JP4118283B2 - Solder ball mounting method and solder ball mounting apparatus - Google Patents

Description

The present invention relates to a solder ball mounting method and a solder ball mounting apparatus for mounting solder balls to be solder bumps on a printed wiring board.

Solder bumps are used for electrical connection between the package substrate and the IC chip. The solder bump is formed by the following process.
(1) A step of printing flux on connection pads formed on the package substrate.
(2) A step of mounting solder balls on connection pads on which flux is printed.
(3) A step of reflowing to form solder bumps from the solder balls.

In the process of mounting the solder balls on the connection pads described above, for example, the printing technique disclosed in Patent Document 1 is used. In this printing technique, as shown in FIG. 12A, a ball alignment mask 116 provided with an opening 116a is placed on the printed wiring board 30 at a position facing the connection pad 75, and a squeegee 124 is used to solder the solder balls 78s. Was dropped on the connection pad 75.
JP 2001-267331 A

As ICs are highly integrated, the solder bumps on the package substrate are required to be further reduced in diameter and pitch. For this reason, the solder balls have a smaller diameter than sand grains having a diameter of less than 200 μmΦ, and the method of using the above-described ball alignment mask and squeegee together causes variations in the height of the solder bumps, resulting in a reduction in quality.

That is, when the diameter of the solder ball is reduced, the weight ratio with respect to the surface area is reduced, and the phenomenon of adsorption of the solder ball due to intermolecular force occurs. In the prior art, solder balls that tend to agglomerate are sent in contact with the squeegee, so that the solder balls are damaged and some of them are chipped. If a part of the solder ball is missing, the volume of the solder bump differs on each connection pad, so that the height of the solder bump varies as described above. If there is a solder bump having a small volume, thermal stress concentrates on the solder bump, resulting in a decrease in connection reliability.

Further, the surface of the printed wiring board is not flat. In particular, the build-up multilayer wiring board has large surface irregularities. When the ball alignment mask is placed on the printed wiring board, a recessed portion is formed in the ball alignment mask along the unevenness of the printed wiring board. When a solder ball having a diameter of less than 200 μmΦ is handled, the squeegee 124 cannot follow the depression on the ball alignment mask 116 having a depression as shown in FIG. It will be pushed and crushed, making it difficult to carry. Even if the squeegee is made of a soft material for this measure, as shown in FIG. 12C, the tip portion of the squeegee 124 is bent, and the solder ball 78s enters and is crushed. Thus, with the method using a squeegee, it has become difficult to mount a solder ball having a diameter of less than 200 μmΦ on the connection pad with a normal solder volume.

An object of the present invention is to provide a solder ball mounting method and a solder ball mounting device capable of reliably mounting a solder ball having a diameter of less than 200 μmΦ on a connection pad.

To achieve the above object, the invention of claim 1 uses a ball alignment mask having a plurality of openings corresponding to connection pads of a printed wiring board, and mounts solder balls to be solder bumps on the connection pads of the printed wiring board. A solder ball mounting method for
A cylindrical member having an opening facing the ball alignment mask is positioned above the ball alignment mask, and air is sucked by the cylindrical member, whereby a solder ball is placed on the ball alignment mask immediately below the cylindrical member. Collect
By moving the cylindrical member in the horizontal direction, the solder balls assembled on the ball alignment mask are moved, and the solder balls are dropped onto the connection pads of the printed wiring board through the openings of the ball alignment mask. Is a technical feature.

The invention of claim 2 is a solder ball mounting device for mounting a solder ball to be a solder bump on a connection pad of a printed wiring board,
A ball alignment mask having a plurality of openings corresponding to connection pads of the printed wiring board;
A cylindrical member that is located above the ball alignment mask and collects solder balls directly under the opening by sucking air from the opening;
A moving mechanism for moving the cylindrical member in a horizontal direction, and moving the solder ball assembled on the ball alignment mask by moving the cylindrical member, through the opening of the ball alignment mask, And a moving mechanism for dropping the solder ball onto the connection pad of the printed wiring board.

The invention of claim 3 is a solder ball mounting device for mounting a solder ball to be a solder bump on a connection pad of a printed wiring board,
A ball alignment mask having a plurality of openings corresponding to connection pads of the printed wiring board;
A cylindrical member that is located above the ball alignment mask and collects solder balls directly under the opening by sucking air from the opening;
A moving mechanism for moving the cylindrical member in a horizontal direction, and moving the solder ball assembled on the ball alignment mask by moving the cylindrical member, through the opening of the ball alignment mask, A moving mechanism for dropping the solder ball onto the connection pad of the printed wiring board, and the clearance between the lower end of the opening of the cylindrical member and the ball alignment mask is set to the front-rear direction and the left-right direction with respect to the moving direction of the cylindrical member. The technical feature is that the direction is different.

According to an eighth aspect of the present invention, there is provided a ball alignment mask having a plurality of openings corresponding to connection pads in a connection pad area of a printed wiring board, and mounting solder balls to be solder bumps on the connection pads of the printed wiring board. A solder ball mounting method,
A cylindrical member having a lower end of an opening whose clearance with the ball alignment mask is different in the front-rear direction and the left-right direction with respect to the moving direction is positioned above the ball alignment mask, and air is sucked by the cylindrical member. The solder balls are assembled on the ball alignment mask immediately below the cylindrical member, and the solder balls assembled on the ball alignment mask are moved by moving the cylindrical member in the horizontal direction, thereby aligning the balls. The technical feature is that the solder ball is dropped onto the connection pad of the printed wiring board through the opening of the mask for use.

