JPH01162343A - Bonding wire - Google Patents

Abstract

PURPOSE:To inhibit the age sofening of Ag in a mounting state subsequent to bonding to improve its mechanical characteristics and also, to contrive to stabilize the hardness of a ball by a method wherein a prescribed amount of Ca is added to the high-purity Ag. CONSTITUTION:Ca, 0.0005-0.02wt.%, is added to high-purity Ag. According to such a way, as the recrystallization temperature of a core material is enhanced and the age softening of the Ag can be inhibited to hold a high tensile strength, the mechanical nature of the Ag can be improved. Moreover, as the upper limit of the amount of added Ca is regulated, a ball, which is formed at the time of bonding, is sufficiently soft and also, becomes one near a true sphere. As a result, a failure of an Si chip can be prevented and the reliability of a bonding work can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides bonding wires for semiconductor devices made of Ag;
Alternatively, regarding a bonding wire for a semiconductor device in which a core material made of Ag is coated with a covering material made of Au, the aging softening of Ag can be suppressed and the mechanical properties can be improved, especially in the mounted state after bonding, and the ball hardness can be improved. This invention relates to a bonding wire that can stabilize the temperature.

[Conventional technology]

Bonding wires have conventionally been used to connect A1 vapor deposition pads, which are chip electrodes of semiconductor elements, to lead frames connected to external leads or to cases. The method of connecting this bonding wire to the vapor deposition band includes a thermocompression bonding method in which the tip of the wire is heated by arc discharge or the like to melt it to form a pole, and this ball is pressed to the vapor deposition pad. , a thermosonic bonding method (hereinafter both methods will be referred to as pole bonding method) that uses ultrasonic vibration in combination with the thermocompression bonding method has been adopted.

Techniques using high-purity Ag wires as bonding wires used in such pole bonding methods have been published in numerous documents, patent publications, and the like. An example of this is the one described in Japanese Patent Application Laid-open No. 169341/1983, which states that the purity of the Ag line is 99.97wt%.
It is proposed to do as follows.

On the other hand, Ag is easily oxidized in a molten state, and Ag itself tends to undergo migration, so depending on the usage conditions, the reliability as a bonding wire may be poor when used alone. Therefore, as a bonding wire capable of solving the problems of oxidation and migration of Ag, for example, there is a bonding wire disclosed in Japanese Patent Laid-Open No. 56-21354. This is a high purity A with a purity of 99.99w10 or higher.
This is a composite bonding wire in which the outer periphery of a core material made of g is coated with a coating material made of high purity Au with a purity of 99.99W10 or higher.

According to this wire, it is possible to prevent oxidation that impairs bonding properties, and also to avoid the occurrence of migration.

[Problem that the invention seeks to solve]

However, it is known that high-purity Ag for boat fishing has a low softening point and is susceptible to aging softening even at room temperature. The problem is that the properties become unfulfilled over time. This point is important for the above Ag-
The same applies to Au composite bonding wires,
The strength of the entire wire decreases due to aging softening of Ag.

Therefore, the inventors of the present invention have developed a bonding wire that suppresses aging softening of the above-mentioned high-purity Ag and improves mechanical properties (Japanese Patent Application No. 173509/1982).
. This is made by adding a predetermined amount of a specific element such as C11 to an Ag core material. According to this bonding wire, since a specific element such as Cu that increases the recrystallization temperature is added, aging softening of the core material can be suppressed, and the mechanical properties can be improved accordingly. However, when we further investigated the bonding wire containing elements such as Cu mentioned above, we found that if the amount of added elements such as Cu is too large,
It was found that reliability was slightly inferior in terms of ball hardness.

Therefore, an object of the present invention is to specify the types and amounts of additive elements that can suppress aging softening of high-purity Ag and maintain pole hardness in bonding wires for semiconductor devices.

[Failure to solve the problem]

The first invention of the present application provides high purity Ag with 0.0005 to 0.0
A bonding wire characterized by adding 2% by weight of Ca, and a second invention is a bonding wire in which the outer periphery of a high-purity Ag core material is coated with a high-purity Au coating material, in which the core material contains o , ooos~0.02% by weight of Ca is added.

Here, the reason why the amount of Ca added is regulated will be explained. If the amount of Ca added is 0.0005% by weight or less, the amount is too small to achieve the original objective of suppressing aging softening. Moreover, if it exceeds 0.02% by weight, the recrystallization temperature increases commensurate with the amount added.

Not only is it impossible to obtain an improvement in tensile strength, but the core material becomes brittle and workability is reduced. Furthermore, during pole molding, the shape of the pole may deviate from a true sphere and become distorted, or the ball may harden significantly, causing damage to the vapor deposition pad.
Since the ball hardness targeted by the present invention could not be ensured, the upper limit of the amount of Ca added was set at 0.02% by weight.

[Effect]

According to the bonding wire according to the present invention, high purity Ag
Since 0.0005 to 0.02% by weight of Ca is added to the core material, the recrystallization temperature of the core material increases, aging softening can be suppressed, high tensile strength can be maintained, and mechanical properties can be improved. In addition, since the upper limit of the amount of Ca added is regulated, the ball formed during bonding is sufficiently soft and close to a true sphere, which prevents damage to the Si chip and improves the reliability of bonding work. .

