JP2004311524A - Bump flattening device, bump flattening method, and bump bonding unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a large number of gold bumps formed on a substrate, such as a wafer or the like, to be shaped well and made uniform in height. <P>SOLUTION: The wafer 40 where the bumps are provided on its top surface is placed on a mounting stand 16, the heads of the gold bumps on the wafer 40 are pressed down with the lower end of a rotating roller 18, and the mounting stand 16 is horizontally and relatively moved to the rotating roller 18. At this point, the mounting stand 16 is moved at such a speed that the relative speed of the mounting stand 16 to the lower part of the rotating roller 18 becomes nearly zero. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a bump flattening apparatus and method for aligning bumps formed on a substrate, and a bump bonding apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a method of forming projecting electrodes called bumps on a plurality of electrodes on a semiconductor element and connecting and mounting the electrodes on the semiconductor element and the electrodes on a wiring board. The bump is formed by attaching a metal in a molten state to an electrode on a semiconductor element. Then, the semiconductor element is attached to the wiring board so that the bumps and the electrodes on the wiring board are connected to each other, thereby electrically connecting them.
[0003]
In order to make such a connection, it is desirable that the heads of the bumps have the same height. This is because if the heights of the bumps are not uniform, connection failure occurs in some of the electrodes. Further, it is desirable that the upper surface (crushed surface) is substantially circular and that the bump itself does not fall down. When the crushed surface of the bump has an elliptical shape, the crushed surface, which is the contact surface, protrudes from the electrode of the wiring board, which causes a short circuit or poor contact. Further, when the bumps fall down, there is a problem that the position of the crushed surface, which is the contact surface with the wiring board, is shifted. For this reason, conventionally, bump flattening has been performed in which the heights of the bumps are uniformly adjusted after the bumps are formed.
[0004]
For example, Patent Document 1 discloses a bump flattening apparatus in which a semiconductor element on which a plurality of bumps are formed is pressed by a pressing member having a pressing surface to make the height of the bump uniform. Thereby, the heights of the plurality of bumps on the semiconductor element can be made uniform. However, the apparatus disclosed in Patent Literature 1 has a problem that flattening can be performed only in units of semiconductor elements singulated from a wafer. In other words, after bumps are formed in the state of a wafer, they are singulated, taken out for each semiconductor element, and bump flattened. As a result, the entire process becomes complicated, and the production time of the semiconductor device is prolonged.
[0005]
Here, a technique of enlarging the pressing surface of the pressing member in Patent Literature 1 and flattening the entire wafer can be considered. However, a large number of bumps are formed on the entire wafer, and a very large pressing force is required to press all of them. A bump flattening apparatus having such a pressing force is large and expensive, and is not practical.
[0006]
As a solution to this problem, Patent Document 2 discloses a method of pressing a bump by moving a roller on a wafer on which the bump is formed. As described above, the bump can be pressed with a small force by moving while partially pressing the roller.
[0007]
[Patent Document 1]
JP 2000-40766 A [Patent Document 2]
Japanese Patent Publication No. Hei 7-93305
[Problems to be solved by the invention]
However, the method described in Patent Literature 2 has a problem that the shape of the bump is easily crushed. That is, when the roller is moved while being partially pressed by the roller, not only a vertical downward pressing force on the head of the bump but also a force in the moving direction of the roller is applied. For this reason, the bump head is flattened, but is simultaneously pulled in the moving direction, and the crushed surface tends to have an elliptical shape. In addition, the bumps themselves tend to fall down. In that case, as described above, various problems such as a short circuit and displacement occur.
[0009]
In view of the above, an object of the present invention is to provide an apparatus and a method capable of forming a flat bump on a substrate on which a large number of bumps are formed, such as a wafer.
[0010]
[Means for Solving the Problems]
The bump flattening apparatus of the present invention includes a mounting table for mounting a substrate having a plurality of bumps disposed on an upper surface, a rotating roller for pressing a head of the bump on the substrate at a lower end, and a rotation for rotating the rotating roller. A driving mechanism and a horizontal movement mechanism for horizontally moving the mounting table relative to the rotary roller are provided, and the lower end of the rotary roller and the mounting table are relatively almost stationary.
[0011]
Therefore, the roller can be moved while applying only a vertically downward pressing force to the bump head on the substrate. Thereby, the heights of the heads of the bumps formed on a substrate having a large area such as a wafer can be made uniform.
