JPH0154858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a ball forming device for a wire bonder that forms a ball at the tip of a wire by electric discharge.

(Background of the Invention) Conventionally, as a ball forming apparatus for forming a ball at the tip of a wire by spark discharge, for example, a method disclosed in Japanese Utility Model Application Publication No. 57-80841 is known.
In this method, a high voltage is directly switched by a switching element, and therefore an expensive high voltage power supply and a high withstand voltage switching element are required. Also, since only high voltage is applied, the arc is unstable and
This has the fatal drawback that a good ball cannot be formed.

By the way, recently, in order to stabilize the arc and form a good ball, for example, as shown in Japanese Patent Application Laid-open No. 57-40947, a high voltage and low current are applied between the electrode and the ball to form an arc. Once the arc is formed, it is preferred to apply a low voltage and high current to form a ball.

However, this method requires two power supply circuits, and since the high voltage is directly switched by the thyristor as a high voltage discharge switching means, a circuit to operate the thyristor is required, making the circuit extremely complicated. become. Also, since a large-capacity, high-voltage capacitor must be used as a discharging capacitor, charging time is slow.
Wire bonding speed per wire
Requires 0.4~0.6 seconds. Furthermore, since the high voltage is directly switched by the thyristor as described above, the rise and fall of the high voltage is slow, making it difficult to precisely control the discharge time and discharge current, and to output a large current.

(Object of the Invention) An object of the present invention is to provide a ball forming device for wire bonding which has a simple circuit, can perform wire bonding at high speed, and can precisely control discharge time and discharge current.

(Embodiment of the Invention) An embodiment of the present invention will be described below with reference to FIG. When forming a ball, the clamper 1 clamps the wire 2 and the wire 2 inserted into the capillary 3
The discharge electrode 4 is moved below the tip of the wire 2 so as to maintain a predetermined gap.

The ball forming device that applies a voltage between the tip of the wire 2 and the discharge electrode 4 is constructed as follows. A capacitor 11 is connected to a low voltage generating circuit 10 that outputs a low voltage E ₁ (for example, 200 to 300 V). On the output side of the capacitor 11, one output line is connected to a switching element 12 such as a transistor,
Diode 13 and variable resistor 1 for adjusting discharge current
4 to the clamper 1, and the other output line is directly connected to the discharge electrode 4. A timer 16 having a variable resistor 15 for varying the discharge time is connected to the switching element 12.

Therefore, the output voltage E ₂ of the switching element 12
outputs a low voltage that is slightly smaller but approximately equal to the low voltage _E1 . Also, a variable resistor 14 for adjusting discharge current
The output voltage _E3 is a voltage slightly smaller than the output voltage _E2 , for example, 200 to 300V. This output voltage E ₃
Since this becomes a discharge sustaining voltage as described later, this output voltage will be referred to as a discharge sustaining low voltage hereinafter. Therefore, the relationship between the voltages E ₁ , E ₂ , and E ₃ is as shown in the following equation.

E ₁ ≒E ₂ ≧E ₃ (1) Furthermore, the input line of a transformer 17 is connected to the output line of the switching element 12 and the other output line of the capacitor 11, and this transformer 17
Boosted to an output voltage _E4 of 600-1800V. On the output line side of the transformer 17, one output line is connected to the discharge current adjusting variable resistor 14 via a diode 18.
The other output line is connected to the input line of the discharge electrode 4. Here, the diodes 13 and 18 are provided to prevent mutual interference between the output voltages _E2 and _E4 . Voltage E ₅ which is the sum of the output voltage E ₄ and the discharge sustaining low voltage E ₃
Since E is the discharge starting voltage as described later, this voltage _E5 will be referred to as the discharge starting high voltage hereinafter. Therefore,
The relationship between voltages E ₂ , E ₄ , and E ₅ is as shown in the following equation.

E ₅ >E ₄ >E ₂ (2) Therefore, from equations (1) and (2), the relationships among the voltages E ₁ to E ₅ are as follows.

E ₅ >E ₄ >E ₁ ≒E ₂ >E ₃ ...(3) Next, the effect will be explained. Low voltage generation circuit 1
0, a low voltage is applied to the capacitor 11.
The low voltage E ₁ of the low voltage generating circuit 10 is controlled by a timer 16 to drive the switching element 12 . The output voltage _E2 of this switching element 12 is set to a discharge sustaining low voltage via a discharge current adjusting variable resistor 14.
It becomes E ₃ . Further, a part of the output voltage E ₂ of the switching element 12 is boosted to a high voltage E ₄ by the transformer 17. The output voltages E ₃ and E ₄ are simultaneously applied to the wire 2 and the discharge electrode 4 as a high voltage for starting discharge E ₅ =E ₃ +E ₄ .
applied in between. When the discharge is started by this discharge starting high voltage _E5 , the voltage due to the low voltage _E1 from the capacitor 11 due to the drooping characteristics of the transformer 17,
That is, the discharge sustaining low voltage E ₃ is applied between the wire 2 and the discharge electrode 4, and the discharge continues for the time set by the timer 16. The voltage and current waveforms at this time are shown in FIG. In this case, when no discharge occurs, the waveform becomes a dotted line.

In this way, the low voltage E ₁ of the low voltage generation circuit 10
(E ₂ to be exact) is boosted by the booster 17 to generate a high voltage, and when discharge is started by this high voltage, a low voltage is automatically applied due to the drooping characteristics of the booster 17, so the circuit becomes very easy. Also, since the low voltage generation circuit 10 is used as a power source,
As the capacitor 11, a capacitor 11 for low voltage and large capacity can be used, and the charging time becomes faster. the result,
Wire bonding speed per wire
It takes 0.1 to 0.3 seconds, approximately doubling productivity.
Furthermore, since the low voltage _E1 of the low voltage generating circuit 10 is switched by the switching element 12, the switching element 12 does not need to be for high withstand voltage. Therefore, a large current Darlington transistor or the like can be used as the switching element 12, and the rise and fall are quick, and the discharge time and discharge current can be precisely controlled.

(Effects of the Invention) As is clear from the above description, according to the present invention, the circuit can be simplified, the speed of wire bonding can be increased, and the discharge time and discharge current can be precisely controlled.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure shows discharge waveforms, where a is a voltage waveform diagram and b is a current waveform diagram. 2...Wire, 4...Discharge electrode, 10...Low voltage generation circuit, 12...Switching element, 17...
...Transformer, E ₁ , E ₂ ... Low voltage, E ₃ ... Voltage for maintaining discharge, E ₄ ... High voltage, E ₅ ... Voltage for starting discharge.

Claims (1)

[Claims] 1. A ball forming device for a wire bonder that applies a voltage between a wire and a discharge electrode to form a ball at the tip of the wire, which includes a low voltage generation circuit, a switching element that switches the low voltage of the low voltage generation circuit, and a switching element that switches the low voltage of the low voltage generation circuit. and a transformer that boosts the output voltage of the element to output a high voltage, and simultaneously applies the output voltage of the switching element and the output voltage of the transformer as a high voltage for starting discharge between the wire and the discharge electrode. After the discharge is started by the discharge starting high voltage, the output voltage of the switching element is applied as a discharge sustaining low voltage between the wire and the discharge electrode due to the drooping characteristic of the transformer. Characteristic ball forming device for wire bonder.