JPS6039840A - Ball forming device for wire bonder - Google Patents

Abstract

PURPOSE:To make a ball small, and to enable to perform stable control of wire bonding by a method wherein a voltage and a current are made to be formed in the plural number of stages, and made variable without interrupting a spark temporarily. CONSTITUTION:A timer 14 is set to discharge hours T1, and a timer 15 is set to discharge holding hours T2 larger than the discharge hours T1 respectively. The timers 14, 15 are driven at the same time according to a timer driving circuit 16, electric power source ciecuits 10, 11 are switched by seitching elements 12, 13, and output voltages E1, E2 are outputted. The output voltages E1, E2 are outputted at the same time at first, a discharge voltage E3 E1+E2 is applied between the tip of a wire 2 and a discharge electrode 4 to start discharge, and after the hours T1, only the output voltage E2 of the electric power source circuit 11 is applied as the discharge holding voltage. After the discharge hours T2, the output voltage E2 becomes to zero. Because a discharge current is changed according to a variable resistor 19, the current is changed also in proportion to the voltage.

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) As the degree of integration of semiconductor integrated circuits such as LSIs and ICs increases, the pads on the chips are becoming smaller. For this reason,
In ball bonding, the problem is how to form a small ball at the tip of the wire.

By the way, the conventional ball forming device was developed in U.S. Pat.
As shown in Japanese Patent No. 841, only a high voltage is applied and the voltage and current cannot be varied during discharge, so in order to form small balls, the voltage, current and time must be reduced. However, although this method makes the ball smaller, it is not round but becomes oval, which deteriorates the stability of the ball and the stability of bonding.

On the other hand, in the device shown in Japanese Patent Laid-Open No. 57-40947, the voltage and current can be varied during discharge, so the stability of the ball is slightly improved compared to the conventional example. However, since this method consists of a circuit in which the spark is temporarily interrupted when the voltage and current are switched from the first stage to the second stage, the stability of the discharge is poor and it is difficult to form small balls.

(Object of the Invention) An object of the present invention is to provide a ball forming device for a wire bonder that can stably form a small ball at the tip of a wire.

(Embodiment of the Invention) An embodiment of the present invention will be described below with reference to FIG. When forming the ball, the wire 2 is clamped by the clamper 1, and the discharge electrode 4 is moved below the tip of the wire 2 so as to maintain a predetermined distance from the tip of the wire 2 inserted through the capillary 3. Then, a voltage is applied to the tip of the wire 2 and the discharge t by the ball forming device between the four poles, and a ball is formed at the tip of the wire 2.

The ball forming device is constructed as follows. two first and second power supply circuits] 0.11, and one output line 10a of each of these power supply circuits 10 and 11.
, lla are connected to switching elements 12, 13 such as transistors, respectively. The switching elements 12 and 13ζ are each timer 1 that adjusts the discharge time.
A timer drive circuit 16t is connected via terminals 4 and 15. The other output line tab6 of the first power supply circuit 10 is the output of the switching element 13? '4' d l 3 a
is connected. Also switching elements 12.13
output lines 12a, 13a and the first and second power supply circuits 10.
The other output line of 11] Ob and llb are connected through diodes 17 and 18, respectively.

Here, the diodes 17.18 are provided to prevent mutual interference between the output voltages of the first and second power supply circuits 10.11. The output line 12a of the switching element 12 is connected to the clamper l via the variable resistor 19 for adjusting the sleeping current, and the other output line 11b of the second power supply circuit 11 is connected directly to the discharge/electrode 4. There is.

Next, the action will be explained. Now, the timer 14 is set to a discharge time T, and the timer 15 is set to the discharge time T and a longer discharge maintenance time T, respectively. During discharging, the timer drive circuit 1.6f simultaneously drives the timer 14.15, and the voltage of the first power supply circuit 10 is applied to the switching element 1.
The voltage of the second power supply circuit 11 is switched by the switching element 13 and becomes the output voltage E2. Here, the power supply circuits 10 and 11 are set in advance so that JBl≧Etl. That is, at the beginning of AE, output voltages E and E are output simultaneously, and a discharge voltage E8p is applied between the tip of the wire 2 and the discharge electrode 4, and discharge is started. After the discharge time TI, the switching element 12 is turned off by the timer 14, so that the output voltage l of the second power supply circuit 1 is
! 2 is applied between the tip of the wire 2 and the discharge electrode 4 as a discharge sustaining pressure 1i. Timer 15 after discharge time T2
As a result, the switching element 13 turns off, and the output voltage J becomes zero. FIG. 2 shows the voltage waveform in the above state l. Here, since the discharge current is changed by the variable resistor 11, the current also changes in proportion to the voltage.

In the case of this embodiment, since the variable resistor 9 is provided in the final discharge voltage section, when the discharge current value is large, the resistance value of the variable resistor 19 is small and no problem occurs. However, if the discharge current value is small, for example, 100 mA or less, the resistance value will exceed the practical range, which is not preferable.

In this way, the voltage and current for starting the discharge and the voltage and current for maintaining the discharge can be set separately, and the voltage and blood flow can be varied by 5T without temporarily interrupting the spark. This allows the ball to be made smaller and more stable to control. - As an example, g, -=R2=800V
When an experiment was conducted with T+ = 15078 and '12 = 3 to 20 m5, very good results were obtained.

FIG. 3 shows another embodiment of the invention. In this embodiment, the output lines 10a and Ila of the power supply circuits 10 and 11 are
Variable resistors 20 and 21 for current adjustment are provided. Therefore, the current values of the voltages E and E can be set independently, and the range of the discharge current and the current value can be widened, making it effective even when the discharge current is small.

In the above embodiment, the case was explained in which the voltage and current were varied in two stages. It may be made to vary in steps or more. If the material of the wire is easily oxidized, such as aluminum or copper, the tip of the wire is placed in an atmosphere of an inert gas or a mixed gas to generate electric discharge, as in the conventional method. Further, in each of the above embodiments, a positive voltage is applied to the wire 2, but a negative voltage may also be applied.

(Effects of the Invention) As is clear from the above description, according to the present invention, the ball pressure and current can be varied in multiple stages without temporarily interrupting the spark, so the ball can be made small and stable. Can be controlled.

[Brief explanation of the drawing]

2...Wire, 4...Discharge electrode, 1O1ll・
...'Power supply circuit, 12.13...Switching element, 14.15...Timer. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A ball forming device for a wire bonder that forms a ball at the tip of a wire by applying a voltage between a wire and a discharge electrode, which includes a plurality of power supply circuits and a method for removing dirt and dirt corresponding to these power supply circuits. A plurality of switching elements provided to switch voltages of corresponding power supply circuits, and a plurality of timers respectively provided corresponding to these switching elements and adjusting driving time of the corresponding switching elements, the plurality of switching elements said output voltages are summed and applied between said wire and said discharge electrode. A ball forming device for a wire bonder characterized by connecting a plurality of switching elements.