According to the solder ball mounting method of claim 1, the solder ball mounting device of claim 2, and the solder ball mounting method of claim 8, the cylindrical member is positioned above the ball alignment mask, and from the opening of the cylindrical member Solder balls are gathered by sucking air, and the cylindrical member is moved in the horizontal direction, so that the gathered solder balls are moved on the ball alignment mask, and solder is passed through the openings of the ball alignment mask. Drop the ball onto the connection pad on the printed circuit board. For this reason, a fine solder ball can be reliably mounted on all the connection pads of the printed wiring board. Further, since the solder ball is moved in a non-contact manner, unlike the case of using a squeegee, it can be mounted on the connection pad without damaging the solder ball, and the height of the solder bump can be made uniform. Furthermore, a solder ball can be appropriately placed on a connection pad even on a printed wiring board having a large undulation on the surface, such as a build-up multilayer wiring board. In addition, since the solder balls do not aggregate due to non-contact, one solder ball can be reliably mounted on the connection pad.

The solder ball mounting apparatus according to claim 3 and the solder ball mounting method according to claim 8, wherein the clearance between the opening at the lower end of the cylindrical member and the ball alignment mask is in the front-rear direction and the horizontal direction with respect to the moving direction of the cylindrical member. Therefore, the force applied to the solder ball from four directions (front and rear, left and right) is uneven due to the airflow flowing through the clearance. For this reason, the collision frequency between the solder balls decreases in the cylindrical member assembled by the air flow, and the solder balls easily fall into the opening of the ball alignment mask. In addition, chipping of solder balls is reduced and the solder bump volume is likely to be stable.

In the solder ball mounting device according to claim 4, the clearance between the opening at the lower end of the cylindrical member and the ball alignment mask is wider than the clearance on the left and right in the moving direction of the cylindrical member. As the cylinder member moves, it can be moved back and forth in the direction of travel. That is, the solder ball moves with the movement of the cylindrical member, but when the cylindrical member changes from the stationary state to the moving state, first, the solder ball is once after the relative position is changed to the rear side from the central position of the cylindrical member. The airflow from the rear overtakes the center position and comes to the front. Then, it goes to the rear side by the airflow from the front. That is, as the cylindrical member moves, the solder ball moves back and forth and back and forth in the direction of travel from the central position of the cylindrical member, and easily falls into the opening of the ball alignment mask.

In the solder ball mounting device according to claim 5, since the opening of the cylindrical member is substantially rectangular, the solder balls are assembled into a rectangular shape, and the solder ball is efficiently mounted on the connection pad in the connection pad region having a substantially rectangular shape. can do.

In the solder ball mounting device according to the sixth aspect, since the plurality of cylindrical members are arranged in correspondence with the width of the printed wiring board, the solder balls can be reliably secured only by feeding the plurality of cylindrical members in the direction perpendicular to the column direction. It can be mounted on all connection pads on the printed wiring board. Here, the connection pad region is a region of 75A in FIG. 8A and includes a connection pad located on the outermost periphery, and is a rectangular region having the smallest area. As shown in FIG. 8B, x and y in the case where the connection pads 75 are not arranged in a rectangular shape are set so that the rectangular area of the connection pad region 75A is minimized including the outermost connection pads. To do.

In the solder ball mounting device according to the seventh aspect, since the solder balls remaining on the ball alignment mask can be collected by the suction cylinder, the surplus solder balls remain and do not cause troubles such as failure.

First, the structure of the multilayer printed wiring board 10 manufactured using the solder ball mounting method and mounting apparatus according to the embodiment of the present invention will be described with reference to FIGS. 6 shows a cross-sectional view of the multilayer printed wiring board 10 and FIG. 7 shows a state in which the IC chip 90 is attached to the multilayer printed wiring board 10 shown in FIG. As shown in FIG. 6, in the multilayer printed wiring board 10, conductor circuits 34 are formed on both surfaces of the core substrate 30. The top surface and the back surface of the core substrate 30 are connected via a through hole 36.

Furthermore, a conductor circuit 58 for forming a conductor circuit layer is formed on the conductor circuit 34 of the core substrate 30 via an interlayer resin insulating layer 50. The conductor circuit 58 is connected to the conductor circuit 34 via the via hole 60. A conductor circuit 158 is formed on the conductor circuit 58 via an interlayer resin insulation layer 150. Conductor circuit 158 is connected to conductor circuit 58 via via hole 160 formed in interlayer resin insulation layer 150.

A solder resist layer 70 is formed above the via hole 160 and the conductor circuit 158. By providing the nickel plating layer 72 and the gold plating layer 74 in the opening 71 of the solder resist layer 70, the connection pad 75 is formed. ing. A solder bump 78U is formed on the upper connection pad 75, and a BGA (ball grid array) 78D is formed on the lower connection pad 75.

 As shown in FIG. 7, the solder bumps 78 </ b> U on the upper surface side of the multilayer printed wiring board 10 are connected to the lands 92 of the IC chip 90. On the other hand, the lower BGA 78D is connected to the land 96 of the daughter board 94.

