JPH07183322A - Device for producing uniform ball by electric-discharge machining - Google Patents

Abstract

PURPOSE:To provide a device for correcting ball size to form balls of uniform diameter from metal wire. CONSTITUTION:The title device comprises a constantly keeping device of a spherical diameter is composed a constant-current feedback circuit 8 for feeding back the voltage across a resistance element 7 connected in series with a discharging gap to a pulse-width variable pulse generating circuit 11, an integrating circuit 9 for integrating fixed currents after high voltage begins to be generated, a comparison circuit 10 for comparing an output from the integrating circuit 9 with a control signal from a terminal 17 and transmitting a signal stopping the generation of high voltage when both voltage coincides, and a high-voltage generating circuit 1 for generating high voltage for discharge by an output from the pulse generating circuit 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for making the diameter of a small ball small when making a small ball at the tip by electric discharge machining of fine metal wires.

[0002]

2. Description of the Related Art Pads on an integrated circuit chip and lead frames are connected to each other by thin metal wires called bonding wires. As the thin metal wire, a “gold” wire having a thickness of 20 to 30 μm is often used. As a connection method, a thermocompression bonding ball bonding method, an ultrasonic combined thermocompression bonding ball bonding method or the like is generally adopted.

In the thermocompression bonding method as the prior art shown in FIG. 5, the high DC voltage generated in the high DC voltage generating circuit 1 is applied to the discharge electrode 3 via the terminal 2. Normally, the voltage of the electrode 3 is negative and the gold wire side is grounded. Then, the gold wire 5 is pulled out downward from the tip through a hollow cylindrical body called a capillary 4, and the tip of the gold wire 5 is melted by high pressure discharge to form a gold ball. The discharge at this time is obtained by causing a spark between the grounded gold wire and the discharge electrode 3 to which a high voltage is applied. At this time, the diameter of the gold ball is 2 to the wire diameter.
It is 2.5 times, and it is necessary to suppress the variation in diameter within a range of ± several μm in order to maintain good bonding quality.

Next, a wire clamp provided immediately above the capillary 4 is opened to lower the capillary 4 and the gold wire 5, and the tip of the gold wire 5 is placed on an aluminum pad of a chip (not shown). Thermocompression-bond the formed gold ball. The capillaries 4, which allow the gold wire 5 to pass inside after the pressure bonding, move away from the chip together with the gold wire 5 and ascend to once stop.

The stage on which the chip and the lead frame are mounted is slightly moved, and then the stage is moved until the capillary is positioned at a position where a wire is to be bonded next, for example, the lead frame. After that, the capillary is lowered and the gold wire is pressure bonded. Then, the wire clamp is closed to raise the capillary and the wire clamp to cut the wire, and then only the wire clamp is lowered to expose a required amount of gold wire to the tip of the capillary. A gold ball is made at the tip by the following electric discharge machining. The above operation is repeated.

It has been found that the diameter of the gold ball produced at this time is substantially determined by the discharge current, the discharge time and the gap between the gold wire and the discharge electrode. The discharge is to start discharge when the voltage between the gold wire and the discharge electrode becomes high and the insulation of the air in the vicinity thereof is broken. Once the discharge was initiated, the ionized air maintained a low voltage discharge (300-700 V).

[0007]

Conventionally, a high voltage is often applied after the discharge electrode is moved with respect to the gold wire and the gap between the tip of the gold wire and the tip of the gold wire is set as narrow as about 0.5 mm. In recent years, in order to simplify the device itself and to omit the electrode moving mechanism, a device with an electrode fixed has been put into practical use. At that time, the gap is set to a large value such as 1.2 mm. When the gap between the electrode and the tip of the gold wire is increased due to the electric discharge machining, the discharge voltage becomes higher than 4 kV.
In order to make the sphere diameter generated by electrical discharge machining constant,
It was thought that it would be effective to make the current at the time of discharge constant, but the prior art did not disclose any concrete means for making the current constant.

