Ultrasonic vibration measurement of a wire bonder for ball bonding using a laser Doppler vibrometer

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Application as usage

Application as usage

A wire bonder is a device that connects a conductance wire between a silicon chip, which is a core of IC or LSI, and a lead frame. Currently, ultrasound waves are generally used for wire bonding and the ultrasonic vibration application condition is focused on as one of the important parameters that determine the quality of bonding. To achieve stable bonding, the vibration amplitude at the tip of the capillary must be stabilized and therefore, the need for direct measurement of the vibrations at the tip of the tool is increasing each year.

This application shows a method for measuring capillary vibration conditions (microscopic displacement) using a laser Doppler vibrometer.

The ultrasonic wave mechanism section that is used for a wire bonder comprises a bolting Langevin type transducer, a metal horn for increasing the vibration amplitude, and a tool, which is a solderless terminal (or capillary). In general, a vibration frequency of around 60 kHz or recently sometimes 100kHz is applied.

The vibration condition of a capillary using the laser Doppler vibrometer (microscopic displacement) cannot be measured under the situation that wire bonder is being carried out bonding operation continuously (auto bonding). Because the laser light cannot follow up the bonding machine during operation. By using "manual bonding·step mode", which function enables a single bonding operation only once, capillary vibration condition at the moment of a bonding operation can be measured.

Configuration

	Model name	Product name
1	LV-1710	Laser Doppler Vibrometer
2	LV-0030	Large-format magnetic stand
3	LV-0015	Fine-positioning XY-stage
4	LV-0016	Fine-positioning Z-stage
5	LV-0017A	Large size tripod
6	LV-0018A	Steel plate (magnetized iron sheet)
7	LV-0301	90-degree reflecting mirror　(use at the time of lead frame measurement)
8		Digital oscilloscope (or an equivalent high-speed storage oscilloscope)

Example of measurement data

When a wire bonder is used for along period of time, fatigue conditions are accumulated in the oscillator and horn, thereby starting oscillation that is different from the initial state. By recording oscillation values at the tip of the horn after replacing with a new oscillator or a horn, the oscillator and the horn can be maintained quantitatively based on the change of the oscillation values of the tip of the horn. In particular, measurement of the increase/decrease of oscillation amplitude at the tip of the horn and capillary in proportion to the increase/decrease of the intensity on the drive signal side provides useful data for the subsequent maintenance. Since the resolution of a laser Doppler Vibrometer does not depend on the measurement distance, the data can be digitized with high resolution, measurement is performed in the vicinity of an action point, and measurement data fluctuation rate is high. Therefore, it has an advantage of the easy detection of differences. In particular, when a problem occurs in an oscillator or a metal horn, it can be comparatively easily detected if the initial data is available.

画面データ（キャピラリの振動速度波形とUＳ元信号波形１）

Top:Capillary oscillation velocity waveform
Bottom:Original US (ultrasonic wave) signal
Each waveform of the bottom section:Zoom waveform of 10μs/div

画面データ（キャピラリの振動速度波形とUＳ元信号波形のFFT解析データ１）

Frequency analysis data by FFT

画面データ（キャピラリの振動速度波形とUＳ元信号波形２）

Top:Capillary oscillation velocity waveform
Bottom:US(ultrasonic wave)signal
Each waveform of the bottom section:Zoom waveform of 10μs/div

画面データ（キャピラリの振動速度波形とUＳ元信号波形のFFT解析データ２）

Frequency analysis data by FFT

Measurement point

Since the characteristics vary depending on the type of the IC that is manufactured and the bonder/wire that are used, industry standards cannot be created so that individual handling is applied. Therefore, since some time for creating standards is required, the method will not be effective immediately. As constant monitoring is not possible, some experience is necessary for measurement.

A capillary, which requires periodic replacement, involves replacement work. The amplitude of the tool may change at bonding depending on the capillary installation position against the horn and the fixation screw tightening torque. The oscillation amplitude also varies depending on the material and the shape of the tool.

The impact of the relative oscillation of the bonder main unit and the sensor of the laser Doppler vibrometer is so minimal that it cannot be observed from the capillary oscillation data in proportion to the frequency component of the oscillation velocity. However, if the floor under the bonder or the laser Doppler vibrometer sensor fixing tripod that is installed wobbles relatively significantly due to insufficient strength, it is difficult to deliver the laser beam steadily to the cap of the capillary cylinder, disabling data of a satisfactory S/N ratio. In this case, the oscillation impact must be reduced by providing an optical vibration elimination platform under the tripod.

Revised:2012/07/02

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