SU761198A1 - Apparatus for ultrasonic welding - Google Patents

Description

The invention relates to ultrasonic welding, can be used in equipment for micro welding in microelectronic production.

A device for ultrasonic welding 5, containing an electro-acoustic transducer, a phase shifter, a power amplifier, a feedback circuit, a master oscillator, is known [1].

A disadvantage of the known device is that it does not possess reliable excitation of the transducer when operating at low output power and with low tool loading forces.

It is also known a device for ultra-15 acoustic welding, containing a generator of the noise frequency spectrum, a power amplifier, an electro-acoustic transducer [2].

In a known device, an electroacoustic converter is excited both at its main resonant frequency, and at all harmonics and side resonant frequencies.

A disadvantage of the known device is the low efficiency of conversion of electrical energy into mechanical energy, since the bandwidth of a high-quality electroacoustic transducer is much smaller than the band of the noise spectrum. In addition to 30

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This, in the welding tool in most cases, there are complex types of oscillations due to the excitation of the transducer at side resonances, which increases the strength spread of the joints.

The closest solution to the technical nature and the achieved result to the invention is a device containing a series-connected power amplifier, electro-acoustic transducer, mechanical resonance sensor, a circuit of automatic frequency control, driving an independent excitation generator [3].

With this device, an ultrasonic welding method is implemented, in which, during the formation of a welded joint, the frequency of ultrasonic vibrations of the instrument is changed from the value required to destroy and remove surface oxide films to the magnitude of the intensification of diffusion processes and the connection of the materials to be contacted or a low-frequency or high-frequency harmonic is applied to the main frequency basic vibrations.

A disadvantage of the known device for ultrasonic welding is the great difficulty in controlling the welding process, in which, when switching welding

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mode with a resonance frequency in a different frequency / = 2/1/1, v. e. equal to n-harmonic frequency f / _i, decreases the amplitude of the oscillation converter, which is insufficient to maintain the welding process.

In addition, the frequencies of additional resonances of the electroacoustic transducer may differ by several kilohertz from the corresponding harmonic of the main resonant frequency C. At high excitation frequencies, the device leaves the resonant mode of operation. The conversion efficiency drops sharply.

The aim of the invention is to improve the quality of welding.

This goal is achieved by the fact that a switch and additional master oscillators of independent excitation are tuned into the device, tuned to different resonant frequencies of the electroacoustic converter, while the master oscillator outputs are connected to the switch inputs, the output of which is connected to the power amplifier, and master oscillator inputs are connected to the output auto-tuning circuits

FIG. 1 shows the proposed device, a block diagram; in fig. 2 - amplitude-frequency characteristic of the electro-acoustic transducer.

The device contains an electro-acoustic transducer 1, an amplifier 2 power, a switch 3, driving the generators

4–6 independent excitations, a frequency auto-tuning circuit 7, a mechanical resonance sensor 8, a working tool 9.

The device works as follows.

After loading the tool 9 on the materials to be welded, the switch 3 according to the program connects to the amplifier 2 power the master oscillators 4-6, the adjusted frequencies / 2/2 and / 3, respectively. In the initial period of the welding process, when it is necessary to destroy the oxide films on the contact pads and create physical contact over a large area, the switch 3 switches on the master oscillator 4, which is tuned to a low resonant frequency / 1 of the converter. After creating a physical contact at the stage of formation of the centers of interaction of the connected elements, the switch 3 connects the generator 5, tuned to the resonant frequency / ₂ , corresponding to the average frequency of the characteristics of the converter. At the final

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stage of the welding process to accelerate diffusion processes and increase the depth of the volume interaction of the connected elements of the switch 3 is connected master oscillator 6 with a large resonant frequency / 3.

When the resonant frequencies of the mechanical oscillations of the electroacoustic transducer 1 change during the welding process, the signal from the sensors 8 is fed to the input of the frequency-locked loop 7, which controls the frequency of the master oscillators 4-6.

A device for ultrasonic welding has been tested on a model for assembling semiconductor devices. As a result of the tests, a high strength of wire connection was obtained, and the average level of strength was 5–8% higher than when assembled with previously known devices. This allows you to increase the efficiency of the equipment and the yield percentage of suitable devices

Claims (1)

Claim A device for ultrasonic welding, containing a power amplifier connected in series, an electro-acoustic transducer, a mechanical resonance sensor, an automatic frequency control circuit, an independent excitation master oscillator, characterized in that, in order to improve the quality of welding, a switch and additional master oscillators of independent excitation are introduced into the device, to different resonant frequencies of the electroacoustic transducer, while the outputs of the master oscillators are connected to the inputs switch, the output of which is connected to the input of the power amplifier, and the inputs of the master oscillators are connected to the output of the circuit of the automatic frequency control.