〔Example〕

Hereinafter, specific examples will be described to clarify the effects of the bonding wire of the present invention.

First, an embodiment of the first invention of the present application will be described.

In this example, high purity Ag (99°999w10
) was added with Ca in the amount shown in M1 to M7 in Table 1, respectively, and a billet of 20φ was made from it. Next, each billet was wire-drawn to a diameter of 25 μm using a wire-drawing machine, and the wire drawability (number of wire breaks per 10 km of product) was examined. Furthermore, the wire immediately after the above processing, the wire maintained at room temperature for 108.30 days after the processing, and the wire maintained at room temperature for 108.30 days after the processing, and
Tensile strength was measured for each of the wires fat-extinguished in silicone oil at 10°C.

Table 1 shows the test results, and as is clear from the table, in the wire drawability evaluation, the amount of Ca added was 300 PPM.
When the number exceeds (No. 7), the number of disconnections increases, but below this (No. 1 to 5), no breakage occurs at all. Moreover, when the above-mentioned addition amount was 3 PPM (No. 1), the tensile strength decreased significantly as 10 and 30 days passed from immediately after wire drawing, and the effect of suppressing aging softening was not obtained. on the other hand,
When the Ca content is 5 PPFI or higher, the tensile strength increases as the addition amount increases, even after wire drawing, after 10 days, after 30 days, and after treatment at 250 °C, and the aging It can be seen that the softening suppressing effect was obtained. Therefore, in order to satisfy both the requirements of wire drawability and suppression of aging softening, it is appropriate that the amount of Ca added be within the range of 5 to 200 PPM.

Next, the drawn Ag wire was bonded using a pole bonding method, and the shape of the ball and the hardness of the ball when it was crimped were measured. Here, as the above bonding conditions, the arc discharge (wire anode) is constant, and the oxygen concentration is 50 PPM during ball forming and bonding.
The atmosphere was controlled to be as follows. The number of samples in each of the above measurements was 50, and the number of balls out of 50 was distorted, and the ball hardness was 1.
Bonding was performed 50 times to the wafer on which μm of Aβ-3i was deposited, and the number of cracks that occurred in the S1 wafer was determined.

The results are shown in Table 2. As is clear from the table,
The amount of Ca added is 300 PPM (ltk+, 7
), the distortion of the ball and the number of cracks increase rapidly, and from this result, the amount of Ca added is 20
It is desirable to set it to 0 PPl'l or less.

As was found from the above examples, the effect of suppressing aging softening,
And from the viewpoint of ball hardness, the amount of Ca added is 0°0005 ~
It is necessary to limit the amount within the range of 0.02% by weight.

Next, an embodiment of the second invention of the present application will be described.

Table 1 Table 2 In this example, high purity A g (99,99W10)
A composite bonding wire material was prepared by covering a core material with a covering material made of high purity Au (99,999W10). At this time, the above-mentioned coating material added a certain amount of Ca of 25 PPM, and the above-mentioned core material was
It was assumed that the amount of the value shown in was added. Then, as shown in FIG. 1, this bonding wire material is
The bonding wire 1 was obtained by wire drawing so that the outer diameter of the coating material 3 was 3.6 μmφ and the outer diameter of the covering material 3 was 25 μmφ.

For each bonding wire, the wire drawability (number of wire breaks per 1Q km of product), ball shape, and ball hardness were measured in the same tests as in the above examples. Note that the bonding was performed in the atmosphere.

As is clear from Table 3, the amount of Ca added is 300
When PPM (No. 14) is exceeded, the number of disconnections increases dramatically compared to the Ag wire alone, and this is thought to be due to peeling due to the difference in deformation resistance between the core material 2 and the sheathing material 3, and peeling at the joint. . Furthermore, it can be seen that when the amount added is 300 PPM or more in Table 3, both the number of ball deformations and the number of cranks increase.

In this example, the effect of suppressing aging softening was investigated using the same method as in the case of the Ag wire, but when the amount of Ca added was 5.
At PPM or less, satisfactory results were not obtained for both 30-day retention strength and 250°C high temperature strength. For these reasons, in the above examples as well, the amount of Ca added was set at 5 to 200.
It is appropriate to keep it within the PPM range.

〔Effect of the invention〕

As described above, according to the bonding wire according to the first invention of the present application, 0.0005 to 0.02% by weight of Ca is added to high-purity Ag, and according to the second invention, the Ag core material is made of Au.
Since the core material is coated with a coating material and 0.0005 to 0.02% by weight of Ca is added to the core material, aging softening of the Ag core material can be suppressed and mechanical strength can be maintained over a long period of time. This has the effect of maintaining a predetermined hardness and improving the reliability of bonding work.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional front view of a bonding wire for explaining in detail the second invention of the present application. In the figure, 1 is a bonding wire, 2 is a core material, and 3 is a covering material. Patent Applicant Kobe Steel Co., Ltd. Representative Patent Attorney Tsutomu Shimofu Figure 1

Claims (2)

[Claims] (1) A bonding wire characterized by adding 0.0005 to 0.02% by weight of Ca to high-purity Ag. (2) The outer periphery of the core material whose main component is high purity Ag is high purity A.
In a bonding wire coated with a coating material containing u as a main component, 0.0005 to 0.02% by weight is added to the core material.
A bonding wire characterized by adding Ca.