JPH08203955A - Bonding device - Google Patents

Abstract

(57) [Summary] [Objective] To provide a bonding apparatus capable of monitoring the bonding state in real time and reducing the production of defective products. [Structure] Focusing on that a current value flowing from a driver provided in a control device 18 to a drive motor 15 for driving a bonding tool 8 follows a fluctuation of a bonding load, and a current detection sensor 23 samples this current value. In the evaluation section 24, the bonding state is evaluated by comparing the vibration center value, the amplitude and the vibration cycle of the waveform of the current value with the reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding apparatus such as a wire bonding apparatus or a single point bonding apparatus for connecting electrode terminals using a needle-shaped bonding tool.

[0002]

2. Description of the Related Art As a method of mounting a semiconductor chip on a mounting board such as a printed circuit board or a lead frame, there has been a conventional method
There is a method called wire bonding. This wire bonding method is a method of connecting the terminals or leads of the semiconductor chip and the mounting substrate to each other using a gold wire (gold wire).

This wire bonding method is a connection method which is carried out by inserting the gold wire into a needle-shaped bonding tool (capillary). First, the tip of the gold wire extended from the lower end surface of the bonding tool. A spherical "ball" is formed by melting a part by electric discharge or the like.

Then, the bonding tool is driven to press the ball onto the electrode pad of the semiconductor chip, which is the first bonding point, and ultrasonic vibration is applied to bond the ball.

When the bonding to the first bonding point is completed, the bonding tool is moved to the electrode pad side of the mounting substrate, which is the second bonding point, while paying out the gold wire, and with respect to this electrode pad. Also performs the same joining.

Finally, the gold wire is clamped by a wire clamper and pulled upward to cut the gold wire right above the portion bonded to the second bonding point.

In the wire bonding method, such an operation is repeated for each electrode pad of the semiconductor chip to make individual connections. by the way,
In recent years, semiconductor chips have become larger and more highly integrated, and accordingly, the electrode pads to be connected by wire bonding of the semiconductor chips are often multi-terminaled, narrowed in pitch, and miniaturized.

Accordingly, there is a demand for finer and more accurate wire bonding. Further, in order to maintain the productivity of the semiconductor device, one connection has to be performed at a higher speed.

That is, as compared with the conventional wire bonding, there is a case where finer bonding must be performed with high accuracy and high speed. When performing such bonding, the gold wire and the bonded portion (first, second
It is an important point to control the bondability with the (bonding part of).

The quality of the bondability is determined by the pressing state of the wire (ball) by the tool and the application state of ultrasonic vibration. Therefore, in order to maintain the good bondability, it is necessary to control the pressing force and ultrasonic vibration of the tool, but conventionally, monitoring during bonding was not performed and the product after bonding was kept constant. The bondability is evaluated by sampling inspection every time, and the pressing force of the tool and the ultrasonic vibration are adjusted based on this.

[0011]

However, the above-described conventional wire bonding method has problems to be solved as described below. That is, in the conventional wire bonding method, since the wire bonding apparatus is adjusted based on the evaluation of the bondability by the sampling inspection, a large number of defective products are produced until the worker finds the bond failure. There is a risk that the production yield will be deteriorated.

Further, the cause of the defective joint may not be identified only by inspecting the product, and the cause of the defective occurrence may not be removed promptly. Furthermore, when a defective product is manufactured due to a temporary or sudden cause, such a defective product may not be found by only the sampling inspection, and the quality of the product may deteriorate.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a bonding apparatus capable of monitoring the bonding state in real time and reducing the production of defective products. .

[0014]

According to a first aspect of the present invention, there is provided a tool, and in a bonding apparatus for connecting electrode terminals by driving the tool, a driving actuator for driving the tool, Bonding is performed by comparing a current value detected by the drive circuit connected to the drive actuator, current detection means for detecting a current flowing from the drive circuit to the drive actuator with a predetermined reference value. And an evaluation means for evaluating the state of.

The second means is, in the bonding apparatus of the first means, swingably held, holds the tool on the swing tip side, and swings to swing to drive the tool. However, the drive actuator is a drive motor that drives the oscillator to swing.

A third means is the bonding apparatus of the second means, wherein ultrasonic vibration applying means for applying ultrasonic vibration to the lead or wire joining portion through the tool in the oscillating body. Is provided.

