JP3379904B2 - Torch power supply for wire bonding - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torch power supply for wire bonding in a semiconductor manufacturing apparatus, and more particularly to a power supply for forming a ball.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional wire bonding apparatus and torch power supply. In the figure, a wire 1 delivered from a wire spool 2 is delivered from a tip of a bonding tool 4 through a clamper 3, and a torch power supply 5
A negative potential is applied to the electrode 6 from the tip of the wire 1 and the electrode 6
A discharge is generated between the wire and the ball, and the heat forms a ball 1a at the tip of the wire 1. When the ball 1a is formed,
The electrode 6 is retracted, and the bonding tool 4 is lowered as shown in FIG. The wire 1 is bonded to the frame 9. In this bonding, ultrasonic waves from the ultrasonic oscillator 10 are applied to the ultrasonic horn 11, and ultrasonic vibrations in the horizontal direction with respect to the metal surface of the pellet 8 are transmitted by applying pressure. Between the contact surfaces, the oxide film covering the surface of the metal is destroyed and activated metal appears. When pressure is applied to the activated metal, the distance between the active molecules is reduced and metal bonding is performed.

The ball 1a described above is suitable for bonding to the pellet 8, but as a precondition therefor, the bonding pad area of the pellet 8 is changed and the wire 1 is
An appropriate ball diameter is required according to changes in the diameter of the ball.
Thousands of volts are required to initiate the discharge.
If this is to be discharged only by the constant current circuit of the torch power supply 5, the components used in the circuit must have high withstand voltage. Moreover, since the current is several tens of mA, the total wattage is large. Further, conventionally, the current value is 20 mA to 30
A ball was produced under the conditions of mA and discharge time of about 1 mS to 10 mS. As a harmful effect to these, the discharge state may change or the discharge may be interrupted depending on the surrounding environment and the state of the electrodes.

On the other hand, the softness of the ball has an important meaning in bonding. Comparing the bonding states with an ultrasonic oscillator of the same power, it was found that the soft ball has a much better bonding adhesion from the comparison of the pressure bonding ball size and the like. In the past, when a ball was generated, the current was immediately cut off, so that the ball was rapidly cooled and a stable soft ball could not be generated. The energy to generate the ball is determined by the voltage generated between the current and the gap, and the discharge time. In order to make balls of the same size, it is necessary to keep this energy constant, but controlling the discharge time has not been conventionally performed.

[0005]

The problems to be solved by the present invention are as follows. (1) In order to manage the discharge start timing for ball generation, the discharge is surely started. (2) In a torch power supply that generates a ball by generating an electric discharge between a torch electrode and a wire, it is possible to make a ball with good ball size stability, good sphericity, and little eccentricity. (3) A soft ball is produced in order to perform bonding with a small power and a high yield. (4) The discharge time is automatically controlled to reduce variations in ball size.

[0006]

In order to solve the first problem, a discharge is generated between the tip of the wire and the electrode by the electric power output from the constant current circuit, and a ball is applied to the tip of the wire. In the torch power supply for wire bonding to form, a high voltage generation circuit for starting discharge is provided separately from the constant current circuit, and after the discharge is started, application of high voltage from the high voltage generation circuit is stopped. . In order to solve the second problem, the constant current circuit is provided with a current setting unit and a time setting unit that adjust the magnitude of the discharge current and the length of the discharge time. In order to solve the third problem, a means for supplying a small heat-retention current smaller than the discharge current is provided after the discharge current is stopped. In order to solve the fourth problem, a means for automatically controlling the discharge time according to the gap voltage between the tip of the wire and the electrode is provided. In this case, a means for detecting the gap voltage, a means for generating a pulse having a frequency corresponding to the magnitude of the gap voltage, and a means for counting the pulses are provided, and the discharge current is stopped when a predetermined number of pulses are counted. To do so. As another means, an integrating means for integrating the gap voltage and a comparing means for comparing the output of the integrating means with a set voltage from the outside are provided, and the discharge current when the output of the integrating means reaches the set voltage. To stop.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the examples shown in the drawings. FIG. 1 is a block diagram showing the overall configuration of the present invention. In the figure, 1 is a wire, 2 is a wire spool, 3 is a clamper, 4 is a bonding tool, 5 is a torch power supply (constant current circuit), 6
Is an electrode, 12 is a high voltage generating unit, 13 is a current setting unit, 14 is a time setting unit, 15 is a control unit, and 16 is a resistor.

