JP3189402B2 - Bump forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump forming method,
More specifically, the present invention relates to a bump forming method for forming bumps having a uniform height on an upper surface of a chip by wire bonding means.

[0002]

2. Description of the Related Art It is known that bumps are formed on a chip by wire bonding means to produce a flip chip or the like. The wire bonding means brings the lower end of the wire led out of the capillary and the torch closer, and generates a spark at the lower end of the wire by generating an electric spark by applying a high voltage to the torch in that state,
Next, the capillary is lowered, this ball is pressed against the chip electrode by the lower end of the capillary and bonded, then the wire is clamped by a clamper, and the wire is pulled up, thereby cutting the wire from the joint between the ball and the wire. A bump is formed.

By the way, if the wire is clamped, pulled up, and cut, the cut portion of the wire becomes unstable,
There is a problem that the remaining portion of the wire protrudes from the upper surface of the bump in various lengths, and the height of the bump tends to vary.

As a conventional means for solving such a problem, for example, a method described in Japanese Patent Application Laid-Open No. 57-163919 is known. In this method, the capillary is lowered, the ball at the lower end of the wire is pressed against the electrode on the upper surface of the chip, then the capillary is raised, and the capillary is moved slightly horizontally, and then the capillary is lowered again, and the ball is lowered. Is pressed strongly against the ball by the lower surface of the capillary, and then the wire is clamped by a clamper and pulled up, thereby cutting the wire from the joint between the wire and the ball.

[0005]

However, in this conventional method, the capillary is lifted, moved horizontally, and so on so that the wire is pulled up by the clamper and the wire is easily cut off from the joint. The operation of re-lowering is performed in a very short time, and it is difficult to control the pressing force when the capillary is pressed again to the ball. The lower surface of the ball is too squashed to form a bump with a low height, and if it is bumped, the ball contacts the adjacent electrode, causing electrical failure.If the pressing force is too small, the upper surface of the ball is sufficiently flat However, there is a problem that the bumps are high in height.

Further, according to the conventional means, the bonding portion is insufficiently weakened, so that it is difficult to reliably cut the wire from the bonding portion, and the uncut portion of the wire remains and protrudes on the upper surface of the bump. There is a problem that the height tends to vary.

Accordingly, an object of the present invention is to provide a bump forming method capable of forming a bump having a uniform height, in which a wire is hardly left uncut on the upper surface of the bump.

[0008]

According to the present invention, the capillary is brought into sliding contact with the upper surface of the bump by lowering the capillary while pressing the ball at the lower end of the wire against the electrode of the chip by lowering the capillary . By moving the wire over the enormous part of the wire while moving it slightly, applying a pressing force to the capillary and pressing the wire against the bump upper surface, raising the capillary, clamping the wire with a clamper and pulling it up, The wire is cut from the base of the pressing point.

[0009]

According to the above construction, the wire can be reliably cut from the base of the pressing point, so that the uncut portion of the wire does not remain on the upper surface of the bump, and a good-shaped bump having a constant height can be formed. .

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a side view of a wire bonding apparatus. A capillary 2 is held at the tip of the horn 1, and a wire 3 is inserted through the capillary 2. A vibrator 4 for vibrating the horn 1 in US (ultrasonic) is attached to a base end of the horn 1 and is coupled to a rotor 5.

The rotor 5 is rotatably mounted on a pin 7 of a bearing 6 so as to be rotatable in a vertical direction. A block 11 is mounted on the pin 7. At the rear of the block 11, two upper and lower rods 12 are extended, and a cam follower 13 is mounted on the tip of the rod. The cam follower 13 is in contact with the eccentric cam 14. This eccentric cam 14 is driven by a motor 16 to rotate. Reference numeral 15 denotes the rotation axis. When the motor 16 is driven, the eccentric cam 14 rotates,
The block 11 rotates about the pin 7 and the horn 1 swings up and down about the pin 7.

A shaft 21 is provided upright on the rotor 5. A shaft 22 is also provided upright on the upper surface of the block 11, and the shaft 21 and the shaft 22 are connected by a coil spring 23. The horn 1 is repelled by the spring force FA of the coil spring 23 so as to rotate downward (counterclockwise). A touch sensor 24 is provided inside one shaft 21.