[0012]
Here, the substrate is preferably a wafer, but may be, for example, a semiconductor element having a large number of bumps formed thereon. The material of the bump to be flattened is preferably a gold bump, but may be another material. Further, the horizontal moving mechanism may move any of the mounting table and the rotating roller as long as the mounting table is relatively moved with respect to the rotating roller. Further, to make the lower end portion of the rotating roller and the mounting table relatively relatively stationary means to make the moving speed and direction of the rotating roller and the mounting table uniform.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0014]
FIG. 1 shows a block diagram of a bump flattening apparatus 10 according to an embodiment of the present invention. This is roughly divided into an apparatus main body 12 and a control unit 14 thereof.
[0015]
The apparatus main body 12 includes a mounting table 16 on which the wafer 40 is mounted, a rotating roller 18 and a peripheral mechanism thereof. The mounting table 16 is provided with a moving unit 20 including a horizontal moving mechanism 26, a vertical moving mechanism 22, and a rotating mechanism 24. The mounting table 16 can be moved horizontally, vertically and rotationally by the driving force transmitted from the moving unit 20. The position, angle and moving speed of the mounting table 16 are detected by the respective detectors 28 and 30 and output to the control unit 14 described later. The control unit 14 calculates and outputs a signal for drive control to the mobile unit 20 based on the output information.
[0016]
The rotary roller 18 is provided with a roller drive mechanism 32 for driving the rotary roller 18 to rotate, and is driven based on a signal from a drive control device 38. The rotation speed of the rotation roller 18 is detected by the speed detector 34 and output to the main control unit 36.
[0017]
The control unit 14 mainly includes a drive control device 38 that outputs a drive control signal for the moving unit 20 and the roller drive mechanism 32 and a main control unit 36 that calculates a control value based on information from the speed detectors 30 and 34 and the like. Separated. The main controller 36 records the speed detected by the position / angle detector and the speed detectors 30 and 34, and calculates a control value for drive control based on the information. The calculated value is output to the drive control device 38, and the drive control device outputs a drive control signal to the moving unit 20 and the roller drive mechanism 32 based on the value.
[0018]
The bump flattening device 10 may be a single unit, or may be provided together with or incorporated in a bump bonding device.
[0019]
Next, the apparatus main body 12 of the bump flattening apparatus 10 will be described in detail with reference to FIG. FIG. 2 is a perspective view of the apparatus main body. In the drawings, motors that are attached to each moving mechanism and generate a driving force are not shown.
[0020]
The rotation roller 18 is a rotation roller 18 having a diameter of 50 mm provided above the mounting table 16 and is capable of rotating about an axis in the X direction. The rotation roller 18 is provided with a motor, and the drive control device 38 controls the rotation direction and speed of the motor. Thereby, the rotation direction and the speed of the rotating roller 18 are controlled.
[0021]
The mounting table 16 is a table for mounting and holding the wafer 40, and has a cutout portion 16 a for positioning the wafer 40. When the wafer 40 is placed, the notch 16a is aligned with the orientation flat of the wafer 40. In order to prevent the mounted wafer 40 from shifting, the mounting table 16 has a vacuum suction mechanism, and holds the wafer 40 by its suction force.
[0022]
Further, the mounting table 16 is provided with a rotating mechanism 24 (not shown) so that the mounting table 16 can be rotated 360 degrees in a horizontal plane. The driving of the rotation mechanism is also controlled by the drive control device 38. The rotation angle is detected by the angle detector 28 and is output to the main control unit 36.
[0023]
The vertical movement mechanism 22 includes a sliding member 42 fixed to the mounting table 16, an inclined member 44 provided below the sliding member 42, and a driving unit (not shown) for sliding the sliding member 42 in the Y direction. ing. The upper surface of the inclined member 44 is an inclined surface having a predetermined angle, and the position of the upper surface is higher toward the near side in the drawing. The bottom surface of the sliding member 42 is an inclined surface having the same angle as the inclination of the inclined member 44, and the upper surface of the inclined member 44 can be slid in the Y direction by the driving means. Then, by sliding the sliding member 42 on the upper surface of the inclined member 44, the mounting table 16 fixed to the upper surface of the sliding member 42 can be moved in the vertical direction. The moving distance and direction of the sliding member 42 are controlled by the drive control device 38 so that the height of the mounting table 16 can be adjusted in units of 1 μm.
[0024]
The horizontal moving mechanism 26 is provided below the inclined member 44. This is a moving stage for moving the inclined member 44 in the Y direction by a motor (not shown). By moving the inclined member 44, the mounting table 16 above the inclined member 44 can be moved in the Y direction, that is, the direction perpendicular to the rotating roller 18.