In FIG. 1, a voltage of several thousand volts is required to start the discharge between the tip of the wire 1 and the electrode 6, but if the constant current circuit 5 alone is used for discharging, The components used in the circuit must have high withstand voltage. Moreover, since the current is several tens of mA, the total wattage is large. For this reason, the high voltage generator 12 is separately provided. The high-voltage generator 12 discharges the current of the constant current circuit 5 to trigger the current to flow out. The voltage is high, but the current is very small. This high voltage is generated by the trigger signal from the bonder. When the discharge starts and the current of the constant current circuit 5 starts to flow, the current detector senses it and automatically stops the high voltage generation from the high voltage generator 12.

The high voltage generator 12 automatically stops after 2 mS when no current flows after the high voltage is generated by the start signal from the bonder. The level of initial high voltage can be adjusted from 2000V to 6000V by the semi-fixed variable resistance, depending on the length of the gap between the wire and the electrode.

FIG. 2 is a time chart of the above voltage and current. (A) is a trigger signal and (b) is a high voltage generator 1.
2 shows the output voltage, (c) shows the discharge current, (d) shows the gap voltage, and (e) shows the change in size of the ball 1a formed at the tip of the wire.

In FIG. 2, T ₀ is an initial high voltage application region until the start of discharge, which changes depending on the gap length between the wire tip and the electrode 6. The wider the gap, the longer T ₀ . T ₁ is a discharge area, and the ball 1 a is generated at the tip of the wire 1 in this area. The gap voltage V _G changes depending on the gap length, and the ball generation time also changes.

Further, conventionally, the current value I ₁ = 20 mA to 3
A ball was produced under the conditions of 0 mA and discharge time T ₁ = ₁ mS to ₁₀ mS. The adverse effect on these is that the state of discharge changes depending on the surrounding environment and the state of the electrodes,
The discharge was sometimes interrupted.

To solve this, a ball is generated in a short time. To generate the same ball diameter as the conventional formula,
Naturally, it is necessary to increase the current value. The current value was set to about twice that of the conventional method, and the discharge time was set to about 1/5.
The current value and the discharge time are set by the current setting unit 13 and the time setting unit 14 in FIG. From the experimental result with the wire of 25 μm, it was confirmed that the ball diameter of 35 μm to 80 μm can be stably generated.

Next, a method of forming a soft ball will be described. The softness of the ball has an important meaning in bonding. Comparing the bonding states with an ultrasonic oscillator of the same power, the softer ball is
It was found from the comparison of the pressure bonding ball size, etc. that it was very good. In the past, as a method for making soft balls, the current was cut off immediately when the ball was generated,
After the ball is generated, a small current I _{2 is} generated in the section T ₂ of FIG.
Switch to and keep the ball warm, then shut off the current. As a method of switching to the current for heat retention, there are a case where the current value is suddenly dropped to the set current value and a case where the current value is gradually dropped.

The current value I ₂ and time T ₂ for heat retention can be set by setting conditions. This is because the ball may grow depending on the setting. For this reason, it is necessary to empirically collect data and make optimum settings. In the present embodiment, the current value I2 is set to about 5 mA to 10 mA by the scale 1-10 of the adjusting knob (not shown) in the current setting unit 13 of FIG. The time T ₂ is adjusted by the time setting unit 14 in FIG. Here, in comparing the softness of the balls, no difference is observed in the measured values in the cold state. One of the confirmation methods is a comparison by measuring the pressure bonding ball size after bonding. In the bonding with the ultrasonic oscillator of the same power, the difference in the crimping ball size was clearly recognized. It can be seen that softer balls can be bonded with less power.

Next, an embodiment for automatically controlling the discharge time will be described. The energy that creates a ball is
It is determined by the voltage generated between the current and the gap and the discharge time. To make balls of the same size, this energy needs to be constant. Energy (P) = current (I) × gap voltage (V) ×
Time (T) In the above equation, the current is constant because it is a constant current, and the gap voltage automatically changes depending on the gap length. If the time is constant, the energy also fluctuates as the gap length fluctuates. In order to keep the energy constant, it is necessary to shorten the time as the gap voltage increases.

In order to solve the above, a V / F converter is utilized. The relationship between the current, the gap voltage and the time is as shown in FIG. The current (I ₁ ) and time (T ₁ ) are set according to the conditions. The gap voltage is automatically generated. A V / F converter can be used as one of the methods of controlling the discharge time by utilizing this automatically generated gap voltage.

