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Flux Removal : Key to Enhanced PCB Performance and Longevity

solder flux cleaning

Maintaining and cleaning PCBs and PCBA involves an important step known as flux removal and cleaning. This process is crucial for both the blank circuit board, as well as for the board that holds all the necessary electronic components to ensure the proper functioning of the PCB. Flux cleaning can offer several advantages, including better electrical performance, increased reliability, and corrosion prevention. This article explores the benefits of proper flux cleaning, outlines the various methods to clean flux, and provides recommendations for products that can be used for the same.

What Is Flux

The term “flux” can have various meanings, according to the dictionary. However, it has a different implication in the printed circuit board industry. Technicians use flux to solder electronic components correctly to different types of PCBs. Flux is a necessary element in the proper solidification and connection of electrical components using a different kind of soldering process. 
It is crucial to note that the application of solder flux paste or solder flux can leave residues on the boards, which can slowly corrode the components and cause damage to the PCBs. These tailings can also lead to etching or inhibition on the printed boards. Therefore, it is essential to clean the residues to prevent inhibition and etched wiring on PCBs and avoid obstructing other electrical components.

Types of Flux

cleaning flux from pcb

Rosin Flux

Rosin flux is a substance made from natural resin found in pine trees. This resin is processed to create different types of flux used in soldering.

There are three main types:

Rosin (R) flux: This type is used on clean surfaces and doesn’t leave any leftover material after soldering.

Rosin Mildly Activated (RMA) flux: It contains certain ingredients that help clean solder-coated surfaces and allow the melted solder to spread out well.

Rosin Activated (RA) flux: This type is the most powerful among the rosin fluxes, but it leaves some residue after the soldering.

No-clean flux

No-clean fluxes do not require any cleaning after completing the soldering process. Regardless, the remaining no-clean flux residue may affect the bonding of conformal coatings. Thus, it is advisable to clean the flux residue whenever feasible to avoid any potential issues.

Water-soluble Flux

The flux used in soldering, known as organic acid (OA) flux, contains a mixture of resin and other organic substances. Water-soluble flux is highly effective in promoting good flux activity, leading to excellent soldering results. It can remove oxides and impurities from the surface, thereby facilitating wetting and cleaning. Nevertheless, it is important to exercise caution while cleaning as it may lead to contamination on the PCB board.

Why Is Flux Removal Important

no clean flux

Enhance the Visual Appeal of Printed Circuit Boards

The appearance of the board is an important factor that reflects on the quality of the PCB manufacturer’s work. A visible greasy residue around a solder joint can raise concerns for incoming QC inspectors. Similarly, if the flux residue chars and leaves spots on the solder joints, it may look like an actual defect—a solder joint void or blow hole. If the flux residue is from a rework process, it acts as a fault tag in the rework area, drawing attention to the work even if there is no need for concern.

Enhancing the Reliability of PCB Through Flux Removal

The dependability of an object hinges entirely on the nature of the end product. When considering computer keyboards, their malfunction does not pose a life-threatening risk. Consequently, an EMS supplier has the option to skip the cleaning process and use a no-clean flux. Conversely, a board failure could result in fatality, necessitating stringent standards. Post-component assembly cleaning becomes necessary in this scenario, requiring thorough testing to ensure its effectiveness.

Preventing PCB Corrosion

Flux removal is a key step in corrosion prevention. Residual flux on circuit boards contains acids that, if left unattended, attract moisture from the surrounding air, potentially causing component corrosion on the PCB. To safeguard against environmental pollutants, consider housing the PCB in protective enclosures or applying a conformal coating. This coating acts as a barrier against trapped air while allowing moisture to escape from the underside. However, a drawback is that the coating must be stripped and replaced with a fresh application when reworking the PCB.


