JP2001007146A - Wire bonding method and apparatus - Google Patents

Abstract

(57) [Problem] To correct eccentricity of a ball caused by abnormal discharge or the like and prevent bonding failure. SOLUTION: After a ball 4 is formed at the tip of the wire 2 by discharging and melting the tip of the wire 2 led out from the tip of the capillary 1, the ball 4 is brought into contact with the electrode 6 of the semiconductor pellet 5 after the ball is formed. Then, the eccentricity of the ball 4 is corrected by applying ultrasonic vibration to the capillary 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a wire bonding method and apparatus, and more particularly to correction of eccentricity of a ball formed by discharging and melting a wire tip.

[0002]

2. Description of the Related Art FIG. 3 is a view for explaining a conventional wire bonding method. In the conventional wire bonding method, as shown in FIG. 3, a discharge is generated between the distal end of the wire 2 derived from the distal end of the capillary 1 and the discharge electrode 3 (FIG. 3A). Is melted to form a ball 4 (FIG. 3B). The capillary 1 is lowered onto the electrode 6 of the semiconductor pellet 5 to press the ball 4 against the electrode 6, and the ball 4 is applied by applying ultrasonic vibration to the capillary 1. After being bonded to the electrode 6 (FIG. 3c), the capillary 1 is moved onto the lead 7 of the lead frame while the wire 2 is being led out, and then lowered, the wire 2 is pressed against the lead 7 and ultrasonic vibration is applied to the capillary 1. To join the other end of the wire 2 to the lead 7 (FIG. 3).
d) At a predetermined timing in the process of raising the capillary 1 while extracting the wire 2, the wire clamper 8 moving upward together with the capillary 1 is closed, and the wire 2 is cut near the joint with the lead 7 (FIG. 3e). .

In this conventional technique, ultrasonic vibration is applied to the capillary 1 only when the ball 4 formed at the tip of the wire 2 contacts the electrode 6 of the semiconductor pellet 5.

[0004]

However, in the above-described conventional wire bonding apparatus, as shown in FIG.
a may be eccentric with respect to the center axis L2 of the wire 2. When such an eccentric ball 4a is used for bonding, there has been a problem that a predetermined bonding force cannot be obtained or a bonding defect such as the bonded ball 4a protruding from the electrode 6 occurs.

[0005] Various events are involved in the formation of the eccentric ball. For example, the eccentric ball 4a is generated due to the lateral swing of the capillary 1 generated while the ball is hardened by natural cooling after the discharge or an abnormal discharge.

Accordingly, the present invention has been made to solve the above-mentioned problem, and it is possible to prevent a bonding defect caused by an eccentric ball by correcting the eccentricity of a ball formed at a wire tip. An object of the present invention is to provide a wire bonding method and apparatus.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a ball is formed by discharging and melting a tip of a wire derived from a tip of a capillary, and the ball is used as a bonding point. In the wire bonding method of abutting and bonding the wire to the bonding point, after the ball is formed by the discharge melting, ultrasonic vibration is applied to the capillary before the ball is abutted on the bonding point. Thus, the eccentricity of the ball is corrected.

According to a second aspect of the present invention, the amplitude of the ultrasonic vibration is substantially twice the amplitude of the ultrasonic vibration applied to the capillary when the ball is bonded to the bonding point. I do.

A third aspect of the present invention is characterized in that the ultrasonic vibration for correcting the eccentricity of the ball is applied to the capillary immediately after the formation of the ball.

According to a fourth aspect of the present invention, the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is stopped when the hardening of the ball is completed.

According to a fifth aspect of the present invention, the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is applied to the bonding point without stopping even when the curing of the ball is completed. It is characterized by contact.

According to a sixth aspect of the present invention, there is provided a wire for forming a ball by discharging and melting a tip of a wire derived from a tip of a capillary, contacting the ball with a bonding point, and joining the wire to the bonding point. In the bonding apparatus, after the ball is formed by the discharge melting, before the ball is brought into contact with the bonding point, a means for correcting eccentricity of the ball by applying ultrasonic vibration to the capillary is provided. It is characterized by.

