JPH0317377B2 - - 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. 5 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 that forms 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, conventionally, by adopting a discharge generation method such as applying a constant voltage between the electrodes 8 of the wire 1 or adding a constant current circuit to control the current during discharge,
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] A first aspect of the present invention is 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 discharge condition setting means for setting a discharge current to be applied to the wire and a discharge command time; a discharge generating means for causing the set discharge current set by the discharge condition setting means to flow through the wire for the set discharge command time;
Current presence detection means detects the presence or absence of a discharge current flowing in a discharge circuit including a wire during discharge and outputs the detection result as a binary signal; and an integrator integrates the output value of the current presence detection means; Normal discharge condition setting means predetermines the integral value of the integrator as a good level under a condition in which a ball diameter of The ball diameter determining means compares the ball diameter with a good level and determines whether the ball diameter has reached a certain value.

The second aspect of the present invention is 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, and the discharge current and discharge command to be given to the wire. discharge condition setting means for setting a time; discharge generating means for allowing the set discharge current set by the discharge condition setting means to flow through the wire for the set discharge command time; and discharge current flowing in a discharge circuit including the wire during discharge. a current presence/absence detection means for detecting the presence or absence of the ball and outputting the detection result as a binary signal; an integrator for integrating the output value of the current presence/absence detection means; It has a normal discharge state setting means that predetermines the integral value of the integrator as a good level, and a ball diameter determining means that compares the integral value of the integrator with the good level and determines whether the ball diameter has reached a certain value. The present invention is characterized in that the discharge by the discharge generating means is terminated on condition that the ball diameter determining means determines that the ball diameter has reached a certain value.

[Operation] The ball diameter is determined by the amount of charge given to the wire during discharge, that is, the product of discharge current and discharge time. Therefore, according to the first aspect of the present invention, when the amount of charge to be given to the wire in order to form a constant ball diameter is set in the discharge condition setting means as the discharge current and the discharge command time, the discharge generating means A discharge current is passed through the wire for the set discharge command time.
Further, the current presence/absence detection means detects the presence or absence of a discharge current flowing in the discharge circuit including the wire, and outputs a signal of logic level "1" while the discharge current is flowing, and the integrator outputs a signal of logic level "1". Integrate. As a result, even when the amount of charge to be applied to the wire is changed by changing the discharge current in response to a change in the diameter of the ball formed on the wire, the rate of increase in the integral value accumulated by the integrator remains constant. Become. Therefore, when the set discharge command time has elapsed, it is determined whether the ball diameter has reached the initially determined diameter by comparing the integrated value of the integrator with the good level preset in the normal discharge state setting means. can. This results in
It is possible to increase the ball diameter of various sizes with a simple device configuration without the need for a complicated control circuit, and without the need for detailed adjustment of the ball diameter judgment criteria, that is, the ball diameter level, according to the various ball diameters. Can be determined accurately and easily.

Furthermore, according to the second aspect of the present invention, compared to the first aspect of the present invention described above, the discharge by the discharge generating means is terminated on the condition that the ball diameter determining means determines that the ball diameter has reached a certain value. As a result, the bonding work can be started immediately after a proper ball is formed, and the overall bonding speed can be shortened.

[Embodiment] Fig. 1 is a block diagram showing a ball forming device according to a first embodiment of the present invention, Fig. 2 is a waveform diagram showing control waveforms used in the ball forming device, Fig. 3A,
B is a schematic diagram illustrating the integration state of the charge amount equivalent value.

The ball forming device 10 includes a discharge condition setting section (discharge condition setting means) 11, a discharge generation device (discharge generation means) 12, a discharge current detection section 13, a current presence/absence detection section (current presence/absence detection means) 14, an integrator 15, A normal discharge state setting section (normal discharge state setting means) 16 and a ball diameter determination section (ball diameter determination means) 17 are provided. The ball forming device 10 also includes a discharge voltage detection section 18 and a voltage presence/absence detection section 19.

The discharge generator 12 has a built-in constant current power supply circuit, and generates a discharge between the tip 21A of the wire 21 and the electrode 22 based on the discharge commands A1 to A3 to form a ball at the tip 21A of the wire. 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.

