JPH0570935B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wire bonding apparatus for semiconductors and the like, and particularly to a method for efficiently bonding by eliminating pellet damage caused to surfaces to be bonded during wire bonding.

[Technical background of the invention and its problems]

In a bonding method in which a sensor detects when the wire contacts the surface to be bonded, and an ultrasonic wave is applied simultaneously with this detection signal or after a certain period of delay, when the ultrasonic wave is applied at the same time as the wire contacts the bonding surface, , the ultrasonic wave is applied before the gold ball is completely deformed by the pressure, that is, in the process of deforming the gold ball by the pressure.
Since ultrasonic waves are applied under high pressure, the formation speed of the joint alloy layer is fast, the joint strength is high, and the bonding time can be shortened. However, some types of pellets have the disadvantage of being susceptible to pellet damage.

Conversely, if the time from the start of pressure application to the application of ultrasonic waves is relatively long, ultrasonic waves will be applied after the gold ball has been completely deformed by pressure application.
Pellet damage is small, but the formation of the bonding alloy layer is slow and the bonding time is long. In hybrid ICs, several types of ICs are mounted on a single substrate, and some are resistant to pellet damage during bonding, while others are weak. Normally, in order to increase the bonding speed and increase the production volume, when bonding is performed at the same time as the above-mentioned contact and at the same time as the ultrasonic wave is applied, there is a problem that pellet cracks tend to occur. Further, the latter method of delaying had the problem that it was difficult to increase the speed.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for efficiently bonding pellets by eliminating pellet damage during bonding and shortening the bonding speed.

[Summary of the invention]

That is, in a wire bonding method in which a wire inserted into a capillary at the tip of a tool arm contacts a surface to be bonded, and bonding is performed by applying ultrasonic waves to the capillary.
Based on the detection of the wire contacting the surface to be bonded, the time to apply ultrasonic waves can be set individually for each bonding point or every several bonding points, and based on this set time. The present invention provides a wire bonding method characterized by bonding.

[Embodiments of the invention]

An embodiment in which the present invention is applied to wire bonding of a hybrid IC will be described below with reference to the drawings. 1 in FIG. 1 is an X, Y table.
On the front upper surface of this X, Y table 1, there is a rotating shaft 2.
A support stand 3 is provided. A tool lifter arm 4 is pivotally attached to the rotating shaft 2 of the support base 3 so as to be vertically movable. A tool arm holder 6 is fixed to this tool lifter arm 4 via a leaf spring 5, and a tool arm 7 is attached to this tool arm holder 6. A bonding head, such as a capillary 8, is provided at the tip of the tool arm 7 so as to face a pellet 9, which is a surface to be bonded. Further, a linear motor 10 as a first drive source is provided between the tool lifter arm 4 and the tool arm, and is adapted to apply a bonding load to the capillary 8 via the tool arm 7.

On the other hand, a linear motor 11 serving as a second drive source for driving the tool lifter arm 4 is provided on the upper center surface of the X, Y table 1. The tool lifter arm 4 is swung up and down by this linear motor 11, and the tool arm 7 is moved up and down. At the tip of the tool lifter arm 4, there is a means for detecting the contact of the bonding wire with the part to be bonded, for example, an eddy current gap sensor 12 for detecting the relative position between the arm 4 and the tool arm 7. The gap sensor 12 is connected to a start pulse generating circuit 14 via an amplifier 13. The start pulse generating circuit 14 is connected to an ultrasonic oscillator 15, and the ultrasonic waves generated by the ultrasonic oscillator 15 are transmitted to the capillary 8 via a transducer 16 provided at the rear of the tool arm 7. Reportedly. The ultrasonic output may be configured to be adjustable so that it can be selected as appropriate.

Next, the procedure of the above wire bonding method will be explained. The gap between the tool arm 7 and the tool lifter arm 4 is detected by a gap sensor 12, and a linear motor 10 as a first drive source is controlled so that the gap becomes a predetermined value. As a result, the tool arm 7 and the tool lifter arm 4 are integrated in a servo-locked state and move up and down. In this state, the tool lifter arm 4 starts swinging, and at the same time the capillary 8 moves. When a bonding wire holding means, such as a wire inserted into a capillary 8, comes into contact with a pellet 9, which is a surface to be bonded, a gap sensor 12 detects this, and uses this as a detection signal to control the operation of an ultrasonic oscillator 15. The signal is sent to the start pulse generation circuit 14. Then, the ultrasonic oscillator 15 is caused to oscillate by the pulse from the start pulse generating circuit 14, and ultrasonic waves are applied to the capillary 8 for a certain period of time to perform wire bonding. Furthermore, wire bonding is performed by applying ultrasonic waves in the same way to the lead frame side on which the IC is mounted, and this process is repeated.

Thus, the application of ultrasonic power to the capillary is controlled based on the detection signal from the gap sensor 12.

Next, the timing of the start pulse generation from the start pulse generation circuit 14 will be explained.

For example, several types of pellets are placed on a single substrate in a hybrid IC. Some of these pellets have a thin SiO ₂ layer the size of an aluminum pad and are susceptible to damage during bonding, while others have a thick SiO ₂ layer and are resistant to damage during bonding, and they are a mixture of both. For pellets that are resistant to pellet damage, apply ultrasonic waves as shown in curve 1 in Figure 2, and use a sensor to detect when the wire is in contact with the tool curve as shown in curve 1 in Figure 3, and use that signal as a trigger to apply ultrasonic waves. Bonding was performed using a method that shortened the bonding time, for example by outputting a start pulse at the same time as contact detection. In addition, for pellets that are susceptible to pellet damage, as shown in curve 2 in Fig. 2 and curve 2 in Fig. 3, a start pulse is output with a delay from the above-mentioned signal, for example, by 5 msec, and ultrasonic waves are applied. Bonding method eliminates pellet damage.

All of these delay times are stored in memory in advance for each pellet and each pad, and are controlled by a computer program.

The amount of delay time can be appropriately selected depending on the degree of pellet damage. Figure 3 shows a state 6 in which the ball 62 at the tip of the wire is deformed by being pressurized sequentially from the time when it comes into contact with the pellet 61.
3 is a diagram illustrating the timing of ultrasound application (US waveform) with respect to the change in No. 3.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to perform optimal bonding at high speed in accordance with the degree of damage at each bonding point in a large-scale hybrid IC or an IC having a pad on the element.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a graph diagram of bonding strength, and FIGS. 3 and 4 are illustrations of ultrasonic application timing operation. 7...Tool arm, 8...Capillary, 9...
...Surface to be joined, 12...Sensor, 15...Ultrasonic oscillator.

Claims (1)

[Claims] 1. In the wire bonding method, in which the wire inserted into the capillary at the tip of the tool arm contacts the surface to be bonded, ultrasonic waves are applied to the capillary to perform bonding. A wire bonding method characterized in that the time until applying ultrasonic waves can be set individually for each bonding point or every several bonding points based on the detected time, and bonding is performed based on the set time.