Tips for Cleaning PCB Flux

Tips for Cleaning PCB Flux


PCB fluxes are chemicals that assembly companies need to use before and during soldering. It can do things like cleaning, so why clean these PCB fluxes? FS Technology will explain to you in detail in this article.

What is PCB Flux

Flux needs to be used many times during the PCBA board manufacturing process. It is a chemical chemical cleaner. Flux is not only used for hand soldering, but also in various process flows in PCB turnkey assembly. FS Technology uses it because it helps us to clean and remove the oxide protective film from all metal surfaces. It is well known that when a metal is exposed to air, a protective oxide film will appear on its surface due to the oxygen and moisture in the air. This protective film is like a metal coat, it will prevent our staff from hand welding like a body armor.

The role of PCB flux in PCB assembly

Before soldering: Because the storage of the turnkey company is not in accordance with the specifications, the metal PCB board is directly exposed to the air, and it undergoes a redox reaction. So FS Technology will use PCB flux to clean it before soldering. On the one hand, it can eliminate the oxide coat on the surface of the circuit board through chemical reaction, and on the other hand, it can clean the dust on the surface of the circuit board. By cleaning the circuit board, the welding effect of the SMT patch can be better.

Circuit boards that require cleaning of PCB flux

During the welding process: the tools used for welding will generate a lot of heat, and the metal is easily oxidized under heating conditions to form an oxide protective film. This protective film seriously affects the welding, resulting in false welding and false welding. In order to make the soldering go smoothly, we will use a lot of flux during the PCB soldering process, and place it to oxidize. In addition, since flux is a chemical agent, it will destroy the surface tension of the material being soldered, preventing re-oxidation of the solder and the soldered surface during soldering. The main components of flux are organic acids, resins and other components. Due to its special properties, it helps to transfer heat to the weld zone.

Why Clean PCB Flux

Through the content of the appeal, you must have this question: the function of PCB flux is so strong, why do we need to clean PCB? Don’t worry, FS Technology will tell you why.As mentioned earlier, PCB flux is a chemical substance that is acidic, while the circuit board is a metallic substance. When the PCB manufacturing factory uses this substance, if it is not cleaned in time, the residual flux on the PCB surface will slowly swallow and destroy the circuit board and the main board. This can lead to secondary etching or inhibition on the printed board. Therefore, cleaning the flux is a necessary step for a qualified turnkey PCB company to assemble a PCB. FS Technology will do many cleanings after using flux, before soldering, after soldering, and before shipment.

Ways to Clean PCB Flux

Commonly used methods of cleaning flux

If you are soldering flex PCBs and thick copper PCBs with flux, this will leave a thick soapy residue on the PCB assembly. Therefore, the waste of soldered components must be removed first before cleaning such PCBs, otherwise it will cause PCB damage and improper wiring.

Using Flux on the PCB

If you are using a traditional circuit board, you can directly follow the steps below:

Step 1: Remove the Flux

The ability to remove flux from the board depends largely on the type of solder remover used. Many turnkey PCB assembly companies use isopropyl, which FS Technologies believes is the best flux. If you’re making your own PCB, you can make some homemade PCB flux.

How to make the flux remover:

  • 850 ml 95% pure ethanol
  • 100 ml of 95% pure isopropyl alcohol
  • 50 mL ethyl acetate solution

The purity of the chemical liquid is the most important in the whole production process, you must choose a reputable store to buy it, like FS Technology. Using chemical volumetric flasks can help you accurately and quickly measure the basic amounts of these three chemical liquids. In order to maintain the concentration of the solution, be sure to cover these solutions when storing them, because the ethyl group evaporates very easily and dust from the air can enter the liquid. Next, you need to mix these chemicals, you can rest assured that they will not cause harm to you. Pour the chemicals into the mixing vessel in order while mixing. First pour ethanol, then isopropanol, and finally ethyl acetate solution. After stirring it well, the PCB desolder you need is ready.

Step 2: Clean Flux Residues

Since electronic components are very fragile, in order to ensure that the circuit board is not damaged when cleaning the PCB, you need to prepare a clean and soft brush in advance.

Dip a soft bristle brush into the freshly formulated PCB flux and brush it over the board. Of course you can also use a spatula to spread the solution on the soldering board

Let stand for a few minutes to allow the solution to fully react with the stain. The role of the isopropyl and ethyl solutions is to soften the residue for less subsequent work.

FS Technology recommends that you do not put pressure on the circuit board when cleaning, and patiently scrape the entire board. Cleaning does not require any skill, the only thing required is patience.

Conventional solutions for cleaning PCB flux

You can use “Poly Clens” to clean flux from PCB pads. It’s a very simple way to draw on a circuit board with a brush. This chemical is made from a mixture of surfactants, alcohol and thinners.

Cleaning the PCB with a solution

All you need to do is pour some “Poly Clens” into a metal container, make sure it’s a metal container. Then apply it evenly on the circuit board that needs to be cleaned, wait a few minutes and brush off the dissolved residue on the board

How to clean up flux residue after copper pipe welding

Most turnkey PCB assembly companies clean solder residue from copper tubes. FS Tech thinks this is very easy, all it takes is strong acid vinegar and a clean brush. If the copper tube on the board is too long, you can use a brush attached stick to reach the farther corners.


Whether it is an amateur PCB manufacturer or a professional turnkey PCB company, these methods can be used. If you want more detailed PCB knowledge, you can go to FS Technology’s PCB blog to inquire.


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