JPS63238234A - Bonding wire - Google Patents

Abstract

PURPOSE:To provide a bonding wire in which neck cutting by a heat cycle is prevented by forming the covered zone of high pure copper on the outer circumference of the core wire of a copper alloy incorporated with limited ratio of Sb. CONSTITUTION:The core wire 1 is formed from the copper alloy in which the recrystallization temp. is increased by incorporating 30-250wt.ppm Sb into high pure copper having >=99.99wt.% purity. The outer circumference of said core wire 1 is covered by the covered zone 2 of the high pure copper having >=99.99% purity to form the bonding wire A. The concn. of the elements involved in the copper alloy of the core wire zone 1 is dissolved and diluted in the case of forming a ball by fusing the tips together at the time of bonding. The hardness of the ball is therefore regulated to the suitable value and chip cracks can be prevented. The thermocompression bonding and ultrasonic compression bonding with an outer lead can be easily executed as well since the soft high pure copper is used for the covered zone 2.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to improvements in copper-based bonding wires used to connect electrodes of semiconductor element chips and external leads.

"Prior Art" Conventionally, gold wires have been mainly used as bonding wires for connecting chip electrodes and external leads of semiconductor devices such as ICs and LSIs, but gold wires have the disadvantage of being extremely expensive. Therefore, from the viewpoint of economy and conductivity, the use of copper wire and copper alloy wire as a substitute for gold wire has recently been considered.

By the way, bonding wires generally have the following (1)
The characteristics described in ~(5) are required.

(1) When a ball is made by melting the tip of a bonding wire to be connected to an electrode of a semiconductor element chip, the ball has a shape close to a true sphere, and moreover, this true spherical ball is stable. It can be manufactured by

(2) When bonding the ball to the electrode of the semiconductor element chip, stable bonding strength can be obtained without causing chip cracking.

(3) Mechanical strength and high-temperature strength are high, and wire breakage does not occur during bonding.

(4) No neck breakage (breakage at the boundary between the ball and the bonding wire) due to thermal cycling.

(5) Thermocompression bonding and ultrasonic bonding to external leads through plastic deformation are possible.

"Problems to be Solved by the Invention" In light of these demands, the inventors of the present application have developed a copper-based bonding wire that satisfies the characteristics described in (1) to (5) above. For this purpose, experiments were repeatedly conducted using high-purity copper wires with a purity of 99.99% or higher, or various copper alloy wires manufactured based on these high-purity copper wires. As a result, although high-purity copper wires do not suffer from problems such as chip cracking, they often break necks due to thermal cycling. On the other hand, with copper alloy wire, no problems such as neck breakage occurred, but chips were often cracked due to the ball being harder than high-purity copper wire, and wedge bonding with external leads was made using high-purity copper wire. It was more difficult than the line.

In view of the above-mentioned background, the present invention was made based on the knowledge obtained through repeated surface marking experiments, and it is possible to prevent neck breakage due to thermal cycles, and it is possible to prevent neck breakage due to thermal cycles. It is an object of the present invention to provide a bonding wire that can control the hardness of a ball to eliminate chip cracking and that can be easily thermocompressed and ultrasonically bonded to an external lead.

``Means for Solving the Problems J'' In order to solve the above-mentioned problems, the present invention provides
A core wire is formed from a copper alloy made of high-purity copper of 9% or more and 30 to 250 ppm of Sb as an element that increases the recrystallization temperature of high-purity steel. % or more of high-purity copper.

Embodiment The drawing shows a cross-sectional structure of a bonding wire A according to an embodiment of the present invention, and this bonding wire A has a structure in which a core wire portion 1 is covered with a covering portion 2.

The core wire portion 1 is made of high purity copper with a purity of 99.99% or more,
As an element that increases the recrystallization temperature, Sb is added at 30 to 250%.
The wire is made of a copper alloy with a weight ppm content. The reason why high-purity copper with a purity of 99.99% or more is used here is to obtain a copper alloy whose ball hardness is even slightly low. Furthermore, the concentration of sb contained in the copper alloy is limited to the above range because if the sb content is less than 30 ppm by weight, there is no effect of increasing the recrystallization temperature of the copper alloy. The concentration of sb contained in it is 2
This is because if the concentration is higher than 50 ppm by weight, it is necessary to reduce the ratio of the core wire portion in order to obtain an appropriate ball hardness, and as a result, the core wire portion becomes too thin and neck breakage occurs.

Further, the covering portion 2 is made of high purity copper with a purity of 99.99% or more. Here, the reason why the purity of the covering part 2 is set to such a value is that if the copper wire has a purity of less than 99.99%, the ball Ii! This is because the hardness of the ball becomes the same as that of a copper alloy wire, making it impossible to control the ball hardness to an appropriate level.

In addition, in the bonding wire A, it is preferable that the coverage ratio of the covering part 2 to the core wire part I is set in the range of 10 to 90%. The reason for this limitation is that the ratio of the covering part 2 is 9.
If the value exceeds 0%, neck breakage is likely to occur, and 10%
This is because chip cracking is likely to occur if the value is less than .