The object of the present invention is to correct the sphere diameter in order to effectively stabilize the sphere diameter produced by improving the above-mentioned drawbacks and suppressing the discharge current during discharge even if the discharge gap becomes large. An object of the present invention is to provide an electric discharge machine having means.

[0009]

FIG. 1 is a block diagram showing the principle configuration of the present invention, in which 1 is a high voltage generating circuit, 2 is a high voltage terminal, 3 is a discharge electrode, 6 is a thin metal wire, and 7 is a metal wire. Resistance element, 8 is feedback circuit, 9 is integration circuit, 10 is comparison circuit, 1
Reference numeral 1 is a pulse generation circuit, and 17 is an external control signal terminal.

The present invention has the following structure in a producing apparatus for producing a small sphere at the tip of a thin metal wire by applying a DC high voltage to the gap between the thin metal wire and an electrode to cause discharge. That is, a high voltage is generated by a pulse generation circuit with a variable pulse width applied through a feedback circuit that feeds back the voltage across the resistance element connected in series with the discharge gap through a constant current, and the output pulse of the pulse generation circuit. High voltage generating circuit, an integrating circuit that integrates a predetermined current from the time when the discharge current is generated by the high voltage generating circuit, compares the integrating circuit output with a set value from an external control signal terminal, and outputs the integrating circuit output. When it reaches the set value, the comparator circuit sends out a signal for stopping the high voltage of the high voltage generating circuit.

[0011]

High-voltage generating circuit 1 using a known circuit
As a result, a high voltage is generated at a predetermined timing, and at about the same time, a discharge is started between the discharge electrode and the thin metal wire. The discharge current is fed back to the pulse generation circuit 11 via the discharge electrode 3, the metal thin wire 6, the resistance element 7, and the feedback circuit 8. This feedback operation is to make the current flowing through the feedback circuit constant.

When the discharge current flows, the voltage across the resistor element 7 is integrated by the integrating circuit 8. And comparison circuit 1
At 0, the integrated voltage E is compared in amplitude with a control voltage from the outside. When the integrated voltage matches the control voltage, the comparison circuit 10 outputs an output signal to that effect and stops the high voltage generation of the high voltage generation circuit 1. Therefore, the discharge current also stops.

Therefore, when the size of the discharge gap is narrow, the discharge is controlled to be short-time discharge, and when the discharge gap is wide, the discharge is controlled to be long-time discharge. It is constant regardless of size. That is,
The feedback circuit 8 and the voltage comparison by the comparison circuit 10 are
It is a means of correcting the ball diameter.

[0014]

FIG. 2 is a diagram specifically showing the structure of a high voltage generating circuit 1 as an embodiment of the present invention. In FIG. 2, 2
Is a high voltage terminal, 11 is a pulse generation circuit whose pulse width is controlled, 12 and 13 are transistors, 14 is a positive voltage source terminal,
Reference numeral 15 is a transformer, and 16 is a rectifying / smoothing circuit including a full-wave rectifier and a capacitor.

The pulses generated in the pulse generation circuit 11 are 180 degrees out of phase with each other, so that the transistors 12 and 13 are alternately conducted, and a substantially pulsed high-voltage current is supplied to the secondary side of the transformer 15. Occur. The alternating current becomes a negative DC high voltage through the rectifying / smoothing circuit 16 and is connected to the discharge electrode 3 at the terminal 2. Incidentally, 14 is a voltage source terminal of positive voltage, which is a power source for operating the transistors 12 and 13.

The resistance element 7 is inserted between the electrode 3 and the ground side of the full-wave rectifier. Therefore, the voltage across the resistance element 7 is proportional to the magnitude of the current flowing from the high voltage terminal 2 by discharging. The voltage across the resistance element 7 is fed back to the pulse generation circuit 11 whose pulse width is controlled via the feedback circuit 8. As a result, the pulse width is controlled so that the current flowing through the resistance element 7 is made constant. The pulse generation circuit whose pulse width is controlled operates on substantially the same principle as the pulse width modulation circuit.

