JPH0653221A - Formaiton method of bump - Google Patents

Abstract

PURPOSE:To provide a means wherein the scrap of a wire is hardly left on the surface of a bump and bumps whose height is even can be formed. CONSTITUTION:The formation method is constituted of a process wherein a capillary 2 is lowered and a ball 3A is pressed to an electrode for a chip 8, of a process wherein the pressure force of the capillary 2 is read out and the capillary 2 is moved slightly to the transverse direction so as to climb over a wire swollen part on the surface of a bump, of a process wherein a pressure force is exerted on the capillary 2 and a wire 3 is pressed to the surface of the bump and of a process wherein the capillary 2 is raised, the wire 3 is clamped and pulled up by a clamper 35 and the wire 3 is cut from the root of a pressure point.

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 the 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 manufacture a flip chip or the like. The wire bonding means brings the torch closer to the lower end of the wire drawn out from the capillary, and in that state a high voltage is applied to the torch to generate an electric spark to form a ball at the lower end of the wire.
Next, lower the capillary and press this ball against the electrode of the chip by the lower end of the capillary to bond it, then clamp the wire with a clamper and pull up the wire to cut the wire from the ball-wire junction. The bumps are formed.

By the way, if the wire is clamped, pulled up and cut as it is, the cut portion of the wire is not stable,
There is a problem in that the uncut portion of the wire remains and protrudes from the upper surface of the bump in various lengths, and thus the height of the bump tends to vary.

As a conventional means for solving such a problem, for example, a method disclosed in Japanese Patent Laid-Open No. 163919/1982 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, and then the capillary is raised, the capillary is moved slightly horizontally, and then the capillary is lowered again to move the ball. The wire is cut from the joint between the wire and the ball by strongly pressing the rising part of the wire from the above to the ball by the lower surface of the capillary and then clamping the wire with a clamper and pulling it up.

[0005]

By the way, in this conventional method, in order to weaken the joint so that the wire can be easily pulled up by the clamper to cut the wire from the joint, the capillary is raised, moved horizontally, Although the work of re-lowering is performed, since this series of operations is performed in an extremely short time, it is difficult to control the pressing force when the capillary is pressed against the ball again. The lower surface of the ball will be crushed too much to form a low-height bump, and if it becomes hard, the ball will contact the adjacent electrode and cause electrical failure.If the pressing force is too small, the upper surface of the ball will be sufficiently flat. However, there was a problem in that the bumps became high in height.

Further, in this conventional means, the brittleness of the joint is insufficient, and it is difficult to reliably cut the wire from the joint, and the uncut portion of the wire remains and protrudes on the upper surface of the bump. There was a problem that the height was likely to vary.

Therefore, an object of the present invention is to provide a bump forming method capable of forming bumps having uniform heights, in which uncut wires are less likely to be left on the upper surface of the bumps.

[0008]

SUMMARY OF THE INVENTION In the present invention, the capillary is lowered and the pressing force of the capillary is reduced while the ball at the lower end of the wire is pressed against the electrode of the chip, and the capillary is expanded on the upper surface of the bump. After moving over the part and moving it slightly horizontally, pressing force is applied to the capillary there to press the wire against the bump upper surface, then the capillary is raised, and the wire is clamped by the clamper and pulled up Try to cut the wire from.

[0009]

According to the above structure, the wire can be reliably cut from the root of the pressing point, and therefore the uncut residue of the wire does not remain and protrude on the upper surface of the bump, and the bump having a constant height can be formed. .

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a side view of the 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 the US (ultrasonic wave) is attached to a base end portion of the horn 1, and is connected to a rotor 5.

The rotor 5 is rotatably mounted on a pin 7 of a bearing 6 in a vertically rotatable manner. A block 11 is pivotally attached to the pin 7. Two upper and lower rods 12 are extended at the rear of the block 11, and a cam follower 13 is axially attached to the tip of the rod 12. The cam follower 13 is in contact with the eccentric cam 14. The eccentric cam 14 is driven by a motor 16 to rotate. Reference numeral 15 is its rotation axis. When the motor 16 is driven, the eccentric cam 14 rotates,
The block 11 rotates around the pin 7, and the horn 1 swings up and down around the pin 7.

A shaft 21 is erected on the upper portion of the rotor 5. A shaft 22 is provided upright on the front portion of the upper surface of the block 11, and the shaft 21 and the shaft 22 are connected by a coil spring 23. The spring force FA of the coil spring 23 causes the horn 1 to be elastically rotated downward (counterclockwise). A touch sensor 24 is provided inside the one shaft 21.

The shaft 21 is normally pressed against the touch sensor 24, but as described above, the motor 16 drives the horn 1 to rotate downward together 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). As such landing detection means, other than this, impedance detection means, eddy current detection means utilizing electromagnetic induction, and the like are also applied. 1
Reference numeral 0 is a guide rail of the lead frame 9.

A bracket 31 extends horizontally at the rear of the rotor 5, and a coil 32 is arranged 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 form a voice coil motor (VCM). The magnet 33 is mounted on the inner surface of the block 11. When the coil 32 is energized, a magnetic force FB is generated. This magnetic force FB acts as a repulsive force in the direction of rotating the horn 1 upward, that is, in the direction of reducing the spring force FA.

