JPH0456326A - Formation of gold bump - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bump forming method for forming bumps (metal protrusions) on a semiconductor chip in semiconductor wireless bonding.

[Conventional technology]

In recent years, as IC chips have become multipolar, the wire bonding method that has been used until now has been replaced with the wire bonding method, which does not use thin metal wires, to connect the electrodes of IC chips and lead frames due to economic efficiency and connection reliability. Wireless bonding method is being adopted.

In this wireless bonding method, it is necessary to form bumps (metal protrusions) on electrode portions on the IC chip for connection to leads. As an example of a method for forming this bump, the following method has been conventionally provided.

That is, as shown in FIG. 3, a ball 2 was formed at the end of a thin gold alloy wire l using an electric torch, and this ball 2 was crimped onto the electrode part of an IC chip 3 as shown in FIG. After that, as shown in FIG.
This method connects the ball (bump) 2 left on top to the lead (frame).

The above method has the advantage that it is very effective because the bumps can be formed using a wire bonder used in conventional wire bonding, and there is no need to prepare new equipment.

[Problem to be solved by the invention]

However, when forming the bump 2 by the above method, after the ball 2 at the tip of the thin gold alloy wire 1 is crimped and bonded onto the IC chip, when the thin gold alloy wire I is gripped by a clamper and torn from the hole 2, the hole 2 is removed. - A relatively long tail 5 remained on the neck portion 2a of the bump 2, and its length became unstable, making it impossible to obtain a good bump. Further, in order to solve this problem, gold alloy fine wires that are more likely to break at the neck portion 2a are being developed by adding special elements, but they cannot be said to be perfect yet.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for forming gold bumps that can form highly accurate bumps with a short tail length and a constant tail length. The purpose is

[Means to solve the problem]

In order to achieve the above object, the present inventors conducted intensive research and found that a ball with a diameter of 3.5 to 55 times the diameter of the gold alloy thin wire was formed at the tip of the gold alloy thin wire with a diameter of 10 to 25 μl. It has been found that the tail remaining on the bump can be made shorter than before, and that variations in length can be eliminated and stabilized.

The present invention was made based on the above knowledge, and the diameter of the gold alloy thin wire is set to 10 to 25 μm, and the diameter of the ball formed at the tip of the gold alloy thin wire is set to 35 times the diameter of the gold alloy thin wire. It is set to 5.5 times.

[Effect]

In normal wire bonding, the diameter of the thin gold alloy wire is set to 20 to 38μ, and a hole 2.0 to 3.0 times the diameter of the thin gold alloy wire is formed at the tip. In the method for forming gold bumps of the invention,
As shown in Figure 1, the diameter of the gold alloy thin wire 1 is 10 to 2.
By setting the diameter to 5 μm, the strength of the thin gold alloy wire l becomes smaller, and by setting the diameter d of the ball 2 to 3°5 to 5.5 times the diameter of the thin gold alloy wire 1, the diameter d of the ball 2 decreases. Since the difference between the diameter of the thin gold alloy wire 1 and the diameter of the thin gold alloy wire 1 increases, the thin gold alloy wire 1 becomes easier to break from the neck portion 2a of the ball 2, and the length of the tail 5 becomes shorter as shown in FIG. and its length is stable.

Here, the diameter of the gold alloy thin wire was set to 10 to 25 μm because if it was less than 10 μm, the wire diameter would be too thin and difficult to handle, and the gold alloy thin wire would be passed through when forming the bump. On the other hand, if the diameter exceeds 25 μm, the strength of the gold alloy thin wire is sufficiently large, and even if the difference between the diameter of the ball and the diameter of the gold alloy thin wire is increased, the gold will not flow from the ball. This is because when the thin alloy wire is torn off, slipping occurs between the thin gold alloy wire and the clamper, resulting in variations in the tail.

Also, the diameter of the ball is 3.5 to 5.5 degrees of the diameter of the gold alloy thin wire.
The reason why we set it to 5 times is that if it is less than 3.5 times, the effect of stabilizing the tail will not be sufficient, and if it exceeds 5.5 times, the ball will become too large and will protrude from the electrode part of the IC chip. This is because

〔Example 〕

Next, the method for forming a gold bump of the present invention will be specifically described based on Examples.

Five types of gold alloy thin wires with diameters of 10μ1115μI, 20μπ, 25μl, and 30μM were prepared, a ball was formed at the tip of each gold alloy wire, and this hole was crimped to the electrode part of the IC chip to form the gold alloy thin wire. A gold bump was formed by tearing the ball from the ball that had been gripped and crimped with a clamper.

In the table on the next page, Examples I to 12 relate to the gold bump forming method of the present invention, in which the diameter of the gold alloy thin wire (wire) is 10 to 2-5 μm, and the diameter of the shiny ball is 3.5 μm to 3.5 μm of the wire diameter. 5 to 5.5 times, and Comparative Examples 13 to 18 are as follows:
The wire diameter and/or the ball diameter are outside the conditions of the present invention.

Then, in Examples 1 to 12 and Comparative Examples 13 to 18, the tail lengths and variations thereof of 500 gold bumps each formed were investigated.

The results are shown in the table.

As is clear from the results shown in the table, in Examples 1 to 12, the tail length is shorter than in Comparative Examples 13 to 18, and the variation σ is smaller, making it possible to obtain highly accurate gold bumps. . In Comparative Example 16, although the tail length is relatively short, the variation σ is extremely large, making it impossible to obtain highly accurate gold bumps.

Margin below [Effects of the Invention] As explained above, according to the gold bump forming method of the present invention, by setting the diameter of the gold alloy thin wire to 10 to 25 μm, the strength of the gold alloy thin wire is reduced, and the ball By setting the diameter of the ball to 35 to 5.5 times the diameter of the thin gold alloy wire, the difference between the ball diameter and the diameter of the thin gold alloy wire increases, so the thin gold alloy wire becomes easier to break from the neck of the ball.
Therefore, it is possible to obtain highly accurate gold bumps with short tail lengths and stable lengths.

[Brief explanation of drawings]

Figures 1 and 2 are for explaining the method of forming a bump according to the present invention. Figure 1 is a cross-sectional view showing a state in which a hole is formed at the tip of a thin gold alloy wire, and Figure 2 is a cross-sectional view of the chip. A cross-sectional view showing a gold bump formed on an electrode. Figures 3 to 5 show a conventional bump forming method. Figure 3 is a cross-sectional view showing a state in which a ball is formed at the tip of a thin gold alloy wire. FIG. 4 is a sectional view showing the state in which the ball is crimped to the tip electrode, and FIG. 5 is a sectional view showing the bump formed on the tip electrode. 1... Fine metal wire, 2... Ball (bump) 2a/neck part, 3... IC chip electrode part, 5... Tail.

Claims (1)

[Claims] In the method for forming gold bumps, the gold bumps are formed on the semiconductor chip by pressing a ball formed at the end of the gold alloy thin wire onto the semiconductor chip and cutting the ball and the gold alloy thin wire. The diameter of the alloy thin wire is 10~
25 μm, and the diameter of the ball before being crimped onto the semiconductor chip is set to 3.5 to 5.5 times the diameter of the gold alloy thin wire.