Ultrasonic Systems for Precise Cleaning Applications
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How a Megasonic Cleaning System Removes Submicron Particles from Delicate Components

February 27, 2017

How a Megasonic Cleaning System Removes Submicron Particles from Delicate ComponentsMegasonic cleaning systems use high frequency generators and transducers operating in the MHz range to clean delicate parts such as silicon wafers, and related microelectronic devices. Semiconductor manufacturing processes rely on repeated cleaning operations, and megasonic systems clean more rapidly and more completely than other cleaning methods in many applications. Megasonic cleaning systems are especially effective in the removal of submicron particles during the manufacturing process of semiconductors, MEMs, LCD screens and solar panels.

How Megasonic Cleaning Systems Work

All ultrasonic and megasonic cleaning systems work by generating cavitation bubbles in a cleaning solution. As a megasonic wave propagates through the fluid, wave troughs produce areas of low pressure where microscopic bubbles form. When the high pressure wave peak arrives, the bubbles collapse and release a substantial amount of energy. The energy from many small bubbles collapsing at the same time acts on surface contaminants of the devices being cleaned, breaking up, dissolving and removing the contamination.

As the system frequency rises, the waves are closer together and there is less time for bubbles to form. As a result, higher frequencies produce smaller bubbles and gentler cleaning action as the collapsing bubbles produce less energy. For MHz frequencies, the bubble size approaches the size of the submicron particles, but the energy released by the collapsing bubbles is small enough that it doesn’t damage the semiconductor wafer surface. It is however strong enough to dislodge the particles.

Submicron particles are hard to remove because they are small enough to be embedded in the boundary layer between the solid wafer and the free-flowing cleaning solution. Even when the cleaning solution moves quickly under pressure, the boundary layer remains static and holds the tiny particles in place. During megasonic cleaning microscopic bubbles move right up to the particles and, when a bubble collapses, the resulting energy burst dislodges the particle. The megasonic cleaning system produces a current that takes the particle away from the wafer surface and prevents it from becoming attached again.

This process effectively removes almost all particles from the surface of the semiconductor parts and results in fewer defects in the final product. Semiconductor manufacturing facilities can improve product quality and produce fewer defective products.

Megasonic Cleaning System Characteristics and Features

A megasonic cleaning system consists of a high frequency generator capable of producing MHz frequencies, a corresponding transducer and a tank to hold the cleaning solution and the parts to be cleaned. Ideally the unit can operate over a range of frequencies to let operators adjust the system to meet the cleaning performance they need. Adequate cleaning power is required and the system should not need extensive set-up and calibration.

Kaijo has extensive expertise and broad experience with ultrasonic and megasonic cleaning systems. The company can advise customers on the best cleaning methods and can help customers select the system, equipment and features best suited for their process. The Quava megasonic cleaning system is a cost-effective solution that can operate at lower ultrasonic frequencies of 26 kHz to 200 kHz as well as higher megasonic frequencies of 430 kHz, 750 kHz and 950 kHz with up to 1200 watts per generator. The company also offers the desktop compact Quava Mini system, the US Shower, the Mega Tube and the Spot Shower for additional megasonic cleaning applications. These components complement Kaijo’s range of products, allowing the company to support customers in all their megasonic cleaning applications.

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7 Things to Consider When Selecting Ultrasonic Cleaners

February 15, 2017

7 Things to Consider When Selecting Ultrasonic CleanersUltrasonic cleaning systems can clean many parts better than other cleaning methods because of the intense scrubbing action of cavitation bubbles generated by the ultrasonic waves. While ultrasonic cleaners often work faster and clean more completely than conventional cleaners, they have to be suited for the cleaning application. Facility managers and other decision makers have to be familiar with ultrasonic cleaning system characteristics and features so they can select cleaners that perform up to expectations. Below are seven things to consider when selecting ultrasonic cleaners. Kaijo can help ensure that such considerations result in the selection of systems that will improve cleaning performance.

  1. What frequency do you need?

The frequency determines the size of the cavitation bubbles and the intensity of the cleaning action. Low frequencies down to about 20 kHz generate comparatively large bubbles for robust cleaning action to remove heavy contamination from rugged parts. Higher frequencies up to 200 kHz generate progressively smaller bubbles for more gentle cleaning of delicate components. The highest frequencies up to the MHz range can be used for cleaning fragile parts such as electronic microcircuits and medical equipment. For flexible applications an ultrasonic cleaner with multiple frequency ranges is useful.

  1. What cleaning power do you need?

While the ultrasonic frequency determines the bubble size and cleaning intensity, the system’s power in watts gives the overall cleaning capacity. Larger tanks need more power. A cleaning solution tank of about 400 by 400 mm and 250 mm deep requires about 1200 W.

  1. What size of tank do you need?

The longest dimension of the largest part to be cleaned determines the size of the tank required to clean the part. Kaijo has a variety of standard tank sizes and can build custom tanks for special requirements. If a basket is used, the part has to fit in the basket and the tank has to be slightly larger.

  1. Do you need a basket?

Baskets fit inside the tank and hold the parts to be cleaned away from the walls and tank floor. Some tanks use the bottom of the tank as a membrane to transmit the ultrasonic waves, causing parts resting on the bottom to vibrate against the tank. This can cause damage to the part and to the tank.

  1. Do you need heating?

Heating the cleaning solution can speed up cleaning and improve performance when contaminants include grease and oil that can be softened with heat. For contaminants not affected by heat there is little benefit in heating the cleaning bath.

  1. What cleaning solution should you use?

While industrial ultrasonic cleaners can work with plain water, adding mild detergents to the cleaning solution can improve cleaning performance. In some cases, slightly acidic or slightly alkaline cleaning solutions will help soften or dissolve the contaminants to be removed.

  1. Do you need sweep mode?

Sweep mode varies the ultrasonic frequency slightly around the set frequency value. For example, a system set to 38 kHz might cycle through 35 to 41 kHz in a continuous variation. Fixed frequencies result in dead spots without bubbles and hot spots with too many bubbles in the cleaning tank. Parts may resonate at a fixed frequency and suffer damage. Sweeping the frequency avoids these problems.

Kaijo can help with considerations such as these to ensure customers select the ultrasonic cleaning system that meets their requirements. Kaijo’s extensive experience in ultrasonic technology and the company’s broad range of ultrasonic cleaning equipment mean that expert advice is available to ensure the systems customers select deliver the improved cleaning performance and increased productivity they expect. If you would like a free consultation on how Kaijo’s ultrasonic cleaners can be used for your cleaning application call Kaijo or email [email protected].

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