According to a seventh aspect of the present invention, the amplitude of the ultrasonic vibration is approximately twice the amplitude of the ultrasonic vibration applied to the capillary when the ball is bonded to the bonding point. It is a device to do.

An eighth aspect of the present invention is an apparatus wherein the ultrasonic vibration for correcting the eccentricity of the ball is applied to the capillary immediately after the formation of the ball.

According to a ninth aspect of the present invention, the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is stopped when the hardening of the ball is completed.

According to a tenth aspect of the present invention, the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is applied to the bonding point without stopping even when the curing of the ball is completed. The device is characterized by being brought into contact with the device.

[0017]

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

FIG. 1 is an explanatory view showing one embodiment of the wire bonding method of the present invention. First, the tip of the wire 2 derived from the tip of the capillary 1 and the discharge electrode 3
Then, a discharge is generated (FIG. 1 a), and the tip of the wire 2 is melted to form the ball 4.

Next, ultrasonic vibration is applied to the capillary 1 (FIG. 1b).

Thereafter, as in the prior art, the capillary 1 is lowered onto the electrode 6 of the semiconductor pellet 5 and the ball 4
Is pressed against the electrode 6, and ultrasonic vibration is applied to the capillary 1 to join the ball 4 to the electrode 6 (FIG. 1).
c) then moving the capillary 1 onto the lead 7 of the lead frame while pulling out the wire 2 and lowering it,
The wire 2 is pressed against the lead 7 and the capillary 1 is pressed.
The other end of the wire 2 is bonded to the lead 7 by applying ultrasonic vibration to the wire 1 (FIG. 1d). 8 is closed, and the wire 2 is cut near the joint with the lead 7 (FIG. 1e).

As described above, the eccentric ball 4a (FIG. 4a) may be generated due to the rolling of the capillary 1 or the abnormal discharge during the hardening of the ball by natural cooling after the end of the discharge.

After the discharge is completed, until the formed ball is hardened by natural cooling, the ball and the root portion of the wire immediately above the ball (the neck portion 33 of the ball 4a shown in FIG. 4a) are in an unhardened state, and an external force is applied. Weak state against Therefore, if this weak state is used in reverse, even if the center of gravity of the ball 4a is displaced from the central axis L2 of the wire 2, this displacement can be corrected by ultrasonic vibration.

The eccentric ball 4a has a weight mg of the ball 4a, a straight line L1 passing through the neck 33 and the ball center (center of gravity) and a straight line L1 passing through the center of the ball (center of gravity). The angle θ formed by the center axis L2,
In addition, a force F (F = mg × D1 × sin θ) according to the distance D1 between the neck 33 and the center of the ball is acting.
That is, a force acting on the ball 4a so as to be in the state of the ball 4b shown in FIG. 4B is acting. Therefore, when ultrasonic vibration is applied to the capillary 1 before the hardening of the neck portion 33 is completed, the ball 4a is gradually corrected to a state without eccentricity like the ball 4b or a state close to it.

Even when the neck portion 33 is in an uncured state, when the capillary 1 is stationary (ie, when ultrasonic vibration is not applied to correct the eccentricity of the ball 4a), the ball 4a The power to maintain the state of
The ball 4a surpasses the force of trying to be in the state of the ball 4b.
It has been confirmed by the inventor that this state is maintained.

On the other hand, a good ball 4 having no eccentricity
In b, the center of gravity of the ball 4b is on the center axis L2 of the wire 2. That is, no moment for rotating the ball 4b acts on the ball 4b. Therefore, even if the ultrasonic vibration is applied, the position of the ball 4b is maintained without eccentricity.

That is, in the present embodiment, the eccentricity of the ball can be corrected by the application of the ultrasonic vibration, and the application of the ultrasonic vibration does not adversely affect the ball without eccentricity. Regardless of whether or not the ball is eccentric before the application of the ultrasonic vibration, a ball without eccentricity can be obtained after the application of the ultrasonic vibration, and the bonding failure can be prevented.

