JPH059624A - Bonding wire - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a bonding wire used for connecting a chip electrode on a semiconductor element and an external lead, particularly a bonding wire in which a neck portion immediately above a gold ball is not easily broken by vibration. [Structure] High purity gold with a purity of 99.999% by weight or more,
Eu of 0.00002 to 0.004% by weight and Ca of 0.2.
0001 to 0.003% by weight, Ge 0.0001 to
0.003 wt% and Be 0.0001 to 0.00
Bonding wire consisting of alloy wire containing 1% by weight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonding wire used for connecting a chip electrode on a semiconductor device and an external lead.

[0002]

2. Description of the Related Art Gold wires, which are often used for connecting chip electrodes of semiconductor elements such as transistors, ICs, and LSIs to external leads, have a purity of 99.999 in order to improve their mechanical strength and heat resistance. A method of adding a trace amount of another metal element to high-purity gold of not less than wt% has been adopted. For example, high purity gold containing Ca, Be and Ge (Japanese Patent Publication No. 57-35577) and La containing rare earth elements such as La, Ca, Be and Ge (Japanese Patent Publication No. No. 12022) is proposed.

However, due to the recent trend of increasing the number of pins in semiconductor devices, the lengthening of the external leads has led to the phenomenon that the gold ball neck portion is broken due to vibrations generated in the bonding process and subsequent processes. It was The cause of this fracture is that the crystal structure immediately above the ball becomes a coarse recrystallized structure due to the heat effect on the gold wire during ball formation, and the strength is reduced to about 70% of the strength of the gold wire before ball formation.

[0004]

SUMMARY OF THE INVENTION The present invention aims to provide a bonding wire that has solved the problem that the neck portion just above the gold ball is broken by vibration, which has not been solved sufficiently by the conventional alloy gold wire. Is.

[0005]

The bonding wire of the present invention is made of high purity gold having a purity of 99.999% by weight or more, and E
u is 0.00002 to 0.004% by weight and Ca is 0.0
001-0.003% by weight, Ge 0.0001-0.
The alloy wire is characterized by containing 003% by weight and 0.0001 to 0.001% by weight of Be.

[0006]

Function Eu has the effect of increasing the mechanical strength of the gold wire and preventing the coarsening of the crystal grains directly above the ball due to the heat effect when forming the gold ball, and when coexisting with Ca, the effect becomes remarkable. If Eu exceeds 0.004% by weight, the loop height becomes low, and if it is less than 0.00002% by weight, the above effect is insufficient. Therefore, 0.00002 to 0.004% by weight is necessary. The rare earth elements such as La and Ce also have the above-mentioned effect, but when containing Eu, the content is 0.000.
Even if the minimum value is 02% by weight, the effect is large.
Is an atomic radius compared to other rare earth elements such as La and Ce,
It is considered that the physical properties such as the ionic radius have unique values.

[0007] Ca, like Eu, has the effect of increasing the mechanical strength of the gold wire and preventing the coarsening of the crystal grains directly above the ball due to the heat effect when forming the gold ball, but its content is 0.000.
If it is less than 1% by weight, there is no effect, and if it exceeds 0.003% by weight, the improvement in mechanical strength is remarkably reduced, and Ca is deposited on the surface of the gold ball when it is formed, and the bondability with the chip electrode is Since it inhibits, it is necessary to contain 0.0001 to 0.003% by weight.

Ge is effective in stabilizing the mechanical strength of a wire containing Ca. Be improves the loop shape and the higher the content, the higher the loop height, but 0.0
If it is less than 001% by weight, there is no effect, and if it exceeds 0.001% by weight, the crystal grain boundary immediately above the ball becomes brittle. Eu, C
Since a decreases the loop height as the addition amount increases, it is necessary to improve the loop height by adding Be.

[0009]

Example: For high-purity gold having a purity of 99.999% by weight or more,
Eu or the like is added to have various compositions, and melted in a high-frequency induction furnace in hydrogen gas using a high-purity carbon crucible,
A mother alloy was obtained. This master alloy and high-purity gold were mixed, and a gold alloy having the composition shown in Table 1 was melted in a high-frequency induction furnace in a vacuum using a high-purity carbon crucible. Next, after groove groove processing was performed, wire drawing was performed to draw wire with a diameter of 0.03 mm.

The bondability and other characteristics shown in Table 1 were investigated using the obtained bonding wire. For tensile strength at room temperature, this wire was heat-treated so that the breaking elongation at room temperature was 6%, and a tensile test was carried out at room temperature. The results are shown in Table 1. In the repeated bending test, as shown in FIG. 1, ball bonding (10 cm long wire was ultrasonically thermocompression bonded onto a gold-plated lead frame (7 mm × 7 mm). Ball diameter was 90 μm). 5g) hanging, wire and + 45 ° -45
The necking portion was repeatedly bent (20 times / minute) by rotating the bonding surface so as to form an angle of °, and the fatigue strength of the neck portion was compared by the number of times of bending until breakage. The results are shown in Table 1.

[0011]

[Table 1]

In Table 1, the loop height was obtained by using a metallurgical microscope to determine the relative displacement amount when the lead frame surface was focused and when the rope highest portion was focused. The bondability was evaluated by the force (shear strength) required for peeling the pressure-bonded ball.

By comparing Test Nos. 1 to 9 and 10 to 14, the bonding wire according to the present invention has excellent properties such as bondability as a bonding wire, and particularly, the number of repeated bending tests is large and the strength against vibration is large. I understand.

[0014]

As described above, the gold wire of the present invention eliminates the drawbacks of the conventional bonding wire and enables the yield and reliability of the bonding process to be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a repeated bending test.

[Explanation of symbols]

 1 Gold-plated lead frame 2 Ball neck 3 Bonding wire 4 Weight

Claims (1)

Claims: 1. High purity gold having a purity of 99.999% by weight or more, 0.00002 to 0.004% by weight of Eu, 0.0001 to 0.003% by weight of Ca, and Ge. 0.0001
~ 0.003 wt% and Be 0.0001-0.0
A bonding wire made of an alloy wire containing 0.1% by weight.