JPH0813062A - Gold wire for bonding - Google Patents

Abstract

PURPOSE:To produce a gold alloy wire for bonding, extremely useful for accelerating the miniaturization, thinning, and increase of pins of semiconductor equipment. CONSTITUTION:A bonding wire can be obtained by incorporating, by weight, 0.0001-0.005% Yb, further at least one kind among 0.0001-0.001% Be, 0.0001-0.003% Ca, and 0.0001-0.005% Ge, or further, besides the above, 0.0001-0.005% Eu into high purity gold of >=99.999% purity. By this method, the reliability in a bonding neck part and joining strength at the time of bonding can be enhanced and a greater number of electrodes can be disposed, and further, stable loop formation is made possible because of excellent high temp. strength and a small ball can be formed into perfect sphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding gold alloy wire used for connecting an electrode of a semiconductor element and an external lead portion, and more specifically, in assembling a semiconductor device.
The present invention relates to a bonding gold alloy wire that significantly reduces the extent to which the neck portion of the bonding wire is damaged due to an increase in ultrasonic output.

[0002]

2. Description of the Related Art Conventionally, in assembling a semiconductor device, an ultrasonic combined thermocompression bonding method has been mainly used as a method for bonding a semiconductor element upper electrode and an Au plated terminal portion of a lead frame with a metal wire. In recent semiconductor devices, the mounting density has increased to make them smaller, thinner, and have more pins, and as a result, the electrode area on the semiconductor element is reduced and the bonding area of the bonding part is reduced, resulting in a bonding force similar to the conventional one. It is becoming difficult to secure them. On the other hand, attempts have been made to apply high frequency vibration by increasing the ultrasonic output during bonding.

On the other hand, as a demand for increasing the number of pins, short wiring is required while using a large number of lead wires, and in order to cope with this, in the process of forming a loop using a bonding apparatus, a loop formation Form a loop after severely bending and deforming the ball neck in the opposite direction,
Attempts have been made to stabilize the loop height and loop shape by performing so-called reverse deformation. In such a situation, the neck portion of the bonding wire is subjected to high-frequency vibration due to an increase in ultrasonic output, and the ball neck portion is subjected to a severe reverse deformation and a severe load is applied to the neck portion. There are problems that the reliability in the vibration test in the state is low and that the ball neck has a disconnection defect when exposed to the environment of the heat cycle due to the heat generation of the semiconductor.

With respect to such a problem, Japanese Patent Laid-Open No. 962/962
No. 4 gazette discloses that a neck portion immediately above a gold ball is less likely to be broken by a repeated bending test.
Eu, Ca, Ge, high purity gold of 9.999% by weight or more,
A bonding wire containing a predetermined amount of Be has been proposed. However, when high-frequency vibration is applied due to an increase in ultrasonic output, which is a more severe bonding condition, and when severe loop formation such as reverse deformation is performed,
The reliability of the ball neck is not sufficient.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a semiconductor device that is small, thin, and has a large number of pins. Therefore, for bonding, the objects (1) to (3) below can be achieved at the same time. An object is to provide a gold alloy wire. (1) A gold alloy wire that has excellent fatigue characteristics in terms of reliability of the neck portion of a bonding wire that has undergone thermocompression bonding in which ultrasonic waves are used in combination with ultrasonic waves and reverse deformation is applied during loop formation. In addition, the gold alloy wire has excellent breaking performance when exposed to a heat cycle environment. (2) As the number of electrodes increases, it is required to reduce the size of the electrodes in order to arrange more electrodes. Therefore, it is possible to form a small ball into a true sphere and high bonding strength. Must be a gold alloy wire. (3) A gold alloy wire with high strength at high temperature to enable stable loop formation.

[0006]

In order to achieve the above object, the first invention of the present application is to provide 99.999% by weight or more of high-purity gold with ytterbium (Yb): 0.0001 to 0.0.
Beryllium (Be): 0.
0001 to 0.001% by weight, calcium (Ca):
0.0001 to 0.003% by weight, germanium (G
e): A gold wire for semiconductor element bonding, containing at least one of 0.0001 to 0.005% by weight.

The second invention of the present application is 99.999% by weight.
Ytterbium (Yb): 0.000 in the above high-purity gold
1 to 0.005% by weight and europium (Eu): 0.
0001 to 0.005% by weight, beryllium (Be): 0.0001 to 0.001% by weight, calcium (Ca): 0.0001 to 0.003% by weight, germanium (Ge): 0.0001 It is a gold wire for semiconductor element bonding, characterized in that it contains at least one of 0.005% by weight to 0.005% by weight.

In the first and second inventions, the ytterbium (Yb) content is 0.0005 to 0.005.
It is more preferable to set it as the weight%.

[0009]

The detailed structure of the present invention and its operation will be described below. The starting material used in the present invention has a purity of 99.
It contains 999% by weight or more of gold and the balance consists of unavoidable impurities. Yb, Be, Ca, G as the starting material
By combining e and Eu so as to have the above-mentioned composition, the ultrasonic combined thermocompression bonding with increased ultrasonic output is performed by the synergistic effect of the metal elements, and the reverse deformation is performed during the loop formation. With respect to the reliability of the neck portion of the bonding wire added with, it is possible to obtain a gold alloy wire having excellent fatigue characteristics and excellent breaking performance when exposed to a heat cycle environment.

