How to use this guide
Flux cleaning is less about “stronger chemistry” and more about matching residue type to a cleaning mechanism and then proving cleanliness with a repeatable test plan. This guide helps you align process engineering, QA, EHS, and procurement on:
- Residue mapping: what’s on the board (rosin/resin, activators, ionic species, under-component entrapment).
- Chemistry choice: saponifiers (aqueous) vs semi-aqueous vs solvent/engineered solvents.
- Rinse strategy: water quality, rinse staging, and dry-out.
- Verification: fast screening + periodic “deep” validation to protect reliability.
Need a fast recommendation?
Share your flux type (no-clean / rosin / water-soluble), assembly density (fine pitch, BGA, QFN), wash equipment (inline/ batch / ultrasonic / spray-in-air), water availability (DI/RO), and constraints (VOC, discharge, material compatibility). We’ll suggest a cleaning package with COA/SDS fields and a verification plan.
Where it fits: why cleaning matters in electronics
Typical process steps
- Soldering (reflow / wave / selective)
- Flux residue formation (rosin/resin + activators)
- Wash (chemistry + energy + time)
- Rinse (staged) + dry
- Cleanliness verification + release
Common KPIs
- Low ionic contamination (reliability)
- No visible residue / no staining
- Stable conductivity / low leakage risk
- High yield (no rewash loops)
- Low total cost (chemistry + water + downtime)
Reality check: Even “no-clean” flux can be wash-required depending on coating/conformal requirements, high-voltage designs, harsh environments, or customer specs. Always treat cleanliness as a reliability requirement, not a cosmetic one.
Flux residues: what you’re trying to remove
| Residue type | Behavior | What works | Typical failure mode |
|---|---|---|---|
| Rosin/resin (RMA/RA) | Hydrophobic, can form tough films; traps ionic species beneath | Semi-aqueous or engineered solvents; some aqueous with proper surfactant + heat | “Looks clean” but ionic residues remain under film |
| No-clean residues | Low solids but can polymerize; hard to access under components | Engineered solvents or tailored semi-aqueous; process energy (spray/impingement) matters | White residue / haze; re-deposition during dry |
| Water-soluble (OA) flux | Usually ionic and hygroscopic; easier to dissolve | Aqueous + good rinse; saponifier sometimes unnecessary | Rinse quality drives leakage/corrosion risk |
| Activator/ionic species | Promote corrosion and leakage if left behind | Staged rinse with DI/RO + monitored conductivity; validated wash chemistry | High ROSE / conductivity drift; field failures |
Chemistry options: aqueous vs semi-aqueous vs solvents
| Option | How it cleans | Best fit | Commercial/EHS notes |
|---|---|---|---|
| Aqueous saponifier | Alkalinity + surfactants break down resins and emulsify soils; requires strong rinse | Water-soluble flux; many rosin residues with correct heat/energy | Controls: concentration, temperature, pH, foam; wastewater handling planning required |
| Semi-aqueous | Solvent phase dissolves resin; followed by water rinse to remove solvent + ionic residues | Rosin/no-clean residues; dense assemblies; when pure aqueous struggles | Often higher chemical cost, but can reduce rewash and improve yield |
| Engineered solvent (non-water rinse) | Dissolves resin/no-clean residues; may use displacement/rinse solvents | Low-water environments; targeted cleaning; quick dry requirements | VOC/flammability and materials compatibility must be confirmed; ventilation and exposure control essential |
Process window: the controls that actually move results
Flux cleaning is a balance of chemistry + temperature + mechanical energy + time. Most “mystery failures” come from drift in concentration, water quality, or inadequate rinse/dry.
| Control | What it impacts | What to monitor | Typical drift symptom |
|---|---|---|---|
| Concentration | Solvency / saponification strength | Titration, refractive index, or conductivity proxy (by chemistry) | Residue remains; rewash loops increase |
| Temperature | Reaction rate and solubility; viscosity | Tank and at-nozzle temperature | White residues / haze; incomplete removal |
| Mechanical energy | Under-component penetration, boundary layer disruption | Spray pressure/flow, impingement, ultrasonics (if used) | Localized residues under BGA/QFN edges |
| Rinse quality | Removal of ionic species and chemistry carryover | Rinse conductivity, staged rinse design, DI makeup rate | High ionic contamination, corrosion risk |
| Drying | Prevents redeposition and water spots | Dry time/temp, air quality, board orientation | Water spotting / streaking / residues appearing after dry |
Rinse quality: where reliability is won or lost
If your wash removes flux but your rinse is weak, the board can fail in the field. Rinse is not “extra”— it’s the step that controls ionic residues and chemistry carryover.
- Use staged rinses: dirty-to-clean progression reduces total water use while improving final cleanliness.
- Control final rinse conductivity: set a numeric target for “release” and trend it by shift/lot.
- Mind entrapment: dense assemblies need sufficient rinse time and flow path to flush under components.
Bath planning: simple consumption + carryover estimate
Use this as a planning tool for procurement and cost comparison. It estimates concentrate usage based on tank size and setpoint, plus approximate daily top-up from drag-out (carryover). Validate with real line data.
