JPS5917977B2 - Ball forming method in wire bonder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ball forming method in a wire bonder.

Generally, when assembling semiconductor components, by displacing the capillary that holds the wire relative to the lead frame of the semiconductor component, the wire is guided to the pellet attached to the lead frame and the lead frame by thermocompression bonding or ultrasonic bonding. Rebond and cut the wire by raising the clamper.

Since the clamper remains closed after cutting, a certain length of wire is exposed below the capillary. An electric toner is discharged at the tip of this wire to form a ball. Conventionally, the method of determining the quality of the ball by detecting the discharge current when forming a ball at the tip of a wire using an electric torch was disclosed in Japanese Patent Laid-Open No. 5
It is known from Japanese Patent Application Laid-open No. 2-106677, Japanese Patent Application Laid-Open No. 53-58762, and Japanese Patent Application Laid-Open No. 54-9576.

When discharging using an electric torch in this way;
The quality of the ball is greatly affected by the variation in the gap between the wire tip and the electrode. The inventor investigated this gap and found that the gap varies greatly even when a fixed length of wire is protruding from the bottom of the capillary.

That is, when the υ wire is cut by the lifting of the clamper as described above, the wire is cut at the base of the bonding portion, so the tip of the wire is bent. Since the degree of this bending varies and is not constant, the gap between the tip of the υ wire and the electrode changes greatly. For this reason,
Even if a certain length of wire protrudes, if the gap is large, a normal ball will not be formed, resulting in a poor ball forming yield and a reduction in machine operating efficiency. To avoid this, it is possible to apply a thicker voltage, but if the wire of a certain length protrudes and the gap is normal, more current than necessary will flow, causing the ball to melt and fall. This is not preferable because it will be considered defective. The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a method for forming a ball in a wire bonder that can reliably form a ball even if the tip of the wire is bent. The present invention will be explained below with reference to illustrated embodiments. The wire 2 wound around the wire holder 1 passes through a clamper 3 and a capillary 4, and is bonded onto a pellet 6 placed on a heat block 5 and a lead frame T. Thereafter, the wire 2 is cut by the clamper 3. When the electrode 8 for the electric torch is directly below the wire 2, when high voltage is generated by the high voltage generating power supply 9, a discharge occurs between the wire 2 and the electrode 8, and the ball 2a is instantly attached to the tip of the wire 2.
make. At this time, the conductor # connecting between the high voltage source 9 and the electrode 8
A detection core 11 disposed in the conductor 10 senses the discharge current flowing through the conductor 10, amplifies it with an amplifier 12, and outputs it to the determination circuit 1.
Judgment is based on 3.

In this case, when the gap between the tip of the wire 2 and the electrode 8 becomes large, the current flowing through the conductive wire 10 also becomes small, and the change in the applied voltage becomes small. The above method is disclosed in Japanese Patent Application Laid-Open No. 53-58762. In the present invention, if the judgment result by the judgment circuit 13 is smaller than the current flowing during normal ball forming, that is, if there is a mis-discharge, this mis-discharge signal is input to the high voltage generation power source 9, and this signal generates a high voltage. The power source 9 again applies a higher voltage or greater power than the previously applied voltage.

In this way, since a voltage υ larger than the normal voltage that forms a normal ball is applied, a normal ball is formed even if the gap between the tip of the wire 2 and the electrode 8 is larger than the specified value due to bending of the tip of the wire. . If a normal current does not flow through the conducting wire 10 even after this, the determination circuit 13 outputs a signal indicating defective ball formation for the first time. Of course, if the wire 2 is cut and does not come out from the tip of the capillary 4, there will be no spark, no current will flow, and the machine can be stopped immediately. In the above embodiment, the current flowing through the conductive wire 10 connecting the high voltage generating power source 9 and the electrode 8 was detected, but the detection core 11 was arranged in the conductive wire 14 connecting the high voltage generating power source 9 and the end 2b of the wire 2. Alternatively, the current flowing through the wire 2 may be detected.

Alternatively, voltage may be detected instead of current. As is clear from the above explanation, according to the ball forming method in a wire bonder according to the present invention, a normal ball can be formed even when the wire tip is bent and there is a large gap between the wire tip and the electrode, so that the machine operation rate can be improved. is significantly improved.

[Brief explanation of drawings]

The figure is a schematic structural explanatory diagram showing one embodiment of the method of the present invention. 2... Wire, 2a... Ball, 4... Capillary, 8... Electrode, 9... High voltage generation power supply, 11...
Detection core, 13...determination circuit.

Claims (1)

[Claims] 1. In the ball forming method in a wire bonder, in which a ball is formed at the tip of the wire by discharging an electric torch, the current or voltage is detected, and in the case of a mis-discharge, a voltage higher than the previously applied voltage is applied to the electric torch again. A method for forming a ball in a wire bonder, characterized in that a ball is formed by applying an electric voltage.