JPH0714871A - Wire bonding method - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a wire bonding method performed in a manufacturing process of a semiconductor device or the like, and by stabilizing the state such as the diameter and hardness of the ball formed at the tip of the wire without variation, The purpose is to reliably bond small-diameter balls. A ball is formed by a wire bonding method in which a voltage is applied between the tip of the wire 5 and the torch electrode to melt the tip of the wire 5 to form a ball, and the ball is pressure-bonded to a bonded portion. Step 1 of detecting the temperature of the tip of the wire 5 immediately before, Step 2 of setting an appropriate torch condition for the temperature of the tip of the wire 5 detected in Step 1, and the condition set in Step 2 Step 3 of forming a ball on the tip of the wire 5 is included.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding method performed in a manufacturing process of semiconductor devices and the like.
In wire bonding, a wire feeding member called a capillary feeds a predetermined amount of a metal wire and operates the capillary to crimp the wire onto a pad and a lead of a semiconductor element or the like.

When crimping a wire to a pad, a method of forming a ball having a predetermined diameter at the tip of the wire is employed to ensure stable connection. In recent years, as the degree of integration of semiconductor devices has increased, the pads on semiconductor elements have become smaller, and accordingly, the balls formed at the tip of the metal wire must also have a small diameter.

It is required to accurately form the ball at the tip of the wire whose diameter is reduced in this way so that the size and hardness of the ball do not vary.

[0004]

2. Description of the Related Art A conventional wire bonding method will be described with reference to FIGS. FIG. 7 is a diagram for explaining the principle of ball formation, and FIG. 8 is a diagram for explaining the basic method of wire bonding. As shown in FIG. 7, the metal wire 32 wound around the reel 31 is sent out via the clamper 33 and the capillary 34. With the wire 32a protruding from the tip of the capillary 34 by a predetermined length, the torch electrode 36 connected to the power supply 35 is positioned near the wire tip 32a, and a predetermined voltage is applied from the power supply 35.

When voltage is applied, arc discharge is generated between the wire tip 32a and the torch electrode 36, the wire tip 32a is heated and melted, and a ball is formed. After the ball is formed at the tip of the wire tip 32a as described above, the ball is connected to the pad on the semiconductor element by operating the capillary 34. FIG. 8 is a sectional view showing a state in which wire bonding between the pad and the lead terminal is performed.
The wire having the ball formed at the wire tip 32a by the above-described method is connected to the pad 37 by lowering the capillary 34 to the pad portion. At this time, since the ball is heated and is in a soft state, it is crushed by the tip of the capillary 34, the oxide film on the ball surface is broken, and the new surface is exposed, so that the ball is connected with a predetermined bonding area.

The amount of protrusion of the wire from the tip of the capillary 34 is controlled by the clamper 33. The clamper 33 is in an open state when the pad is connected rather than a closed state when the ball is formed. Then, by lowering the capillary 34, the ball is held by the tip of the capillary 34, and the ball is connected to the pad. After that, with the clamper 33 open, the capillary 3
4 is moved to the lead terminal 38 of the lead frame, the wire is fed by a predetermined amount, and the capillary 34
By pressing the tip against the lead terminal 38, the wire 32 is connected to the lead terminal 38. Again, the capillary 34
The connection is performed by crushing the wire 32 by the tip.

After the connection, the clamper 33 is kept open at a predetermined interval, and the capillary 34 is moved upward in this state. Along with this movement, the wire 32 is sent out from the tip of the capillary 34. Predetermined amount of wire 3
When 2 is sent out, the clamper 33 is closed. Since the portion of the wire 32 connected to the lead terminal 38 is crushed and thinned, if the capillary 34 is moved further upward with the clamper 33 closed, the wire 32 will be cut from this connection portion. .

By the above operation, the bonding between the pad 37 and the lead terminal 38 is completed, and by repeating this, a plurality of pads of the semiconductor element 39 and the lead terminal are connected. Although not shown, the operation of the capillary 34 is performed by using a motor as a drive source.

Generally, a lead frame is formed with a plurality of stages on which semiconductor elements are mounted and simultaneously manufactures a plurality of semiconductor devices. Therefore, also in wire bonding, the lead frame is transferred to a plurality of semiconductor devices continuously. Normally, the ball at the tip of the wire is formed immediately after bonding, and when there is a waiting time until the bonding of the next semiconductor element after the bonding of one semiconductor element is completed, the formed ball is Cools and becomes hard.

When the bonding is performed on the pad in such a state, the deformation amount of the ball is reduced and the bonding area is reduced, so that a sufficient bonding force cannot be obtained. Therefore, in order to prevent the formed ball from cooling and to have a stable hardness, a method has been considered in which the ball is formed immediately before bonding, that is, after the capillary moves to a predetermined pad.