A fourth means is the bonding apparatus of the first means, wherein the evaluation means uses the vibration center value, the amplitude and the vibration cycle of the waveform of the current value for the comparison. It is a thing.

A fifth means is characterized in that, in the bonding apparatus of the first means, the evaluation means has a display means for displaying a comparison result and an evaluation of the bonding state.

[0019]

According to such means, the current value flowing through the actuator and the drive motor from the drive circuit is detected, and the vibration center value, amplitude and vibration cycle of the waveform of this current value are compared with the reference value to determine the bonding state. Can be evaluated, and the bonding state can be monitored in real time.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The main operation of wire bonding has already been described in the description of the prior art, and will be omitted. First, the configuration of the wire bonding apparatus will be briefly described with reference to FIG.

The bonding apparatus has a base (not shown), and a bonding stage 1 and a bonding body 2 are provided on the base. As shown in FIG. 1, a printed circuit board 4 formed by die bonding a semiconductor chip 3 is held and fixed on the bonding stage 1. On the upper surface of the semiconductor chip 3 and the upper surface of the printed board 4, a plurality of electrode pads 3a, 4a which are wire-connected to each other by this device are provided.
(First and second bonding points) are respectively formed.

The bonding body 2 comprises an XY table 6 provided on the base and a bonding head 7 attached to the XY table 6. The structure of the bonding head 7 will be described below.

Reference numeral 8 in FIG. 1A is a bonding tool for performing a wire bonding operation. The bonding tool 8 has a needle-like shape with a thin tip, and has an insertion hole (not shown), through which a gold wire shown in FIG. 9 is inserted, formed over the entire length in the vertical direction. There is.

The bonding tool 8 is held on the tip of an ultrasonic horn shown in FIG. 10 with its axis substantially vertical. The other end of the ultrasonic horn 10 is connected to the ultrasonic oscillator 11.

An ultrasonic oscillator (piezoelectric element or the like), not shown, is built in the ultrasonic oscillator 11, and the ultrasonic oscillator is connected to the other end of the ultrasonic horn 10. Therefore, by applying a voltage to the ultrasonic vibrator to oscillate the ultrasonic vibration, the ultrasonic vibration is transmitted to the bonding tool 8 via the ultrasonic horn 10.

Further, this ultrasonic oscillator 11 is shown in FIG.
The ultrasonic oscillator 11 is housed in a casing indicated by, and is swingably held via a rotary shaft 14 that horizontally projects from the side surface of the ultrasonic oscillator 11. That is, the bonding tool 8 is driven in the vertical direction when the ultrasonic oscillator 11 swings.

On the other hand, a rotary motor 15 connected to the rotary shaft 14 is attached to the side surface of the casing 13, and the bonding tool 8 is operated at a predetermined speed by operating the motor 15. It is designed to be driven up and down by acceleration. Further, the motor 15 is configured to generate a force corresponding to a predetermined bonding load when the wire 9 is bonded (pressed) to the lower end surface of the tool 8.

On the other hand, the gold wire 9 used for wire bonding is drawn out from a wire spool (not shown) provided above the tool 8 and inserted into the tool 8, and then the tip end is placed under the tool 8. It is exposed by a predetermined size from the end face.

When performing wire bonding, a spherical ball 9a is formed at the tip of the wire 9 by heating by electric discharge, as described in the section of the description of the conventional example.

Further, above the bonding tool 8, a wire clamper 16 which moves up and down together with the bonding tool 8 is provided. This wire clamper 1
6 is used for cutting the gold wire 9 and the like.
Has a role of holding the wire 9 immovably with respect to the bonding tool 8.

Next, a control system for controlling the bonding apparatus will be described with reference to FIG. First, the rotary motor 15 is the driver 1 provided in the control device 18.
The driver 19 is connected to the terminal 9 and operates by applying a predetermined current from the driver 19.

Further, as shown in FIG.
A position detector 20 for detecting the rotation angle of the rotation shaft 14 (the swing angle of the ultrasonic oscillator 11) and a speed detector 21 for detecting the rotation speed (swing speed) are attached to the. The position detector 20 and the speed detector 21 are also connected to the control device 18.

