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PCB flux – the most comprehensive guide for this PCB surface-cleaning material


We often see PCB flux in the PCB production and PCB assembly process. PCB flux is a chemical cleaning agent that is used during and before the soldering of electronic components to a circuit board. Besides this, do you really know PCB flux? In this article, let’s explore more questions– why/when/how use it? What’s its types and material? and so on. What-is-flux-in-PCB

What is flux in PCB?

PCB flux is a material that helps keeping away the impurities and oxides that can rust the metal on the board. The PCB flux is a good insulator of electricity, which makes it ideal for use in electronic applications as a flux. PCB flux is an important component of electronic circuits especially for the PCB circuit board and materials which are used in semiconductor devices. PCB flux is often used as a protective coating on PCBs, but it can also be used as a component of other products like printed circuit boards (PCBs).

PCB Flux is also used to clean parts of a circuit board before they are soldered together. The PCB flux helps to remove oxidation from the metals hence preventing from excessive corrosion that occurs when the parts come into contact with each other. Apart from this flux also decreases surface tension making it easier for solder to stick.

What is PCB flux made of?

Common fluxes are actually the resin acids which are the acidic materials contained in rosin or in chemical terms known as ammonium chloride. They are used mainly in the soldering process of copper and tin. When applying there are few additional chemicals added to them. HCL and Zinc Chloride is added for the soldering of galvanized iron or different surfaces that include zinc. Similarly, Borax is the option chosen for the brazing, braze welding, forge welding etc.

What are the properties of PCB flux?


PCB flux is a substance that allows for easy soldering of electronic components. The properties of this substance depend on what type of PCB flux is used and how it is applied to the electronic components.

A number of different types of PCB flux are available for use in PCBs, including rosin core, tin/lead and tin/bismuth. Each type has its own properties and uses. Normally PCB flux has a high viscosity and it melts at a higher temperature along with being good electrical insulator, which shows that they can withstand the PCBs being hot, and they can also be used to melt other materials such as lead, tin, or copper.

In short, the properties of PCB flux that enables it to be an ideal material for the soldering process are listed below

1) High melting point

2) High viscosity

3) Electrical Insulator

4) Decreases surface tension

What are the types of PCB flux?


There are various types of fluxes being used for soldering depending on their material and application in PCBs. These types are; Rosin, No-Clean, Water Soluble, and Rosin Substitutes.

Rosin Flux is a mixture of rosin and an organic solvent that increases the adhesion between two surfaces. Rosin Flux can be used on paper, metal, wood, and plastic surfaces. Rosin Substitutes are different from Rosin Flux because they do not contain any rosin at all. They are made by mixing resin with polyethylene glycol (PEG), which makes them water soluble.

The next type is the Water-Soluble Fluxes which contain a high concentration of water in their formula to make them more likely to dissolve in water rather than oil or other solvents like rosin or rosin substitutes. These types of fluxes are often used for bonding things together because they won’t damage the metal.

Which flux is best for soldering?

Among all the mentioned types, the best and the most common PCB flux used for soldering is Rosin and its substitutes. It is the most basic one and has been in practice for centuries. Natural rosin is made from naturally obtained pine tar resin. This pine tar resin is afterwards mixed in some solvent. After that this resin is distilled so what we obtain is a clear, transparent white rosin which is later used for soldering.

How do you use flux on PCB?

Prior to select and place, the PCB flux paste is deposited to interface of PCBs, and then when pushed through an infrared soldering machine, it warms to produce the soldered junctions. PCB flux paste is used in conjunction with laser reflow equipment during PCB construction.


Does flux protect PCB?

PCB flux is used in metallic soldering for 3 motives: it eliminates any deteriorated metals from areas which are to be soldered, it shuts away air, avoiding additional oxidizing, and it enhances the wet qualities of the fluid glue by aiding coagulation.

The purpose of PCB flux is really to prolong the life of the targeted electrical equipment. It shields PCB circuitry from corrosion, contaminants, and humidity. As a result, even in difficult environments, the circuit printed panel may perform flawlessly.

Is flux bad for PCB?

PCB flux is a strong acidic fluid that is used during the process of soldering to eliminate oxide layer and generate excellent mechanical connections. The disadvantage is that the PCB flux deposit left over after soldering might cause electronic malfunctions and electrical leakage.

Can I solder without PCB flux?

Yes, it is possible to solder without using PCB flux. Although it is useful in the soldering because the flux assists the breaking down of the oxides on the metals, but it’s not really required. Furthermore, most solder currently has a resin core that acts as a PCB flux and aids in the breakdown of oxides. So, it’s obvious that soldering will be very effective if PCB flux is applied to it otherwise the PCB boards can be soldered without it as well.

How to remove the flux residue on PCB?


To remove PCB flux leftovers out of a repair location of PCBs, you need to soak a cotton/foam in isopropyl alcohol also known as rubbing alcohol. You can also use any other cleaning solution for it as well. Once applied you need to message the area.

While this could be sufficient for no-clean fluxes, when the aim is a visibly clean PCB, it may not be sufficient when more significantly active fluxes, such as Rosin or aqueous, are involved. Keep in mind that PCB flux leftovers cannot evaporate with the solvent.

A few of the residues will seep into in the swabs if the fluxes are dissolved, but the majority will eventually settle onto the PCB surface exposed. These whitish leftovers are frequently more difficult to eliminate than the original fluxes.


PCB flux is an amazing aid when it comes to desoldering process and soldering process. It is also essential for the PCB assembly process. This article pertains to explain this in great detail. Besides, if you are looking for PCBA companies or a PCB maker, then you can visit IBE website where you can find PCB design and PCBA service as well as related informational articles.



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