Here, the discharge condition setting unit 11 sets the amount of charge that should be given to the wire 21 in order to form a constant ball diameter as the discharge current I and the discharge command time T, and the discharge generating device 12 sets the discharge condition setting unit 11. Part 1
A set discharge current I set by No. 1 is caused to flow through the wire 21 for a set discharge command time T. FIGS. 3A and 3B show the amount of charge to be given to the wire 21 at the current discharge command time T.
In this example, T1 is constant and is changed according to changes in the discharge current. For example, when the ball diameter is small, the discharge current is set to I1, and when the ball diameter is large, the discharge current is set to I1.
2 (>I1). Of course, the discharge command time T can also be changed.

The current presence/absence detection unit 14 detects each discharge command A1 to A3.
, the discharge current i1 from the discharge current detection unit 13
~i3, and outputs the detection result as a binary signal. That is, the current presence/absence detection section 14
When the discharge state is normal and the discharge current i1 is flowing, it outputs a logic level "1" signal indicating that there is a current, and when the discharge state is open and the discharge current i2 does not flow, it outputs a logic level signal indicating that there is no current. Outputs a “0” signal.

The integrator 15 integrates the output value of the current presence/absence detection section 14, that is, accumulates a value equivalent to the amount of charge applied to the wire 21.

The normal discharge state setting unit 16 predetermines the integral value of the integrator 15 in a state in which a constant ball diameter is to be formed, that is, in a state in which the minimum amount of charge required for the wire 21 is given, and sets it to a good level L.
It is set as . The setting method will be described later.

The ball diameter determination unit 17 compares the integral value of the integrator 15 with the good level L preset in the normal discharge state setting unit 16 at the time when the discharge command time T set in the discharge condition setting unit 11 has passed, and determines whether the ball diameter It is determined whether the diameter has reached a certain value and outputs the determination result, such as outputting a good signal G, to the bonding device.

By the way, if it is assumed that normal discharge is performed over the entire discharge command time T1, and if the discharge current detected by the discharge current detection section 13 is not binarized but is integrated by an integrator, the integral value increases. As shown in Fig. 3A, the rate changes every time the discharge current changes, and the ball diameter determination criteria are changed accordingly.
Fine adjustments are required as shown in 12. On the other hand, when the discharge current detected by the discharge current detection unit 13 is binarized and integrated as in this embodiment, the rate of increase in the integral value is as shown in FIG. 3 regardless of the discharge currents I1 and I2. It becomes constant as shown in B. This characteristic is utilized in this embodiment to determine whether the ball diameter has reached a certain value.

Here, an example of how to set the discharge current and discharge command time set in the discharge condition setting section 11 and the good level L set in the normal discharge state setting section 16 will be explained.

First, in the initial setting stage, an operator experimentally applies a certain discharge current i to the wire 21 and observes a ball being formed while causing a normal discharge between the wire 21 and the current 22. Then, determine whether the time it takes to form a ball with the minimum ball diameter currently required is appropriate, taking into account factors such as bonding speed, and adjust the discharge current i until it is determined to be appropriate. Adjust. Note that this work requires the wire diameter, the required ball diameter,
This can be done efficiently if the relationship between the discharge currents is available as data in advance. In this way, the discharge current I1 is first determined, and the ball with the minimum diameter required now is determined at the time shown in FIG. 3B.
Assuming that it is formed by Ta, the good level L is determined here.

The above description assumes that normal discharge is performed during the entire time period Ta, but it is conceivable that no discharge may occur temporarily for some reason during actual discharge. Taking these into consideration, the discharge command time T1, which is longer than the previously determined time Ta, is determined. In determining this discharge command time T1, factors such as the bonding speed mentioned above are taken into consideration.

Also, if the next required ball diameter is large,
It is necessary to increase the amount of charge applied to the wire. For this purpose, it is sufficient to increase at least one of the discharge current I and the discharge command time T. In this embodiment, if the same discharge command time T1 is used as before, the discharge current I is increased. This is necessary. For this reason, the operator increases the discharge current from the current I1 and increases the time in the normal discharge state.
The current I2 is set in the discharge condition setting unit 11 so that a ball having the minimum diameter next required at Ta is formed.

Next, a method for determining whether the ball diameter has reached a certain value in actual bonding work will be described in detail.