The position detector 20 and the speed detector 21 described above.
As shown in FIG. 2, the detection signal from the controller 1
It is adapted to be input to the arithmetic and control unit 22 provided in the inside 8. The arithmetic control unit 22 is configured to operate the position detector 20.
And the rotational angle, angular velocity, angular acceleration of the rotary shaft 14 or the height (position), speed, acceleration, etc. of the bonding tool 8 are obtained from the detection signal from the speed detector 21.
These are compared with a predetermined target value, and an operation signal for reducing the difference is issued to the driver 19.

The driver 19 operates the rotary motor 15 by applying a current to the rotary motor 15 based on the operation signal. In addition,
The detection by the position detector 20 is performed at every predetermined sampling time, and the calculation control unit 2
2 is configured to cause the bonding tool 8 to perform a desired operation by feedback control.

Further, a current detection sensor (detection resistor) 23 functioning as the current detection means of the present invention is provided between the driver 19 and the rotary motor 15.
The current detection sensor 23 detects the current flowing through the coil of the rotary motor 15 and outputs it to an evaluation section (evaluation means) 24 shown in the drawing.

The output signal (current value) from the current detection sensor 23 is input to the A / D converter shown by 25 in the figure through an amplifier and sampled. Then, the sampled current value is input to the CPU 26.

A reference value setting section (evaluation means) 27 is connected to the CPU 26. The reference setting unit 27 generates a reference value used for bonding evaluation and inputs the reference value to the CPU 26.

The CPU 26 evaluates the bonding by comparing the reference value with the sampling current value. Hereinafter, this evaluation method will be described together with the bonding operation.

This method is a method of understanding the fluctuation of the bonding load applied to the bonding tool 8 from the fluctuation of the sampling current value (current value flowing through the coil of the motor) and evaluating the bonding based on this.

That is, even when a constant current application command is given to the driver 19 from the arithmetic control unit 22, if the load applied to the rotary motor 15 changes during the bonding, the feedback corresponding thereto is given. The value of the current flowing through the coil of the rotary motor 15 changes due to the control.

Since the load applied to the rotary motor 15 is proportional to the load applied to the bonding tool 8, that is, the bonding load, the value of the current flowing through the coil of the motor 15 is detected (sampled) and its fluctuation is investigated. It is possible to understand the above-mentioned bonding load and eventually the bonding state.

FIG. 3 is a graph showing the relationship between the bonding load and the sampled current value. This figure will be described together with the bonding operation. First, when a ball 9a is formed at the tip of the gold wire 9 led out from the bonding tool 8 as shown in FIG. 1, the bonding tool 8 is driven downward by the operation of the rotary motor 15. It In this state, the bonding load is almost zero as shown by (a) in FIG.
Is.

When the bonding tool 8 brings the ball 9a into contact with the electrode pad 3a of the semiconductor chip 3 which is the first bonding point, the bonding tool 8 stops descending. At this time, a reaction force (impact force) is generated in the bonding tool 8 so that the bonding load is increased as shown in FIG.

On the other hand, when the bonding tool 8 is stopped, the rotation of the rotary motor 15 is stopped, so that a current is applied to the rotary motor 15 to further lower the bonding tool 8 (feedback control).
As a result, as shown in FIG. 3B, the current value (sampling current value) flowing through the coil of the rotary motor 15 increases, and the bonding load increases.

The current detecting sensor 23 is capable of detecting such an increase in current value in a state (real time) substantially without delay with the increase in the bonding load.

When the ball 9a comes into contact with the electrode pad 3a of the semiconductor chip 3, it can be known from the output from the position detector 20 or the like, so that the arithmetic control unit 22 causes the driver 19 to operate. Emits an activation signal,
A current value capable of obtaining a desired bonding load is applied from the driver 19 to the rotary motor 15.

The desired bonding load is indicated by F in the graph of FIG. 3 (a), and the current value by which this bonding load can be obtained is indicated by A in the graph of FIG. 3 (b). There is.

The initial bonding load is shown in FIG.
As shown by the first peak in (a), it greatly rises above the predetermined bonding load F. this is,
This is due to the impact load generated by the contact of the ball 9a with the electrode pad 3a and the motor current application (driving force) by the feedback control as described above.

Then, the change in the bonding load vibrates cyclically around the predetermined bonding load F after passing through the first peak. As described above, the periodic vibration is caused by the vibration when the bonding tool 8 collides with the electrode pad 3a or the mechanical vibration of the entire device, which causes the bonding tool 8 to generate a small vibration. This is because the bonding load changes accordingly.