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

The bearing 6 is installed on the X table 42 and the Y table 43. Therefore, when each of the tables 42 and 43 is driven, the horn 1 moves in the X direction and the Y direction. 44 is a torch. This torch 44
Driven by a driving means (not shown), the capillary moves to a position directly below the wire 3 led out from the lower end of the capillary 2, and a high voltage is applied to the torch 44 there. Electric sparks are generated and balls 3A are generated.

This wire bonding apparatus has the above-mentioned structure, and its operation will be described with reference to FIGS. 3 and 4. 3A to 3C and FIG. 4A.
(C) shows a series of operations. With the tip 8 positioned directly below the capillary 2, the torch 44 is brought close to the lower end of the wire 3 as shown in FIG.
After forming A, the torch 44 is retracted to the side and the motor 16 is driven. Then, the capillary 2 descends, 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,
Becomes a flat bump 3B as shown in the figure, and is bonded to the electrode 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 is stopped, but the motor 16 still continues to drive, and the block 11 further rotates counterclockwise in FIG. 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 a well-known control means, and the coil 32 is energized immediately before the ball 3A lands on the electrode 20 or at the same time as it lands, and a magnetic force (repulsion) is generated. Force) FB occurs. This repulsive force FB is almost equal to the spring force FA of the coil spring 23,
Therefore, the descending 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 an enlarged wire portion formed inside the tapered opening at the lower end of the capillary 2.

Next, in this pressed state, the X table 42 is driven to slightly move the capillary 2 in the lateral direction (X direction) (see FIG. 3C). In this case, the pressing force F1
Since = FA-FB is zero or almost zero, the lower end of the capillary 2 easily slides over the enlarged portion 30 while easily sliding over it, and from the position shown in FIG. 3 (b) to FIG. 3 (c).
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, as shown in FIG.
It moves to the position of the chain line.

Next, in that state, the energization of the coil 32 is stopped or reduced to reduce the repulsive force FB to zero or small. Then, as shown in FIG. 4 (a), the capillary 2 is elastically bulged 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 vibrate the capillary 2 in the US direction, the wire 3 is bonded to the slope 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 a degree.

When the pressure is applied 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. The wire 3 is slightly moved horizontally in the intersecting Y direction (see FIG. 4 (b)), and then the power supply to the coil 32 is stopped or reduced again, and the wire 3 is bumped.
Press strongly against the upper surface of B. At this time, the vibrator 4 is driven again to vibrate the capillary 2 in US. B is the second pressing point.

Next, as shown in FIG. 4 (c), the motor 16 is rotated in the reverse direction to raise the capillary 2, and the clamper 35 clamps the wire 3 to pull up the wire 3, so that the wire 3 moves at the pressing point B. Since it is weakened at the base, it is easily cut from the base to complete the bump 3B.

FIG. 5 shows the bump 3 thus completed.
It is a perspective view of B. Wire 3 is point A and point B
Since it is pressed against the upper surface of the bump 3B, it is flatly deformed and firmly bonded, and it is surely cut from the root of the point B, and the uncut portion of the wire 3 remains and protrudes on the upper surface of the bump 3B. It is possible to form the bumps 3B having a flat upper surface and no variation in height. In this embodiment, after the wire A is strongly pressed twice at the points A and B, the wire 3 is cut by the clamper 35 so as to cut the wire 3, but the wire 3 is cut on the upper surface of the bump 3B at the point B. After pressing, move the capillary 2 slightly horizontally and
The strong pressing may be performed for the second time, and such 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 is pressed at the point B for the second time.
Although the wire 3 was cut, after the process shown in FIG. 4A, that is, after pressing at the point A, the capillary 2 is lifted as it is without moving to the point B, and the wire is moved by the clamper 35. It is also possible to clamp 35 and cut the wire 3 from the root of the point A.

FIG. 6 shows the bump 3B in this case. In this case as well, the bumps 3B having no height variation can be formed, but 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 is likely to remain and protrude. Therefore, as in the above embodiment,
It is desirable to perform pressing at least twice at points A and B.

[0030]

According to the present invention, while the ball at the lower end of the wire is pressed against the electrode of the chip, the pressing force is reduced to move the capillary laterally, where the wire is strongly pressed against the upper surface of the bump. After that, since the capillary is raised to cut the wire, the wire can be surely cut from the root of the pressing point, and a bump having a flat upper surface and having no height variation can be easily formed.

[Brief description of 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 a wire bonding apparatus according to an embodiment of the present invention.

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

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

FIG. 5 is a perspective view of a bump according to an 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]

 1 Horn 2 Capillary 3 Wire 3A Ball 3B Bump 8 Chip 20 Electrode 30 Wire Enlarged Part 35 Clamper 44 Torch A, B Pressing Point

Claims (2)

[Claims] 1. A step of forming a ball with a torch at a lower end of a wire led out from 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 over the bumped wire on the upper surface of the bump to move in the lateral direction. A bump forming method comprising: a step of pressing on the upper surface; and a step of raising the capillary, clamping the wire by a clamper and pulling it up to cut the wire from the root of the pressing point. 2. A step of forming a ball with a torch at a lower end of a wire led out from a capillary held by a horn, a step of lowering the capillary to press the ball against an electrode of a chip, In the lowered state, the pressing force of this capillary is reduced so that this capillary moves over the enlarged wire part on the upper surface of the bump and moves laterally, and the pressing force is applied to the capillary to move the wire to the upper surface of the bump. The step of pressing the wire to the upper surface of the bump again by reducing the pressing force again and moving the capillary slightly horizontally in a direction intersecting the lateral direction. Pressing process and pushing up 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.