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To Clean or Not To Clean Flux

To Clean or Not To Clean Flux

Flux is a necessary element of soldering.  Soldering fills the gaps between electrical or mechanical components so that a mechanical, thermal or even electric connection is created.

Flux removes the oxide layer so the solder can bond to the surfaces.  Flux not only aids in the soldering process by removing dirt and films, but it also increases the wetting of the solder which can help it flow more smoothly.

Should You Clean Flux After Soldering?

When you solder your circuit board, there always is flux residue that is left behind from the flux.  And if you are uncertain as to whether to clean the flux after soldering, the answer is yes, you should. 

Below Are A Few Reasons Why It is Recommended to Remove Flux Residues:

Enhances the Reliability of Electronic Components & PCB’s

By removing the flux around the PCB, it will help improve the overall performance, the appearance of the board as well as long-term durabilityFlux residues are acidic. They can corrode the components and damage the PCB over time if the residue isn’t properly cleaned.

Helps to Prevent Corrosion

Flux residues left on electronic circuit boards are acidic. If they aren’t removed with a cleaning process, the residues can attract moisture from the air and lead to corrosion of component leads, and PCB contacts.

Improves the Appearance of the PCB

If the flux isn’t cleaned off, it can form spots from the residue and make it look not only dirty, but like a possible defect.  There are small particles called solder balls that can be encapsulated inside the flux and should be cleaned off. By cleaning the flux, it can look better which can be especially important when selling PCBs to customers.

Could Affect Adhesion of Conformal Coatings

If there are residues from the flux left on the PCB before a conformal coating process, it can prevent the coating from adhering. This can occur because there could be small amounts of gas or steam that can affect the adhesion.    

Prevent Dendritic Growth from Ionic Contamination

There can be polar or Ionic particles that are left from the flux residue.  When these particles are exposed to moisture from the air and then a current is applied, it can link into a branch or chain that is called a dendrite.  Since these dendrites are conductive, any flux left on the circuit board could cause leakage or even over time, a short circuit and therefore the flux should be removed.  If a no-clean flux is used, there isn’t as much of a concern.

Should You Clean a No-Clean Flux?

Ironically, sometimes.  A no-clean flux might need to be cleaned for most of the above reasons.  While no-clean fluxes were supposed to eliminate the need for PCB cleaning, this isn’t the case.  No-clean fluxes have salt activators that when in contact with other chemicals or heat can leave behind a white residue.   And, therefore, long-life or critical components should be cleaned after soldering.  Short-life consumer products, however, do not need to be cleaned.

If you have any questions about which flux is best for your assembly, please contact our technical support team.  We have many different flux types from which you can choose.