In the bonding wire A having the above structure, the core wire portion l
Since a copper 1 alloy with a high recrystallization temperature is used in the process, neck breakage due to thermal cycles can be prevented. In addition, when the tip of the bonding wire A is melted to form a ball during bonding, the high purity copper of the coating part 2 dilutes the concentration of elements contained in the core wire part 1 and controls the hardness of the ball to an appropriate level. In addition, chip cracking can be prevented. In addition, for bonding wire A,
Since high-purity copper is used for the covering portion 2, wedge bonding with external leads can be easily performed.

"Manufacturing Example" A copper alloy core wire with the components shown in Table 1 is coated with high-purity copper in the proportions shown in Table 1, and then repeatedly subjected to wire drawing and intermediate heat treatment to create a copper-based bonding wire with a diameter of 30 μm. I made several. In addition, in the samples shown in Table 1, the coating portion was made of copper with a purity of 99.999%.The mechanical properties and bonding properties of each bonding wire shown in Table 1 were measured. The measurement results are shown in Table 2. In addition, when bonding was performed using a combination of thermocompression bonding and ultrasonic waves, sample No. 1 = No. 9
could be easily wedge bonded. In addition, in Table 2, "good" ball shape means that the shape of the ball formed by melting the tip of the bonding wire is close to a true sphere, and "deformed" means that the ball shape is distorted from a true sphere. This indicates a state where the degree of

Table 2 In Table 2, Samples No. 2 to No. 6 are samples manufactured with the alloy components limited in the present invention with a coverage rate within the range of 10 to 90%, and all of them have a ball shape close to a true sphere. The core wire portion 1 has a high recrystallization temperature and can be bonded without chip cracking. Samples No. 2 to No. 6 all had high high-temperature strength and ball hardness at appropriate values. Also, sample No.), No2i! The Sb content of each core wire portion 1 was set to 30 ppm by weight, and sample No.
Sample No. 1 has a coverage rate of 5% for coating portion 2, and Sample No. 2 has a coverage rate of 10% for coating portion 2. Sample No. 1 has a higher ball hardness than sample No. 2, and is less susceptible to chip cracking. It is occurring. On the other hand, in samples No. 6 and No. 7, the coverage rate of the coating portion 2 was 90%, and in sample No. 6, the Sb content in the core wire portion 1 was 250% by weight, PPl was 11%, and in the sample No. 7, the Sb content in the core wire portion 1 was 90%.
Although the samples had a B content of 300 ppm by weight, sample No. 7 had higher ball hardness than sample No. 6, causing chip cracking and the ball shape deviating from the pearl shape.

Furthermore, in sample No. 8, the Sb content in the core wire portion l was set to 30,000.
Weight I) 111% This sample has a coverage rate of 95% in the covered portion 2, but the high temperature strength is lower than that of Samples No. 2 to No. 6, and the ball shape deviates from a true sphere. In addition, Sample No. 9 in which the bonding wire was formed from high-purity copper forming the coating portion 2, Sample No. 01 and No. 1 in which the bonding wire was formed from a copper alloy forming the core wire portion 1, Sample No. 9, and Sample N.

In IO, the recrystallization temperature is low, and in sample Notl, the ball hardness is high, causing chip cracking.

In view of the above measurement results, the coverage rate of the covering part 2 is 10~
A range of 90% has been found to be preferred.

By the way, in samples No. 2 to No. 7 in which the coverage of the coating portion 2 was defined in the range of 10 to 90%, the Sb content was set to 30%.
For sample No. 2 with weight ppm, other sample No.
Sample No. 3 to No. 7, the recrystallization temperature of the core wire portion l was slightly lower, and the Sb content was 10 ppm by weight.
In this case, the recrystallization temperature is significantly lower even when the core wire portion l is 100%. Furthermore, the coverage rate of the covering part 2 is set to 10~
Even for samples No. 2 to No. 7 that were specified in the range of 90%, sample No. 7 had an Sb content of 300 weight and 31 ppm.
In some cases, chip cracking occurs.

In view of the above results, in the present invention, the Sb content is limited to a range of 30 to 250 ppm by weight.

"Effects of the Invention" As explained above, the present invention has the advantage of adding 30 to 2 Sb to the core wire.
Since a copper alloy containing 50% by weight and a high recrystallization temperature is used, it is effective in preventing neck breakage due to thermal cycling, which has been a problem with conventional bonding wires made of high-purity copper.

In addition, since the core wire is covered with a coating made of high-purity copper, when the tip is melted to form a ball during bonding, the concentration of elements contained in the copper alloy of the core wire is reduced to the high purity of the coating. Since the steel is melted and diluted, the hardness of the ball can be controlled to an appropriate value, which has the effect of preventing chip cracking.

Furthermore, since high-purity copper, which is softer than copper alloy, is used for the covering portion, thermocompression bonding and ultrasonic compression bonding with external leads can be easily performed.

[Brief explanation of the drawing]

The drawing is a sectional view showing an embodiment of the present invention. A...Bonding wire, ■...Core wire portion, 2...Coating portion.

Claims (1)

[Claims] S is added to high-purity copper with a purity of 99.99% (wt%) or higher as an element that increases the recrystallization temperature of this high-purity copper.
A core wire portion is formed from a copper alloy containing 30 to 250 ppm by weight of
A bonding wire formed with a coating made of the above-mentioned high-purity copper.