Technical Report on Ultrasonic Vibration Measurement of Wire Bonds Using Laser Doppler Vibrometer 3

Laser Doppler Vibrometer Ono Sokki LV-1800
XYZ stage with magnetic stand Ono Sokki LV-0030 + LV-0015 + LV-0016
Large tripod Ono Sokki
Tripod Mounting Plate (Magnetic Iron Plate) Ono Sokki LV-0018A
Digital oscilloscope (OSC) or an equivalent high-speed storage oscilloscope (with 1M or more memory equipped)
BNC-BNC cable x1, probe x1 (depending on the device, alligator clip-BNC cable, etc.)
90° reflection mirror (used for measuring lead frames) Ono Sokki LV-0301

Attach the tripod mounting plate to the tripod and secure the magnetic stand with the XYZ stage.
Remove the sensor head of the LV-1800 from the main unit and attach it to the magnetic stand.
Extract the voltage signal from the ultrasonic transmitter of the wire bonder* and connect it to CH 1 of the OSC.
*Varies by manufacturer. Refer to the bonder's manual.
Input the speed output from LV-1800 into channel 2 of the OSC.

Turn the power ON. We will perform a warming up for more than 20 minutes.
Manually move to the bonding position where you want to measure the capillary.
Shine the laser light on the capillary and adjust the lens focal length and micro stage so that the reflection level indicator lights up steadily in the green range (without blinking). At this time, confirm that the 'ERROR' indicator on the sensor/body does not light up or blink.

The item ③ is the most technically demanding part of the entire operation. The impact of the relative vibration between the bonding device and the sensor on the measurement results is so minor that it cannot be observed from the capillary vibration data due to the frequency components of that vibration speed. However, if the bonding device or the floor where the tripod is set lacks stability and shakes relatively significantly, it becomes difficult to stably irradiate the laser light onto the top of the capillary cylinder, and it is not possible to maintain the level indicator stably to obtain data with good signal-to-noise ratio (S/N). As a countermeasure, the influence of vibrations can be mitigated by placing an optical vibration isolation table under the tripod.

The laser focus position on the capillary should be set as close to the tip of the capillary as possible; however, depending on the type of capillary, the tip may bend under load, so it is recommended to set it at the position where it begins to taper. An important point is that if the focus position is significantly changed with each measurement, the correlation of the data will be lost, so adjustments should be made using the XYZ stage to keep it nearly the same.
For a speed range above 60 kHz in the vibration domain, it is recommended to select 1 m/s/V. *It is advisable to use the speed output of the Laser Doppler Vibrometer rather than the displacement output. In the case of displacement output, low vibration displacements from the floor are picked up simultaneously, but for vibration speed, there is a significant difference between the vibration speed of the capillary and the vibration speed of the floor, so this influence does not appear in the data.
Keep both the HPF and LPF filters in the off state.

The vibrator has the characteristic of generating large vibrations at a specific frequency (resonant frequency), but the frequency can change depending on the conditions. Therefore, a feedback circuit is established in the oscillator driving the vibrator for frequency control. Furthermore, the vibrations propagated through the metal horn are amplified, resulting in an amplitude of several micrometers at the tool tip when unloaded. To perform stable bonding, it is necessary to stabilize the vibration amplitude at the tool tip. As a result, the need for direct measurement of the vibrations at the tool tip has been increasing year by year.

I will turn on the power.
Only display the waveform that I want to show.
- CH key
- light up
Set the input coupling to AC.
- INPUT key
- AC
Set the probe's attenuation ratio ^※

Observe the probe's damping ratio and set the damping ratio.
- INPUT key
- Probe
- 1:1 or 1:10
Set the voltage axis sensitivity optimally to about 2 V per division.
- V/DIV key
- rotary knob
Set the trigger mode to single.
- MODE key
- SINGLE
Set the trigger level and trigger source to CH 1 (approximately 0.5 V).
- LEVEL / SOURCE Key
- CH 1
- rotary knob
Set the trigger position to (-4 div)
- POSITION/DELAY Key
- -4 divided by
Set the storage memory capacity to 1 M or more.
- ACQ Key
- Length
- 1M
Set the time axis for each bonding time (1 ms/div to 10 ms/div).
- TIME / DIV Knob
Make the OSC wait for a trigger.
- START/STOP key

After completing the setup, perform a manual test oscillation. At that time, confirm that the OVER or ERROR display on the LV-1800 is not lit. If the OVER indicator is lit, it means the speed range is too low or the settings are incorrect, resulting in insufficient light intensity. Check the OSC display; if the waveform exceeds 10 V in a single amplitude, the range is inappropriate. Change to a range that does not exceed 10 V. If no data is displayed during oscillation, it may be due to the start button not being pressed or an incorrect trigger level setting. Please reset the trigger level so that the US oscillation waveform can be displayed.

Enlarge the waveform display at any position.
- POSITION key
- Bring the position you want to enlarge to the center of the screen using the rotary knob.
- Select the zoom magnification with the ZOOM key and rotary knob.
to display a spectrum
- Turn on the SHIFT and FFT key.
- Select the waveform you want to display in the spectrum using Trace.
- Turn ON FFT.
Read each waveform using cursors (which can be set in two locations).
- CURSOR key
- Turn ON the CURSOR.
- rotary knob
to print out
- COPY key