JPH0669290A - Wire bonding apparatus and method - Google Patents

Abstract

PURPOSE:To improve close contact strength of a lead with a wire in the case of wire bonding by using an ultrasonic wave and thermal energy by varying a vibrating direction of the wave according to a position of the lead. CONSTITUTION:A wire bonding method using both an ultrasonic wave and thermal energy varies a vibrating direction of the wave according to a position of a lead. Two bonding stages for wiring a semiconductor device to leads are provided. Oscillating directions of the waves are varied by 20-29 degrees on bonding stages 12, 13, and one semi-product is wire bonded twice on the stages 12, 13. In this case, two bonding heads 5, 5' are, for example, provided, and vibrators 3, 3' to be placed on the heads 5, 5' to oscillate the ultrasonic waves are so mounted that an angle alpha of the oscillating directions 2 of the waves is 20-90 degrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding apparatus and a wire bonding method, and more particularly to a wire bonding apparatus and a wire bonding method using ultrasonic thermocompression bonding.

[0002]

2. Description of the Related Art A wire bonding method for connecting a pad, which is an electrode on a semiconductor element, and a lead with a fine metal wire for electrical conduction includes an ultrasonic bonding method and a thermocompression bonding method. However, the thermocompression bonding method and the ultrasonic thermocompression bonding combined method are generally used to bond the pad and the lead with the most widely used gold wire.

In the thermocompression bonding method, since it is necessary to heat a semiconductor element or a bonded portion such as a lead at a temperature of about 300 to 350 ° C., a copper material is used when the lead frame is deformed or a copper material is used for the lead frame. Oxidation is accelerated in a short time, and a polyimide tape is stuck on the lead to prevent vibration of the lead, and epoxy adhesive is applied on both sides under the lead to reduce the thermal resistance of the semiconductor device. Some films have copper plates attached to them, and there is a problem that these films or adhesives may deteriorate or soften at high temperatures.
The mainstream is to perform wire bonding by an ultrasonic thermocompression combined method capable of wire bonding at about 00 ° C.

The ultrasonic thermocompression bonding method is a method of performing wire bonding by using both thermal energy and ultrasonic energy, and FIG. 6 shows an outline of this bonding apparatus. In FIG. 6, a bonding stage 7 having a heating mechanism
A pad and lead 16 on the semiconductor element 18 are provided by a gold wire (not shown) supplied from the tip of the capillary 8 above.
Connect to and. At this time, the ultrasonic wave generated by the vibrator 3 attached to the bonding arm 1 propagates in the bonding arm 1 in the vibration direction 2 and is transmitted to the capillary 8 to act on the joint between the gold wire and the bonded portion. . Bonding is performed by this ultrasonic energy and the thermal energy supplied from the bonding stage 7.

[0005]

With the high integration of semiconductor elements, the number of pins of semiconductor devices has been increased and the lead width has become narrower. The smaller the width of the lead, the weaker the strength of the lead, the insufficient rigidity of the lead against the ultrasonic wave applied when joining the wire and the lead, and the lead vibrates with the ultrasonic wave. It is becoming difficult to apply ultrasonic waves.

In particular, as shown in FIG. 7, a heat sink 20 which is also used as an element mounting portion in order to reduce the thermal resistance of the semiconductor device.
In a lead frame having a structure in which the adhesive 21 is applied to the leads 16 via the films 19 coated on both sides, the leads are likely to vibrate during wire bonding, so that the ultrasonic waves acting on the joint surface between the leads and the wire are small and improper. It becomes stable and it becomes difficult to join the wire on the lead.

FIG. 9 shows a lead frame with a heat sink,
When the lead thickness is 150 μm and the lead width is 100 μm, the relationship between the angle θ between the lead forming direction and the ultrasonic vibration direction (see FIG. 9) and the lead-side pull strength is shown. θ is 90 de
The closer to g, the weaker the wire pull strength is. 8
The strength is improved by 50% at 0 deg and 9 at 70 deg.
It can be seen that the improvement is 0% or more. This is because as the lead forming direction becomes closer to a right angle with respect to the ultrasonic vibration direction, the rigidity of the lead with respect to the vibration direction becomes weaker and the ultrasonic waves vibrate the entire lead and ultrasonic energy is generated at the bonding surface between the wire and the lead. It is thought that this is because it does not work.

As described above, depending on the lead forming direction, as shown in FIG.
In the above, assuming that the angle 25 formed by the lead forming direction 24 and the ultrasonic vibration direction 2 is θ, when θ becomes close to 90 deg, the ultrasonic energy is less likely to act on the joint surface between the lead 16 and the wire, and This tendency becomes more pronounced as the bonding force with the leads becomes weaker, especially as the lead width becomes narrower, and the bondability between the leads and the wire is impaired, resulting in a higher rate of non-bonding.

