How to Clean Electronic Components and PCB Assemblies in an Ultrasonic Cleaner
Cleaning an electronic assembly in an ultrasonic bath is a sequence problem. Every common failure traces to a step skipped or run out of order: a bath that was never degassed, boards resting on the tank bottom, a flammable solvent poured into a heated tank, a board powered up with rinse water still trapped under its components. Run the steps in order and the bath does what it is built to do: reach every surface the liquid touches and lift flux without harming the substrate.
The chemistry choice behind this procedure is covered in Ultrasonic Cleaning Solutions for Electronics; this article is the operating procedure that goes with it, from compatibility check to cleanliness verification. It is written around Branson EC Electronics Cleaner and Branson heated ultrasonic baths, carried by Process Equipment & Supply, Branson’s largest stocking distributor in the United States and a Branson chemistry specialist serving the electronics, industrial, and laboratory markets since 1970. ProEquip is also Branson’s exclusive EC distributor in the United States, so the chemistry this process depends on ships from their stock.
Quick reference. The process in one glance:
- Yes, you can clean electronics in an ultrasonic cleaner, with a water-based chemistry, a heated bath, and a few component precautions.
- The sequence: compatibility check, charge and degas the bath, load in a basket, run the cycle, rinse in deionized water, dry completely, verify.
- Working numbers: EC at 2 to 5% in water, 140°F (60°C), 5 minute starting cycle at 40 kHz.
- Never put alcohol, gasoline, or any flammable solvent in an ultrasonic tank, and never power a board that is not fully dry.
In this guide:
- When Ultrasonic Cleaning Is the Right Method for an Assembly
- What You Need Before You Start
- The Ultrasonic Cleaning Process, Step by Step
- Cleaning PCB Assemblies: Flux Removal Notes
- Safety: What Never Goes in an Ultrasonic Tank
- The Process at a Glance
- Frequently Asked Questions
- Ordering and Support
When Ultrasonic Cleaning Is the Right Method for an Assembly
Ultrasonic cleaning earns its place on densely populated assemblies because cavitation reaches everywhere the liquid does: under low-profile components, inside plated through-holes, between connector pins, and around fine-pitch devices where a swab or spray cannot work. Bare boards, post-reflow and post-wave assemblies, connectors, contacts, and most component packages clean well in a properly run bath.
A short list of items needs triage before anything goes in:
- Crystals, oscillators, and MEMS devices (microphones, sensors) can be sensitive to ultrasonic energy at their resonant frequencies. Check the component manufacturer’s guidance and use reduced power or a shorter cycle when they are present.
- Unsealed electromechanical parts, open relays, un-potted transformers, and speakers can trap solution internally.
- Batteries and accessible cells come off before cleaning; they never go in the bath.
- Fully cured conformal coating needs a removal process. A cleaning cycle will not strip it.
For how ultrasonic cleaning compares with manual wiping, spray systems, and vapor degreasing, and for the chemistry selection logic itself, see Ultrasonic Cleaning Solutions for Electronics. The rest of this article assumes the method fits.
What You Need Before You Start
Chemistry. EC Electronics Cleaner, the semi-aqueous concentrate Branson formulated for PCB and component work. It mixes with water at 2 to 5% by volume, is non-flammable, and is compatible with the mixed materials on a populated board. One quart charges a 5-gallon bath at the top of the range.
A heated bath sized to the work. Electronics cleaning runs at 40 kHz with heat, so the bath must hold temperature at 140°F (60°C). Size the tank to the largest board or basket load you run:
| Bath | Tank Capacity | Fits | Typical Use |
|---|---|---|---|
| Branson CPX1800H | 0.5 gallon (5.5 x 6 x 4 in) | Small boards, components, connectors | Rework and repair benches |
| CPX2800H, CPX3800H, CPX5800H | Intermediate sizes | Single full-size boards, small batches | Lab and light production |
| Branson CPX8800H | 5.5 gallons (19.5 x 11.5 x 6 in) | Basket loads of full-size assemblies | Batch production |
| CH cleaning tanks with GCX generators | Industrial scale | Continuous high-volume loads | Production lines |
The heated CPX units reach 156°F (69°C), comfortably above the 140°F (60°C) operating point this process runs at, and offer a reduced 70% power setting for delicate components. The full range is under ultrasonic cleaning equipment.