Next, the reason why the composition of the gold alloy thin wire of the present invention is limited as described above will be explained. [Yb] Yb is at least 1 of Be, Ca, and Ge.
In coexistence with seeds, it shows an excellent effect in improving the reliability of the ball neck portion. If the Yb content is less than 0.0001% by weight, the reliability of the ball neck portion is low, and if it exceeds 0.005% by weight, good ball formation cannot be achieved.
Therefore, the Yb content is 0.0001 to 0.005% by weight.
I decided. When Yb is contained alone, the effect of improving the reliability of the ball neck portion is insufficient, so Be, C
It is necessary to coexist with at least one of a and Ge.
A more preferable range of Yb content is 0.0005 to 0.0.
It is 05% by weight, and in this range, a more excellent effect is exhibited in improving the reliability of the ball neck portion.

[Be, Ca, Ge] At least one component of Be, Ca, and Ge exhibits excellent effects in improving the reliability of the ball neck portion and improving the high temperature strength in the coexistence with Yb. The content of Be, Ca, and Ge is 0.
If it is less than 0001% by weight, the reliability of the ball neck portion is insufficiently improved, and high temperature strength cannot be obtained. If the Be content exceeds 0.001% by weight, good ball formation cannot be achieved. If the Ca content exceeds 0.003% by weight, a good ball shape cannot be formed, electrode cracks are likely to occur during bonding, and the bonding strength during bonding becomes smaller. If the Ge content exceeds 0.005% by weight, electrode cracking during bonding tends to occur. Therefore, the Be content is 0.0001 to 0.001.
% By weight, a Ca content of 0.0001 to 0.003% by weight, and a Ge content of 0.0001 to 0.005% by weight.

[Eu] Eu is Yb, Be, Ca,
In the coexistence with at least one component of Ge, it exhibits an excellent effect of improving the reliability of the ball neck portion. In the present invention, it is necessary to coexist at least one component of Yb and Be, Ca, Ge, and Eu of 0.
Even if they coexist in the range of 0001 to 0.005% by weight, the same effect can be obtained in improving the reliability of the ball neck portion.

[0013]

EXAMPLES Examples will be described below. Example 1 The composition shown in Table 1 was adjusted to 99.99.
9% by weight of a metal alloy and a master alloy containing each element are melted in a vacuum melting furnace, cast, and then repeatedly subjected to cold working and heat treatment using a groove roll and a wire drawing machine to obtain a final wire diameter of 30 μm and an elongation of 4%
It was finished so that it would be a fine line. Using this thin wire as a bonding wire, ultrasonic thermocompression bonding was performed on the semiconductor element electrode using a high-speed automatic bonder. After making the ultrasonic wave output 0.5 W and performing the first ball joining, once move the capillary in the direction opposite to the loop formation and set the reverse angle to 60 degrees with respect to the vertical direction, and bend the ball neck part severely. To deform and then form a regular loop. First, a high-temperature strength, ball shape, and vibration test were performed using a thin wire, and after bonding on a semiconductor element electrode, bonding strength, electrode cracking at the time of bonding, and a heat cycle test were performed. The measurement results are shown in Tables 2 and 3.

[Examples 2 to 19 / Comparative Examples 1 to 8] Fine lines were finished and tested in the same manner as in Example 1 except that the compositions shown in Table 1 were used. The measurement results are shown in Tables 2 and 3.

The measuring method was as follows. [Bonding Strength] After bonding was performed using a high-speed automatic bonder, the shear load between the ball pressure bonding portion and the A1 electrode was measured and displayed using a bonding strength tester (shear tester). [High temperature strength] Using a tensile tester in an atmosphere of 250 ° C for 2
After holding for 0 seconds, a tensile test was performed as it was, and the maximum load was displayed. [Ball shape] Gold balls were prepared using an electric torch incorporated in a high-speed automatic bonder, and the size, sphericity, and surface state of the gold balls were observed using a scanning electron microscope. The size of the gold ball is 2.5 times the wire diameter, that is, the diameter is 75
The sphericity and the surface condition were measured in comparison with a comparative sample with μm as a reference. When 10 pieces are measured and all are good, "good",
When even one piece was defective, it was evaluated as "poor". [Electrode cracking during joining] 100 using a high-speed automatic bonder
A bonding test was performed on each piece, and those having no electrode cracking defect were indicated by “◯”, and those having even one cracking defect were indicated by “x”.