[0025]
In the present embodiment, the mounting table 16 is moved. However, as long as the mounting table 16 is moved relatively to the rotating roller 18, the rotating roller 18 may be moved. For example, the mounting table 16 may be fixed and moving means for moving the rotating roller 18 horizontally and vertically may be provided. In addition, any of the rotation, horizontal, and vertical movement mechanisms may have a configuration other than the above. Further, it is preferred that there be a rotation and up and down movement mechanism, but any of the movement mechanisms may be missing.
[0026]
Next, the gold bump 46 and the wafer 40 to be flattened will be described. On the upper surface of the wafer 40, a large number of shaped gold bumps 46 are provided. As shown in FIG. 3A, the gold bump 46 before bump flattening has a shape such that its head protrudes thinly, and its height h is about 60 μm. However, this height is an approximate numerical value, and the heights of the gold bumps 46 are not uniform as a whole. If the gold bumps 46 are attached to the wiring board in this state, connection failure occurs in some of the gold bumps 46. Therefore, in the bump flattening, as shown in FIG. 3B, the gold bumps 46 are flattened by crushing the thin protrusions of the heads, and the heights thereof are made uniform. At this time, the height h of the gold bump 46 is about 35 μm. That is, about 25 μm is crushed. At this time, it is desirable that the crushed surface 46a, which is the upper surface of the gold bump 46, is substantially circular, and that the gold bump itself does not fall.
[0027]
Incidentally, for example, in an 8-inch wafer 40, when the gold bump 46 is formed at a rate of 1 mm 8 per ^{2 (8bump} / mm ^2), the number of the bumps is approximately 250 000 in the entire wafer 40. If a force of 1N is required to press one of the gold bumps, a force of about 25.5 t is required to press all of them simultaneously on the surface. It can be seen that the bump flattening device having such a pressing force is poor in feasibility. Therefore, as described later, bump flattening is performed by moving while pressing with a roller capable of partially applying a pressing force.
[0028]
Next, a flow of flattening the gold bumps 46 disposed on the upper surface of the wafer 40 using the bump flattening apparatus 10 will be described.
[0029]
When flattening the gold bump 46, first, the wafer 40 is mounted on the mounting table 16. In this case, the mounting table 16 is moved to the lowest position by sliding the sliding member 42. Further, the horizontal moving mechanism 26 is driven to move the mounting table 16 to a position shifted from the rotating roller 18. Then, in this state, the wafer 40 is mounted on the mounting table 16. At this time, the wafer 40 is placed so that the notch 16a provided on the placement table 16 and the orientation flat of the wafer 40 are aligned. The mounted wafer 40 is held by the vacuum suction means provided on the mounting table 16 and its position is prevented from being shifted.
[0030]
Next, the mounting table 16 is rotated by the rotation mechanism, and the angle of the wafer 40 is adjusted. The angle is adjusted so that the rotating roller 18 and the direction in which the gold bumps 46 are arranged intersect. This will be described with reference to FIG. FIG. 4 is a diagram illustrating the wafer 40 and the rotating roller 18 placed on the mounting table 16 as viewed from above. When the rotating roller 18 is set so that the direction in which the gold bumps 46 are arranged is non-parallel, the number of the gold bumps 46 (shown in black in the drawing) pressed by the rotating roller 18 depends on the number of the arranged rotating rollers 18. It can be seen that the number is smaller than the case where the directions are parallel. As described above, approximately 1N is required to press one gold bump 46, and when a large number of gold bumps are pressed, a larger pressing force is required. That is, when the direction of disposition of the rotating roller 18 and the gold bump 46 is parallel, a large pressing force is required. Therefore, the mounting table 16 is rotated by the rotation mechanism so that the rotation roller 18 is in a direction crossing the arrangement direction of the gold bumps 46. Thereby, it can be pressed with a small force.
[0031]
Next, the rotation roller 18 is rotated, and the mounting table 16 is horizontally reciprocated by the horizontal movement mechanism 26. Further, at the time of the reciprocating turn, the mounting table 16 is raised by about 1 μm by sliding the sliding member 42 by a small distance. That is, the mounting table 16 is reciprocated horizontally while gradually reducing the distance between the rotating roller 18 and the mounting table 16. Thus, the head of the gold bump 46 can be gradually pressed.
[0032]
This will be described in more detail with reference to FIG. When the distance is reduced by 1 μm, the rotating roller 18 presses the head of the gold bump 46 by 1 μm. The pressing width d at this time can be expressed by Expression (1), where R is the radius of the rotating roller 18 and p is the rising distance of the mounting table 16.