On the other hand, the control unit 22 changes the current value applied to the rotary motor 15 in order to stabilize the bonding load according to the change in the bonding load. Therefore, the current value obtained by the sampling is approximately proportional to the fluctuation of the bonding load. That is, as shown in FIG. 3B, the sampling current value is periodically oscillated around the predetermined current value A except for the portion corresponding to the initial impact load.

The amplitude B at this time is determined by the rotary motor 1
It is proportional to the fluctuation range of the load applied to 5, that is, the fluctuation range of the load of the bonding tool. The current fluctuation cycle C is proportional to the load fluctuation cycle of the bonding tool 8.

That is, it is possible to know the actual fluctuation of the bonding load by looking at the amplitude B of the sampling current value, the fluctuation cycle C and the vibration center value. CPU2
Reference numeral 6 compares these values with the reference value set by the reference value setting unit 27 to evaluate the bonding.

Next, the setting of the reference value will be described. When the bonding conditions change, the behavior of the bonding tool 8 changes from the normal case, so that the bonding load also changes, and the waveform of the sampling current value changes accordingly.

That is, when the change in the behavior of the bonding tool 8 is large, the value at the center of the current value vibration is
There is a large shift from the predetermined current value A, the amplitude B of the vibration becomes very large, or the cycle C becomes long or short.

When the behavior of the bonding tool 8 is greatly changed as described above, sufficient bonding strength cannot be obtained between the ball 9a (wire 9) and the electrode pads 3a and 4a, or the bonding time is long. It is conceivable that the shape of the ball 9a struck or crushed by pressing becomes nonstandard and a short circuit problem may occur between the adjacent electrode pads 3a.

From the viewpoint of preventing such a situation, the reference value setting section 27 provides a reference for normal bonding based on the waveform of the sampling current value when normal bonding is performed. The allowable range of the vibration center current value, the allowable range of the amplitude, and the allowable range of the cycle (these are referred to as reference values) are defined.

Then, the CPU 26 compares each value of the vibration center current value, the amplitude B, and the cycle C obtained from the waveform of the sampled current value with the above reference value, and each of the above values becomes the above reference value. If it is out of the range, it is determined that a bonding failure has occurred.

When the CPU 26 is connected to the arithmetic control section 22 and detects that the bonding failure has occurred, the arithmetic control section 2 is based on that fact.
2 is issued to stop the above-mentioned bonding operation.

The CPU 26 also stores the waveform of the sampling current value at that time, which is stored in FIG.
Display on the monitor, etc. By seeing this, the operator can understand the cause of the defect by experience, and thus remove the cause of the defect.
For example, when the amplitude B is too large, the vibration of the machine is the main cause, so the mounting failure, the change over time of the parts, etc. are investigated.

Then, when the cause of the defect is removed, the apparatus is operated again to continue the wire bonding. With such a configuration, the effects described below can be obtained.

First, in the case where a bonding failure (bonding failure) occurs, the apparatus can be stopped immediately, and the same bonding failure can be effectively prevented from occurring continuously.

That is, as a factor causing the bonding failure, the bonding stage 1 holding the printed circuit board 4 vibrates for some reason, the printed circuit board 4 is not sufficiently fixed, and the above-mentioned change due to a change with time. Examples of this include “rattle” of the ultrasonic oscillator 11 and the ultrasonic horn 10, and mounting failure when parts are replaced. Due to such factors, the above-mentioned bonding failure occurs when a desired bonding load (including ultrasonic vibration) cannot be transmitted to the bonding portion.

When the above-mentioned factors have a great influence on the bonding load, the shape of the crushed ball 9a (9) may be out of the standard or the bonding strength may be lowered, as described above. is there.

In the conventional example, the bonding state is evaluated by a sampling inspection after a predetermined number of wire bonds are bonded. Therefore, until a worker finds the above bonding defect, wire bonding having the same bonding defect is performed. There was a possibility that they would go on continuously. Further, if a joint failure occurs due to a temporary or sudden factor, there is a possibility that it cannot be detected by the above sampling inspection.

