Why I Don't Recommend Ultrasonic Cleaning for PCBs

Hi! My name is Dmitrii. In this article, I'll explain why I do not recommend using ultrasound for cleaning printed circuit boards (PCBs) and electronics. However, I will also show you how to use a cleaning bath correctly. Let's try to find out why ultrasound can damage PCBs.

Ultrasound at 40 kHz works well with water-based cleaning liquid for removing contaminants from metal, such as medical instruments, solder paste stencils, metal parts, and automotive components. However, ultrasound is only effective on hard surfaces like metals. The softness of PCB textolite makes ultrasound much less effective. Many users pour unknown liquids into the bath and do not follow proper temperature settings, which further reduces cleaning efficiency. Keep in mind that in the electronics industry the recommended cleaning liquid temperature for PCBs is 50°C (122°F). In professional manufacturing, ultrasound is used solely for cleaning metal stencils.

The PCB cleaning quality improves significantly when there is liquid movement inside the bath, which can be achieved through air bubbling. This is done by placing tubes with small holes at the bottom of the bath and pumping air through them - similar to an aquarium air system. The moving liquid helps wash away contaminants and soldering flux residues from under components and microchips. Without proper cleaning liquid movement, dirt removed by ultrasound may remain trapped under microchips and SMD/DIP components, and residues can collect between BGA solder balls and pinouts. Once dried, this increases the risk of white residue forming on the conductors and may even cause current leakage.

For bubbling baths maintained at 50°C (122°F), you can use:
• VIGON US
• VIGON A250
• VIGON FA+
• Surclean SC 2500
• Chemtronics ES132
• Aquanox
• Ionox
Of course, there are many more PCBs cleaning liquid available, but the key point is that they must be water-based.

Distilled water is obtained through primary distillation in a distiller, whereas deionized water is purified by passing it through anion and cation resin filters, activated carbon filters, and mechanical filters. Both processes aim to produce pure H₂O with empty ionic bonds—free from attached contaminants, salts, or minerals.

Always rinse PCBs in a second, identical bath filled with distilled water. In another video, I discuss distilled water and proper PCB cleaning. The rinse water temperature should be maintained at 50°C (122°F), and you should monitor water conductivity using a TDS meter—replacing it if readings exceed 1–2 μS/cm. Also, remember to periodically replace the cleaning liquid in the first bath as it becomes contaminated.

A household TDS meter will show 0 μS/cm for clean distilled water, although it might not display decimal values. For accurate measurement, use a conductivity meter with decimal precision.
• Distilled water has a conductivity of 18 MΩ·cm, which equals 0.056 μS/cm.
• Water should be replaced when it reaches 5 MΩ·cm, which equals 0.2 μS/cm.
Since high-purity distilled water and precise TDS meters is expensive, a simple approach is to replace water when readings reach 1–2 μS/cm. Ideally, measure directly in MegaOhms, though that requires investing in a laboratory conductivity meter.

Some models shown on screen include:
• YSI 3200
• Thermo Scientific Orion Star A212
• Hanna Instruments HI98197
• Hach HQ440d
• Mettler Toledo SevenExcellence

After rinsing, PCBs must be dried at 60°C (140°F) for 1 hour. This step is crucial for removing residual water from under connectors, components, and microchips.

There are several major drawbacks to using ultrasound for PCB cleaning:
• Vibrations can damage high-sensitivity components soldered onto the PCB, such as sensors, MEMS devices, accelerometers, frequency generators, gyroscopes, and some types of microphones.
• Microvibrations can cause damage to any component, leading to unnecessary repairs and wasted time and money.
• Ultrasound does not offer any significant cleaning advantages for electronics while carrying a high risk of damage.

Below is the recommended procedure for using an ultrasonic bath for PCB cleaning (note: this setup is intended for the rinsing bath, not the initial cleaning bath:
• Place air pipes in parallel throughout the bottom of the bath and connect them to a standard aquarium compressor.
• Fill the bath with distilled or deionized water.
• Ensure that the PCB can be fully submerged vertically in the bath.
• Measure water resistance – it should be 0 μS/cm in household TDS meter.
• Lower the basket into the bath.
• Set the temperature to 50°C (122°F) and turn on the heater.
• Do NOT turn on the ultrasound!
• Wait for the water to heat up.
• Place the PCB in the basket vertically.
• Let PCBs cleaning for 10 minutes. Instead of using air bubbles, pumps or filtration systems can also be used to move the liquid within the bath. In industrial applications, a liquid filtration system circulates the water inside the tank.

Thank you for reading!