JPH0574876A - Wire bonding equipment - Google Patents

Abstract

(57) [Abstract] (Correction) [Purpose] A wire bonding device for connecting a connection electrode on a semiconductor integrated circuit and an inner terminal of a package side lead with a thin wire, and the device can be formed without a bonding failure. The purpose is to improve work efficiency by continuing work without stopping as much as possible. A detecting means for detecting a vibration waveform of a vibrator 2 for driving a bonding tool 4, and an inference means for inferring a good or bad bonding state by fuzzy inference by comparing a vibration waveform obtained from the detecting means with a reference vibration waveform. , And bonding control means for controlling the bonding conditions based on the inference result of the inference means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding apparatus for connecting a connecting electrode on a semiconductor integrated circuit and an inner terminal of a package side lead with a fine wire, and more particularly to an ultrasonic wave utilizing ultrasonic vibration. It is about bonding.

[0002]

2. Description of the Related Art Wire bonding is a technique used to electrically connect an aluminum electrode and a lead with a fine wire (wire) in a semiconductor manufacturing process. Sonic bonding is often used.

In ultrasonic bonding, ultrasonic vibration is applied to an aluminum wire through a tool under a constant load to cause a plastic flow similar to that under pressure at high temperature to cause the wire to weld on an aluminum electrode. is there. Since this plastic flow is accompanied by macroscopic deformation of the wire and wave motion by ultrasonic waves, the oxide film at the interface between the two metals is destroyed and atomic bonding is made by contact with the new surface.

In wire bonding, the wire may be broken or the wire may slip out of the insertion hole. Therefore, conventionally, a vibration waveform at the time of bonding is observed to detect a bonding failure. That is, in the normal bonding state, paying attention to the vibration waveform being attenuated after a predetermined time has passed from the start of the bonding operation, detecting an electric signal corresponding to the vibration waveform of the vibrator, and comparing it with the reference electric signal after a predetermined time has passed, When the vibration waveform is not attenuated and is larger than the reference electric signal, the wire is disconnected, the wire is broken, or the cause is unknown but it is in a state where it is not bonded, so immediately issue a signal to operate the stop device or alarm device, Stop the machine. This prevents the wire from being blown out due to wire breakage or wire disconnection, thereby improving the reliability of the wire bonding apparatus.

[0005]

In the above-mentioned prior art, the vibration waveform at the time of bonding is utilized, and when the vibration waveform after a lapse of a predetermined time is larger than the reference electric signal, it is judged as abnormal and the machine is stopped. Therefore, even if the bonding strength is insufficient due to surface stains, lot differences, etc., but if the bonding time can be increased to a sufficient strength, it is judged as abnormal and the machine is stopped.

Further, although various experiments and studies are repeated to find the optimum bonding condition and set the value to carry out wire bonding, there are cases where the bonding is not carried out due to wire disconnection or wire breakage. Further, the bonding strength may not be sufficient due to surface stains, lot differences, and the like. In the former case, an abnormality is detected and the bonding is stopped, but in the latter case, normal bonding can be performed by changing the bonding condition, and the bonding operation can be continued without stopping and without causing a defective bonding. However, it is very difficult to detect the bonding state and change it to the bonding condition corresponding to it.

According to the present invention, the defective bonding state is detected, the bonding condition is changed to eliminate the defective bonding, and the bonding work is continued without stopping the apparatus as much as possible to improve the working efficiency. The purpose is to

[0008]

A wire bonding apparatus according to the present invention detects a vibration waveform of a vibrator for driving a bonding tool, and compares the vibration waveform obtained from the detection means with a reference vibration waveform to fuzzy. An inference means for inferring the quality of the bonding state by inference,
Bonding control means for controlling the bonding conditions based on the inference result by the inference means.

[0009]

In the structure of the present invention, the detecting means detects the vibration waveform of the vibrator for driving the bonding tool, and compares the detected vibration waveform with the reference vibration waveform obtained from the vibration waveform at the time of normal bonding by the inference means. Then, the quality of the bonding state is inferred by fuzzy inference.
To infer the quality of the bonding state, for example, the difference between the voltage of the vibration waveform after the lapse of a predetermined time from the start of bonding and the voltage of the reference vibration waveform at the same time, and the attenuation rate of the vibration waveform up to this time are set as fuzzy inputs, Fuzzy inference is performed based on a predetermined fuzzy rule. From this inference result, the bonding can be stopped, the bonding conditions,
For example, the bonding control means controls the bonding state so that the bonding state becomes normal by changing setting values such as ultrasonic wave application time, ultrasonic wave output, or load.

