OF SYMBOLS 1 Wiring board 2 Mask 3 Semiconductor element connection pad 4 Opening part 6 Solder ball 7 Rotating squeegee 8 Recovery squeegee

Claims (1)

On the upper surface of the wiring board having a plurality of semiconductor element connection pads to which electrodes of the semiconductor element are connected, an opening capable of accommodating one solder ball at each position corresponding to the semiconductor element connection pad is provided. A first step of placing a flat solder ball mounting mask and placing a large number of solder balls on one end side of the mask, and on the mask from the one end side to the other end side The solder ball is dropped into the opening by a rotating squeegee that rotates in a direction that sweeps the solder ball forward about a rotation axis parallel to the upper surface of the mask and pushes the solder ball. a second step of leaving a portion of the remainder of the solder balls in a state of being dispersed on the mask toward the upper mask the solder balls is dispersed to the one end from the other end The solder ball is dropped into the opening by a rotating squeegee that rotates in the direction of sweeping the dispersed solder balls forward about a rotation axis parallel to the upper surface of the mask and moves the solder balls. A third step of leaving a part of the remaining solder balls in a state of being dispersed on the mask, and the mask on which the solder balls are dispersed on the mask from the other end side toward the one end side. And a fourth step of scraping the remaining solder ball toward the one end side by a recovery squeegee that moves while pushing the solder ball.

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