Rinse water and handling. Deionized water for rinsing (heated DI if you clean to Class 3), a stainless mesh basket or board fixtures so parts never rest on the tank bottom, and ESD-safe handling throughout. Plan a way to dry thoroughly: filtered compressed air, an air knife, or a low-temperature oven.
The Ultrasonic Cleaning Process, Step by Step
The numbers below are process-development starting points. Validate against your actual boards, contamination, and cleanliness target before locking a production process.
Step 1: Check Component Compatibility and De-Power Everything
Confirm nothing on the assembly is powered and remove batteries and cells. Triage the sensitive-component list above: crystals, MEMS devices, unsealed electromechanical parts, potted modules with breathing vents. For anything questionable, check the component datasheet for ultrasonic cautions and plan a reduced-power or shortened cycle.
Step 2: Charge, Heat, and Degas the Bath
Charge the bath with EC at 2 to 5% by volume in water; most shops land at 3 to 4%. If ionic cleanliness testing waits downstream, make the bath itself with deionized water. Bring the bath to 140°F (60°C), then run it empty for 5 to 10 minutes. Fresh solution holds dissolved gas that absorbs cavitation energy; degassing makes the first load clean as consistently as the fifth.
Step 3: Load Boards in a Basket, Never on the Tank Bottom
Place boards in a mesh basket or fixture with space between them, oriented so trapped air can vent and no board shadows another. Parts resting directly on the tank floor dampen cavitation and can be damaged by transducer contact. Do not overload: cleaning quality falls faster than throughput rises.
Step 4: Run the Cycle
Start at 5 minutes at 40 kHz. Extend toward 10 minutes for heavy flux loads; shorten, or use the 70% power setting, for delicate or resonance-sensitive components. Fine-pitch and BGA-dense assemblies sometimes justify 80 kHz or dual-frequency equipment, which cleans tight geometry with gentler cavitation.
Step 5: Inspect Before You Rinse
Lift the basket and look at the solder joints. Remaining varnish-like film means another short cycle; a white haze often means flux was partially saponified and simply needs the rinse. Inspecting now, while the bath is hot and loaded, saves rerunning the whole sequence later.
Step 6: Rinse in Deionized Water
Rinse promptly so dissolved flux and cleaning chemistry do not dry onto the board. A clean DI immersion or spray rinse suits most work; Class 3 assemblies benefit from a heated DI rinse, which improves ionic residue removal. Do not skip the rinse on the theory that the bath looked clean, because dried process solution is itself a residue.
Step 7: Dry Completely Before Power-Up
Drive water out from under components, inside connectors, and around through-holes with filtered compressed air or an air knife, then finish in a low-temperature oven or with warm circulating air. A board that looks dry can still hold moisture under BGAs and in connector bodies. Nothing gets powered, tested, or coated until it is fully dry.
Step 8: Verify Cleanliness
For commercial work, verification is visual inspection under magnification against IPC-A-610 acceptance criteria. For Class 3 and high-reliability work, validate the process with ionic contamination testing in line with IPC J-STD-001’s objective-evidence approach, and re-verify whenever the flux, chemistry, or cycle changes. Verification is what makes the sequence repeatable.
Cleaning PCB Assemblies: Flux Removal Notes
Flux residue is the reason most production baths exist, and the flux type sets the expectations. Rosin fluxes (R, RMA, RA) leave the hard film that ultrasonic cleaning with EC removes well in a standard cycle. No-clean fluxes leave less residue, but the weak organic acids left behind can corrode traces and grow dendrites once the board sees bias and humidity, which is why high-reliability shops clean no-clean assemblies anyway. Water-soluble fluxes are designed for hot DI wash processes; the ultrasonic bath’s role there is usually cleanup of tight-pitch areas where residues linger.
For production throughput, the process scales by the basket: a 5.5-gallon CPX8800H or a CH tank runs full basket loads through the same sequence above, and EC’s 55-gallon drum packaging supports bath charges at that scale. The chemistry depth behind these recommendations, including contamination types and standards context, lives in Ultrasonic Cleaning Solutions for Electronics, with the wider chemistry catalog in The Complete Guide to Ultrasonic Cleaning Solutions.