[0011]

In the method of forming a ball at the tip of a wire immediately before bonding,
Even if there is a waiting time before the next bonding, the balls are formed after the waiting, so that hardening of the balls after cooling can be surely prevented. However, in this case, the wire is cooled before the ball is formed, and the temperature condition is different from that in the case where the balls are continuously formed.

For example, when a ball is formed by applying a voltage of 2400V, the temperature of the tip of the wire rises to about 1200 degrees and melts to form a ball. The wire is not completely cooled and a voltage is applied for the next ball formation while maintaining a temperature of about 400 degrees. On the other hand, when there is a waiting time, the wire is cooled to about room temperature. In such a state, if the balls are formed under the same torch conditions, the diameter of the formed ball will be different due to the difference in temperature conditions.

That is, since the ball formed from the state where the wire is completely cooled is smaller than a predetermined diameter, the bonding area with the pad or the like is also small, and a sufficient bonding force cannot be obtained and there is a high possibility of peeling. Become. On the contrary, based on the ball diameter formed by the wire being cooled,
Other than that, that is, most of the balls have a diameter larger than a predetermined diameter, and it is impossible to reduce the diameter of the balls.

As described above, in the method of forming balls immediately before bonding, variations in ball diameter occur, and it is difficult to perform bonding management in terms of ball diameter, bonding area, etc., especially in ball formation where the diameter is reduced. Become. It is an object of the present invention to facilitate management and reliably bond a small-diameter ball by stabilizing the state of the ball such as the diameter and hardness of the ball formed at the tip of the wire when performing wire bonding without variation. I am trying.

[0015]

According to the present invention for solving the above-mentioned problems, a voltage is applied between the tip of the wire 5 and the torch electrode 6 to melt the tip of the wire to form a ball. In a wire bonding method including a step of crimping a wire to a bonded portion, a step 1 of detecting the temperature of the tip of the wire 5 immediately before forming the ball and an appropriate torch condition for the temperature detected in the step 1 are set. It is characterized by including Step 2 and Step 3 of forming a ball at the tip of the wire under the torch conditions set in Step 2.

[0016]

The state of the diameter and hardness of the ball formed at the tip of the wire is greatly affected by the temperature of the wire tip immediately before the ball is formed. Therefore, if the ball is formed after detecting the wire tip temperature immediately before ball formation as described above and setting the torch condition appropriately according to the temperature at this time, even if there is a difference in wire temperature, torch condition Since the correction is performed, it is possible to obtain a predetermined ball diameter.

[0017]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a diagram showing the basic steps of the wire bonding method of the present invention, and FIG. 2 is an apparatus configuration diagram for carrying out the basic steps of FIG. As shown in FIG. 1, the wire bonding method of the present invention includes a step 1 of detecting the temperature of the wire tip immediately before ball formation, a step 2 of setting an appropriate torch condition for the detected temperature, and a set torch condition. The step 3 of forming a ball at the tip of the wire is performed, and then the ball is connected to the pad of the semiconductor element which is the bonded portion.

As shown in FIG. 2, the bonding apparatus for carrying out this basic process is a wire 5 made of metal such as gold.
For discharging the arc, a torch electrode 6 for generating an arc discharge between the wire 5 protruding from the tip of the capillary 4, a ball formation controller 7 for controlling various conditions for ball formation, and a ball formation controller 7 for ball formation. A trigger signal generating circuit 7 for generating a trigger signal of the above, and a temperature sensor 12 for detecting the temperature of the tip of the wire 5 in the vicinity of the capillary 4, and a power source 9 and a torch in the ball formation control unit 7. Condition setting circuit 1
0, the temperature detection circuit 11 is provided.

In such a bonding apparatus, the feeding of the wire 5 from the capillary 4 is controlled by opening and closing the clamper 13 installed above the capillary 4, and the wire 12 is first projected from the tip of the capillary 4 by a predetermined amount. Let The temperature of the projected wire 5 is detected by a temperature sensor 12 installed in the vicinity thereof, and the result is constantly sent to the temperature detection circuit 11 in the ball formation control unit 7.

The capillary 4 operates with a motor (not shown) as a drive source according to the coordinates stored in advance, and when it is located on the pad of the semiconductor element to be bonded, it is a trigger for starting ball formation. A signal is sent from the trigger signal generation circuit 8 to the ball formation control unit 7
It is sent to the internal temperature detection circuit 11. From these signals, the temperature detection circuit 11 recognizes the temperature of the tip of the wire 5 at the time when the trigger signal is received, that is, immediately before ball formation.
The result is sent to the torch condition setting circuit, and the torch conditions such as voltage, current, and application time for forming a ball having a predetermined diameter under that temperature are set to optimum values. This value is experimentally determined by forming a ball under each condition in advance.

