JPH0719789B2 - Gold alloy fine wire for bonding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gold alloy fine wire having excellent heat resistance, which is used for joining an electrode on a semiconductor element and an external lead.

(Prior Art and Problems) Conventionally, a gold thin wire has been used as a bonding wire for connecting an electrode on a silicon semiconductor element and an external lead. The reason why gold fine wires have been frequently used in this way is that the gold balls are formed into a perfect spherical shape, the formed gold balls have an appropriate hardness, and the pressure during bonding may damage the silicon semiconductor element. It was because there was no reliable connection, and its reliability was extremely high. However, when the fine gold wire is applied to an automatic bonder and the tip of the fine gold wire is melted to form a gold ball and joined, the fine gold wire has a low recrystallization temperature and lacks heat resistance. If the tensile strength is insufficient and a wire break occurs, or the thin gold wire that has been bonded without breaking the wire is broken by resin encapsulation, or if the semiconductor element is protected by a resin for encapsulation, a wire flow will occur, causing a short circuit. There is a problem.

In order to solve this problem, various bonding elements have been added with a small amount of additional elements in high-purity gold to improve the breaking strength and heat resistance to the extent that the shape and hardness of the gold balls formed during connection are not impaired. Although gold alloy thin wires have been published, there is a problem that they are not suitable for thin package devices, which are rapidly becoming widespread in recent years, because the loop height of the junction is high and unsuitable.

(Problems to be Solved by the Invention) The present invention has been made in view of the above problems, and improves tensile strength at room temperature and high temperature, and reduces the loop height of bonding to provide a thin package device. The object is to provide a suitable gold alloy fine wire for bonding.

(Means for Solving Problems) In the present invention, high purity gold having a purity of 99.99% by weight or more is added to yttrium 3 to 100 ppm by weight and calcium 1 to 50 ppm by weight.
m, germanium 5 to 50 ppm by weight, and beryllium 1 to
10 weight ppm each is added, and the total amount of these additional elements is 1
This is a gold alloy thin wire for bonding in the range of 0 to 110 ppm by weight.

The present invention, by adding yttrium and calcium to improve the heat resistance to high purity gold germanium and beryllium to further improve the mechanical strength at room temperature, while improving the heat resistance by the additive action of these additional elements, The addition of beryllium cooperates with germanium to further improve the mechanical strength at room temperature, prevent wire flow, reduce the loop height at the time of joining, and make it suitable for a high-speed automatic bonder.

When the amount of yttrium added is less than 3 ppm by weight,
The heat resistance is not improved, wire flow is exhibited by the influence of the sealing resin, and the loop height varies, resulting in unstable joining. On the other hand, if the amount of yttrium added exceeds 50 wtppm, the heat resistance effect is saturated and does not improve much regardless of the addition, and if it exceeds 110 wtppm, an oxide film is formed on the ball surface, Distortion occurs in the ball shape,
In addition, yttrium breaks out into the crystal grain boundaries of gold and causes brittleness, which hinders wire drawing. The preferable addition amount is 3 to
It is 60 weight ppm.

When the amount of calcium added is less than 1 ppm by weight, it lacks the additive action with yttrium and germanium, the heat resistance becomes unstable, the loop height varies, and a slight wire flow is exhibited. On the other hand, if it exceeds 50 ppm by weight, an oxide film is formed on the surface of the ball, distortion occurs in the shape of the ball, and calcium breaks out into the crystal grain boundaries of gold to cause brittleness, which hinders wire drawing. The preferable addition amount is 1 to 40 ppm by weight.

When the addition amount of germanium is less than 5 ppm by weight,
The mechanical strength at room temperature cannot be further improved. Conversely, 50 weight ppm
If it exceeds, the oxide film is formed on the surface of the ball, the shape of the ball is distorted, the crystal grain boundary is broken by recrystallization during bonding, and the neck breakage is likely to occur. The preferable addition amount is 5 to 30 ppm by weight.

When the amount of beryllium added is less than 1 ppm by weight, the mechanical strength at room temperature is not improved. On the other hand, if it exceeds 10 ppm by weight, in addition to coarsening of crystal grains due to recrystallization at the time of bonding, a bamboo-like joint is generated, neck breakage occurs, and ball shape is distorted. It reduces the reliability of bonding. The preferable addition amount is 1 to 6 ppm by weight.

Therefore, the total addition amount of yttrium, calcium, germanium, and beryllium is set to 10 to 110 ppm by weight, and the preferable total addition amount is 10 to 60 ppm by weight.

(Example) Hereinafter, an example will be described.

Using electrolytic gold with a gold purity of 99.99% by weight or more, the gold alloys with the chemical components shown in Table 1 are melt-cast in a high-frequency vacuum melting furnace, the ingot is rolled, and then wire drawing is performed at room temperature. A fine gold alloy wire having a wire diameter of 25 μmφ is continuously annealed in the air atmosphere and tempered so that the elongation value becomes 4%.

Table 1 shows the results of examining the obtained gold alloy fine wire for normal temperature tensile strength, high temperature tensile strength (250 ° C., holding for 30 seconds), joint loop height, wire flow during molding, and ball shape.

The loop height of the junction is measured by observing the top height of the loop formed and the electrode surface of the chip with an optical microscope after joining between the electrode on the semiconductor element and the external lead using a high-speed automatic bonder. Measure its height.

For wire flow, the electrodes on the semiconductor element and external leads are joined with a high-speed automatic bonder, set in the mold of a thin mold, the sealing resin is injected, and the resulting package is observed by X-ray. Then, the strain of the bonding line due to the sealing resin, that is, the maximum bending distance from the straight line bonding and the bonding span distance were measured, and the quality of the wire flow was evaluated from the strain value.

○ mark: Strain value less than 3% (suitable for thin package) △ mark: Strain value 3 to 10% × mark: Strain value 11% or more Ball shape is obtained by electric torch discharge using high speed automatic bonder When observing the gold alloy balls with a scanning electron microscope, oxides are generated on the surface of the balls, those with a dented ball shape, those that cannot be joined to the electrode of the semiconductor element in a good shape are marked with x, and good Was evaluated with a circle.

As can be seen from Table 1, Examples 1 to 8 are yttrium, calcium, germanium,
Since beryllium is suitable in both the individual addition amount and the total amount, it has good heat resistance and can form a low junction loop height, and the influence of the wire flow due to the sealing resin can be ignored. In addition, since the ball shape is also good, reliable joining is possible.

However, in Comparative Example 1, the total amount of elements was 8.5 weight ppm and below the allowable limit, and yttrium was 2 weight ppm and beryllium was 0.5 weight ppm, both of which were below appropriate amounts, and therefore heat resistance was not improved. The wire flow is affected by the sealing resin, and the loop height varies, resulting in unstable joining, and inferior mechanical strength at room temperature. . In Comparative Example 2, calcium, germanium, and beryllium are all appropriate amounts, but yttrium is 120 wtppm, which exceeds the allowable limit, and the total amount of elements is 127 wtppm, which exceeds the allowable limit. An oxide film is formed on the surface of the formed ball, the shape of the ball is distorted, and yttrium is precipitated at the crystal grain boundaries of gold to cause brittleness, which hinders wire drawing, which is not preferable. Comparative Example 3 has a total amount
Although it is within the allowable limit at 81 ppm by weight, an oxide film is formed on the ball surface because calcium exceeds an appropriate amount,
The ball shape is distorted, and calcium precipitates at the gold grain boundaries to cause brittleness, which hinders wire drawing, which is not preferable. Further, in Comparative Example 4, since both calcium and germanium are in appropriate amounts, synergistic action with yttrium and germanium is lacking, heat resistance becomes unstable, loop height varies, and a slight wire flow is exhibited. It is not preferable because the mechanical strength at room temperature cannot be further improved or a problem occurs. Comparative Example 5 has a total amount of 83
Weight ppm is within the allowable limit, but due to the large amount of germanium, an oxide film is formed on the ball surface, causing distortion in the ball shape, causing crystal grain boundary rupture due to recrystallization during bonding, and neck breakage. It tends to occur, which is not preferable. In Comparative Example 6, the total amount is 84 wtppm, which is within the allowable limit, but since beryllium exceeds 12 wtppm at an appropriate amount, recrystallization at the time of bonding causes coarsening of the crystal grains and causes a bamboo-like joint. In addition, the neck is broken and the ball shape is distorted, so that the reliability of bonding with the microelectrode is lowered, which is not preferable. In Comparative Example 7, each element is in an appropriate amount, but since the total amount exceeds 120 ppm by weight, the ball shape may be distorted, an oxide film may be formed on the surface, and the electrode of the semiconductor element may have a good shape. It is not preferable because problems such as the inability to join can occur. In Comparative Example 8, the amount of calcium exceeds the appropriate amount, the total amount also exceeds the appropriate amount, and yttrium is not added. Therefore, the heat resistance is hardly improved, and the wire flow is exhibited due to the influence of the sealing resin. An oxide film was formed on the surface, the ball shape was distorted, and calcium was precipitated at the crystal grain boundary of gold to cause brittleness, which hinders the wire drawing process and was completely unsuitable for actual applications. Thus, the comparative example could not be put to practical use in any case.

As can be seen from the results, the examples according to the present invention have good heat resistance, and can form the loop height of the joint low,
The influence of the wire flow due to the sealing resin can be ignored, and the ball shape is good, so that reliable bonding can be performed.

(Effect) As described above, the gold alloy thin wire according to the present invention contains high-purity gold containing yttrium and calcium which improve heat resistance.
Furthermore, by adding germanium and beryllium that improve the mechanical strength at room temperature, the heat resistance is improved by the synergistic action of these additional elements, and the addition of beryllium cooperates with germanium to further improve the mechanical strength at room temperature. Since it can be used, it has excellent tensile strength at room temperature and high temperature, it can be formed with a low loop height for joining, there is no wire flow due to the sealing resin, it can sufficiently support a high-speed automatic bonder, and the formed ball shape is also spherical. Therefore, there is an advantage that it can be put to practical use with high reliability as a bonding line for thin package devices. Therefore, it has a great contribution to the industry.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiichi Fujimoto Inventor, Eiichi Fujimoto 2-3-1 Iwata-cho, Higashi-Osaka City, Osaka (56) References JP-A-60-30158 (JP, A) Kaisho 53-105968 (JP, A)

Claims (1)

[Claims] 1. High purity gold with 3 to 100 ppm by weight of yttrium,
Calcium 1-50 wtppm, Germanium 5-50 wtpp
m, and beryllium 1-10 ppm by weight, respectively,
A fine gold alloy wire for bonding, wherein the total amount of these additional elements is in the range of 10 to 110 ppm by weight.