[Heat Cycle Test] After forming a loop and sealing with an epoxy resin, the temperature was set to −10 ° C. for 30 minutes and 150 minutes.
A heat cycle test was conducted 2000 times at a temperature of 30 minutes. 1
00 samples were subjected to measurement, and the presence or absence of disconnection was confirmed by a continuity test. The number of broken wires was expressed as a breakage rate (%). [Vibration Test] Test Material Preparation Method Bonding was carried out in the same manner as in Example 1 except that the lead frame 1 plated with silver was used as the substrate material instead of the semiconductor element electrode, and used as a sample for the vibration test. Test method Using the vibration tester 2 shown in FIG. 1, the wire 3 having the tip bonded to the lead frame 1 is held by the clamp 4, and a vibration test is performed under the following conditions in which the wire 5 is oscillated to the left and right sides about the axis 5 and fracture The number of vibrations up to was measured. Span distance (L ₁ ): 150 μm Bilateral amplitude (L ₂ ): 26 μm Vibration frequency: 40 Hz (40 times per second) The same test was repeated 3 times, and the average values obtained are shown in Table 3.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

As is apparent from the measurement results of Tables 2 and 3, the products of the present invention shown in Examples 1 to 19 were subjected to ultrasonic thermocompression bonding with increased ultrasonic output,
Also, even when bonded under severe conditions with reverse deformation applied during loop formation, the bonding strength measured by the shearing force at the ball bonding part is 46.5 g or more, and the high temperature strength by the tensile test is 13.5 g or more. In addition, the ball shape is all good in terms of size, sphericity, and surface condition, and there are no electrode cracking defects during bonding, and an accelerated test that includes a thermal cycle as a bonding part reliability test. However, the fracture rate was as good as 1% or less, and in the vibration test, the number of vibrations leading to fracture was 10,000 or more, which was an excellent effect. Furthermore, the Yb content is 0.0
In Examples 2 to 19 which are 005 to 0.005% by weight, the number of vibrations leading to breakage in the vibration test is 12,000.
More than one times and showed a better effect.

On the other hand, in the case of Comparative Example 1 containing no Yb, which was similarly bonded under severe conditions, the fracture rate in the thermal cycle test was 8%, and in the vibration test it was 64%.
Fracture occurred at 00 times. Further, in the case of Comparative Example 2 in which the Yb content exceeds the range of the present invention, a satisfactory effect was not obtained in the shape of the ball. In the case of Comparative Example 3 containing Eu instead of Yb of the product of the present invention, although a slight improvement effect was observed as compared with the case of Comparative Example 1, the effect was still insufficient and the fracture rate in the heat cycle test was 5 %, 7 in vibration test
Fracture occurred at 800 times. Further, in the case of Comparative Example 4 containing Ce instead of Yb, the results were lower than those of Comparative Example 1 in both the fracture rate in the thermal cycle test and the vibration test. In addition, in the case of Comparative Example 5 containing Yb but not containing Be, Ca, or Ge, a slight improvement effect was observed as compared with Comparative Example 1 as in Comparative Example 3, but the effect was still insufficient. However, the fracture rate in the heat cycle test is 4%, the fracture rate is 7200 times in the vibration test, and the high temperature strength is small. Furthermore, even if Yb is included, Be, C
Comparative Example 6 in which the contents of a and Ge exceed the range of the present invention,
In the case of Nos. 7 and 8, satisfactory results were not obtained in any of the bonding strength, the ball shape, and the electrode crack.

[0022]

As described above, the present invention is 99.99.
A gold alloy wire for bonding, characterized by containing a predetermined amount of at least one of Yb and Be, Ca, Ge in high-purity gold of 9% by weight or more, or a predetermined amount of Eu in addition thereto. Therefore, ultrasonic combined thermocompression bonding with increased ultrasonic output was performed, and even when bonded under severe conditions with reverse deformation added during loop formation, the fracture rate in the thermal cycle test was small, Since the number of vibrations leading to disconnection in the vibration test is large, it can be seen that the reliability of the bonding neck portion is extremely higher than that of the conventional product. In addition, since the bonding strength during bonding is high, more electrodes can be arranged, and the excellent high temperature strength enables stable loop formation, and the advantage that small balls can be formed into a true sphere. Can be achieved at the same time. Therefore, it is possible to provide a gold alloy wire for bonding which is very useful for promoting miniaturization, thinning and multi-pinning of a semiconductor device.

[Brief description of drawings]

FIG. 1 is a simplified diagram showing an outline of a vibration test.

[Explanation of symbols]

 1: Lead frame 2: Vibration tester 3: Bonding wire 4: Clamp 5: Amplitude center axis

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shin Takaura 8-5-1 Shimorenjaku, Mitaka City, Tokyo Tanaka Denshi Kogyo Co., Ltd. Mitaka Factory

Claims (2)

[Claims] 1. High purity gold of 99.999% by weight or more contains ytterbium (Yb): 0.0001 to 0.005% by weight, and further beryllium (Be): 0.0001.
~ 0.001% by weight, calcium (Ca): 0.000
1 to 0.003% by weight, germanium (Ge): 0.0
A gold wire for semiconductor element bonding, containing at least one of 001 to 0.005% by weight. 2. Ytterbium (Yb): 0.0001 to 0.005 wt% and europium (Eu): 0.0001 to 0.00 in high purity gold of 99.999 wt% or more.
Beryllium (Be): 0.0
001 to 0.001% by weight, calcium (Ca): 0.
0001 to 0.003% by weight, germanium (Ge):
A gold wire for bonding a semiconductor element, containing at least one of 0.0001 to 0.005% by weight.