Normally, the shaft 21 is pressed against the touch sensor 24. However, as described above, the motor 16 is driven to rotate the horn 1 downward integrally with the block 11,
When the lower end of the capillary 2 lands on the upper surface of the chip 8 or the upper surface of the lead frame 9 on which the chip 8 is mounted,
The shaft 21 separates from the touch sensor 24 and detects this landing (see FIG. 2). In addition, as such a landing detection unit, an impedance detection unit, an eddy current detection unit using electromagnetic induction, and the like are also applied. 1
Reference numeral 0 denotes a guide rail of the lead frame 9.

At the rear of the rotor 5, a bracket 31 extends horizontally, and a coil 32 is disposed on the upper surface thereof. Further, a magnet 33 is arranged so as to face the coil 32. The coil 32 and the magnet 33 constitute a voice coil motor (VCM). This magnet 33 is mounted on the inner surface of the block 11. When the coil 32 is energized, a magnetic force FB is generated. The magnetic force FB acts as a repulsive force in a direction for rotating the horn 1 upward, that is, in a direction for reducing the spring force FA.

An arm 34 extends forward from the upper front of the block 11. A clamper 35 is attached to the tip of the arm 34. The clamper 35 is driven by a solenoid (not shown) to open and close,
The wire 3 is held, and the held state is released.

The bearing 6 is installed on an X table 42 and a Y table 43. Therefore, when each of the tables 42 and 43 is driven, the horn 1 moves in the X and Y directions. 44 is a torch. This torch 44
The torch 44 is driven by a driving unit (not shown) to move directly below the wire 3 derived from the lower end of the capillary 2, and a high voltage is applied to the torch 44, so that the lower end of the wire 3 and the torch 44 Electric spark is generated, and the ball 3A is generated.

The operation of this wire bonding apparatus is as described above. Next, the operation will be described with reference to FIGS. 3 (a) to 3 (c) and FIG. 4 (a)
(C) shows a series of operations. With the tip 8 positioned immediately below the capillary 2, the torch 44 is moved closer to the lower end of the wire 3 as shown in FIG.
After forming A, the motor 16 is driven by retracting the torch 44 to the side. Then, the capillary 2 descends, and the ball 3A lands on the electrode 20 formed on the upper surface of the chip 8 (see FIG. 3B), and due to the pressing force of the capillary 2,
The ball 3A is strongly pressed against the electrode 20, and the ball 3A
Are flat bumps 3B as shown, and are bonded to the electrodes 20. FIG. 2 shows the state at the time of landing.

When the ball 3A lands on the electrode 20, further lowering of the horn 1 and the capillary 2 stops, but the motor 16 continues to be driven, and the block 11 in FIG. 2 further rotates counterclockwise. Therefore, touch sensor 2
4 is separated from the shaft 21, and it is detected that the ball 3A has landed on the electrode 20.

The height of the lower end of the capillary 2 is controlled by well-known control means. Immediately before or simultaneously with the landing of the ball 3A on the electrode 20, the coil 32 is energized to start the magnetic force (repulsion). Force) FB occurs. This repulsive force FB is substantially equal to the spring force FA of the coil spring 23,
Therefore, the downward force (pressing force) of the capillary 2 at this time
F1 becomes almost zero as shown in (Equation 1).

[0021]

(Equation 1)

Therefore, in the state shown in FIG. 3B, the lower surface of the capillary 2 is lightly pressed against the upper surface of the ball 3B.
Reference numeral 30 denotes a wire bulging portion formed inside the tapered opening at the lower end of the capillary 2.

Next, the X table 42 is driven in this pressed state to slightly move the capillary 2 in the lateral direction (X direction) (see FIG. 3C). In this case, the pressing force F1
= FA-FB is zero or almost zero, so that the lower end of the capillary 2 slidably touches the enlarged portion 30 without any difficulty while sliding over the enlarged portion 30, and from the position shown in FIG.
Move to the position shown in. In the figure, N is the locus of the lower end of the capillary 2 in this case. If the capillary 2 is moved in the X direction without reducing the pressing force F1, the capillary 2 cannot get over the enlarged portion 30, and the enlarged portion 30 is peeled off from the upper surface of the bump 3B, and FIG.
Move to the position indicated by the dashed line.

Next, in this state, energization of the coil 32 is stopped or reduced, and the repulsive force FB is reduced to zero or small. Then, as shown in FIG. 4A, the capillary 2 is repelled downward by the coil spring 23, and the wire 3 is pressed against the right slope C and the upper surface of the bump 3B. At this time, by driving the vibrator 4 to cause the capillary 2 to vibrate in the US, the wire 3 is bonded to the inclined surface of the enlarged portion 30 and the upper surface of the bump 3B. In the figure, A is a pressing point at this time. The bonding force F1 at this time is 50 g.
It is about.