Materials & compatibility checks (electronics is unforgiving)
Electronics assemblies include sensitive materials: solder mask, conformal coatings, inks, labels, plastics, elastomers, and sometimes acrylics or polycarbonates. A cleaner that removes flux can also damage a label adhesive or haze a clear plastic cover.
| Area | Risk | What to verify |
|---|---|---|
| Plastics (PC/ABS/PMMA) | Stress cracking, haze, swelling | Soak test at temperature + exposure time; inspect for whitening/haze |
| Elastomers (EPDM/NBR/Viton) | Swelling and seal failure | Gasket compatibility list; measure swell and hardness change |
| Metals | Corrosion / staining | pH control; inhibitor presence; post-clean dryness and rinse quality |
| Labels/inks | Bleeding, adhesive loss | Rub test after wash; barcode readability; adhesive retention |
| Conformal coat process | Coating de-wetting and adhesion loss | Surface energy checks; cleanliness validation prior to coating |
Verification: prove cleanliness (not just “looks clean”)
A practical verification program uses fast, frequent checks plus periodic deeper validation. Your customer or reliability requirement determines how strict you must be.
| Method | What it tells you | Use it for | Limitations |
|---|---|---|---|
| Visual + UV inspection | Gross residue and staining | Line-side screening | Can miss ionic residues under films or components |
| Ionic contamination (ROSE-style) | Overall extractable ionic level | Trending cleanliness by lot/process changes | Does not localize where residues remain; extraction conditions matter |
| SIR / leakage testing | Electrical reliability risk from residues | Qualification and major process changes | Longer test cycle; used less frequently |
| Rinse conductivity trending | Rinse “health” and carryover | Daily process control | Not a direct measure of under-component residues |
Simple rule: If failures show up as corrosion, leakage, or coating defects, treat rinse quality and ionic verification as mandatory—not optional.
Troubleshooting: symptom → likely cause → first actions
- Likely causes: incomplete rinse, chemistry carryover, hard water minerals, redeposition during dry.
- First actions: strengthen final rinse (DI/RO), add/extend staged rinses, check final rinse conductivity target, verify dryer profile.
- QC tip: wipe test + rinse conductivity trend often identifies the culprit quickly.
- Likely causes: insufficient mechanical energy/impingement, short dwell, chemistry not matched to no-clean residues.
- First actions: increase spray energy/flow, extend dwell, raise temperature within safe limits, evaluate semi-aqueous or engineered solvent approach.
- Process note: Under-component access is often the bottleneck—chemistry alone may not fix it.
- Likely causes: rinse deterioration, overloaded wash bath, insufficient bath control, contaminated DI system.
- First actions: check rinse conductivity and DI quality, refresh rinse stage, verify concentration control method (titration/RI), consider bath dump cadence.
- Likely causes: surfactant-rich formulation, excessive agitation, contamination with other detergents.
- First actions: select low-foam grade, verify dosing, reduce agitation where possible, avoid incompatible defoamers without testing.
- Likely causes: chemistry too aggressive for plastics/inks/adhesives; temperature too high; exposure time too long.
- First actions: confirm compatibility list, reduce temperature/dwell, switch to a safer chemistry family, test on coupons before production.
Specification & acceptance checks (procurement-ready)
For electronics cleaning, small formulation changes can shift performance or compatibility. Protect yourself with measurable specs and change control.
| Spec / COA item | Why it matters | Suggested requirement |
|---|---|---|
| Identity & traceability | Consistency and root-cause capability | Product grade + manufacturer + lot/batch on each shipment |
| Concentration / actives | Controls solvency and cost-in-use | COA min/max; define measurement method |
| pH (if aqueous) | Corrosion and cleaning mechanism | COA range + recommended operating window |
| Foam profile | Inline machine stability | Low-foam or specified foam test limit |
| Residue & rinseability statement | Prevents post-dry haze/films | Supplier declaration + your on-line verification plan |
| Materials compatibility list | Avoids damage to plastics, labels, seals | List of compatible materials + exclusions + test conditions |
| SDS + transport | Storage, VOC, handling controls | Latest SDS; confirm ADR/IMDG/IATA class if shipped |
Handling & storage
- Storage: keep sealed; avoid temperature extremes; follow SDS incompatibilities.
- Mixing: always add concentrate to water when instructed; avoid splashing/aerosols.
- Spill control: electronics cleaning areas should be tidy—many cleaners create slip hazards.
- Waste: plan wastewater treatment/discharge limits early (especially for aqueous/saponifiers).
RFQ pack (copy/paste)
- Residue: flux type (no-clean/rosin/water-soluble), solder process (reflow/wave/selective), board density (BGA/QFN/fine pitch).
- Equipment: inline/batch, spray/ultrasonic, wash/rinse stages, tank sizes, filtration, dry method.
- Operating window: temperature, dwell time, mechanical energy constraints, throughput.
- Water: DI/RO availability, rinse staging, target final rinse conductivity.
- Compatibility: plastics/elastomers/labels/inks, sensitive components, conformal coat requirements.
- Verification: desired screening method (visual/UV, ionic test, rinse trending) and acceptance targets.
- Commercial: monthly volume, packaging (drum/IBC), delivery country, Incoterms, shelf life.
- Documentation: SDS, COA per lot, change control statement.
Need a compliant alternative?
If you’re battling white residue, ionic failures, or under-BGA cleaning, we can propose a better-matched chemistry route (often via rinse staging and process tuning, not just “stronger” cleaner) with procurement-ready specs.
Educational content only. Always follow site EHS rules and the supplier SDS for safe use. Validate chemistry compatibility and cleanliness verification for your assemblies before full production.