FIG. 3 is a diagram showing a specific configuration of the current integration circuit 9 and the comparison circuit 10 in FIG. 1 as another embodiment of the present invention. 3, 18 is a terminal to which the voltage at one end of the resistance element 7 in FIG.
Is a switch, 20 is an operational amplifier, 21 is a terminal for inputting an integrated output to a comparison circuit, 22 is a control voltage application terminal for externally controlling the integration time, 23 is a differential amplifier, 2
Reference numeral 4 represents an output terminal of the comparison circuit.

In the current integrator circuit 9, the switch 19 is opened at the same time when the operation of the pulse generator circuit, that is, the high voltage generator circuit is started. At that time, an integration operation is performed in which the voltage of the terminal 18 rises with time at the output side of the operational amplifier 20, that is, the terminal 21. Next, the terminal 22 of the comparison circuit controls the integration time, that is,
A voltage for externally setting the discharge time is applied, and the differential amplifier 23 performs a comparison operation with the output of the integrating circuit. When the voltage values match, the output terminal 24 of the comparison circuit applies the output signal to the high voltage generation circuit 1, so that the high voltage generation circuit 1 stops the pulse generation operation. The operation is, for example,
This is to disconnect the ground side connection line of the transistors 12 and 13 in FIG.

The description of the operation will be continued with reference to the operation explanatory diagram shown in FIG. In FIG. 4 (A), the vertical axis represents the integrated voltage, the terminal 21 and the comparison voltage, and the voltage at the terminal 22. The horizontal axis represents time. Further, in FIG. 4B, the vertical axis represents the voltage of the terminal 24. The horizontal axis is time.

When the integration operation starts, the integration voltage rises as shown in FIG. 4 (A). When the voltage becomes Vs,
The voltage at terminal 24 in FIG. 3 sends out a signal to stop the pulse generation. At this time, the time of the integration operation is t ₀ .

If the discharge gap, the voltage of each terminal, and the integration operation time are calibrated in advance, the integration operation time, that is, the voltage applied from the outside can be changed even when the discharge gap changes next time. , The time corresponding to t ₀ , for example, t ₁ can be easily set.

[0022]

As described above, according to the present invention, since the discharge current of the high voltage generating circuit is constant due to the pulse of which the pulse width is modulated, the time for which the current value is integrated and set externally is set. The discharge time is controlled in comparison with. Therefore, since the discharge can be easily performed for a predetermined time, even if the discharge gap changes, the spherical diameter of the tip end portion of the thin metal wire becomes constant. That is, even if the device has a simple structure, it is extremely easy to make the sphere diameter constant.

[Brief description of drawings]

FIG. 1 is a block diagram showing a principle configuration of the present invention.

FIG. 2 is a diagram showing an example of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of FIGS. 2 and 3.

FIG. 5 is a diagram showing a conventional technique.

[Explanation of symbols]

 1 High Voltage Generation Circuit 2 High Voltage Terminal 3 Discharge Electrode 6 Metal Wire 7 Resistor 8 Feedback Circuit 9 Current Integration Circuit 10 Comparison Circuit 11 Pulse Generation Circuit 17 External Control Signal Terminal

Claims (1)

[Claims] 1. A manufacturing apparatus for applying a high DC voltage to a gap between a metal thin wire and an electrode to cause a discharge to form a small ball at the tip of the metal thin wire, wherein both ends of a resistance element connected in series with the discharge gap. A pulse generator circuit with a variable pulse width applied through a feedback circuit that feeds back the voltage of the constant current, a high voltage generator circuit that generates a high voltage by the output pulse of the pulse generator circuit, and a discharge by the high voltage generator circuit. An integrator circuit that integrates a predetermined current from the time when the current is generated, and the integrator circuit output is compared with a set value from an external control signal terminal, and when the integrator circuit output reaches the set value, the high voltage generation circuit And a comparator circuit for sending a signal for stopping the generation of the high voltage, and a device for stabilizing the diameter of a sphere by electric discharge machining, comprising: