Ultrasonic cleaning uses sound waves passed at very high frequency through liquid cleaners, which can be alkaline, acid, or even organic solvents. The passage of ultrasonic waves through the liquid medium creates tiny gas bubble, which provide a vigorous scrubbing action on the parts being cleaned. Although the mechanism of this action is not completely understood, it yields very effective cleaning.
It is ideal for lightly soiled work with intricate shapes, surfaces, and cavities that may not be easily cleaned by spray or traditional immersion techniques. Highest degrees of cleanliness can be achieved.
The components of a basic ultrasonic system are the cleaning tank, ultrasonic transducers, and a power supply (generator). A disadvantage of ultrasonic cleaning process is the high capital cost of the power supplies and transducers that comprise the system.
Megasonic cleaning uses high-frequency acoustic energy produced by transducers to generate pressure waves in a liquid. It is a higher frequency version (700-1,000 kHz) of acoustic cleaning than ultrasonics (20-40 kHz). An important difference between the two methods is that there is no significant cavitation in the megasonic range. This significantly reduces the likelihood of surface damage. Parts that are damaged by ultrasonic energy might be cleaned without damage in a megasonic bath using the same solutions.
This technique is effective for removing submicron particles from silicon wafers without damage. Removal of other contaminants depends on the solutions in the tank. Megasonic agitation will increase the removal of other contaminants but is not as aggressive as ultrasonics.
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