When the pressing is performed at the pressing point A in this manner, the coil 32 is energized again to reduce the pressing force to zero or almost zero, and then the Y table 43 is driven to move the capillary 2 in the X direction. Then, the wire 3 is slightly horizontally moved in the intersecting Y direction (see FIG. 4B).
Press strongly against the top surface of B. At this time, the vibrator 4 is driven again to cause the capillary 2 to vibrate in the US. B is the second pressing point.

Next, as shown in FIG. 4C, the capillary 16 is raised by rotating the motor 16 in the reverse direction, and the wire 3 is pulled up by clamping the wire 3 with the clamper 35. Since it is weakened at the base, it is easily cut from the base, and the bump 3B is completed.

FIG. 5 shows the completed bump 3.
It is a perspective view of B. Wire 3 is point A and point B
By pressing against the upper surface of the bump 3B, it is deformed flat and firmly bonded, and is reliably cut from the base of the point B, so that the remaining wire 3 remains on the upper surface of the bump 3B. In addition, a bump 3B having a flat upper surface and a uniform height can be formed. In this embodiment, the wire 3 is strongly pressed twice at point A and point B, and then the wire 3 is cleaved by the clamper 35 to cut the wire 3. However, at point B, the wire 3 is placed on the upper surface of the bump 3B. After pressing, the capillary 2 is further moved slightly horizontally to
The second strong pressing may be performed, and such a pressing operation may be performed any number of times.

In the above embodiment, after the wire 3 is pressed against the upper surface of the bump at the point A, the capillary 2 is moved in the Y direction and the second press is performed at the point B.
The wire 3 was cut, but after the process shown in FIG. 4A, that is, after pressing at point A, the capillary 2 was raised as it was without moving to point B, and the wire was clamped by the clamper 35. 35 may be clamped and the wire 3 may be cut from the base of the point A.

FIG. 6 shows the bump 3B in this case. In this case as well, bumps 3B having a uniform height can be formed, but there is a problem in that the cutting point of the wire 3 is less stable than in the case of the above embodiment, and the uncut portion 3a of the wire 3 tends to remain and protrude. Therefore, as in the above embodiment,
It is desirable to perform at least two pressings at points A and B.

[0030]

According to the present invention, the wire can be reliably cut from the base of the pressing point, and a bump having a flat upper surface and a uniform height can be easily formed.

[Brief description of the drawings]

FIG. 1 is a side view of a wire bonding apparatus according to an embodiment of the present invention.

FIG. 2 is a side view of the wire bonding apparatus according to one embodiment of the present invention.

FIG. 3A is a process diagram of wire bonding according to one embodiment of the present invention. FIG. 3B is a process diagram of wire bonding according to one embodiment of the present invention. Process chart

FIG. 4A is a process diagram of wire bonding according to one embodiment of the present invention; FIG. 4B is a process diagram of wire bonding according to one embodiment of the present invention; Process chart

FIG. 5 is a perspective view of a bump according to one embodiment of the present invention.

FIG. 6 is a perspective view of a bump according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 horn 2 capillary 3 wire 3A ball 3B bump 8 chip 20 electrode 30 expanded wire 35 clamper 44 torch A, B pressure point

Claims (2)

(57) [Claims] A step of forming a ball by a torch at a lower end of a wire led out of a capillary held by a horn; a step of lowering the capillary to press the ball against an electrode of a chip; In a state where the capillary is lowered, the pressing force of the capillary is reduced, and the capillary is slid on the upper surface of the bump.
A step of moving the wire in the lateral direction by moving over the enormous portion of the wire while making contact with it, a step of applying a pressing force to the capillary to press the wire against the upper surface of the bump, and raising the capillary to clamp the wire with a clamper. And cutting the wire from the base of the pressing point by pulling up. 2. A step of forming a ball with a torch at a lower end of a wire led out of a capillary held by a horn, a step of lowering the capillary and pressing the ball against an electrode of a chip. In the lowered state, the pressing force of the capillary is reduced, and the capillary is moved laterally by moving over the enormous portion of the wire on the upper surface of the bump, and applying a pressing force to the capillary to move the wire to the upper surface of the bump. Pressing the wire again, and reducing the pressing force again to move the capillary slightly horizontally in a direction intersecting with the lateral direction, and applying the pressing force again to the capillary so that the wire is again placed on the upper surface of the bump. Pressing step, raising the capillary, clamping the wire with a clamper and pulling it up, Bump forming method which comprises a step of cutting the wire from the base of Into a.