JPH0317376B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ball forming apparatus for wire bonding in semiconductor manufacturing equipment.

[Prior Art] FIG. 3 is a schematic diagram showing a wire bonding apparatus, in which a wire 1 is bonded to a pellet 5 and a lead frame 6 placed on a heater 4 through a clamper 2 and a bonding tool 3. . Subsequently, when the wire 1 is lifted up by the clamper 2, the wire 1 is cut at the portion bonded to the lead frame 6, and its tip is returned to the position shown by the broken line. Further, on the side of the wire tip 1A, an electrode 8 forming an electric torch together with a discharge generator 7 containing a built-in power source is arranged, and a high voltage is applied between the wire tip 1A and the electrode 8. Thus, a discharge is generated and a ball 1B is formed at the wire tip 1A. This ball 1B is suitable for bonding to the pellet 5, but as a premise, an appropriate ball diameter is required in accordance with changes in the bonding pad area of the pellet 5, changes in the diameter of the wire 1, etc.

Therefore, conventional discharge generation methods such as applying a constant voltage between the wire 1 and the electrode 8 or adding a constant current circuit to control the current at a constant level during discharge have been adopted.
Efforts are being made to optimize the ball diameter.

As mentioned above, in order to optimize the ball diameter,
Even if improvements are made to the discharge generation method, it is necessary to confirm that a proper ball has been formed during bonding, that is, to judge whether the ball diameter is good or bad, and to more reliably form a ball with the proper ball diameter. It is.

The conventional method for determining whether the ball diameter is good or bad is to check whether or not current is flowing at a certain instant during discharge.
Alternatively, the discharge state is monitored by detecting whether the voltage applied across the discharge gap is abnormal, and if the discharge state is abnormal, it is determined that the ball diameter is also abnormal. However, in this method, the detection timing of the discharge state is limited to a certain instant during the discharge, and therefore the discharge state at other times is ignored, resulting in poor determination accuracy.

Therefore, as described in Japanese Patent Application Laid-Open No. 60-206145, a method has been proposed in which the detection timing of the discharge state is set at an infinite number of times to improve the determination accuracy.

[Problems to be Solved by the Invention] However, when setting an infinite number of discharge state detection timings and detecting the discharge state at each timing, it is necessary to generate an infinite number of detection timing signals, which requires complicated control. Since a circuit is required, the device configuration becomes extremely complicated.

An object of the present invention is to improve the accuracy of ball diameter determination with a simple device configuration.

[Means for Solving the Problems] The present invention provides a ball forming device for wire bonding that generates a discharge between the tip of the wire and an electrode to form a ball at the tip of the wire. A charge amount setting means for setting a value equivalent to the amount of charge to be given to the wire during discharge in order to form the ball diameter; a charge amount accumulating means for accumulating a value equivalent to the amount of charge given to the wire during discharge; and a charge amount accumulation means. The ball diameter determination means compares the accumulated value of the means with the set value of the charge amount setting means and determines the ball diameter.

[Operation] The ball diameter is determined by the amount of charge given to the wire during discharge. Therefore, according to the present invention,
By accumulating a value equivalent to the amount of electric charge given to the wire at the start of discharge, and comparing the cumulative value of the amount of electric charge with a preset value set in the electric charge amount setting means, it is possible to determine the diameter of the ball. can be determined at any time. As a result, according to the present invention, ball diameter determination accuracy can be improved with a simple device configuration without requiring a complicated control circuit.

Further, in the present invention, the charge amount accumulation means is
By using an integrator that integrates the equivalent value of the discharge current over the discharge time, it is possible to easily accumulate the equivalent value of the amount of charge given to the wire during discharge.

Further, in the present invention, the charge amount setting means sets a value equivalent to the charge amount corresponding to the appropriate ball diameter as the good level, so that the ball diameter determination means determines whether the ball diameter is in an appropriate state (good or bad). can be easily determined.

Further, in the present invention, if the discharge is controlled to end when the ball diameter determining means determines that the ball diameter has reached the appropriate value, the ball having the appropriate ball diameter can be more reliably and efficiently produced. Can be formed.

[Embodiment] FIG. 1 is a block diagram showing a ball forming device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing control waveforms used in the ball forming device.

The ball forming device 10 includes a discharge generating device 11, a discharge current detecting section 12, an integrator (charge amount accumulation means) 1
3. Ball diameter determination section (ball diameter determination means) 14;
A good level setting section (charge amount setting means) 15 is provided. The ball forming device 10 also includes a discharge voltage detection section 16, a shot determination section 17, and an integration stop switch section 18.

The discharge generating device 11 has a built-in constant current power supply circuit, and generates a discharge between the electrodes 22 of the tip end 21A of the wire 21 based on the discharge commands A1 to A3 to form a ball on the wire tip 21A. do.
In this example, the discharge state according to the discharge command A1 is normal, the discharge state according to the discharge command A2 is a faulty state (open) where the discharge gap is too wide, and the discharge state according to the discharge command A3 is a faulty state (open).
It is assumed that the discharge state is in a defective state (shoot) in which the wire 21 is in contact with the electrode 22.

The good level setting section 15 sets a value equivalent to the amount of charge that should be applied to the wire 21 during discharge as a good level l1 in order to form an appropriate ball diameter.

The integrator 13 receives a discharge time t from the discharge generator 11 in response to each discharge command A1 to A3, and receives a discharge current i from the discharge current detector 12.
Given the equivalent values of 1 to i3 (a signal that converts the discharge current into a voltage signal and formats it to an easy-to-handle level), by integrating the above equivalent value of the discharge current flowing through the wire 21 during discharge over the discharge time, Values corresponding to the amount of charge applied to the wire 21 during discharge are accumulated as integral values s1 to s3.

The ball diameter determination unit 14 determines the integral value s of the integrator 13.
1 to s3 to the setting value l of the good level setting section 15.
1 and determines whether the ball diameter is in an appropriate state, and outputs the determination result to the bonding device, such as by outputting a good signal G when the ball diameter is in the appropriate state.

As a result, if the discharge condition is normal,
During the entire generation period of the discharge command A1, the discharge current i1 flows, the integral value s1 exceeds the good level l1, the good signal G is output, and it is determined whether the ball diameter is good.

In addition, when the discharge state becomes open, the discharge current i2 flows only during the period during which the discharge command A2 does not reach the open state, and
The integral value s2 cannot reach the good level l1, and it is determined that the ball diameter is defective.

By the way, when the discharge state is short, since the discharge generating device 11 uses a constant current power supply circuit, the discharge current i3 of almost the same level flows during the entire generation period of the discharge command A3. Therefore, in this case, the integration by the integrator 13 after the point in time when the short determination section 17 determines that a short has occurred is stopped by the operation of the integration stop switch section 18. That is, the short determination unit 17 receives the discharge voltages v1 to v3 detected by the discharge voltage detection unit 16, and detects that the discharge voltage v3 at the time of occurrence of short is smaller than a predetermined short level h, This makes it possible to determine the occurrence of shoots. As a result, the integral value s3 by the integrator 13 when a shot occurs cannot reach the good level l1, and it can be determined that the ball diameter is defective.

Next, the operation of the above embodiment will be explained.

The ball diameter is determined by the amount of charge applied to the wire 21 during discharge. Therefore, according to the above embodiment, the equivalent value of the amount of charge given to the wire 21 at the time of the start of discharge is easily accumulated by integrating the equivalent value of the discharge current over the discharge time by the integrator 13, By comparing the accumulated value of the charge amount with a preset value set in the good level setting section 15, it is possible to easily determine whether the ball diameter is optimized (good or bad). As a result, ball diameter determination accuracy can be improved with a simple device configuration without requiring a complicated control circuit.

Furthermore, when the ball diameter determining section 14 determines that the ball diameter has reached the appropriate value, the ball diameter determining section 14 transmits a discharge termination signal c to the discharge generating device 11, thereby terminating the discharge. good. According to this, a ball having an appropriate ball diameter can be formed more reliably and efficiently.

Note that in the present invention, the discharge generating device 11 is connected to the wire 21.
It is also applicable to a case where a circuit for applying a constant voltage between the electrode 22 and the electrode 22 is built-in. At this time,
When the discharge state becomes short, the occurrence of a defective ball diameter is determined by the following method.

Under constant voltage control, when the discharge state becomes short, the discharge current i3 becomes i3z and the discharge voltage v3
becomes v3z. Therefore, the discharge current detection section 12
A short determination section is provided which determines the occurrence of short by detecting an abnormal rise in which the current i3 detected by the current i3 becomes the current i3z, and based on the determination result of the short determination section, the integration stop switch section 18 is actuated to stop the integration by the integrator 13. Integration after the shot occurs is stopped, allowing the ball diameter determining section 14 to determine whether a defective ball diameter has occurred.

The integrator 1 is not provided with the short determination section mentioned above.
If the integration by 3 is continued even after the shot occurs, the integral value s3 increases to become s3z. Therefore, in this case, the good level l1
Short level l2, which is obtained by adding a certain level to
It is used together with l1 in the ball diameter determining section 14, and the ball diameter determining section 14 can determine that the state in which the integral value s3z exceeds the shot level l2 is the occurrence of a shot, that is, the occurrence of a defective ball diameter.

Further, in the above embodiment, the electric charge amount setting means in the present invention is the good level setting section 15, but the electric charge amount setting means presets a large number of combinations of various ball diameters and corresponding electric charge amounts. It may be something that has already been set. In this case,
The ball diameter determination unit 14 can not only determine whether the ball diameter has reached an appropriate value, but also determine the state of increase in the ball diameter formed by electric discharge at any timing.

[Effects of the Invention] According to the present invention, ball diameter determination accuracy can be improved with a simple device configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a ball forming device according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing control waveforms used in the ball forming device, and FIG. 3 is a schematic diagram showing a wire bonding device. . 10...Ball forming device, 11...Discharge generating device, 12...Discharge current detection section, 13...Integrator (charge amount accumulation means), 14...Ball diameter determination section (ball diameter determination means), 15... ...Good level setting section (charge amount setting means), 21...Wire, 22...
electrode.

Claims (1)

[Claims] 1. In a ball forming device for wire bonding that generates a discharge between the tip of the wire and an electrode to form a ball at the tip of the wire, in order to form a ball with a constant diameter. A charge amount setting means for setting a value equivalent to the amount of charge to be given to the wire during discharge; a charge amount accumulating means for accumulating a value equivalent to the amount of charge to be given to the wire during discharge; 1. A ball forming device for wire bonding, comprising ball diameter determining means for determining the ball diameter by comparing it with a setting value of the setting means. 2. The ball forming device for wire bonding according to claim 1, wherein the charge amount accumulating means is an integrator that integrates the equivalent value of the discharge current flowing through the wire during discharge over the discharge time. 3. In claim 1 or 2, the charge amount setting means sets a value equivalent to the amount of charge necessary to form an appropriate ball diameter as a good level, and the ball diameter determination means determines the ball diameter in an optimized state. A ball forming device for wire bonding that determines 4. A ball forming device for wire bonding according to claim 3, in which the discharge is terminated when the ball diameter determining means determines that the ball diameter has reached an appropriate value during the discharge.