Next, the amplitude of the ultrasonic vibration applied to the capillary 1, the timing of starting the application of the ultrasonic vibration, the timing of stopping the ultrasonic vibration, and the like will be described.

FIG. 2 is a diagram showing the relationship among the movement trajectory of the capillary, the timing of discharge, the timing of ultrasonic vibration, and the ultrasonic output in the present embodiment.

In the present embodiment, as shown in the figure, after the discharge period (t1) for forming a ball is completed, an ultrasonic vibration application period (t2) for correcting eccentricity is started.

After the end of the discharge period (t1) for forming the ball, the capillary falls to the search level SL for the electrode. Ultrasonic vibration application period for eccentricity correction (t2)
Terminates at the same time as the search level SL of the capillary is reached. The output (amplitude) of the ultrasonic vibration during this time is p1.

After the capillary descends to the search level SL, the capillary descends at a search speed to a position where the ball and the electrode come into contact, and presses the ball against the electrode with a predetermined load. At the same time, ultrasonic vibration is applied to the capillary. The output (amplitude) of the ultrasonic vibration during the ultrasonic vibration application period (t3) for bonding to this electrode is p2. After the bonding operation on the electrodes, the bonding operation on the leads is performed.

The amplitude p1 of the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is about twice the amplitude p2 of the ultrasonic vibration applied to the capillary when the ball is bonded (bonded) to the electrode. preferable.

For example, when the ball is bonded to the electrode, the amplitude p2 of the ultrasonic vibration applied to the capillary is
In some cases, the difference between the inner diameter of the hole 30 of the capillary 1 and the diameter 31 of the wire 2 shown in FIG.
This is because the ultrasonic vibration of the capillary 1 is sufficiently transmitted to the ball 4a in contact with the electrode, and is not transmitted much to the wire 2.

However, if the amplitude p1 of the ultrasonic vibration applied to the capillary for correcting the eccentricity is substantially equal to p2, the ultrasonic vibration of the capillary 1 is not sufficiently transmitted to the wire 2 and the eccentric ball 4a The effect of eccentricity correction cannot be obtained sufficiently.

In order to sufficiently transmit the ultrasonic vibration of the capillary 1 to the wire 2, the amplitude p1 is set to the difference 31 between the inner diameter of the hole 30 of the capillary 1 and the wire diameter of the wire 2 shown in FIG. Amplitude p2 during bonding
About twice as large as When ultrasonic vibration having an amplitude about twice as large as the difference 31 between the inner diameter of the hole 30 and the wire diameter of the wire 2 is given to the capillary 1, the wire 2 is sufficiently vibrated by the vibration of the capillary 1, and good eccentricity correction is achieved. The effect is obtained. It should be noted that if the amplitude is too large, it may rather cause the ball to be eccentric. Therefore, p1 is preferably about twice the difference 31 between the inner diameter of the hole 30 of the capillary 1 and the wire diameter of the wire 2 shown in FIG.

Incidentally, the amplitude of the ultrasonic vibration applied to the capillary 1 is generally set to be higher when bonding to a lead than when bonding to an electrode.

It is preferable that the ultrasonic vibration applied to correct the eccentricity of the ball is started immediately after the completion of the discharge melting for forming the ball. That is, as shown in FIG. 2, it is preferable that the end of the discharge melting period (t1) coincides with the start of the ultrasonic vibration application period (t2) for correcting the ball.

The reason is that the ball hardens after a lapse of time from the end of the discharge and the neck portion 33 of the ball 4a shown in FIG. 4A hardens, and the effect of correcting the eccentric ball by the ultrasonic vibration is impaired. It is because. It is possible to start applying the ultrasonic vibration during the discharge melting period (t1), but in this case, it is necessary that the application be performed at least after the ball is formed at the wire tip.

It is preferable that the ultrasonic vibration for correcting the eccentricity is stopped when the hardening of the ball is completed. This is because, after the ball is hardened, the effect of eccentricity correction cannot be expected even if ultrasonic vibration is continuously applied. The time until the ball hardens may be measured, and the application stop timing of the ultrasonic vibration may be set based on the measured time. That is, FIG.
Then, it is considered that the hardening of the ball has been completed when the capillary reaches the search level SL,
Although the application of the ultrasonic vibration is stopped at the same time as the search level SL is reached, the application of the ultrasonic vibration may be stopped at an earlier timing.