(Equation 1)
d = √ (2 × p × R−p ² ) (1)
[0033]
Here, in the present embodiment, since the radius of the rotating roller 18 is 25 mm, d is about 220 μm. That is, the pressing surface of the gold bump 46 on the rotating roller 18 at a certain moment has a width of 220 μm, and at this time, the number of pressed gold bumps 46 is about 350 at the maximum under the same conditions as described above. In this case, the required pressing force is about 350N. Thus, bump flattening can be performed with a small pressing force by pressing with a line by the rotating roller 18 instead of pressing with a surface. In addition, since the pressing surface having the minute width is moved by the movement of the mounting table 16, the bump flattening over a wide area such as the wafer 40 can be performed in a short time.
[0034]
In this way, by rotating the rotating roller 18 and horizontally moving the mounting table 16 by the horizontal movement mechanism 26, a wide area of bump flattening can be performed with a small force.
[0035]
Note that, in the present embodiment, the ascending movement is performed by 1 μm, but other values may be used. The rising distance p may be appropriately changed according to the pressing force, the area of the wafer 40, the number of the gold bumps 46, or the flattening speed.
[0036]
Next, the rotation of the rotating roller 18 and the moving speed and direction of the mounting table 16 when pressing are described. The rotation of the rotating roller 18 and the movement of the mounting table 16 at the time of pressing are performed at such a speed and direction that the lower end of the rotating roller 18 and the head of the gold bump 46 are relatively substantially stationary.
[0037]
The rotating roller 18 is rotating at a constant speed, and the horizontal movement of the mounting table 16 means that the gold bump 46 is also horizontally moving at a constant speed. Here, since the rotating roller 18 is sufficiently large with respect to the gold bump 46, the movement of the lower end portion 18a can be regarded as substantially horizontal movement with respect to the gold bump 46. Therefore, when the moving speed of the mounting table 16 is substantially the same as the rotating speed of the rotating roller 18 and the moving direction is the same, the lower end 18 a of the rotating roller 18 is substantially You will be stationary.
[0038]
As described above, when the lower end portion 18a and the head of the gold bump 46 are relatively stationary, only the pressing force in the vertical direction is applied to the gold bump 46. Therefore, the head of the gold bump 46 is not rubbed by the rotating roller 18, and the crushed surface shape of the gold bump 46 is not crushed. That is, when a force in the moving direction is applied to the gold bump 46, the gold bump 46 is pulled in the moving direction as shown in FIG. 6A, and its crushed surface is substantially as shown in FIG. 6B. It becomes an elliptical shape. In some cases, the gold bump itself may fall down as shown in FIG. However, such a problem can be prevented by applying only a vertical pressing force to the gold bump 46.
[0039]
Further, by repeating horizontal movement while gradually reducing the distance between the rotating roller 18 and the mounting table 16, the head of the gold bump 46 can be gradually crushed, and the collapse of the shape of the gold bump 46 is reduced. You. That is, as described above, by making the rotating roller 18 and the mounting table 16 relatively stationary, it is possible to apply a pressing force only in the vertical direction, but in reality, a slight speed difference occurs. At this time, if the crush amount p is large, the influence of the speed difference becomes large. Therefore, the above-described problem occurs, and the crushed surface becomes an elliptical shape, and the gold bump easily falls. When the crushing amount p is large, that is, when the pressing force is large, a pressing force much larger than the reaction force of the gold bump is applied. In that case, the pressing force does not spread over the entire gold bump, and a large pressing force is applied only to the upper surface thereof. As a result, an unstable shape (FIG. 7B) in which only the upper surface (crushed surface) is widened is obtained. As in the present embodiment, if the horizontal movement is repeated while gradually reducing the distance between the rotating roller 18 and the mounting table 16, such various problems can be avoided.
[0040]
As described above, the horizontal movement is repeated while the distance between the rotation roller 18 and the mounting table 16 is gradually reduced. Then, by repeating about 10 to 15 reciprocations, the gold bump 46 having a shape as shown in FIG. 3A is flattened in a good shape as shown in FIG. 3B.
[0041]
At the time of reciprocating turning, not only the vertical movement of the mounting table 16 but also the change of the angle may be performed. That is, the angle between the rotating roller 18 and the direction in which the gold bumps 46 are arranged is changed at the time of folding. This can be changed by rotating the mounting table 16 by a rotation mechanism at the time of turning back. By changing the angle of the rotation roller 18 with respect to the direction in which the rotation roller 18 is disposed, the shape of the crushed surface can be further prevented from becoming elliptical.
[0042]
As described above, it is difficult to establish a state in which the rotating roller 18 and the mounting table 16 are relatively substantially stationary, and as shown in FIG. May be pulled in the direction of movement. This phenomenon occurs particularly remarkably when the amount of crushing is large, that is, when the vertical movement distance is large. At this time, the crushed surface of the gold bump 46 tends to be elliptical as shown in FIG. In order to prevent such a problem, the mounting table 16 is rotated at the time of turning back and forth, and the angle between the rotation roller 18 and the direction in which the gold bumps 46 are arranged is changed for each horizontal movement. Thus, the gold bumps 46 can be pressed from various directions, and can be prevented from being pressed in an elliptical shape.
[0043]
As described above, according to the present embodiment, it is possible to easily flatten a large number of gold bumps 46 arranged in a wide area such as the wafer 40 with good shape.
[0044]
【The invention's effect】
As described above, according to the present invention, bump flattening can be performed on a substrate, such as a wafer, on which a large number of bumps are formed.
[Brief description of the drawings]
FIG. 1 is a block diagram of a bump flattening apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view of an apparatus main body of the bump flattening apparatus.
FIG. 3 is a side view of a gold bump to be flattened.
FIG. 4 is a diagram of a wafer and a rotating roller as viewed from above.
FIG. 5 is a side view of bump flattening.
FIG. 6A is a side view of bump flattening. (B) It is a top view of a gold bump.
FIG. 7A is a side view of a collapsed gold bump. (B) It is a side view of the gold bump which crushed only the upper surface.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 bump flattening device 12 device main body 16 mounting table 18 rotating roller 18a lower end portion 20 moving unit 22 vertical moving mechanism 24 rotating mechanism 26 horizontal moving mechanism 28 position / angle detector 30 speed detector 32 roller drive mechanism 36 main controller 38 Drive control device 40 Wafer 42 Sliding member 44 Inclined member 46 Gold bump

Claims (11)

A mounting table for mounting a substrate on which a plurality of bumps are disposed,
A rotating roller that presses the head of the bump on the substrate at the lower end,
A roller drive mechanism for rotating the rotating roller;
A horizontal moving mechanism for horizontally moving the mounting table relative to the rotating roller;
With
A bump flattening apparatus characterized in that a lower end of a rotating roller and a mounting table are relatively almost stationary. The bump flattening apparatus according to claim 1, further comprising:
A bump flattening device comprising a vertical movement mechanism for vertically moving a mounting table relative to a rotation roller. The bump flattening apparatus according to claim 1 or 2,
The direction of the rotation axis of the rotating roller is a direction crossing the direction in which the bumps are arranged, wherein the flattening device is a bump flattening apparatus. The bump flattening apparatus according to any one of claims 1 to 3, further comprising:
A bump flattening device comprising a rotation mechanism for rotating a mounting table relative to a rotation roller in a horizontal plane. A mounting step of mounting a substrate on which a plurality of bumps are arranged on a mounting table,
A pressing step of rotating the rotating roller pressing the head of the bump on the substrate at the lower end and horizontally moving the mounting table relative to the rotating roller,
Has,
In the pressing step, the lower end of the rotating roller and the mounting table are relatively substantially stationary with respect to the mounting table. It is a bump flattening method of Claim 5, Comprising:
In the pressing step, the direction of the rotation axis of the rotating roller is a direction intersecting with the direction in which the bumps are arranged. The bump flattening method according to claim 5 or 6,
A bump flattening method comprising a plurality of pressing steps having different horizontal moving directions. The bump flattening method according to any one of claims 5 to 7,
A first pressing step having a horizontal movement in a first horizontal movement direction;
A second pressing step having a horizontal movement in a second horizontal movement direction opposite to the first horizontal movement direction;
A bump flattening method, comprising: The bump flattening method according to any one of claims 5 to 8, wherein
A bump flattening method, comprising a plurality of pressing steps in which a distance between a mounting table and a lower end of a rotary roller is different. The bump flattening method according to any one of claims 5 to 9,
A bump flattening method, comprising: a plurality of pressing steps in which an arrangement direction of a bump and an angle formed by a rotating roller are different. A bump bonding apparatus for bonding a bump to a plurality of electrodes on a substrate, further comprising:
A mounting table for mounting a substrate on which a plurality of bumps are disposed,
A rotating roller that presses the head of the bump on the substrate at the lower end,
A roller drive mechanism for rotating the rotating roller;
A horizontal moving mechanism for horizontally moving the mounting table relative to the rotating roller;
With
A bump bonding apparatus, wherein a lower end portion of a rotating roller and a mounting table are relatively almost stationary.

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