In the present invention, in view of the fact that the fluctuation of the bonding load and the fluctuation of the current value applied to the motor 15 are substantially proportional to each other, the current value is sampled so that the bonding load can be monitored in real time. Then, the bonding state is evaluated by comparing the waveform of this current value with the reference value.
The occurrence of the above-mentioned bonding failure can be immediately detected, and the apparatus can be stopped based on it. As a result, it is possible to effectively prevent a similar defect from occurring continuously.

Further, even if a defective connection occurs due to a temporary factor, such a defect can be effectively removed. Secondly, since it is possible to predict what kind of defect has occurred based on experience from the waveform of the sampling current value, it is possible to quickly eliminate the above-mentioned defect generation factor.

That is, in the conventional example, the wire 9 is simply used.
Since only the bonding strength between the electrode pad 3a and the electrode pad 3a was examined, the cause of the defect could not be found without detailed examination, and it took time to remove the cause of the defect.

However, in the present invention, the waveform of the current value at the time of occurrence of a defect can be seen, and which of the three values of the vibration center value, amplitude, and vibration cycle of the waveform deviates from the reference value. By looking at, it is possible to estimate the defect factor based on the experience. This has an effect that the cause of the defect can be removed quickly.

As described above, the present invention is based on the above first and second aspects.
As a result of having the effect of, the yield of wire bonding,
Productivity and mobility can be improved. Since each point can be bonded accurately and surely, there is an effect that it is possible to effectively cope with the recent tendency of multiple terminals of electrode pads of semiconductor chips, narrow pitch, and miniaturization.

The present invention is not limited to the above-described embodiment, but can be variously modified without changing the gist of the invention. For example, the above-mentioned one embodiment is the wire bonding apparatus, but the present invention is not limited to this apparatus, and other similar apparatus, for example, a semiconductor component by ultrasonically vibrating a needle-shaped bonding tool similarly. It can also be applied to a single-point bonding device that individually joins the inner lead and the outer lead.

In the above embodiment, the rotary motor 15 is used to drive the bonding tool 8. However, the invention is not limited to this, and an actuator such as a piezoelectric element or a linear motor may be used. . Even with such a piezoelectric element, since the electromotive force is generated by the change of the load, the same effect as that of the above-described embodiment can be obtained.

[0072]

As described above, according to the present invention, an actuator for driving a bonding tool from a drive circuit,
Focusing on the fact that the current value flowing in the drive motor follows the fluctuation of the bonding load, the bonding state is evaluated by comparing the vibration center value, amplitude and vibration cycle of the waveform of this current value with the reference value. Is.

With such a configuration, the bonding state can be evaluated in real time, and when a bonding failure occurs, it is effective that the same failure occurs continuously by stopping the device. Can be prevented.

The cause of the defect can be estimated by observing the comparison result displayed on the display means, and the cause of the defect can be removed quickly. Due to these, there is an effect that the yield, quality and productivity of products can be improved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a control system of the same.

FIG. 3 is a graph showing the relationship between the sampled current value and the bonding load.

[Explanation of symbols]

8 ... Bonding tool (tool), 11 ... Ultrasonic oscillator (oscillator), 15 ... Drive motor (drive actuator), 18 ... Control device (drive circuit), 19 ... Driver (drive circuit), 23 ... Current detection sensor (Detection means), 2
4 ... Evaluation unit (evaluation means).

Claims (5)

[Claims] 1. A bonding apparatus comprising a tool and connecting electrode terminals by driving the tool, a driving actuator for driving the tool, a driving circuit connected to the driving actuator, and a driving circuit. A current detecting means for detecting a current flowing from the circuit to the driving actuator; and an evaluating means for evaluating the bonding state by comparing the current value detected by the current detecting means with a predetermined reference value. Characteristic bonding equipment. 2. The bonding apparatus according to claim 1, further comprising an oscillating body which is swingably held, holds the tool on a swing tip side, and swings to drive the tool. The bonding actuator is a drive motor for oscillating the oscillating body. 3. The bonding apparatus according to claim 2, further comprising ultrasonic vibration applying means for applying ultrasonic vibration to a joining portion of the lead and the wire via the tool in the rocking body. Bonding device characterized by being 4. The bonding apparatus according to claim 1, wherein the evaluation means uses a vibration center value, an amplitude and a vibration cycle of a current value waveform for the comparison. 5. The bonding apparatus according to claim 1, wherein the evaluation means has a display means for displaying a comparison result and an evaluation of the bonding state.