[0009]

SUMMARY OF THE INVENTION The present invention provides a method for performing wire bonding by changing the vibration direction of ultrasonic waves according to the lead molding direction in order to enhance the bondability between the lead and the wire, and an apparatus that enables this. An apparatus having two bonding heads and ultrasonic vibrators mounted on these bonding heads so that the angle formed by the vibration direction of ultrasonic waves is 20 to 90 deg.
2. A device with a mechanism to rotate the bonding head. 3. The apparatus is characterized by having a mechanism for rotating the bonding stage and the lead frame holding rail.

[0010]

The present invention will be described below with reference to the drawings.

1A and 1B show a bonding apparatus according to a first embodiment of the present invention, wherein FIG. 1A is a side view and FIG. 1B is a plan view. The transducers 3 and 3'having two bonding heads and generating respective ultrasonic waves are attached at an angle α (26) formed by the vibration direction of the ultrasonic waves. The bonding head 5 is configured such that the capillary 8 can freely move within the range of the bonding stage A12 by the XY table 6, and similarly, the bonding head 5 '.
Is bonded to the bonding stage B1 by the XY table 6 '.
The capillaries can move freely within the range of 3.

A lead frame (not shown) composed of a plurality of semi-finished products on which semiconductor elements are mounted is housed in the lead frame housing section 10 from the lead frame supply section 9 through the lead frame transport rail 4. ing.

In the wire bonding method in the bonding apparatus of the present invention, one semi-finished product on the lead frame on the lead frame carrying rail 4 supplied from the lead frame supply unit is replaced by one semi-finished product shown on FIG. 3 on the bonding stage A12. Wire bonding is performed between the lead 16 and the pad 22 of the semiconductor element 18 at the positions of the areas A and C partitioned by the product dividing lines S and S ', and then the lead frame is conveyed and on the bonding stage B13. Wire bonding the remaining areas B and D shown in FIG. 3 1
Complete the wire bonding of two semi-finished products.

By wire-bonding using the two bonding arms 1 having different ultrasonic wave oscillating directions, when the angle α formed by the vibration directions of the two bonding arms is 40 deg, any lead is Since the wire bonding can be performed at an angle of 70 deg or less with the lead forming direction, the lead and the wire are closely attached as shown in the relationship between the angle θ formed between the lead forming direction and the ultrasonic vibration direction and the lead side pull strength in FIG. The strength can be improved by 90% or more as compared with the case where wire bonding is performed by a conventional method using a conventional wire bonding apparatus.

FIG. 2 is a schematic view showing a wire bonding apparatus according to a second embodiment of the present invention, wherein (a) is a side view and (b) is a plan view. In this wire bonding apparatus, a rotary table 11 controlled by a control unit is installed between a bonding head 5 and an XY table 6, and by rotating the rotary table, wire bonding is performed by a bonding stage A12 and a bonding stage B13. It has a structure that allows operation.
Although the rotary table 11 is located between the XY table 6 and the bonding head 5 in FIG. 2, a rotary table may be provided below the XY table 6.

The bonding method in this bonding apparatus is to bond the positions A and C of the semi-finished product in FIG. 3 on the bonding stage A, then convey the lead frame and send the semi-finished product to the bonding stage B. Further, the bonding head 5 rotates the rotary table 11 so that wire bonding can be performed at the position of the bonding stage B. Bonding at positions B and D in FIG. 3 is performed at the bonding stage B, and the bonding operation for one product is completed.

When the rotation angle of the rotary table is 40 deg, wire bonding can be performed on all the leads at an angle of 70 deg or less between the lead forming direction and the ultrasonic vibration direction. Can be improved.

FIG. 4 is a schematic view showing a wire bonding apparatus of a third embodiment of the present invention, (a) is a side view,
(B) is a plan view. A rotary table 14 controlled by a control unit is installed under the lead frame transport rail so as to rotate the entire lead frame.

In the wire bonding method of the present invention using this wire bonding apparatus, the lead frame is taken out from the lead frame supply section 9, the lead frame is conveyed and one semi-finished product is placed on the bonding stage 15, and then the step shown in FIG. The rotary table is rotated as shown in (a) to wire-bond the positions B and D in FIG. 3, and the rotary table is further rotated so that the AC position in FIG. 3 is oriented in the direction as shown in FIG. 5 (b). By wire bonding, the wire bonding operation of one semi-finished product is completed, and the next semi-finished product is transported onto the bonding stage 15. Repeat this operation for the number of semi-finished products on one lead frame, and after completing the wire bonding of the semi-finished products on one lead frame, rotate the rail to rotate the rail (FIG. 4B).
The rail is returned to the position of and the lead frame is conveyed to the lead frame housing section 10.

When the rotation angle of the rotary table is 40 deg, the lead forming direction is 70 deg for any lead.
Since the wire bonding can be performed at the following angles, the adhesion strength between the lead and the wire can be improved.