Then, under the set torch conditions, a voltage is applied from the power source 9 between the tip of the wire 5 and the torch electrode 6 to generate arc discharge, thereby melting the tip of the wire 5 and melting the ball. To form. As described above, immediately after forming a ball having a predetermined diameter, the capillary 4 is lowered to connect the ball to the pad.

This connection is made by the same mechanism as described in FIG. 7 in the section of the prior art. In the wire bonding method described above, the torch condition is set for each ball formation. However, if the torch condition is corrected only when the wire temperature greatly differs, ball formation can be performed efficiently. it can.

That is, when wire bonding is continuously performed, the temperature of the wire tip immediately before ball formation is almost constant. For example, the torch condition may be corrected only when the bonding interval becomes longer and a large temperature change occurs due to cooling. FIG. 3 is an embodiment of the present invention and shows a configuration diagram of a bonding apparatus for performing the above method. 3 is different from FIG. 2 in the ball formation control unit 14, and the same parts as those in FIG. 2 are denoted by the same reference numerals.

The ball formation controller 14 of this embodiment comprises a temperature detection circuit 19, a reference temperature setting circuit 18, and a temperature comparison circuit 1.
7, a torch condition correction circuit 16 and a power supply 15. In such a bonding apparatus, as in the apparatus of FIG. 2, the wire 5 is moved from the tip of the capillary 4 by a predetermined amount.
The temperature of the wire 5 thus projected is detected by the temperature sensor 12, and the result is constantly sent to the temperature detection circuit 19 in the ball formation controller 14.

The temperature detecting circuit 19 recognizes the temperature of the tip of the wire 5 immediately before the ball is formed, based on the signal from the trigger signal generating circuit 8. On the other hand, the reference temperature setting circuit 18
Wire 5 when wire bonding is performed continuously
Set the reference temperature from the tip temperature. Thus, the actual wire tip temperature and the reference temperature obtained by the temperature detection circuit 19 and the reference temperature setting circuit 18 are compared with each other by the temperature comparison circuit 17.
And the size is judged.

As a result of this comparison, when the actual wire tip temperature is higher than the reference temperature, the torch condition is not corrected, and only when the actual wire tip temperature is lower than the reference temperature, the torch condition correction circuit 16 is used. The condition is corrected. After that, under the set torch conditions,
By applying a voltage between the tip of the wire 5 and the torch electrode 6 from the power source 15 to generate arc discharge,
The tip of the wire 5 is melted to form a ball. Immediately after forming a ball having a predetermined diameter in this way, the capillary 4 is lowered to connect the ball to the pad.

After the torch condition is corrected and the ball is formed once, the torch condition is returned to the normal condition as before correction. Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a flow chart showing the bonding method of this embodiment, and FIG. 5 is a configuration diagram of a bonding apparatus for realizing the method of this embodiment.

In the previous embodiment, the temperature of the tip of the wire 5 was directly detected and the torch condition was set based on the result. However, since the temperature of the wire 5 decreases in proportion to the passage of time, In this embodiment, the ball formation interval is measured,
The torch condition is set according to the time. That is, the temperature detection is replaced with the measurement of the ball formation interval, and the temperature detection is indirectly performed.

When a ball is formed at the tip of the wire, a trigger signal for starting the ball formation is first generated. As shown in FIG. 4, from the time t1 when the trigger signal is generated, before the previous ball formation. The trigger interval T is detected by subtracting the previously generated trigger signal generation time t0 generated and stored at. Next, the detected trigger interval T is compared with the preset reference interval T0.

As a result of this comparison, if trigger interval T ≦ reference interval T0, ball formation is started as it is under the preset normal torch condition. On the other hand, when the comparison result is that the trigger interval T> the reference interval T0,
After the torch conditions are corrected, ball formation is started.
The wire bonding method in this embodiment can be realized by the bonding apparatus shown in FIG. Figure 5
In the above, the same parts as those in the previous embodiment are designated by the same reference numerals.

The ball formation controller 20 in the bonding apparatus of this embodiment comprises a trigger interval correction circuit 25, a reference interval setting circuit 24, an interval comparison circuit 23, a torch condition correction circuit 22 and a power supply 21. Similar to the previous embodiment, in this apparatus, the wire 5 is fed out from the capillary 4 by controlling the opening and closing of the clamper 13 to project the wire 5 from the tip of the capillary 4 by a predetermined amount.

After that, the capillary 4 is moved by the motor 26 so as to be positioned above the pad which is the bonded portion. The motor 26 moves the capillary 4 according to the coordinates stored in advance. The trigger signal generation circuit 8 recognizes that the capillary 4 is located on a predetermined pad and the operation of the motor 26 is stopped, and sends a trigger signal for ball formation to the trigger interval measurement circuit 25 of the control unit 20. To do.

