PCB flux is a chemical cleaning and protecting agent for strong and reliable connections during PCB soldering. When using it on PCB boards, the flux removes oxides and contaminants and protects the metal surface to ensure a strong and clean metallurgical bond. PCB soldering flux is a key to achieving consistent and defect-free soldering in PCB manufacturing, but it’s also important to clean it up for both appearance and long-term performance. Here, we will delve into how to clean flux residues from PCBs manually with simple tools and several other alternative PCB cleaning methods.
Why Need to Clean PCB Flux?
Flux plays an important role during soldering to ensure non-oxides and strong solder joints, but it can be a problem once the soldering process is finished.
Improve PCB Appearance: Flux leaves obvious tracks on the board and its stickiness can trap dust, lint, and other contaminants on the board. Messy appearance impacts visual effect and may interfere with heat dissipation and electrical insulation. Cleaning flux from PCB makes the board neat and professional, especially essential for those commercial products.
Prevent corrosion: Flux can attract moisture from the air, leading to oxidation and corrosion in solder joints and copper traces. Effective cleaning protects sensitive and miniature components from such slow damage.
Enhance electrical performance: Residues from flux can be conductive to conduct small currents, and removing them can effectively eliminate leakage paths.
Ensure long-term reliability: Removing flux minimizes risks of electrical faults, corrosion, and intermittent connections, contributing overall durability and reliability of the electronic device. Clean solder joints are more likely to contribute to the overall durability of devices.
Meet high-standard requirements: Certain industries, such as aerospace, medical devices, and automotive electronics, require strict clean standards. Cleaning is an indispensable procedure to ensure rigorous requirements and ultimate safety in critical applications.
Avoid adhesion problems with conformal coating: Residues can prevent the coating from adhering properly, leading to bubbles, peeling, or weak coverage. Cleaning flux ensures a strong and secure coating bond, offering maximum protection.
How to Remove Solder Flux from Circuit Board Manually?
Manual cleaning is the simplest way of flux cleaning. It typically uses high-purity isopropyl alcohol(IPA, ≥99%) onto residues and scrubs with an ESD-safe brush or lint-free wipes. IPA dissolves flux residues, and the brush and wipe help remove them from the surface.
It is typically practical for repair works, prototyping, and small-scale PCBs. With low cost, easy operation, and widely available materials, it can be easily achieved at home. This also means it is inconsistent for large-scale PCB cleaning and high-reliability applications.
To clean the partial PCB flux
When you only need to clean localized areas like rework components, you can follow my next steps:
1. Prepare tools: 99% IPA, lint-free wipes, ESD-safe brushes
2.1 Apply IPA and scrub: Drop or spray a small amount of IPA onto the contaminated area. Use an ESD-safe brush swab to loosen flux residues.
2.2 Dip Wipe with IPA: Dip lint-free cloths and wipe the board gently to remove residues, avoid spreading the fluid everywhere, especially for those one-off components
3. Wipe & absorb: Use a lint-free wipe to absorb dissolved flux, preventing redeposition.
4. Repeat if needed: For stubborn residues, reapply IPA and brush again.
5. Dry the area: Let IPA evaporate. Optionally, use a fan or a hair dryer to help with ventilation.
Tips:
- Remember to wipe and clean thoroughly in case of residue and fiber remaining.
- Always work in a well-ventilated area for better alcohol ventilation
- Avoid household alcohol, which contains impurities
- Avoid oversaturating the board to prevent flux spread.
- Always brush in one direction to avoid spreading residues.
To clean the whole PCB flux
When the entire board needs to be flux-free after soldering, you can try the next steps:
1. Prepare tools: 99% IPA, lint-free wipes, ESD-safe brushes, a Box larger than PCB size, and Flux remover.
2.1 PCB IPA bath: Immerse the PCB into the container with IPA for 10 seconds(or spray IPA across the whole PCB), letting it flow and dissolve flux residues; Use an ESD-safe brush to scrub component leads and board surface.
2.2 Flux remover: Use the PCB flux remover, which is equipped with a bottle of IPA and a detachable brush; Squeeze lightly while brushing across the area with flux.
3. Absorb dissolved residues: Use lint-free wipes to mop up excess solvent.
4. Secondary rinse: Apply a second flow of IPA over the PCB to flush away loosened residues.
5. Dry thoroughly: Allow IPA to air-dry completely, or blow-dry with clean compressed air or hair dryer to prevent residues trapped under ICs.
6. Inspection: Use magnification or UV light (if flux is fluorescent) to verify cleanliness.
Tips:
- Ensure IPA is high-purity (≥99%) to avoid water spots or mineral contamination.
- For boards that need conformal coating later, ensure complete flux-free cleaning.
- Always tilt the board so residues flow off instead of pooling.
Which Type of PCB Flux Works Better in Manual Cleaning?