First, when the discharge state is normal, the discharge current i1 flows during the entire generation period of the discharge command A1, and the integral value s1 after the elapse of the discharge command time T1 exceeds the good level L, so the good signal G is output. , the ball diameter is determined.

In this case, as shown by the two-dot chain line in FIG. 3B, even if there is a non-discharge period during the discharge, the integral value after the discharge command time T1
If S1' exceeds the good level L, it is determined that the necessary amount of charge has been added to the wire 21,
The ball was judged to be in good shape.

However, when the discharge state becomes open, the discharge current i2 is generated only during the period when the discharge command A2 does not reach the open state.
Even if the ball is flowing, the integral value s2 cannot reach the good level L, and it is determined that the ball diameter is defective.

By the way, when the discharge state is short, since the discharge generating device 12 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, due to the presence of the discharge voltage detection section 18 and the voltage presence/absence detection section 19, the output signal of the current presence/absence detection section 14 after the occurrence of short is detected by the integrator 1.
5 shall not be accumulated. That is,
Discharge voltages v1 to v3 detected by the discharge voltage detection unit 18
becomes v3, which is smaller than the predetermined shot level h. Therefore, when the discharge voltage is higher than the short level h, the voltage presence/absence detection unit 19 outputs a signal with a logic level of 1" indicating that the voltage is present, and when the discharge voltage is lower than the short level h, it indicates that there is no voltage and outputs a signal with a logic level of 0". Output. The integrator 15 receives the output signal of the current presence/absence detection section 14,
Taking the AND of the output signals of the voltage presence/absence detection section 19,
This allows the output signal of the current presence/absence detection section 14 to be accumulated only when there is no short state (voltage present).

As a result, the integral value s3 by the integrator 15 when a shot occurs cannot reach the good level L, and it can be determined that the ball diameter is defective.

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

First, when the discharge command time and T1 of the discharge current I1 are set in the discharge condition setting section 11 as described above, the discharge generator 12 causes the discharge current to flow through the wire 21 for the set discharge command time. Furthermore, the current presence/absence detection section 14 detects the presence or absence of a discharge current flowing through the wire 21, and outputs a signal with a logic level of 1" while the discharge current is flowing, and the integrator 15 outputs a signal with a logic level of 1".
1". As a result, in response to a change in the diameter of the ball formed in the wire 21, the wire 21
Even when the discharge current applied to the ball is changed to I2, the rate of increase in the integral value accumulated by the integrator 15 remains constant, and the good level L used to determine the ball diameter remains the same regardless of the magnitude of the discharge current. be able to. Therefore, by comparing the integrated value of the integrator 15 after the elapse of the set discharge command time preset in the discharge condition setting section 11 with the gut level L, it is possible to determine whether or not the ball shape has reached the initially determined constant value. can be determined. As a result, according to the above-mentioned embodiment, the device configuration is simple without requiring a complicated control circuit, and without the need for fine adjustment of the ball diameter determination criteria according to various ball diameters. Ball diameters of various sizes can be determined easily and with high precision.

Next, other embodiments of the present invention will be described.
Since the configuration is almost the same as the previous embodiment, it will be explained using FIG. 1. In this example, the discharge generating device 12 sets the discharge current I set in the discharge condition setting unit 11 by setting the discharge time T only for the wire 2.
The difference is that the discharge is terminated on the condition that the ball diameter determining section 17 determines that the ball diameter has reached a certain value. Therefore, as shown by the dotted line 25 in FIG.
2 is now entered. Regarding the timing to end the discharge on the condition that the ball diameter determination unit 17 determines that the ball diameter has reached a certain value,
First, as shown in FIG. 4A, the integrator 15
It is conceivable that the ball diameter determination section 17 determines that the ball diameter has reached a certain value, that is, immediately after the integral value of the ball diameter reaches the good level L. Second, as shown in FIG. 4B, it is also possible that a certain period of time (ΔT) has elapsed since the integrated value of the integrator 15 reached the good level L.
In any case, in the case of the previous embodiment, at least the discharge command time T set by the discharge condition setting section 11 was required to form the ball, whereas in the present embodiment, the ball diameter reached a certain value. Since the discharge is terminated on the condition that the discharge is completed, the bonding work can be carried out immediately thereafter, and the overall bonding speed can be greatly improved.

Note that in the two embodiments described above, the discharge generating device 12 may have a built-in circuit for applying a constant voltage between the wire 21 and the electrode 22. At this time, if the discharge state becomes short, determine whether the ball diameter is defective using the following method.When the discharge state becomes short under constant voltage control, the discharge current i3 becomes i3z in Fig. 2. , the discharge voltage v3 becomes v3z. Therefore, a shoot judgment is provided to determine the occurrence of short by detecting an abnormal rise in which the current i3 detected by the discharge current detection section 13 becomes the current i3z, and based on the judgment result of this short judgment section, the integrator 15 determines the occurrence of short after the short occurs. The integration is stopped, and the ball diameter determining section 16 is able to determine whether a defective ball diameter has occurred.

In addition, in the two embodiments, the discharge command time T is constant T1 regardless of the required ball diameter, and the discharge current is varied. If the diameter is extremely large, it becomes necessary to lengthen the discharge command time T as well. This means that, for example, in a group where the diameter of the wire 21 is in the range of d1 to d2 (d1 + △d1), it is possible to obtain the required balls within the same discharge command time, but if the diameter of the wire 21 is in the range of d2 to d3. In the group within the range of (d2+Δd2), the discharge command time T must be made longer than in the former group. For this reason, the diameter of the wire 21 is from the level L1, d2 corresponding to the diameter from d1 to d2.
By separately setting the good level L2 corresponding to d3, the ball diameter can be determined while keeping the good level L constant at least within the group.

[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 the first embodiment of the present invention, Fig. 2 is a waveform diagram showing control waveforms used in the ball forming device, and Fig. 3 A and B are electric charge equivalent values. FIGS. 4A and 4B are schematic diagrams illustrating the integral state of the charge amount equivalent value according to the second embodiment of the present invention.
The figure is a schematic diagram showing a wire bonding device. 10...Ball forming device, 11...Discharge condition setting section (discharge condition setting means), 12...Discharge generating device (discharge generating means), 13...Discharge current detection section,
14... Current presence/absence detection section (current presence/absence detection means),
15... Integrator, 16... Normal discharge state setting section,
17...Ball diameter determination section (ball diameter determination means),
21...wire, 22...electrode.

Claims (1)

[Claims] 1. Discharge current and discharge command to be given to the wire in a ball forming device for wire bonding that generates a discharge between the tip of the wire and the electrode to form a ball at the tip of the wire. discharge condition setting means for setting a time; discharge generation means for causing the set discharge current set by the discharge condition setting means to flow through the wire for the set discharge command time; and presence or absence of discharge current flowing in a discharge circuit including the wire during discharge. and an integrator that integrates the output value of the current presence/absence detection means, and the integrator under a condition where a constant ball diameter is to be formed. The normal discharge state setting means predetermines the integral value of as a good level, and when the set discharge command time of the discharge condition setting means has elapsed, the integral value of the integrator is compared with the good level, and the ball diameter is determined to have reached a certain value. 1. A ball forming device for wire bonding, comprising: ball diameter determining means for determining whether or not the ball diameter is determined. 2 Discharge conditions for setting the discharge current and discharge command time to be given to the wire in a ball forming device for wire bonding that generates a discharge between the tip of the wire and the electrode to form a ball at the tip of the wire a setting means; a discharge generating means capable of causing the set discharge current set by the discharge condition setting means to flow through the wire for the set discharge command time; detecting the presence or absence of a discharge current flowing in a discharge circuit including the wire during discharge; A current detection means outputs the detection result as a binary signal, an integrator integrates the output value of the current presence detection means, and an integral value of the integrator under a condition where a constant ball diameter is to be formed. It has a normal discharge state setting means that is predetermined as a good level, and a ball diameter determining means that compares the integral value of an integrator with the good level and determines whether the ball diameter has reached a certain value. A ball forming device for wire bonding, characterized in that the discharge by the discharge generating means is terminated on condition that the ball diameter determining means determines that the ball diameter has reached the ball diameter. 3. A ball forming device for wire bonding according to claim 2, wherein the discharge generating means terminates the discharge immediately when the ball diameter determining means determines that the ball diameter has reached a certain value. 4. The ball forming device for wire bonding according to claim 2, wherein the discharge generating means terminates the discharge a certain period of time after the ball diameter determining means determines that the ball diameter has reached a certain value.