JPH0654787B2 - Bonding wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bonding wire used for electrical connection of semiconductor devices, and more particularly to a bonding wire used for ball bonding.

[Prior Art] Conventionally, an aluminum-based or gold-based alloy has been used as a bonding wire used for electrical connection of a semiconductor device, and wedge bonding or ball bonding has been used as a bonding method. There is.

Wedge bonding is a method in which a bonding wire is placed on the connection part, pressed with a wedge from above, and pressure-bonded by heating or ultrasonic vibration.
In this method, the tip of the bonding wire is heated by a means such as hydrogen flame or arc discharge to form a ball, and the ball is thickly attached to the connecting portion. Industrially, ball bonding, which has a high work efficiency, is preferably used. As a bonding wire used for this ball bonding, a bonding wire made of a gold-based alloy whose tip is easily spherical due to hydrogen flame or arc discharge is generally used.

However, in such a connection, since the electrode of the semiconductor element to be the connection portion is often aluminum-based,
This is a connection between different metals such as gold and aluminum, and there is a drawback in that an intermetallic compound is generated during heating in a subsequent process and is easily deteriorated. Further, the bonding wire made of a gold alloy has a drawback that the cost is high. Therefore, ball bonding using a bonding wire made of an aluminum alloy has been conventionally desired.

[Problems to be Solved by the Invention] However, the conventional aluminum-based alloy is not suitable for ball bonding because the surface is more easily oxidized than gold and the melting point is low, so that the ball-forming ability is poor. . In particular, ball bonding using a hydrogen flame could not be performed at all.

Ball bonding by the other arc discharge is a method of forming a ball at the tip of the wire by arc discharge between an electrode provided near the tip of the wire and the wire. The root portion of the ball was deteriorated by excessive heat, resulting in a problem that the strength was remarkably reduced or the ball was constricted. further,
Wire diameter 2 commonly used for ball bonding
There is also a problem that a large ball is formed as compared with 0 to 50 μmφ.

Therefore, as a method of solving such a problem, it is conceivable to reduce the energy of arc discharge, but when the energy is reduced, the actual situation is that the arc does not fly and the arc does not discharge. Further, in order to facilitate arc discharge, an argon gas atmosphere has been attempted, but this is not sufficient yet.

An object of the present invention is to provide a bonding wire which solves the above-mentioned problems, enables arc discharge with a small energy, and eventually enables ball bonding by arc discharge.

[Means for Solving Problems] The bonding wire of the present invention is made of K, Cs, Sr, B.
It contains 0.01 to 1% by weight of one or more elements selected from the group consisting of a, with the balance being aluminum. Further, preferably, 0.5 to 2% by weight of one or more elements selected from the group consisting of silicon, magnesium, manganese and copper is contained to improve strength and workability.

[Operation and Effect] The bonding wire according to the present invention is made of K, Cs, S.
An element having a work function selected from the group consisting of r and Ba and having a work function of 3 eV or less, that is, an element which easily emits electrons is 0.0
It is contained in an amount of 1 to 1% by weight, and arc discharge can be performed with smaller energy than that of a conventional bonding wire made of an aluminum alloy.

Therefore, since the arc discharge can be performed without giving excessive energy to the ball formed at the tip of the wire, the ball bonding can be performed without lowering the strength or constriction at the root portion of the ball.

Further, according to the present invention, since ball bonding with an aluminum-based alloy is possible, the problems of deterioration and high cost due to the formation of intermetallic compounds that occur when a gold-based alloy is used are solved, and the reliability of ball bonding is further improved. Can be increased.

In the present invention, the content of one or more elements selected from the group consisting of K, Cs, Sr, and Ba is limited to 0.01 to 1% by weight. If it is less than the above range, the property of forming a small and uniform ball with a small amount of energy is not exhibited, and as a result, no improvement in the ball forming ability is observed, while if it exceeds 1% by weight,
This is because the workability and corrosion resistance may be impaired.

Further, preferably, 0.5 to 2% by weight of one or more elements selected from the group consisting of silicon, magnesium, manganese and copper is contained to improve strength and workability.

[Example] Using an aluminum ingot having a purity of 99.99% as a base, an alloy having the composition shown in Table 1 (% represents% by weight) was melted. After smelting, 10 from the molten metal with a ceramic filter
The billet was continuously cast while removing inclusions of μm or more.

After surface cutting this billet, 10
After forming a wire of mmφ, a stripping, wire drawing and heat treatment were combined to produce a bonding wire of 40 μmφ.

The ball-forming ability and workability of the obtained 40 μmφ bonding wire were evaluated in the following manner, and the results are shown in Table 1.

(I) Ball forming ability A bonding wire having a diameter of 40 μm is passed through a sapphire capillary, and a ball is formed under various electrical conditions by arc discharge between an electrode provided near the tip of the wire and the wire under the spout of argon gas. Was formed, and the state of ball formation was evaluated in the following two stages (◯ and ×), and the ball forming ability was defined.

◯: A ball with a surface shape close to a true sphere is formed, and the wire at the base of the ball does not become thin.

X: The ball forming conditions are narrow and the variations are large. Moreover, the surface shape is not excellent. The base of the ball may be constricted.

(Ii) Workability Workability up to wire drawing up to 40 μmφ was evaluated in the following two stages (◯ and ×).

◯: No change from conventional one.

X: There is a problem in workability as compared with the conventional one.

As is clear from Table 1, the bonding wire of the present invention has remarkably improved ball forming ability as compared with the conventional one.

Claims (2)

[Claims] 1. A bonding wire containing 0.01 to 1% by weight of one or more elements selected from the group consisting of K, Cs, Sr and Ba, and the balance being aluminum. 2. The bonding according to claim 1, further comprising 0.5 to 2% by weight of one or more elements selected from the group consisting of silicon, magnesium, manganese and copper. Wire.