For manual cleaning with IPA, we had better choose those Rosin-based fluxes, especially Rosin Mildly Activated (RMA) flux or Rosin (R). They dissolve well in IPA and are easy to remove with a brush and wipe. RA in rosin-based flux and no-clean flux work, but are not ideal for IPA cleaning, as they are hard to clean. Water-soluble flux is not effective for IPA. Here is a brief introduction to the major flux types and their suitability with IPA manual cleaning.
| Flux Type | Residue Characteristics | Notes / Best Practices |
| Rosin (R) | Mild, non-corrosive, easily dissolved in alcohol | Traditional, safe for sensitive boards, easy with IPA. |
| Rosin Mildly Activated (RMA) | Slightly active, non-corrosive, moderate residues | Recommended for manual cleaning due to IPA solubility. |
| Rosin Activated (RA) | Strongly activated, sticky & corrosive residues | Needs thorough cleaning; not ideal for high-reliability without full wash. |
| Water-Soluble (OA / Organic Acid) | Highly active, corrosive, conductive residues | Must be cleaned quickly with DI water + saponifier; not for IPA. |
| No-Clean Flux | Minimal, inert, sticky/white residues | Cleaning only needed for cosmetic or coating reasons; residues resist IPA. |
Are There Any Alternative Solutions for PCB Flux Cleaning?
Manual flux removal is practical for small works, and there are 3 solutions for medium or large-scale and complex PCB flux cleaning.
| Cleaning Method | Suitable Flux Types | Major Use Cases | Advantages | Limitations |
| Manual (IPA + Brush/Wipe) | Rosin-based, some no-clean | Prototyping, repair, small batch work | Simple, low-cost, localized cleaning | Labor-intensive, less suitable for large volumes |
| Aqueous Cleaning | Water-soluble flux | Medium to large production | Eco-friendly, efficient, low cost per unit | Needs thorough drying, not for rosin-based flux |
| Ultrasonic Cleaning | Rosin-based, no-clean (with solvent), water-soluble | Dense or complex PCBs, fine-pitch components | Reaches under components, very effective | Risk of damaging delicate parts if the power is too high |
| Vapor Degreasing | Rosin-based, no-clean | High-reliability, industrial applications | Thorough, leaves no residue, consistent | Expensive, requires strict safety & environmental handling |
Aqueous Cleaning
Aqueous cleaning uses water-based solutions, typically deionized water to dissolve and remove flux residues. For strong residues, it combines with cleaning agents like saponifiers or detergents to achieve quick and thorough cleaning.
Compared to solvent-based methods, it is eco-friendly and gentle on PCBs, which is suitable for medium- to large-scale PCB volume production with automated cleaning lines. Water-soluble fluxes are specifically formulated for this method, but rosin-based or no-clean fluxes that require solvents don’t work for it. What particularly needs to be noticed is that these cleaning methods require thorough drying to prevent moisture-related failures.
Ultrasonic Cleaning
Ultrasonic cleaning is a highly effective way to remove flux residues. It immerses PCB in a tank of cleaning solvent or DI water and applies ultrasonic waves to achieve thorough cleaning. Cavitation bubbles from waves collapse to achieve even cleaning and take away flux even from tight gaps and fine-pitch components.
Deep penetration and consistent cleaning make this flux removal method prevalent for high-density and complex assemblies like telecom, computing, and precision electronics. Suitable flux types include rosin-based, water-soluble, and certain no-clean fluxes.
Vapor Degreasing
Vapor degreasing is a solvent-based solution that exposes PCB to hot solvent vapors inside a sealed machine. As heat vapors condense on the cooler PCB surface, flux residues are dissolved by and then drip away with the solvent. The PCB surface is clean and dry without water spots or iconic contamination.
This cleaning method is highly controlled and extremely thorough in one step with complete residue-free cleaning, making it suitable for high-reliability industries, like medical and aerospace devices. It is best for rosin-based, no-clean, and some water-soluble fluxes, as they are difficult to remove with water.
Conclusion
Manual PCB flux cleaning remains the most practical and accessible solution for small-scale assemblies, especially useful for those residual projects. You can use an ESD-safe brush and a lint-free wipe with IPA, or a flux remover to clean residues on the whole PCB or PCB partial components. IPA cleaning works well with rosin-based flux like R, but it is not suitable for other flux types. Other alternative solutions, like aqueous cleaning and ultrasonic cleaning, provide more consistent and thorough results, and they are generally used for medium- and large-scale PCB processing and complex assemblies. This also means that the right cleaning method partially depends on the flux type and PCB cleaning scale.
You can easily access IPA cleaning for residual DIY, prototyping, or small batches, and if you want prototypes, small runs, or high-volume production, MOKOPCB stands out as a reliable partner to deliver high-quality boards that meet both performance and cleanliness standards.