[0010]

1 is a block diagram showing an embodiment of a wire bonding apparatus according to the present invention. In the figure, the oscillator 1 vibrates the vibrator 2 by its output, amplifies the vibration by the ultrasonic horn 3, and transmits it to the bonding tool 4. As a result, the joining load changes due to the change in friction of the joining surface between the aluminum wire 5 and the aluminum electrode 6, and the mechanical impedance changes. In order to capture it, the vibration waveform of the oscillator 1 is detected, the waveform is shaped by the filter 7, and the A /
It is converted into a digital signal by the D converter 8 and taken into the CPU 9.

The CPU 9 performs fuzzy inference using the fuzzy rules and membership functions stored in the ROM 10, and stores in the RAM 11 the control amount of the bonding condition based on the inference result and the operation amount. At the same time, this control amount is converted into an analog signal by the D / A converter 12,
It is supplied to the wire bonding controller 13. The controller 13 controls the ultrasonic output of the oscillator 1, the ultrasonic application time (bonding time), or the load of the pressure device 14 based on the input control amount of the bonding condition.

FIG. 2 shows a vibration waveform output from the oscillator 1 during bonding. A waveform A shown by a solid line in FIG. 6A is a waveform at a normal time, and a waveform B shown by a chain line is a waveform when the cause is not clear but not bonded. The waveform C shown in Fig. (B) is the waveform when the bonding tool does not reach the bonding pad and is vibrating in the air, and the waveform D shown in Fig. (C) is when the bonding tool is idle. Is the waveform of.

Further, when the joining strength is not sufficient due to the difference of lots or the contamination of the surface, the progress of the joining load changes, so that the vibration waveform expands like the waveform E shown in FIG. , On the contrary, it changes quickly such that it decays faster or the voltage rises. In any case, the waveform E is an attenuation waveform having the same shape as the waveform A at the time of normal bonding, and is a waveform different only in time or voltage. A reference vibration waveform is obtained from the vibration waveform A at the time of normal bonding, and after a lapse of a predetermined time, it is compared with the reference vibration waveform to judge the quality of bonding.
In FIG. 3, the reference vibration waveform F is shown by a one-dot chain line. This reference vibration waveform F is the time t ₁ to be measured from the vibration waveform A at the time of normal bonding, the voltage V ₂ at the maximum amplitude, and the voltage V at the time of attenuation.
_It was obtained by obtaining ₁ .

Next, the operation when the CPU 9 performs the bonding control by fuzzy inference with the optimum bonding condition stored in the ROM 10 as the initial setting will be described. First, the measured voltage V ₄ of the vibration waveform G at time t ₁ and the voltage V ₁ of the reference vibration waveform F at the same time
The difference V (= V ₄ −V ₁ ) from If the voltage difference V is small, it is inferred that the bonding is normal. Voltage difference V
The smaller the value, the better, and the larger the value, the larger the control amount must be.

However, if the voltage difference V is large, it is not always necessary to increase the control amount, and there are defects such as wire disconnection, wire breakage, or defects that cannot be corrected simply by controlling the bonding conditions. Have to stop. As described above, it is difficult to grasp the bonding state only with the voltage difference V, and it is difficult to clearly determine whether or not the bonding should be stopped and whether or not the bonding can be corrected by the control.

Therefore, the damping rate ΔV of the vibration waveform G up to the time t ₁ is obtained, and this interaction is replaced with a membership function and treated as "fuzzy information". The attenuation rate ΔV is
As shown in FIG. 4, the voltage V ₀ at the maximum amplitude and its time t
₀ is stored, the rate of change of the voltage up to time t ₁ is obtained, and the sign is inverted. ΔV = − (V ₄ −V ₀ ) / (t ₁ −t ₀ ).

Thus, the CPU 9 performs fuzzy inference using the voltage difference V and the attenuation rate ΔV as fuzzy inputs (fuzzy information). Figure 5 shows an example of the membership function.
FIG. 6 shows labels of each membership function, and FIG. 7 shows a table of fuzzy rules. Now, assuming that the control amount to be controlled as a result of fuzzy inference is the ultrasonic wave application time TM, the fuzzy rule states that "if the voltage difference V is small (S) and the attenuation rate ΔV is large (L), the ultrasonic wave is applied. Time TM is unchanged (ZR) "," If voltage difference V is medium (M) and attenuation rate ΔV is large (L), ultrasonic wave application time TM is slightly extended (S) "," If the voltage difference V is abnormal (E) and the attenuation rate Δ is small (S)
In that case, the bonding is abnormal (E). " Since the manipulated variable of the inference result is a numerical expression, if the range of the abnormal label is reached, the bonding is stopped.