[0021]

As described above, according to the present invention, it is possible to wire bond by changing the vibration direction of ultrasonic waves depending on the position of the lead, so that it is possible to increase the adhesion strength with the wire even if the lead width is narrow. . For example, in a lead frame with a heat sink as shown in FIG. 7, the lead is a copper material with a thickness of 0.15 mm and the lead width is 100 μm.
When the ultrasonic vibration direction is one direction as in the conventional case, the angle θ formed between the lead forming direction and the ultrasonic vibration direction is 90d.
As shown in FIG. 9, in the case of the lead of eg, as compared with the lead of which the adhesion strength between the lead and the wire is 60 deg or less as shown in FIG. When the wire bonding is performed by changing the vibration direction of the ultrasonic wave by 40 deg for one semi-finished product in the present invention, θ may be 70 deg or less for any lead. Therefore, the adhesion strength is 10.8 g when θ = 70 deg, which is improved by about 90%, and the reliability of adhesion can be increased. Furthermore, since the adhesion between the lead and the wire is improved, it is possible to bond even the narrower lead width than the current one, and the number of leads can be increased.
Furthermore, a semiconductor device having a large number of pins can be assembled.
Further, since it is possible to reduce the vibration of the leads, it is possible to perform wire bonding with less ultrasonic waves, and it is possible to reduce the wire deformation due to the influence of ultrasonic waves, which enables the wire formation with longer wires and the degree of freedom in designing semiconductor devices. To increase.

From FIG. 9, there is almost no effect if the angle θ formed by the oscillation directions of the two ultrasonic waves in which the effect appears is smaller than θ = 20 deg. It is necessary that the angle is at least 20 deg or more, and the closer θ becomes to 90 deg, the greater the effect. can get.

[Brief description of drawings]

FIG. 1 is a schematic view of a bonding apparatus according to a first embodiment of the present invention, (a) is a side view and (b) is a plan view.

FIG. 2 is a schematic view of a bonding apparatus according to a second embodiment of the present invention, (a) is a side view and (b) is a plan view.

FIG. 3 is a plan view of the semiconductor device for explaining the bonding method of the present invention and a view showing the position of the transport rail of the lead frame, where S and S ′ are bonding positions A, B and
A dividing line that separates C and D.

FIG. 4 is a schematic view of a bonding apparatus according to a third embodiment of the present invention, (a) is a side view and (b) is a plan view.

FIG. 5 is a plan view showing the outline of a bonding apparatus for explaining a third embodiment of the present invention.

FIG. 6 is a schematic view of a conventional bonding apparatus, in which (a) is a side view and (b) is a plan view.

FIG. 7 is a view of a lead frame for a semiconductor device with a heat sink for explaining the present invention, (a) is a plan view,
(B) is the XX 'sectional view taken on the line of (a).

FIG. 8 is a partial plan view of a semiconductor device for explaining the effect of the present invention.

FIG. 9 is a diagram showing the relationship between the angle θ formed by the lead forming direction and the ultrasonic vibration direction and the lead-side pull strength for explaining the effect of the present invention.

[Explanation of symbols]

1 Bonding Arm 2 Oscillation Direction of Ultrasonic Wave 3 Oscillator 4 Lead Frame Conveying Rail 5 Bonding Head 6 XY Table 8 Capillary 9 Lead Frame Supply Section 10 Lead Frame Storage Section 11 Rotary Table 12 Bonding Stage A 13 Bonding Stage B 14 Rotary Table 15 Bonding Stage 16 Lead 17 Lead Frame 18 Lead Frame Conveying Rail 19 Film 20 Heat Sink 21 Adhesive 22 Pat 23 Lead Width 24 Lead Forming Direction 25 Angle between Lead, Forming Direction and Ultrasonic Vibration θ 26 Two ultrasonic waves Angle α 27 of semiconductor element

Claims (6)

[Claims] 1. A wire bonding method using both ultrasonic waves and thermal energy, wherein the vibration direction of the ultrasonic waves is changed depending on the position of the lead. 2. A wire bonding method using both ultrasonic waves and thermal energy, wherein two bonding stages for connecting a semiconductor element and a lead with a thin metal wire are provided, and an ultrasonic wave oscillating direction is provided on each bonding stage. Is changed from 20 deg to 90 deg, and wire bonding is performed on each semi-finished product twice on each stage. 3. A wire bonding method using both ultrasonic waves and thermal energy, wherein a bonding stage and a holding rail of a lead frame on which a semiconductor element is mounted are rotated by 20 deg to 90 deg to wire-bond one semi-finished product. A wire bonding method characterized by carrying out. 4. A wire bonding apparatus for performing wire bonding by using ultrasonic waves and thermal energy in combination, has two bonding heads, and ultrasonic vibrators mounted on these bonding heads are ultrasonic transducers. A wire bonding apparatus, characterized in that the wire bonding apparatus is attached so that an angle formed by an oscillating direction of a sound wave is 20 to 90 deg. 5. A wire bonding apparatus for performing wire bonding by using ultrasonic waves and thermal energy together, wherein a rotary table having a plurality of bonding stages and rotating a bonding head is installed. 6. A wire bonding apparatus for performing wire bonding using ultrasonic waves and thermal energy together, wherein a rotary table for rotating a bonding stage and a lead frame holding rail within a range of 20 deg to 90 deg is installed. Wire bonding equipment.