Abstract
Bonding machines suffer from a problem that a wavering disturbance of air occurs due to heaters and decreases the accuracy of vision sensing for tool positioning. Previous solutions use airflow to clear out heated air from the light path or physical/airflow walls to separate heated air from background air. Although these previous solutions have been in practical use, they have some drawbacks. Airflows reduce the bondability on the chip surface and have negative effects on the generation of FAB (free air ball) at the tip of wires. Physical walls convey heat to cameras and cause their thermal expansion, and the structure of the physical walls may vibrate due to the rapid motion of the other machine components. In order to avoid these drawbacks, we propose a new method that keeps the light path calm using ultrasonic standing wave. The incident ultrasonic wave travels vertical to the light path, and is reflected by a reflection wall. These incident and reflected ultrasonic waves make a standing wave which has a periodic structure of nodes and antinodes. The fluctuation of air is suppressed in this stable structure. To evaluate the performance of the proposed method, experiments were conducted. We took two parameters in the experiments. One was the distance between the light path (observation point) and the reflection wall. The other was the ultrasonic output. The experimental results showed that an antinode of sound pressure of the ultrasonic standing wave was the best part to suppress the fluctuation of the air and moderate ultrasound output was more effective.