The amount of modification of the bonding condition obtained by fuzzy inference is stored in the RAM 11. If the correction amount is similar multiple times consecutively, it can be determined that the optimum bonding condition for the lot or chip is the value after correction, so the initial setting value at the start of bonding is the optimum bonding condition. To the correction value, and thereafter the bonding is performed with the correction value.

In this way, a bonding failure due to a lot difference or surface contamination can be detected, and normal bonding work can be efficiently performed by controlling the bonding condition according to each bonding state without stopping the apparatus. ..

In the above embodiment, the ultrasonic wave application time is taken as the control amount for explanation, but the present invention is not limited to this, and the ultrasonic wave output, the load, or a combination thereof may be used as the control amount. FIG. 8 shows an example of these membership functions. Here, in the label, it is necessary to change "shorten" to "weak" and "longen" to "strong" with the ultrasonic wave application time.

Further, in the above-mentioned embodiment, the voltage was taken as the vibration waveform for explanation, but it may be a current or other one as long as it represents a change in impedance.

[0022]

According to the present invention, by detecting the vibration waveform of the vibrator and comparing it with the reference vibration waveform, it is possible to detect whether or not the bonding state is good, particularly the defects caused by surface contamination, lot difference, etc., and perform bonding. Or stop
Alternatively, since the normal condition is controlled by changing the bonding conditions, defective bonding is reduced, reliability is improved, and the number of stoppages is reduced, and efficient bonding work can be performed.

Further, since the judgment and control of the bonding state are performed by using fuzzy reasoning, and the information from the vibration waveform is replaced with the membership function to be treated as "fuzzy information", a qualitative change is grasped and subtle. It is possible to control the bonding conditions corresponding to various bonding states.

Further, the optimum bonding conditions are initialized and the bonding is started, and after a predetermined time has elapsed, fuzzy inference is performed to control the bonding conditions. Without bonding, the bonding is always performed under the optimum conditions, and when a defect occurs, the condition is controlled for the bonding, so that the bonding can be performed for the normal one without changing the optimum condition.

Further, when changing the initial setting value at the time of starting the bonding, it is not a temporary change of the bonding condition due to a lot difference or the like, but when the optimum bonding conditions are similarly shifted collectively for several chips, Since the initial setting value at the time of starting the bonding is changed from the optimum bonding condition to the correction value, the initial setting value becomes the optimum bonding condition for the lot or chip, so that defects can be reduced and the operation amount can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a vibration waveform of a vibrator.

FIG. 3 is a diagram showing a method of calculating a voltage difference.

FIG. 4 is a diagram showing a method of calculating an attenuation rate.

FIG. 5 is a diagram showing an example of a membership function.

FIG. 6 is a diagram showing labels of membership functions.

FIG. 7 is a diagram showing a table of fuzzy rules.

FIG. 8 is a diagram showing an example of a membership function of another controlled variable.

[Explanation of symbols]

 1 Oscillator 2 Oscillator 3 Ultrasonic Horn 4 Bonding Tool 5 Wire 6 Aluminum Electrode 7 Filter 8 A / D Converter 9 CPU 10 ROM 11 RAM 12 D / A Converter 13 Wire Bonding Controller 14 Pressurizing Device

Claims (4)

[Claims] 1. A detection unit for detecting a vibration waveform of a vibrator for driving a bonding tool, and an inference unit for comparing a vibration waveform obtained from the detection unit with a reference vibration waveform to infer a good or bad bonding state by fuzzy inference. And a bonding control means for controlling a bonding condition based on the inference result of the inference means. 2. The inference means according to claim 1, further comprising a storage means for initializing and storing an optimum bonding condition, the bonding being started under the optimum bonding condition and a predetermined time elapses, and then the bonding is performed by fuzzy inference. A wire bonding apparatus, which is a means for inferring the quality of a state. 3. The inference means according to claim 1, further comprising a first storage means for initializing and storing an optimum bonding condition and a control amount of the bonding condition based on the optimum operation amount inferred by the fuzzy inference. A second storage unit for storing the same, and when the second storage unit stores the same control amount for a predetermined number of times, the initial set value at the time of starting bonding is controlled from the optimum bonding condition to the control amount. A wire bonding apparatus characterized by changing to a correction value added with. 4. The bonding condition according to claim 1, wherein the bonding condition controlled based on the inference result by the inference means is at least one of ultrasonic wave application time, ultrasonic wave output, and load. Wire bonding equipment.