WR+ (f.k.a. TESTRONIC / PLC-200 / LUBETRONIC # 9805) is a penetrating lubricant formulated to displace moisture on mechanical and electrical equipment subjected to humid and corrosive environments. 
WR+ cleans, loosens, lubricates and leaves a thin, durable, waterproof film, which protects metal and electrical parts from the return of corrosion. 

Use Conformal Coatings to Prevent Adhesion Problems

Utilising conformal coating as a corrosion prevention measure is effective. However, residual flux on the PCB before the coating process can cause the coating to detach, especially in areas where the pockets are further apart rather than across the entire surface. Though these coatings are semi-permeable, they allow some moisture penetration that can potentially settle on flux residue and cause corrosion.

Inhibit Ion-Induced Dendritic Growth

Flux residue contains ions that form conductive dendrites when exposed to air. These dendrites pose a risk of current leakage. With no-clean flux, minimal ionic materials are present and are consumed during activation, reducing dendrite formation. However, if the flux remains unactivated, PCB cleaning remains necessary.

Ways to Remove Flux from PCB

remove flux

Overall Spray

When cleaning a PCB without a straw or brush, using a wide-spray method effectively covers a larger area. This technique works well for an overall board clean or as a final rinse post-cleaning. Hold the PCB at an angle to allow the solvent and residues to run off.
For targeted cleaning of specific areas on the board, ensure the area remains saturated with solvent. Inadequately dissolved flux residues can settle and create stubborn white residues that pose greater cleaning challenges. Maintaining a wet environment on the board makes the final rinsing process much easier.
Direct the spray, particularly over solder joint areas where residues accumulate. Allowing the solvent to flow beneath and around components enhances the thoroughness of the cleaning process.


A90H is an ultra-high purity, non-flammable, fast-drying electronic grade solvent for electrical and electronic components, especially those contacts and components sensitive to ordinary solvent cleaners.

Extended Tube/Nozzle

When using a can of flux remover, you’ll notice a small extension tube or straw that comes with it. This tube helps spray with precision and increase the spray pressure for better agitation. You can trim the straw to make it easier to work with if needed.
To use the straw, insert it into the spray button or trigger sprayer while pointing it away from your eyes to avoid accidental spraying. You can then use it to concentrate your cleaning on a particular area of the board, such as around a recently replaced component. For a thorough cleaning, spray each corner of the component to drive the solvent under it, and then spray over the leads.
After you’re done, remove the straw and rinse the area. If you have an aerosol can with a trigger sprayer, you can store the straw in the back or under the trigger to prevent accidental spraying.

Cleaning With a Brush

If you’re dealing with stubborn flux residues, you can use a brush, swab or wipe to provide extra agitation. It’s important to remember to finish off with a rinse if you choose to do so. The brush allows the solvent to flow through it so that you can scrub and saturate the area with solvent simultaneously.
There are two ways to use the brush. Firstly, you can directly clean around components by pulling the trigger to release solvent as you move the brush over heavily fluxed areas. Make sure to gently scrub so you don’t damage fine leads, and keep the area wet as you go through your cleaning process. Remove the brush and give the PCB a final rinse when you’re done.
Alternatively, if you have a very isolated area to clean and don’t want to risk cross-contamination, you can use a wipe to absorb the flux residues. Simply place the wipe over the component, pull the trigger to release the solvent, and scrub through the wipe. This breaks up the flux residues and allows them to absorb into the wipe.

Conclusion: Flux Removal

Flux removal and cleaning stands as a crucial step in preserving PCBs and PCBA functionality. This article underscores its role in preventing corrosion, enhancing electrical performance, and improving PCB aesthetics. Exploring flux types and residue impacts emphasises the need for suitable cleaning methods. Whether employing sprays, precision tools, or brushes and wipes, the goal remains consistent: effective residue removal without damage. Recommendations for products like moisture displacers and conformal coatings stress preventive measures. By embracing proper cleaning techniques and products, manufacturers ensure the quality, reliability, and longevity of electronic components, securing optimal performance of their circuits and devices.

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