JPS60193352A - Wire bonding device - Google Patents

Abstract

PURPOSE:To enable to form a favorable atmosphere with a small quantity of inactive gas at a wire bonding device having an electric torch counter electrode by a method wherein gas flow paths of two channels, and opening holes of two pieces to flow out gas upwards are provided. CONSTITUTION:Space between a discharge electrode 6 and a capillary 2 is held to an inactive atmosphere according to inactive gas currents 7', 8' blown out from doubly opening holes 7, 8 surrounding the discharge electrode 6. Entangling in of air can be checked according to the doubly atmospheric gas currents, and an atmosphere favorable for formation of a ball can be realized. The double atmosphere is supplied according to inactive gas flow paths 7'', 8'' in an electric torch counter electrode 3. Because the inactive gas currents thereof coincide with the direction of motion of charged particles generated by electric discharge in the direction toward the capillary from the discharge electrode, electric discharge is stabilized, and bonding can be executed without a hitch. Accordingly, bonding having reliability can be attained even by a wire easily oxidizable such as Al.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wire bonding device, and mainly relates to a nail head wire bonding device.

(Prior art and its problems) Connections between internal electrodes (aluminum pads) and external leads on semicircular elements such as transistors and ICs are mainly made by bonding to nails using gold wires, or by bonding using aluminum wires. This is done using ultrasonic wedge bonding. The former is a hydrogen flame (hydrogen torch)
Alternatively, the tip of the gold wire is melted by electric discharge (electric torch) to form a ball (ball up), and then the wires are connected by thermocompression bonding. Although this method has the advantage of being highly versatile and capable of high-speed bonding, since it joins aluminum and gold, it can cause a failure called purple plaque due to the growth of interstitial compounds at the bonding interface. Yes, and unreliable. On the other hand, the latter method uses ultrasonic waves to crush aluminum wires and connect them. Unlike nail head bonding, this method does not require the application of heat and can be connected at room temperature, and is highly reliable since it is an aluminum-aluminum bond. However, due to the directional nature of the wire connection, it is difficult to increase the speed, and since the tensile strength of aluminum wire is low to begin with, there are many cases of wire breakage.Although the cost of the wire itself is low, the manufacturing cost is high. It has shortcomings. Therefore, nail head bonding is used for consumer products, and ultrasonic wedge bonding is used for manufacturing semiconductor devices for communications.

Hydrogen torches and electric torches are used to form balls in nail head bonding, but electric torches are used in high-speed automatic bonding equipment. This is because as the speed of bonding increases, the hydrogen flame of the hydrogen torch cannot keep up with the bonding operation.

Ball formation using an electric torch is performed as follows. As shown in Figure 1, the tip of the wire 1 is led out from the capillary 2, the electric torch counter electrode 3 is brought directly below the wire, high voltage is applied between the wire and the electric torch counter electrode, and a spark is generated between the two. Creates an electrical discharge and melts the tip of the wire,
A ball 4 is formed by its own surface tension. During bonding, the counter electrode of the electric torch moves horizontally to a position where it does not interfere with the bonding process. The wire is usually grounded, whereas the electric torch counter electrode is at a positive potential.

Gold is chemically stable, does not oxidize even when melted in air, and is highly malleable, making it easy to perform nail head bonding, so gold is consumed in large quantities as bonding wire.

However, the recent rise in the price of gold has triggered active research and development into nail head bonding using aluminum wire.

Aluminum is highly susceptible to oxidation, so in order to use nail head bonding, it is necessary to control the atmosphere during ball formation. Japanese Patent Application No. 58-139434 discloses that at least wire bonding parts such as wires and heating means such as discharge sparks are housed in a casing isolated from the outside air, and the inside of this casing is maintained in an inert gas atmosphere or vacuum state. A wire bonding apparatus is shown. However, the wire bonding device having such a structure has the following drawbacks. In the first place, wire bonding equipment has a drive unit that makes precise movements such as bonding arms and bonding, so it is possible to
It is very difficult to achieve an airtight seal, and the entire bonding apparatus must be housed in an inert gas flow casing, which results in very poor workability. Also,
Even if the part of the bonding equipment that receives the heat from the IA is absorbed by the casing, not only will the workability be affected, but it will also be difficult to reduce the degree of oxidation in the air inside the casing to a level that will prevent the aluminum balls from becoming brittle. , a large amount of inert gas is required. Furthermore, in order to make the inside of the casing
This is impractical because the installation of ancillary equipment such as an exhaust system is day and night.As a method of locally creating an inert atmosphere at the pole forming part, a nozzle 5 linked to the opposite pole 3 of the blow torch as shown in Fig. 2 is used. It is conceivable to set up a tank and blow inert gas from there. However, in this type of bonding equipment, some amount of surrounding air is drawn in by blowing inert gas, and with metals that easily oxidize such as aluminum, it is difficult to oxidize the ball surface. I can't escape. In addition, since the direction in which the discharge occurs and the direction of the inert gas flow are perpendicular to each other, the discharge becomes unstable.Furthermore, in the case of aluminum, since the specific gravity is small, the gas flow may cause the discharge to become unstable. The shape of the ball is distorted. In such a state, reliable bonding cannot be performed.

(Object of the invention) - The object of the present invention is to improve the workability of conventional wire bonding equipment. Creates an active waste flow,
It is an object of the present invention to provide a wire bonding device that can stably perform nail head bonding even with a hardening wire such as aluminum.