FIG. 8A is a plan view of a multi-layer printed wiring board 10A for multi-cavity. The multilayer printed wiring board 10A is separated by cutting the individual multilayer printed wiring board 10 including the connection pad region 75A along a dashed line in the drawing. FIG. 5 is an explanatory diagram of the process of forming solder bumps on the multi-layer printed wiring board 10A for multi-cavity, and corresponds to the Y1-Y1 cross-sectional view in FIG. As shown in FIG. 5A, the flux 80 is printed on the surface of the multilayer printed wiring board 10A in which the connection pads 75 are formed in the openings 71 of the solder resist layer 70 on the surface. As shown in FIG. 5B, a small solder ball 78s (for example, manufactured by Hitachi Metals, Tamura, diameter 40 μmΦ or more is used on a connection pad 75 on the upper side of the multilayer printed wiring board 10A by using a solder ball mounting device described later. , Less than 200 μm). Solder balls with a diameter of less than 200 μm are desirable for finer processing. If the diameter is less than 40 μmΦ, the solder ball is too light and does not fall on the connection pad. On the other hand, if the diameter exceeds 200 μmΦ, the solder balls cannot be assembled in the cylindrical member because they are too heavy, and there are connection pads on which the solder balls are not placed. In the present invention, it is highly significant to use a solder ball having a diameter of 40 μmΦ to less than 200 μmΦ. In this range, it is advantageous for refinement. Further, in the method in which the solder ball is sucked by the suction head and the solder ball is mounted on the connection pad, since the solder ball is small and difficult to be sucked, the superiority of the method of the embodiment becomes clear.

Thereafter, as shown in FIG. 5C, a solder ball 78L having a normal diameter (diameter: 250 μm) is formed on the connection pad 75 on the lower side of the multilayer printed wiring board 10A by a suction head according to a conventional technique (for example, Japanese Patent No. 1975429). Is adsorbed and placed. Thereafter, it is heated in a reflow furnace, and as shown in FIG. 6, for example, 500 to 30000 solder bumps 78U with a pitch of 60 μm or more and less than 200 μm on the upper side of the multilayer printed wiring board 10A (corresponding to the number of connection pads), lower side For example, 250 BGAs 78D are formed at a pitch of 2 mm. In particular, when the number of connection pads is 2000 or more, the connection pad area becomes large, and therefore, the significance of applying the method of the present invention is high. This is because the bump height is stable due to non-contact, and solder bumps with low height are unlikely to be generated, so that a printed wiring board with high connection reliability can be obtained. When the pitch is less than 60 μm, it becomes difficult to manufacture solder balls suitable for the pitch. When the pitch is 200 μm or more, the present method can be produced without any problem, but it can also be produced by a conventional method. Further, as shown in FIG. 7, after the multi-layer multilayer printed wiring board 10A is cut into individual multilayer printed wiring boards 10, the IC chip 90 is mounted via the solder bumps 78U by reflow. The multilayer printed wiring board 10 on which the IC chip 90 is mounted is attached to the daughter board 94 via the BGA 78D.

With reference to FIG. 5, a solder ball mounting apparatus for mounting a small (less than 200 μm diameter) solder ball 78s on the connection pad of the multilayer printed wiring board described above with reference to FIG.
FIG. 1A is a configuration diagram showing a configuration of a solder ball mounting device according to an embodiment of the present invention, and FIG. 1B is a diagram illustrating the solder ball mounting device of FIG. FIG.

The solder ball mounting device 20 includes an XYθ suction table 14 that positions and holds the multilayer printed wiring board 10A, a vertical movement shaft 12 that raises and lowers the XYθ suction table 14, and an opening that corresponds to the connection pad 75 of the multilayer printed wiring board. A ball alignment mask 16, a mounting cylinder (cylinder member) 24 for guiding a solder ball moving on the ball alignment mask 16, a suction box 26 for applying a negative pressure to the mounting cylinder 24, and excess solder balls are collected. A suction ball removing cylinder 61, a suction box 66 for applying a negative pressure to the suction ball removing cylinder 61, a suction ball removing suction device 68 for holding the collected solder balls, and a mask clamp for clamping the ball alignment mask 16 44, an X direction moving shaft 40 for sending the mounting cylinder 24 and the suction ball removing cylinder 61 in the X direction, and an X direction moving shaft 40 are supported. A moving shaft support guide 42, an alignment camera 46 for imaging the multilayer printed wiring board 10, a remaining amount detection sensor 18 for detecting the remaining amount of solder balls under the mounting cylinder 24, and a remaining amount detection sensor 18. A solder ball supply device 22 for supplying the solder balls to the mounting cylinder 24 based on the detected remaining amount. In the solder ball mounting apparatus 20 shown in FIG. 1, only the X-direction moving shaft 40 for sending the mounting cylinder 24 and the suction ball removing cylinder 61 in the X direction is shown, but a moving mechanism for sending in the Y direction can also be provided.

As shown in the plan view of FIG. 8 (A), the mounting cylinder 24 and the suction ball removing cylinder 61 of the solder ball mounting apparatus 20 are placed on the individual connection pad regions 75A on the multi-layer printed wiring board 10A for multi-piece taking. A plurality of them are arranged in the Y direction in correspondence. Here, one mounting cylinder 24 corresponds to one connection pad area 75A, but the mounting cylinder 24 may be sized to correspond to a plurality of connection pad areas 75A. Here, the Y direction is convenient and may be arranged in the X direction. The XYθ suction table 14 positions, sucks, holds, and corrects the multilayer printed wiring board 10 on which the solder balls are mounted. The alignment camera 46 detects the alignment mark of the multilayer printed wiring board 10 on the XYθ suction table 14, and the positions of the multilayer printed wiring board 10 and the ball alignment mask 16 are adjusted based on the detected position. The remaining amount detection sensor 18 detects the remaining amount of solder balls by an optical method.

Next, a solder ball mounting process by the solder ball mounting apparatus 20 will be described with reference to FIGS.
(1) Position Recognition and Correction of Multilayer Printed Wiring Board As shown in FIG. 2 (A), the alignment mark 34M of the multi-layer printed wiring board 10A for picking multiple pieces is recognized by the alignment camera 46, and the ball alignment mask 16 is detected. Then, the position of the multilayer printed wiring board 10A is corrected by the XYθ suction table 14. That is, the positions of the openings 16a of the ball alignment mask 16 are adjusted so as to correspond to the connection pads 75 of the multilayer printed wiring board 10A.

(2) Solder Ball Supply As shown in FIG. 2B, the solder ball 78s is quantitatively supplied from the solder ball supply device 22 to the mounting cylinder 24 side. In addition, you may supply in a mounting cylinder previously.

(3) Solder ball mounting As shown in FIG. 3A, a predetermined clearance (for example, 0.5 to 4 times the ball diameter) with the ball alignment mask is maintained above the ball alignment mask 16. By positioning the mounting cylinder 24 and sucking air from the suction part 24b, the flow velocity of the gap between the mounting cylinder and the printed wiring board is set to 5 m / sec to 35 m / sec, and the mounting cylinder 24 is directly below the opening 24A. Solder balls 78 s were assembled on the ball alignment mask 16.

Thereafter, as shown in FIGS. 3 (B), 4 (A), and 8 (A), the multilayer printed wiring boards 10A shown in FIGS. 1 (B) and 1 (A) are arranged along the Y-axis. The mounting cylinder 24 is sent in the horizontal direction along the X axis via the X direction moving shaft 40. As a result, the solder balls 78s assembled on the ball alignment mask 16 are moved along with the transfer of the mounting cylinder 24, and the solder balls 78s are moved through the openings 16a of the ball alignment mask 16 to the multilayer printed wiring board 10A. Drop and mount on the connection pad 75. Thereby, the solder balls 78s are sequentially aligned on all the connection pads on the multilayer printed wiring board 10A side.

(4) Removal of Adhering Solder Balls As shown in FIG. 4B, after the surplus solder balls 78s are guided to the position without the openings 16a on the ball alignment mask 16 by the mounting cylinder 24, the suction ball removing cylinder 61 is used. Remove by suction.

(5) Removing the multilayer printed wiring board 10A from the XYθ suction table 14 for removing the board.

According to the solder ball mounting method and the solder ball mounting apparatus 20 of the present embodiment, the mounting cylinder 24 is positioned above the ball alignment mask 16 and air is sucked from the suction portion 24B of the mounting cylinder 24, thereby solder balls. 78s are assembled and the mounting cylinder 24 is sent in the horizontal direction, so that the assembled solder balls 78s are moved on the ball alignment mask 16, and the solder balls 78s are moved through the openings 16a of the ball alignment mask 16. It is dropped onto the connection pad 75 of the multilayer printed wiring board 10A. For this reason, the fine solder balls 78s can be surely mounted on all the connection pads 75 of the multilayer printed wiring board 10A. Further, since the solder ball 78s is moved in a non-contact manner, unlike the case of using a squeegee, the solder ball can be mounted on the connection pad 75 without scratching, and the height of the solder bump 78U can be made uniform. For this reason, it is excellent in environmental resistance tests such as mountability of electronic components such as IC, heat cycle test after mounting, and high temperature / high humidity test. Furthermore, since it does not depend on the flatness of the product, it is possible to appropriately place the solder balls on the connection pads even on a printed wiring board having many undulations on the surface. In addition, since a small solder ball can be surely placed on a connection pad, even in a printed wiring board having a connection pad pitch of 60 to 150 μm and a solder resist opening diameter of 40 to 100 μm, all bumps are bumps. A solder bump having a stable height can be obtained.

Further, since the solder balls are guided by the suction force, the solder balls can be prevented from aggregating and adhering. Furthermore, by adjusting the number of mounting cylinders 24, it is possible to cope with workpieces of various sizes (worksheet-sized multilayer printed wiring boards), so that it can be flexibly applied to various types and small-scale production. Is possible.

In the solder ball mounting apparatus of the present embodiment, as shown in FIG. 1B, a plurality of mounting cylinders 24 are arranged in the Y direction corresponding to the width of the work (multilayer printed wiring board having a work sheet size). By only sending the mounting cylinder 24 in the direction perpendicular to the row direction (X direction), the solder balls can be reliably mounted on all the connection pads 75 of the multilayer printed wiring board 10A.

Further, since the solder ball 78s remaining on the ball alignment mask 16 can be collected by the suction ball removing cylinder 61, an excessive solder ball remains and does not cause a failure such as a failure.