In the trigger interval measuring circuit 25 which has received the trigger signal, the calculation t0 of this trigger signal generation time t1 and the stored time t0 of the previous trigger signal generation.
By executing -t1, the interval T of the trigger signal generation is
Ask for. On the other hand, in the reference interval setting circuit 24, the time during which the tip of the wire is not cooled to a temperature that affects the ball diameter is set as the reference interval T0.

The trigger interval T and the reference interval T0 are compared by the interval comparison circuit 23, and the magnitude thereof is recognized. As a result of this comparison, if T ≦ T0, the torch condition correction circuit 22 does not operate, and a voltage is applied from the power supply 21 so that the preset torch condition is applied to the tip of the wire 5. Forming a ball. That is, since the trigger interval is short and the tip of the wire 5 does not cool enough to affect the ball diameter, the ball is formed under normal torch conditions.

On the other hand, when T> T0 as a result of the comparison in the interval comparison circuit 23, the torch condition correction circuit 22 appropriately corrects the torch condition, and then the corrected torch condition is obtained. A voltage is applied from the power source 21 to form a ball at the tip of the wire 5. (T1, t0
, T, T0 refer to Fig. 4) Torch conditions include voltage itself, voltage application time, current, etc.
The optimum value is set by correcting these values. This value is experimentally determined by forming a ball under each condition in advance.

As described above, immediately after forming a ball having a predetermined diameter, the capillary 4 is lowered to connect the ball to the pad. In this embodiment, as the torch conditions, the voltage, the voltage application time, and the current were raised, but in addition to this, as shown in FIG. 6, the diameter of the ball formed by ion irradiation to the discharge portion can be changed.

FIG. 6 shows a part of the bonding apparatus. As a result of comparison in the interval comparison circuit 23, T>
When T0 (see FIG. 4) is reached, the torch condition correction circuit 2
A signal is sent to the ion generator 27 connected thereto by 2 and ions are generated and irradiated between the wire 5 and the torch electrode 6. Since the ions have a function of promoting the generation of arc discharge, irradiation of the discharge portion facilitates the formation of balls at the tip of the wire.

Further, as means for promoting the generation of arc discharge, irradiation of hot gas to the discharge part, heating of the torch electrode, etc. can be considered. Therefore, as a torch condition correction when the tip of the wire is cooled, this Even if such a method is adopted, it is possible to obtain a predetermined ball diameter.

[0039]

According to the present invention, the temperature of the wire tip immediately before the ball is formed is detected, and the torch condition is appropriately set according to the temperature at that time, and then the ball is formed. However, since the torch condition is appropriately set according to the variation in the temperature, the variation in the ball diameter does not occur and the desired ball diameter can be stably obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing basic steps of a wire bonding method of the present invention.

FIG. 2 is a device configuration diagram for carrying out the basic steps of the present invention.

FIG. 3 is a configuration diagram of a bonding apparatus for explaining an embodiment of the present invention.

FIG. 4 is a flow chart for explaining another embodiment of the present invention.

FIG. 5 is a configuration diagram of a bonding apparatus for explaining another embodiment of the present invention.

FIG. 6 is a configuration diagram of a bonding apparatus for explaining an example of performing ion irradiation of the present invention.

FIG. 7 is a view for explaining the principle of ball formation that has been conventionally used.

FIG. 8 is a diagram for explaining a basic method of wire bonding that has been conventionally used.

Claims (4)

[Claims] 1. A voltage is applied between the tip of the wire (5) and the torch electrode (6) to melt the tip of the wire (5) to form a ball, and the ball is attached to a portion to be joined. In the wire bonding method of crimping, the step (1) of detecting the temperature of the tip of the wire (5) immediately before forming the ball and the temperature of the tip of the wire (5) detected in the step (1) A wire bonding method comprising: a step (2) of setting an appropriate torch condition; and a step (3) of forming a ball at the tip of the wire (5) according to the torch condition set in the step (2). . 2. A reference temperature is set in advance, the reference temperature is compared with the actually detected tip temperature of the wire (5), and the torch is provided only when the actual temperature is lower than the reference temperature. The wire bonding method according to claim 1, wherein the condition is corrected. 3. A voltage is applied between the tip of the wire (5) and the torch electrode (6) so that the tip of the wire (5) is melted to form a ball, and the ball is attached to a bonded portion. In the wire bonding method of crimping, a step of measuring a generation interval (T) of a ball forming trigger signal, a step of setting an appropriate torch condition for the generation interval (T), and a wire ( 5) A step of forming a ball at the tip of the wire bonding method. 4. A reference trigger signal generation interval (T ₀ ) is set in advance, and the reference value (T ₀ ) is compared with the trigger signal generation interval (T) actually obtained. 4. The wire bonding method according to claim 3, wherein the torch condition is corrected only when the actual trigger signal generation interval (T) exceeds the reference value (T ₀ ).