That is, when the gap voltage is input to the V / F converter, a pulse having a frequency corresponding to the input voltage is generated. As shown in FIG. 2F, this means that the output frequency is high when the gap voltage is high, and the frequency is low when the gap voltage is low. The output current pulse is counted, and when the number of pulses reaches the specified count number, the discharge current I
Stop ₁ As a result, when the gap voltage V _G becomes higher, the output frequency becomes higher and the value quickly becomes equal to the specified value. That is, when the gap voltage V _G becomes higher, it acts to shorten the time. On the contrary, the gap voltage V _G
The lower the, the longer the time. By utilizing these effects, even if the designated value (corresponding to the set time) is constant, the energy fluctuation due to the fluctuation of the gap voltage V _G can be eliminated by automatically changing the time.

Instead of using this V / F converter, it is also possible to use an integrator. That is, the gap time is input to the integrator and the output voltage of the integrator is compared with the set voltage from the outside to change the integration time. The slope of the integrator changes according to the input voltage. FIG. 3 is an explanatory diagram thereof, and when the gap voltage is low, the characteristic of a becomes
When the gap voltage is high, the characteristic is b. This waveform is input to the comparator and compared with the external set voltage. It can be seen that when the discharge current is stopped by the output of the comparator, b having a higher gap voltage is stopped earlier in time as shown in FIG. The set voltage from the outside is set by the time setting unit 14 in FIG.

[0020]

According to the present invention, the following effects are exhibited. (1) By providing a high voltage generation circuit for starting discharge,
It is possible to reliably start the discharge, and it is possible to control the size of the generated ball. (2) Since the current value and the discharge time for ball generation can be controlled, it is possible to make a ball with good ball size stability and sphericalness and less eccentricity. Further, by shortening the discharge time, it is possible to generate a ball having good sphericity and less eccentricity because it is less affected by the surroundings.
Furthermore, since small balls can be produced, bonding to a smaller pad becomes possible, which contributes to downsizing of the chip. The sphericity and the eccentricity are very important items in bonding, and by improving them, the performance of the bonder can be greatly improved. In addition, it will be possible to use it as a bump bonder that is expected in the future. (3) Since soft balls can be produced, bonding can be performed with a small power and a good yield. (4) Ball size fluctuation can be reduced by automatically controlling the discharge time.

[Brief description of drawings]

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

FIG. 2 is a time chart of discharge current and the like according to the present invention.

FIG. 3 is an explanatory diagram when an integrator is used in the embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional torch power supply.

FIG. 5 is a partially enlarged view of a ball and a bonding tool.

[Explanation of symbols]

1 wire, 1a ball, 2 wire spool, 3
Clamper, 4 bonding tool, 5 torch power supply, 6 electrodes, 7 table, 8 pellets, 9 lead frame, 10 ultrasonic oscillator, 11 ultrasonic horn,
12 high voltage generating section, 13 current setting section, 14 hour setting section, 15 control section, 16 resistance

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/60

Claims (5)

(57) [Claims] 1. A torch power supply for wire bonding, in which a discharge is generated between a tip of a wire and an electrode by electric power output from a constant current circuit to form a ball at the tip of the wire. Separately from the above, a high-voltage generating circuit for starting discharge is provided, and after the start of discharging, the application of high voltage from the high-voltage generating circuit is stopped, and after the discharge current is stopped,
A torch power supply for wire bonding, characterized in that means for supplying a small current for heat retention smaller than a discharge current is provided . 2. The torch power supply for wire bonding according to claim 1, wherein the constant current circuit is provided with a current setting unit and a time setting unit for adjusting the magnitude of discharge current and the length of discharge time. . 3. The torch power supply for wire bonding according to claim 1, further comprising means for automatically controlling discharge time in accordance with a gap voltage between the tip of the wire and the electrode. 4. A means for detecting a gap voltage and a gap.
Means for generating a pulse with a frequency according to the magnitude of the voltage
And a means for counting pulses, and a predetermined number of pulses
The discharge current should be stopped when
The torch power supply for wire bonding according to claim 3, wherein: 5. A means for detecting a gap voltage and a gap
The output of this integration means
Comparing the set voltage from the unit, the product
The discharge current when the output of the dividing means reaches the set voltage.
The torch power supply for wire bonding according to claim 3, wherein the torch power supply is stopped .