[Example 1]
(1) Preparation of printed wiring board A double-sided copper-clad laminate (for example, MCL-E-67 manufactured by Hitachi Chemical Co., Ltd.) was used as a starting material, and through-hole conductors and conductor circuits were formed on this substrate by a well-known method. . Thereafter, interlayer insulation layers and conductor circuit layers are alternately laminated by a well-known method (for example, “Build-Up Multilayer Printed Wiring Board” published by Nikkan Kogyo Shimbun on June 20, 2000). In the conductor circuit layer, a connection pad area consisting of 120 μmφ, 150 μm pitch, 50 × 50 (lattice arrangement) for electrical connection with the IC was formed, and a commercially available solder resist was formed on the connection pad region. An opening of Φ90 μm was formed on the pad by a photographic method, where the connection pad made of a via hole (a solder bump is formed immediately above the via hole) is preferably a filled via, and the amount of depression and projection (see FIG. 13). ) Is preferably in the range of −5 to 5 μm with respect to the conductor thickness of the conductor circuit 158. If the recessed amount of the filled via exceeds 5 μm (−5 μm), the solder ball and the filled Since the number of contact points of the connection pad made of solder is reduced, the wettability is deteriorated when the solder bump is formed, and a void is easily caught in the solder or is not mounted (missing bump). Since the thickness of the is increased, it is not suitable for finer.
A commercially available solder resist was formed thereon (film thickness 20 μm), and an opening of 90 μmφ was formed in the solder resist on the connection pad by photographic method in order to expose the connection pad.

(2) Solder ball mounting (1) A commercially available rosin flux was applied to the surface (IC mounting surface) of the printed wiring board. Thereafter, the printed circuit board was mounted on the suction table of the solder ball mounting apparatus of the present invention described above, the alignment marks of the printed wiring board and the ball alignment mask were recognized using a CCD camera, and the printed wiring board and the ball alignment mask were aligned. Here, as the ball alignment mask, a Ni metal mask having an opening of 110 μmφ at a position corresponding to the connection pad of the printed wiring board was used. The thickness of the metal mask is preferably 1/4 to 3/4 of the solder ball. Although a Ni metal mask is used here, a ball alignment mask made of SUS or polyimide can also be used. The opening diameter formed in the ball alignment mask is preferably 1.1 to 1.5 times the diameter of the ball used. Next, a mounting tube made of SUS having a size corresponding to the connection pad region (1.1 to 4 times the region where the connection pad is formed) and a height of 200 mm is 0.5 to 0.5 times the solder ball diameter. A Sn63Pb37 solder ball (manufactured by Hitachi Metals Co., Ltd.) having a ball diameter of 80 μm was placed on the ball alignment mask in the vicinity of the periphery of the metal mask (ball alignment mask) while maintaining a 4-fold clearance.

In the first embodiment, Sn / Pb solder is used for the solder balls, but Pb-free solder selected from the group of Sn and Ag, Cu, In, Bi, Zn, or the like may be used. And air was attracted | sucked from the mounting cylinder upper part, the flow rate of the clearance gap between a mounting cylinder and a printed wiring board was adjusted to 5-35 m / sec, and it aggregated in the mounting cylinder. Thereafter, the mounting ball was sent at a moving speed of 10 to 40 mm / sec to move the solder ball, and the solder ball was dropped from the opening of the ball alignment mask to mount the solder ball on the connection pad. Next, after removing excess solder balls from the ball alignment mask, the solder ball alignment mask and the printed wiring board were separately removed from the solder ball mounting apparatus. Finally, the printed wiring board on which the solder balls were mounted in the above (2) was put into a reflow set at 230 degrees to form solder bumps.

[Example 2]
Next, Example 2 will be described with reference to FIGS. In the first embodiment described above, the clearance (gap) between the lower end opening 24O of the mounting cylinder 24 and the alignment mask 16 is formed constant. On the other hand, in the second embodiment, the clearance differs between the front-rear direction and the left-right direction with respect to the moving direction of the mounting cylinder 24. 9A is a front view of the mounting cylinder 24 as viewed from the direction of travel, FIG. 9B is a side view, and FIG. 9C is a plan view of the mounting cylinder 24 as viewed from above. . The mounting cylinder 24 is configured in a cubic shape, and Gap1 between the front wall 24F and the rear wall 24R on the front side in the traveling direction and the ball alignment mask 16 has a right wall 24r and a left wall on the left and right in the traveling direction. It is configured to be larger than Gap2 between 24l and the ball alignment mask 16. That is, the right wall 24r and the left wall 24l are configured to extend below the front wall 24F and the rear wall 24R.

FIG. 10A is a schematic diagram for explaining the movement of the solder ball when the clearance of the mounting cylinder is the same in the front-rear and left-right directions. As shown in FIG. 10 (A), when the clearance of the mounting cylinder is the same in the front and rear, right and left, the force applied to the solder ball group 78G from four directions (front and rear, left and right) by the airflow flowing through the clearance becomes uniform. The frequency of collision between the solder balls is increased in the mounting cylinder 24 gathered by the airflow, particularly at the center position, and it is difficult to fall into the mask opening 16a.

FIG. 10B is a schematic diagram for explaining the movement of the solder ball when the clearance of the mounting cylinder in the second embodiment is different between front and rear and left and right. If the clearance is different in the front-rear direction and the left-right direction, the force applied to the solder ball group 78G from four directions (front-rear, left-right) due to the airflow flowing through the clearance becomes non-uniform, and the inside of the mounting cylinder 24 gathered by the airflow As a result, the frequency of collision between the solder balls decreases, and the solder balls easily fall into the mask openings 16a. As a result of the measurement, it was found that the wind speed flowing in through the front and rear clearances and the wind speed flowing in through the left and right clearances hardly change. In other words, depending on the clearance, the wind speed hardly changed, but the air volume changed and the work volume changed.