Safety: What Never Goes in an Ultrasonic Tank
Never put isopropyl alcohol, ethanol, acetone, gasoline, or any flammable or combustible liquid in an ultrasonic tank. A heated bath running above their flash points turns them into a fire hazard, and cavitation accelerates their evaporation. IPA’s flash point is roughly 54°F (12°C); the bath runs at 140°F. Alcohols belong on a manual wipe bench, not in the tank. The bath chemistry for electronics is water-based and non-flammable by design.
Beyond flammables: never mix chemistries or add bleach or mineral acids to a bath, remove batteries before cleaning, wear gloves and eye protection around heated solution, and follow the Safety Data Sheet on the EC product page for handling and disposal. Spent solution accumulates flux residue and dissolved contamination and falls under industrial wastewater rules in most jurisdictions.
The Process at a Glance
| Step | Action | Working Numbers |
|---|---|---|
| 1 | Compatibility check, de-power, remove batteries | Datasheet check for crystals, MEMS, unsealed parts |
| 2 | Charge, heat, degas | EC at 2-5%, 140°F, degas 5-10 min |
| 3 | Load in basket | Boards spaced, never on tank bottom |
| 4 | Run cycle | 5 min start at 40 kHz; 70% power for delicate parts |
| 5 | Inspect | Re-run short cycle if film remains |
| 6 | Rinse | Deionized water; heated DI for Class 3 |
| 7 | Dry | Air knife or filtered air, then low-temp oven |
| 8 | Verify | IPC-A-610 visual; ionic testing for Class 3 |
Frequently Asked Questions
Run correctly, no. The documented risks are specific: crystals, oscillators, and MEMS devices can be sensitive to cavitation at resonant frequencies, and unsealed parts can trap liquid. Triage those components, use reduced power or shorter cycles where indicated, and dry completely, and the process is safe for production assemblies.
No. Both are flammable, with flash points far below bath operating temperature, and neither belongs in an ultrasonic tank in any quantity. Alcohol wiping is a bench method for spot cleanup. In the tank, use a non-flammable water-based concentrate formulated for electronics.
Yes. Remove batteries and any accessible cells before the board goes in the bath, and make sure nothing is powered. Cleaning a powered or battery-backed assembly risks shorts and corrosion the cleaning was meant to prevent.
Plan on roughly 20 to 30 minutes end to end for a batch once the bath is at temperature: a 5 to 10 minute cycle, a rinse, and drying, which is usually the longest step. The bath heats and degasses once at the start of a session, not per load.
Assemblies are normally cleaned before coating; that pre-coat clean is a primary use of this process. An intact cured coating largely seals the board, and a standard cleaning cycle will not remove it. Stripping cured coating is a separate removal process, not a cleaning cycle.
40 kHz is the standard for general PCB and component work. Fine-pitch, BGA-dense, or especially delicate assemblies sometimes justify 80 kHz or dual-frequency systems, which produce smaller, gentler cavitation bubbles that work into tight geometry.
The sequence is identical; the scale changes. A repair bench runs single boards in a half-gallon CPX1800H. Production runs basket loads in a CPX8800H or CH tank with drum-packaged chemistry, adds bath filtration and monitoring, and formalizes verification. Same steps, same chemistry, different tank.
Ordering and Support
Everything this process needs ships from stock at Process Equipment & Supply, with same-day shipping on orders placed before 2:00 PM EST and free shipping on orders over $125. Chemicals ship by ground only within the continental United States and Canada.
Three ways to take the next step:
- Order the chemistry from the EC Electronics Cleaner product page, in quart cases or 55-gallon drums. ProEquip is Branson’s exclusive EC distributor in the United States.
- Size the bath against your largest board or basket load, from the CPX1800H rework unit to the CPX8800H and CH production tanks.
- Request process guidance for validating this sequence against your boards, flux, and cleanliness class before committing production volume.
For help with bath sizing, chemistry questions, or the full Branson cleaning chemical lineup, contact Process Equipment & Supply at 1-800-539-6336 or sales@proequip.com. ProEquip has carried the Branson line since 1970 and is the largest stocking distributor of Branson equipment in the United States.