(Structure of the Invention) The present invention provides a wire pounding device having an electric torch counter electrode that generates a discharge between a thin metal wire and a discharge electrode, and forms a ball at the tip of the thin metal wire. This wire bonding apparatus is characterized in that it has an electric torch counter electrode that is connected to a gas flow path, surrounds the discharge electrode, and has a double open hole that allows gas to flow upward.

(Detailed Description of Configuration) FIG. 3 is a schematic diagram showing the state of the wire bonding apparatus of the present invention when forming a ball. The ball forming portion 1d, that is, the space between the discharge electrode 6 (shaded in FIG. 3) and the capillary 2 is formed from the double Ua discharge holes 7 and 8 surrounding the discharge polarization 6 by 11y. An inert atmosphere is maintained by different inert gas flows 7' and 8' blown out at different speeds of □1c.

Double atmosphere waste flow prevents air entrainment.
A good atmosphere can be created in the ball forming section. The dual atmospheres are supplied by "inert gas channels 7" and 8" in the electric torch counter electrode 3. This inert gas flow is in the direction from the discharge electrode to the capillary, and the direction of movement of the charged particles generated by the discharge is -a, so that the discharge is stabilized.
Bonding can be performed smoothly.

(Example 1) Aluminum wires having a wire diameter of 30 μffZ were bonded using a wire bonding apparatus according to the present invention. The inert gas used was argon. The condition of the aluminum ball was investigated while changing the flow rate of argon, and the results shown in Table 1 were obtained. Now, by reducing the argon gas flow on the inside and making the flow on the outside several to ten times that of the inside, a spherical ball with a smooth surface and no oxide film can be created.

The presence or absence of an oxide film was determined by the presence or absence of metallic luster on the aluminum balls.

Table 1 Next, the conditions for forming a spherical ball with a smooth surface and no oxide film, namely, the inner argon gas flow at 277V-
1 The outside one is 10? Immediately after bonding, after testing at high temperature and high humidity (85°C - 85° relative humidity - 100 hours), and after testing at high temperature (17
After the test (5°C for 100 hours), a pull test was conducted to measure the strength of the joint. Here, the pull test is a method of hooking a fishhook-shaped jig 9 onto a wire loop, pulling it, and measuring the strength when it breaks, as shown in FIG. Note that the high-temperature commercial storage test and the high-temperature storage test were conducted with the IC exposed without being molded. Table 2 shows the polished rice. All the locations where the pull test broke are as shown in Figure 4, 1.
At position 0, the average strength of the pull test is the tensile strength IML of the aluminum wire.6. (Table 2 (Example 2) Pure aluminum wire has a low tensile strength to begin with, so if the bonding speed is increased, the wire will break during bonding. Resulting in.

Therefore, bonding was performed using an aluminum wire doped with 1 atomic silicon and having a wire diameter of 30 μm. The tensile strength of this wire was 16.3 g.

As in Example 1, the inner argon gas flow was set at 2 m/s.
ec, the outer one is 10frL/! lec and bonding was performed, one connection could be made in 0.3 seconds. Immediately after bonding, after high temperature and high humidity storage (85℃ - 85℃ relative humidity - 100 hours) test,
After a high temperature storage test (175° C. for 100 hours), a pull test was conducted to measure the bonding strength of the bonded portion, and the results shown in Table 3 were obtained. All locations where the pull test broke are at the 4th position.
In the IO fitt shown in the figure, it can be seen that the average strength of the pull test is approximately equal to the tensile strength of the wire, and a reliable bond is realized.

In the 'M 1M examples in Table 3 and above, argon is used as the inert gas, but an inert gas such as helium may also be used. Also, the bonding wire is aluminum 11
Although the wires have been described using aluminum and silicon, other oxidizable metal wires such as copper and silver may be used. Note that for wires other than aluminum-based wires, nitrogen gas can also be used as the inert gas. This is because unlike aluminum, it does not form compounds with nitrogen.

(Effects of the Invention) As described in detail above, according to the present invention, the workability of the conventional wire bonding device is not impaired at all, and moreover, a small amount of inert gas is used to form a ball forming part. Because the atmosphere can be created and the nail bonding can be done with confidence, reliable nail bonding is possible even with oxidized wires such as aluminum. It is something.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the state of conventional ball formation. FIG. 2 is a schematic diagram showing how balls are formed by blowing inert gas. FIG. 3 is a schematic diagram showing one embodiment of the present invention. FIG. 4 is a schematic diagram showing the pull test method. l...bonde ink sword ear, 2...geapira 1no,
3... Electric torch counter electrode, 4... Spherical ball, 4'.
... Yuki Sold ball, 5... Inert gas blowing nozzle, 6... Discharge electrode, 7.8... Open hole, 7',
8'...Inert gas flow, 7", 8"...Inert gas flow path, 9...Fish hook-shaped joint, IO...A device that is broken by a pull test.

Claims (1)

[Claims] A wire bonding apparatus having an electric torch counter electrode that generates a discharge between a thin metal wire and a discharge/polarized electrode to form a ball at the tip of the thin metal wire, two gas flow paths;
A wire bonding device characterized by having an electric torch counter electrode having a structure in which double open holes are connected to the gas flow path, surround the discharge electrode, and allow gas to flow upward.