As shown in FIG. 9C, the front and rear clearances of the mounting cylinder 24 should be wider than the left and right clearances. When the front-rear clearance is wide with respect to the left and right, the solder ball can be moved back and forth with respect to the traveling direction in the mounting cylinder 24 as the mounting cylinder 24 moves. That is, as shown in FIG. 9 (C1), when the mounting cylinder 24 is stationary, the solder balls are gathered at the center of the mounting cylinder, but when the mounting cylinder 24 is moved to the left in the figure, the mounting cylinder 24 is mounted. Since the solder ball group 78G moves behind the movement of the cylinder 24, first, the relative position of the solder ball group 78G temporarily changes from the center position of the mounting cylinder 24 to the rear side as shown in FIG. Thereafter, the solder ball group 78G passes the center position by the airflow from the rear and comes to the front side (FIG. 10 (C3)). Furthermore, it goes to the rear side by the airflow from the front. That is, as the mounting cylinder 24 moves, the solder ball group 78G moves back and forth and back and forth from the center position of the mounting cylinder 24 in the traveling direction, and easily falls into the opening 16a of the mask.

In the solder ball mounting apparatus of the second embodiment, since the opening of the mounting cylinder 24 has a substantially rectangular shape, the solder balls are assembled as a substantially rectangular solder ball group 78G as shown in FIG. A) A solder ball can be efficiently mounted on each connection pad 75 in the substantially rectangular connection pad region 75A shown in FIG. In addition, in the solder ball mounting apparatus 20 of the second embodiment, the opening of the mounting cylinder 24 is formed in a substantially rectangular shape. However, the front and rear clearances and the left and right clearances can be made different in a cylindrical shape or an elliptical shape. .

[Evaluation test of Example 1]
Hereinafter, a comparison test is performed between the solder bump manufactured by the solder ball mounting method of the first embodiment having the same clearance between the front and rear and the left and right of the mounting cylinder 24 and the solder bump manufactured by the conventional method (Comparative Example 1). The results will be described.
[Comparative example]
The comparative example is the same as that of Example 1 except that the method of supplying the solder balls to the connection pads is changed.
That is, a solder ball was sent using a squeegee using a conventional method, and the solder ball was dropped from an opening for mounting the ball, and the solder ball was mounted on the connection pad.

[Evaluation test]
After the reflow, 50 bump heights on the solder resist were randomly measured with a laser microscope VX-8500 manufactured by KEYENCE Corporation. In the comparative example, there was a connection pad (missing bump) in which no bump was mounted on the connection pad. Missing bumps were excluded from the measurement.

[result]
Bump height Bump height variation Example 1 35.22 μm 1.26
Comparative Example 32.64 μm 4.18
From this result, it can be seen that even when the same solder balls are used, the bump height is high and the variation in bump height is small in Example 1 of the present invention. This is because in the first embodiment, since the solder ball is not scraped off by a squeegee or the like, the volume of the initial solder ball is maintained and mounted on the connection pad.

In addition, 500 printed wiring boards obtained in Example 1 and the comparative example were prepared and an IC was mounted. The continuity check of the IC mounting substrate was performed and the mounting yield was determined. The result was 90% for the printed wiring board of Example 1 and 3% for the comparative example. After that, 10 samples from each non-defective product are taken at random, and a heat cycle test of −55 × 5 minutes × 125 × 5 minutes is performed 1000 times, from the back side of the printed wiring board (opposite side to the IC mounting side) through the IC. The amount of change in connection resistance of a specific circuit connected to the back surface of the printed wiring board was measured again. The amount of change in the connection resistance is ((connection resistance after heat cycle−initial connection resistance) / initial connection resistance) × 100. When this value exceeds 10%, it becomes defective.
Number of defects Non-defective product example 1 0 100%
Comparative Example 100%
From this result, in Example 1, since the variation in bump height is small, it can be seen that the connection reliability in the bump is high. On the other hand, in the method of the comparative example, the non-defective product that can guarantee the reliability is 0%.

[Evaluation test of Example 2]
Hereinafter, the solder ball mounting method of the second embodiment having different clearances before and after the mounting cylinder 24 described above with reference to FIGS. 9 and 10, the solder ball mounting method of the first embodiment having the same clearance, and the prior art The results of a comparison test with the solder bump manufactured by the above method (comparative example described above) will be described.

[Example 1-1]
In Example 1-1, the mounting cylinder 24 was prepared according to Example 1 with Gap1 before = Gap1 after = 0.15 mm and Gap2 right = Gap2 left = 0.15 mm (Gap1 = Gap2). Here, front, rear, right, and left are front and rear and left and right with respect to the traveling direction of the mounting cylinder.

[Example 1-2]
In Example 1-2, the mounting cylinder 24 was prepared according to Example 1 with Gap1 before = Gap1 after = 0.2 mm and Gap2 right = Gap2 left = 0.2 mm (Gap1 = Gap2).

[Example 2-1]
In Example 2-1, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.18 mm and Gap2 right = Gap2 left = 0.15 mm (Gap1 = 1.2 × Gap2).

[Example 2-2]
In Example 2-2, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.225 mm and Gap2 right = Gap2 left = 0.15 mm (Gap1 = 1.5 × Gap2).

[Example 2-3]
In Example 2-3, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.3 mm and Gap2 right = Gap2 left = 0.15 mm (Gap1 = 2 × Gap2).

[Example 2-4]
In Example 2-4, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.6 mm and Gap2 right = Gap2 left = 0.15 mm (Gap1 = 4 × Gap2).

[Example 2-5]
In Example 2-5, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.24 mm and Gap2 right = Gap2 left = 0.2 mm (Gap1 = 1.2 × Gap2).

[Example 2-6]
In Example 2-6, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.4 mm and Gap2 right = Gap2 left = 0.2 mm (Gap1 = 2 × Gap2).

[Example 2-7]
In Example 2-7, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.75 mm and Gap2 right = Gap2 left = 0.25 mm (Gap1 = 3 × Gap2).

[Example 2-8]
In Example 2-8, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 1.2 mm and Gap2 right = Gap2 left = 0.3 mm (Gap1 = 4 × Gap2).

[Example 2-9]
In Example 2-9, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = 0.18 mm, Gap1 after = 0.2 mm, Gap2 right = 0.15 mm, and Gap2 left = 0.14 mm.

[Example 2-10]
In Example 2-10, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = 0.4 mm, Gap1 after = 0.45 mm, Gap2 right = 0.2 mm, and Gap2 left = 0.15 mm.

[Example 2-11]
In Example 2-11, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 = 0.06 mm and Gap2 right = Gap2 left = 0.04 mm (Gap1 = 1.5 × Gap2).

[Example 2-12]
In Example 2-12, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.1 mm and Gap2 right = Gap2 left = 0.08 mm (Gap1 = 1.25 × Gap2).

[Example 2-13]
In Example 2-12, the mounting cylinder 24 was prepared according to Example 2 with Gap1 before = Gap1 after = 0.08 mm and Gap2 right = Gap2 left = 0.1 mm (Gap1 = 0.8 × Gap2).

(Evaluation Test 1)
500 printed wiring boards with solder balls of each example were prepared and an IC was mounted. The continuity check of the IC mounting substrate was performed, and the mounting yield was obtained. The results are shown in the chart in FIG. In the comparative example, only 3% of good products could be obtained. From this result, it is possible to increase the yield by making the front and rear clearances of the mounting cylinder 24 different from the left and right clearances. In particular, by making the front and rear clearances larger than the left and right clearances, the yield can be increased to 100. It was found that it can be increased up to%.

(Evaluation test 2)
In addition, a heat cycle test of −55 × 5 minutes × 125 × 5 minutes was performed on the printed wiring board (N = 10) obtained in Example 1 and Example 2 and Comparative Example, which were non-defective products in the continuity check test. The measurement was performed 1000 times, and the amount of change in connection resistance of a specific circuit connected from the back surface of the printed wiring board (the surface opposite to the IC mounting surface) to the back surface of the printed wiring board through the IC was measured. The amount of change in the connection resistance is ((connection resistance after heat cycle−initial connection resistance) / initial connection resistance) × 100. If this value is less than ± 3%, it is a non-defective product (in FIG. 11: ◯), 3% to 10% or −3% to −10% is an acceptable product (in FIG. 11: Δ), and other than that (over 10%, or (Less than −10%) was defined as defective (in FIG. 11: x). From this result, it has been clarified that the electrical characteristics can be improved by making at least one of the front, rear, left and right clearances of the mounting cylinder 24 different. It is presumed that this is because the solder ball chipping is reduced and the solder bump volume is stabilized by reducing the collision frequency of the solder balls. In addition, when Gap1 / Gap3 is 3 or less, the air volume is appropriate, so that chipping due to collision between solder balls is reduced, and it is estimated that electrical characteristics (connection reliability) can be improved.

[Comparative Example 2]
In Comparative Example 2, solder bumps were formed using solder paste instead of solder balls in Example 1.

The height of the solder bumps of Example 1 and Comparative Example 2 (height protruding from the solder resist) was measured with a WYKO “NT2000” manufactured by Beco Co., Ltd., and the variation (σ) was calculated. The results were as follows.
σ
Example 1 1.26
Comparative Example 2 2.84

Further, an IC was mounted on the printed wiring boards of Example 1 and Comparative Example 2, and an underfill was filled between the IC and the printed wiring board to obtain an IC-mounted printed wiring board. Thereafter, the connection resistance of a specific circuit connected to the back surface of the IC-mounted printed wiring board from the back surface (the side opposite to the IC mounting surface) of the IC-mounted printed wiring board was measured again as an initial value. After the initial value measurement, the sample was left in an atmosphere of 85 ° C. × 80% for 15 hours, and then a heat cycle test with one cycle of −55 ° C. × 5 minutes to 125 ° C. × 5 minutes was repeated 1000 times, and the connection resistance was measured again. We measured the connection reliability. The amount of change in connection resistance is represented by ((connection resistance value after heat cycle−initial connection resistance value) / initial connection resistance value) × 100, and if the value is within ± 10%, it is acceptable. Beyond that, it is bad. As a result, Example 1 was “pass” and Comparative Example 2 was “bad”.

FIG. 1A is a configuration diagram showing a configuration of a solder ball mounting device according to an embodiment of the present invention, and FIG. 1B is a diagram illustrating the solder ball mounting device of FIG. FIG. FIG. 2A is an explanatory diagram of positioning of the multilayer printed wiring board, and FIG. 2B is an explanatory diagram of supply of solder balls to the mounting cylinder. FIG. 3A is an explanatory diagram of a set of solder balls by a mounting cylinder, and FIG. 3B is an explanatory diagram of a set of solder balls by a mounting cylinder and guidance. FIG. 4A is an explanatory view of the dropping of the solder ball onto the connection pad, and FIG. BB is an explanatory view of the removal of the solder ball by the suction ball removing cylinder. 5 (A), 5 (B), and 5 (C) are explanatory diagrams of the manufacturing process of the multilayer printed wiring board. It is sectional drawing of a multilayer printed wiring board. It is sectional drawing which shows the state which attached the IC chip to the multilayer printed wiring board shown in FIG. 6, and mounted in the daughter board. FIG. 8A is a plan view of a multi-layer multilayer printed wiring board, and FIG. 8B is a plan view of another example of the connection pad region. FIG. 9A, FIG. 9B, and FIG. 9C are explanatory views of the clearance between the mounting cylinder and the alignment mask in the second embodiment. FIG. 10A is a schematic diagram for explaining the movement of the solder ball when the clearance of the mounting cylinder is equal between the front and rear and the left and right, and FIG. 10B is the front and rear clearances of the mounting cylinder in Example 2. FIGS. 10C to 10C are schematic diagrams for explaining the movement of the solder ball when the mounting cylinder is larger than the front-rear clearance and the left-right clearance. It is. It is a graph which shows the evaluation result of Example 2 and a comparative example. 12 (A), 12 (B), and 12 (C) are schematic views showing mounting of solder balls using a conventional ball alignment mask. It is explanatory drawing of the uneven | corrugated amount of a filled via.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printed wiring board 12 Vertical moving shaft 14 XY (theta) suction table 16 Ball alignment mask 16a Opening 20 Solder ball mounting apparatus 22 Solder ball supply apparatus 24 Mounting cylinder (cylinder member)
26 Suction box 40 X direction moving shaft 42 Moving shaft support guide 46 Alignment camera 61 Suction ball removal cylinder 66 Suction box 68 Suction ball removal suction device 75 Connection pad 78s Solder ball 80 Flux Gap1 Front and rear clearance Gap2 Left and right clearance

Claims (8)

A solder ball mounting method for mounting a solder ball to be a solder bump on a connection pad of a printed wiring board using a ball alignment mask having a plurality of openings corresponding to the connection pads of the printed wiring board,
A cylindrical member having an opening facing the ball alignment mask is positioned above the ball alignment mask, and air is sucked by the cylindrical member, whereby a solder ball is placed on the ball alignment mask immediately below the cylindrical member. Collect
By moving the cylindrical member in the horizontal direction, the solder balls assembled on the ball alignment mask are moved, and the solder balls are dropped onto the connection pads of the printed wiring board through the openings of the ball alignment mask. A solder ball mounting method characterized by comprising: A solder ball mounting device for mounting a solder ball to be a solder bump on a connection pad of a printed wiring board,
A ball alignment mask having a plurality of openings corresponding to connection pads of the printed wiring board;
A cylindrical member that is located above the ball alignment mask and collects solder balls directly under the opening by sucking air from the opening;
A moving mechanism for moving the cylindrical member in a horizontal direction, and moving the solder ball assembled on the ball alignment mask by moving the cylindrical member, through the opening of the ball alignment mask, And a moving mechanism for dropping the solder ball onto the connection pad of the printed wiring board. A solder ball mounting device for mounting a solder ball to be a solder bump on a connection pad of a printed wiring board,
A ball alignment mask having a plurality of openings corresponding to connection pads of the printed wiring board;
A cylindrical member that is located above the ball alignment mask and collects solder balls directly under the opening by sucking air from the opening;
A moving mechanism for moving the cylindrical member in a horizontal direction, and moving the solder ball assembled on the ball alignment mask by moving the cylindrical member, through the opening of the ball alignment mask, A moving mechanism for dropping the solder ball onto the connection pad of the printed wiring board, and the clearance between the lower end of the opening of the cylindrical member and the ball alignment mask is set to the front-rear direction and the left-right direction with respect to the moving direction of the cylindrical member. Solder ball mounting device, characterized in that it differs depending on the direction. 4. The solder ball mounting device according to claim 3, wherein the clearance in the front-rear direction with respect to the moving direction of the opening of the cylindrical member is made larger than the clearance in the left-right direction. The solder ball mounting device according to claim 3 or 4, wherein the opening of the cylindrical member has a substantially rectangular shape. 6. The solder ball mounting device according to claim 2, wherein a plurality of the cylindrical members are arranged corresponding to the width of the printed wiring board. 7. The solder ball mounting apparatus according to claim 2, further comprising a suction cylinder for collecting the solder balls remaining on the ball alignment mask. A solder ball mounting method for mounting a solder ball to be a solder bump on a connection pad of a printed wiring board using a ball alignment mask having a plurality of openings corresponding to the connection pads in the connection pad area of the printed wiring board ,
A cylindrical member having a lower end of an opening whose clearance with the ball alignment mask is different in the front-rear direction and the left-right direction with respect to the moving direction is positioned above the ball alignment mask, and air is sucked by the cylindrical member. The solder balls are assembled on the ball alignment mask immediately below the cylindrical member, and the solder balls assembled on the ball alignment mask are moved by moving the cylindrical member in the horizontal direction, thereby aligning the balls. A solder ball mounting method comprising dropping a solder ball onto a connection pad of a printed wiring board through an opening of a mask for use.

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