What is Megasonic cleaning?
The Megasonic-/ ultrasonic generator transforms the main voltage of 50/60 Hz to a frequency corresponding to the operative frequency of the transducer. Piezoelectric transducers bonded on a plate outside of a tank produces high frequency sound waves that propagate through a liquid. Each point along the wave oscillates between a maximum and minimum pressure. When the pressure minimum is below the vapor pressure of the liquid, bubbles are formed in the liquid. When the pressure increases to maximum pressure, the bubbles implode, sending out an intense shockwave of energy as the fluid rushes in to fill the void left by the collapsed bubble - this effect is called cavitation. This energy is referred to as cavitation energy, and is well-suited for removing particles or contaminants from a substrate.
Megasonics compared to Ultrasonics
Different factors can affect the intensity of the cavitation energy in a Ultrasonic / Megasonic processes, such as the surface tension of the liquid or the distance from the substrate to the transducer. The most critical factor however, is the frequency of the sonic waves.
In a typical Ultrasonic cleaning process, the transducer works with a frequency between 25 kHz and 100 kHz. This lower frequency creates larger bubbles up to diameters of 150 µm and creating high cavitation energy when they collapse. Megasonic processes utilize frequencies from 400 kHz up to 5 MHz. These higher frequencies create smaller bubbles and when they collapse, producing a proportionally smaller amount of cavitation energy. The high cavitation energy produced in ultrasonic cleaning can damage sensitive structures of substrates. The gentler cleaning energy produced by Megasonic waves is able to remove particles down to the nanometer range without damaging sensitive devices.
Multiple enlarged cavitation bubble at a frequency of 25 kHz (in moment of implosion)
"Is Megasonic cleaning the new ultrasonic cleaning?" - this article looks at the differences and highlights the use of Megasonic in the semiconductor industry:
|"Is Megasonic cleaning the new ultrasonic cleaning?"