The ultrasonic vibration applied to the capillary for correcting the eccentricity may be continued until the bonding operation to the electrode is completed without stopping after the ball is hardened. Specifically, first, after the discharge is completed, an ultrasonic vibration having an amplitude sufficient to vibrate the wire for eccentricity correction is applied, and then the output of the ultrasonic vibration is reduced to an amplitude that does not vibrate the wire after the completion of ball curing. Then, after the ball is brought into contact with the electrode while applying such ultrasonic vibration, a load necessary for bonding to the electrode is applied to the joint. That is, the ultrasonic vibration may be continuously applied to the capillary from the end of t2 to the start of t3 in FIG.

The vibration direction of the ultrasonic vibration may be the vertical direction, or the horizontal vibration and the vertical vibration may be appropriately combined.

[0042]

As described above, according to the present invention,
After the ball is formed by electric discharge melting and before the ball comes into contact with the bonding point, the eccentricity of the ball can be corrected by applying ultrasonic vibration to the capillary, thereby preventing a bonding failure. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a wire bonding method of the present invention.

FIG. 2 is a diagram showing the relationship between the movement trajectory of the capillary of the present invention, the timing of discharge, the timing of ultrasonic vibration, and the output of ultrasonic vibration.

FIG. 3 is a diagram illustrating a conventional wire bonding method.

FIG. 4 is a diagram showing shapes of an eccentric ball and a non-eccentric ball.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capillary 2 Wire 3 Discharge electrode 4 Ball 5 Semiconductor pellet 6 Electrode 7 Lead 8 Wire clamper

Claims (10)

[Claims] 1. A wire bonding method for discharging and melting a tip of a wire derived from a tip of a capillary to form a ball, contacting the ball with a bonding point, and bonding the wire to the bonding point, A wire bonding method, wherein after forming the ball by electric discharge melting and before bringing the ball into contact with the bonding point, eccentricity of the ball is corrected by applying ultrasonic vibration to the capillary. 2. The amplitude of the ultrasonic vibration is approximately twice as large as the amplitude of the ultrasonic vibration applied to the capillary when the ball is bonded to the bonding point. The wire bonding method as described. 3. The wire bonding method according to claim 1, wherein the ultrasonic vibration for correcting the eccentricity of the ball is applied to the capillary immediately after forming the ball. 4. The method according to claim 1, wherein the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is stopped when the hardening of the ball is completed.
3. The wire bonding method according to item 1. 5. The method according to claim 1, wherein the ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is brought into contact with the bonding point without stopping even after the curing of the ball is completed. The wire bonding method according to claim 1, wherein 6. A wire bonding apparatus for forming a ball by discharging and melting a tip of a wire led out from a tip of a capillary, and bringing the ball into contact with a bonding point to join the wire to the bonding point. A wire comprising means for correcting eccentricity of the ball by applying ultrasonic vibration to the capillary after forming the ball by discharge melting and before bringing the ball into contact with the bonding point. Bonding equipment. 7. The method according to claim 6, wherein the amplitude of the ultrasonic vibration is substantially twice the amplitude of the ultrasonic vibration applied to the capillary when the ball is bonded to the bonding point. The wire bonding apparatus as described in the above. 8. The wire bonding apparatus according to claim 6, wherein the ultrasonic vibration for correcting eccentricity of the ball is applied to the capillary immediately after forming the ball. 9. The ultrasonic vibration applied to the capillary for correcting the eccentricity of the ball is stopped when the curing of the ball is completed.
3. The wire bonding apparatus according to claim 1. 10. The method according to claim 1, wherein the ultrasonic vibration applied to the capillary to correct the eccentricity of the ball is brought into contact with the bonding point without stopping even after the curing of the ball is completed. The wire bonding apparatus according to claim 6, wherein: