How does Megasonic Cleaning work
The Megasonic-/ Ultrasonic Generator transforms the mains 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 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 process, such as the surface tension of the liquid or the distance of the substrate from the transducer.
The most critical factor 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 bigger bubbles up to diameters of 150 µm and creating higher cavitation energy when they collapse. Megasonic processes utilize frequencies from 600 kHz up to 4 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 34 nm without damaging sensitive devices.
Multiple enlarged cavitation bubble at a frequency of 25 kHz