Industries · 3 min read · Updated 2026-09-25

Ultrasonic cleaning in electronics and PCB assembly

Flux after soldering, dust and oxide on connectors, machining residue on housings and heat sinks, particles on sensors and optics. What ultrasonic cleaning does in electronics production and repair, at 40 kHz with deionised rinses, and what must never go in the bath.

Technical guide. Figures are taken from our own spec tables; for your process we confirm the settings with a cleaning trial.

Electronic assemblies and circuit boards

Electronics is the industry that uses the gentle end of ultrasonic cleaning. The parts are small, the soils are thin, the tolerances are in the micron range, and some components can be damaged by the process itself. Done right, an ultrasonic bath at 40 kHz with a deionised rinse is the standard way to clean assembled boards, connectors and precision parts before coating, testing and final assembly.

What is cleaned

  • Populated circuit boards after wave, reflow or hand soldering: flux residues under components, solder balls, fingerprints. The flux article is the detailed process.
  • Connectors and contacts: oxide, dust and lubricant from plating and machining, before plating and after storage.
  • Housings, heat sinks, shields: machining coolant and chips from aluminium and copper parts, before anodising or assembly; see machining residue.
  • Sensors, optical windows, lenses: particles and fingerprints, at low power and short cycles, often in the indirect method in a beaker of the right solvent.
  • Repaired modules: flux and handling residue after rework, before the module goes back into service.
  • Battery components and cell housings: machining and stamping residue before assembly, with a dry stage that leaves no moisture.
  • Stencils, pallets and fixtures: solder paste and flux build-up from the line.

The process

Frequency. 40 kHz throughout. 28 kHz is for castings, not for boards.

Chemistry. Aqueous flux removers or saponifiers for rosin and no-clean fluxes; deionised water with a mild surfactant for water-soluble flux; light-alloy cleaners for aluminium housings; and for optics, the solvent the lens maker specifies, cold, in a beaker.

Temperature. 45 to 55 °C for boards, 50 to 60 °C for metal parts, room temperature for optics.

Time. 3 to 6 minutes for boards, 3 to 5 for parts. Short.

Sweep and adjustable power. A standing wave holds a component at an antinode; sweep prevents it. Adjustable power lets a delicate assembly run at half density.

Rinse. Deionised water, twice, the first with ultrasound to flush under components. Tap water is never used; its ions are the contamination.

Dry. Warm filtered air at 50 to 60 °C until dry under the components; a DT dryer or a drying cabinet, 15 to 30 minutes for boards.

What must not go in

Components with cavities or openings: relays, unsealed switches, some crystals, MEMS microphones and sensors, trimmer potentiometers. Parts marked by their maker as not ultrasonic-cleanable. Batteries and cells. Anything with a paper label that matters. The rule in a production line is a cleaning specification per assembly, qualified once and stored as a programme on the machine.

The machine

Task Machine
Rework bench, prototype shop STS-060 to STS-150, 40 kHz, board rack, deionised rinse in a second unit or a beaker
Production cleaning of boards UMX Pro 50L to 88L with programmes, adjustable power, filtration module; deionised rinse tank; DT dryer or cabinet
Housings and heat sinks after machining UMX Pro 88L to 162L or ST-96, light-alloy cleaner, demineralised rinse, dry
Connectors and small metal parts in bulk STS-300 or ST-40 with fine-mesh inserts, shallow layers
Optics and sensors STS-030 to STS-090, beaker holders, indirect cleaning

Every machine in a board line runs with sweep on and a written programme. The UMX Pro stores the programme per board family, which is what makes the second shift's result the same as the first's.

Cleanliness

For regulated work the measures are resistivity of solvent extract and ion chromatography; for the rest, a UV lamp shows rosin as a fluorescent haze and a loupe shows what the rinse missed. Cleanliness before conformal coating is the usual reason to install the line, and the coating supplier's specification sets the target.

The detailed articles: the whole process for circuit boards after soldering, connectors and charging ports, sensors and microelectronic parts, battery components, housings, heat sinks and shields before assembly, communication equipment components, modules after repair, and a risk guide for precision electronics that lists what must stay out of the bath.

The articles below cover individual parts and processes as they are written. The quote article lists what to send for a board-cleaning line.

Applications in this industry

Assembly prep

Parts and contaminants · 4 min readCleaning electronic parts before assembly with ultrasoundHousings, heat sinks, shields and frames carry oil, chips and fingerprints into the device. How to clean them first, and why conductive particles matter.

Battery

Parts and contaminants · 4 min readUltrasonic cleaning of battery components before assemblyCell cans, lids, tabs, busbars, housings and cooling plates carry oil and particles into welding and bonding. How to clean them; cells never go in a bath.

Connectors

Parts and contaminants · 5 min readUltrasonic cleaning of electronic connectors for reliable contactOxide, flux, dust and old lubricant raise contact resistance. How to clean connectors, pins and charging ports without harming gold, silver or tin plating.

Devices

Parts and contaminants · 4 min readUltrasonic cleaning of communication equipment componentsRF housings, cavity filters, waveguides and antenna parts, often plated aluminium: gentle chemistry, no etching, no loose particles, and dry cavities.

PCB

Parts and contaminants · 5 min readUltrasonic cleaning of circuit boards after solderingWash, deionised rinse, dry, test, coat: the full cleaning process for assembled boards after reflow, wave and hand soldering, and how to prove it worked.

Precision

Parts and contaminants · 4 min readCleaning precision electronics without damageWhich electronic components tolerate ultrasound and which do not, and how frequency, power, time, support and a sample test keep a cleaning process safe.

Repair

Parts and contaminants · 4 min readCleaning electronic modules after repair with ultrasoundRework flux, corrosion after liquid damage and old dust: how to clean a repaired module, what to remove first, and why solvents never go in a heated tank.

Sensors

Parts and contaminants · 4 min readCleaning sensors and microelectronic parts with ultrasoundSensor housings, probes, optical windows and sensor elements before assembly: what ultrasound cleans well, and which sensor types must never go into the bath.
Parts and contaminants · 3 min readRemoving flux residues from circuit boards and assembliesFlux left after soldering attracts moisture, corrodes joints and leaks current between tracks. Which flux types need cleaning, the 40 kHz bath that removes them without harming components, what to keep out of the tank, and how to prove the board is clean.

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Send us the part, the quantity per hour and the soil you are removing. We will size the tank and the frequency with you.

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