How to Clean Flux from PCBs?


The manufacturers apply flux to solder the components on the PCB. There are different fluxes according to the PCB component for fixing them on the board. It ensures an uninterrupted and solid electrical connection between devices. However, it is crucial to remove the excessive flux to avoid blurring the signal traces or defecting the connection. In this article, we have covered the various methods and essential steps to clean flux from the PCB. So, let’s get started.

What types of flux  are on the PCB?

The manufacturers use flux for chemical-based soldering of the elements on the PCB. It is beneficial to fix the components, but excess of it is like a slow poison for the PCB. Following are the three types of flux on the PCB:


Rosin flux is a pine tree extract that contains resin in large quantities. This type of flux is further divided into different types. For instance, Rosin fluxes are compatible with soldering on the clean boards and ensure cleanliness by leaving no remains. RMA flux also cleans the board by wetting it before soldering. RA is an active flux that leaves excessive residues.


Rosin Flux
Rosin Flux

2.No-clean flux

These fluxes allow the manufacturers to use it without worrying about cleaning it after its use. It doesn’t require any more cleaning than other fluxes. It ensures dry board after soldering by absorbing the residues and acids. However, it generally contaminates the PCB. So, it is better to work with it cautiously.

3.Water-soluble flux

This flux contains resin and organic compounds. The water-soluble flux ensures better performance irrespective of the conditions.

Does flux need cleaning during PCB soldering?

There may be a lot of solder slag on the PCB board during the PCB soldering process. That is because the flux (paste) is generally not wholly volatilized during the soldering process, and residues will be left on the board. Does the residue need to be removed?

 It should comprehensively consider various factors such as the quality of the selected flux, product requirements, and production cost. Before knowing whether it needs to be removed, we should first understand two concepts: cleaning and no-cleaning.

The no-clean flux in the PCB industry means there is no need to clean after the  wave soldering,  and it will not cause electrical performance problems. It does not mean that there is no residue after soldering. 

In addition, no-clean flux cannot allow the residue to accumulate together, so white residues are produced easily, such as lead oxide or bromide, which is the reaction product of flux and solder.

If you are doing  PCBA service,  and the customer must remove the residue on the PCBA, then it must be cleaned during the PCBA process. 

If there is conductivity and white residue after cleaning, that is caused by cleanliness. The cleaning flux can generally be divided into two categories: manual cleaning and ultrasonic cleaning.

Methods to clean flux from the printed circuit boards

clean Flux PCBA
clean Flux PCBA

Manual cleaning:

Use hand tools to remove residual flux and dirt from solder joints. The manual cleaning is suitable for all kinds of solder joints.

Pros and Cons:

Simple, good cleaning effect is good, but the efficiency is low. 

Commonly, manual cleaning tools are brushes, tweezers, cotton yarn, etc. When cleaning, it needs the following items:

  • Do not damage the solder joints and components. The cleaning action should be light and not twist and pull the wires on the solder joints or the leads of the components.
  • The cleaning liquid should not be scattered, and do not use the cleaning liquid excessively to prevent the inside of the product where the cleaning liquid is scattered and reduce the product performance.
  • When the cleaning fluid becomes dirty, it should be replaced in time. Cleaning fluids are usually flammable chemicals, preventing fire when using them.
  • Clean it with the daily essential tools at your home

You can clean the flux by simply using your old toothbrush. You will only need an old toothbrush, a clean cloth, and isopropyl alcohol or acetone. Dip the brush in the cleaning liquid and brush on the board to clean the flux. Wipe the wetness with the rag and let it dry.

  • Grab an Acid Brush

You can also clean the flux with an acid brush by dipping its bristles in the solvent and brushing it thoroughly on the board. Wipe and dry it later.

  • With a Poly Clens

You can also use poly clens to brush the flux away from your board. It enables you to directly apply the poly clens cleaning solvent on the PCB, keep stirring for at least 30 seconds,  rinse off, and pay dry the PCB before re-assembling.

Steps to Clean

  • Dip:

Dip the tool you want to use, like the toothbrush or an acid brush, into the isopropyl alcohol or acetone. Ensure that it is clean. Flick the brush after dipping it to remove the excessive amount of the cleaning liquid.

  • Brush all around:

Clean the flux from PCB by applying the brush on all the corners and edges to cover it with alcohol or acetone. Brush the board gently to avoid the breaking of the solder. Repeat the same process until you make it perfectly clean.

  • Wipe:

Wipe the board with a clean cloth to remove the excess liquid. Dip the brush in the distilled water to clean it and let the PCB dry before operating. You can also remove the remaining flux with the canned air or air blow to ensure 100% cleanness of the PCB from flux.

Ultrasonic cleaning:

The high-frequency oscillation of ultrasonic waves produces ultrasonic cleaning to complete the cleaning, and there is an ultrasonic cleaning agent.

The principle of ultrasonic cleaning is under the action of ultrasonic, and the cleaning fluid produces a cavitation effect. The high-strength shock wave produced by the cavitation effect can separate the dirt on the welding points and in the fine cracks and accelerate the process of the cleaning fluid dissolving this dirt.


Fast cleaning speed and good cleaning quality can clean complicated welded parts and dirt in the gap, and it is easy to realize cleaning automation. 

The effect of ultrasonic cleaning is related to many factors, mainly including ultrasonic frequency, sound intensity, nature of cleaning liquid, temperature and cleaning time.


Flux is an essential step in PCB manufacturing, but an excess of everything is bad; the same applies here. Remove the remaining flux after soldering and assembling to place the components on the clean and clear circuit board. Moreover, there are different types of flux. So, it is significant to use the one that suits you and your needs.