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How to Clean Flux Off PCB

In today’s era of electronic devices, PCBs remain an important part that keeps these equipment and machines working. You can now see jam-packed PCBs everywhere from your LED bedside lamp to laptops.

But, we will not go too deep about the different kinds of PCBS and what they are used for. Instead, we will talk about a more fundamental issue here: the importance of cleaning the flux off your PCB.

Solder flux is an integral part of many PCBs because it is what creates the mechanical link between the components. It actually does good things for your electronic devices, but it may also cause some issues if there is too much of it.

In the sections below, we’ll talk a little bit more about the importance of cleaning it off your PCB and several ways to do it.

What Is PCB Flux and Why You Need to Clean It

As mentioned earlier, the main reason flux is there on the PCB is to create a proper link between one component to another. There are actually several flux types used by PCB manufacturers and technicians, but the most commonly-chosen one is the rosin flux.

On top of that, flux can also protect the metal layers from deoxidizing. Unfortunately, if you don’t clean any flux residue off of your PCB, it may gradually eat up the vital elements. This is what we call corrosion and it is mainly caused by the flux’s acidic resin component.

The Best Ways to Clean Flux Off PCB

No-Clean Flux vs. Water Soluble Flux
No-Clean Flux vs. Water Soluble Flux

Cleaning flux off the PCB is a crucial part of keeping corrosion and electrical leakage at bay. Yet, not everyone knows how to do it properly. So, here are several simple ways to keep your PCB working properly and free from damaging flux residue.

Removing Flux with Toothbrush and Isopropyl Alcohol

You can actually use the things lying around your house to clean the flux, such as your old toothbrush. This method is very easy to do and basically costs you nothing. However, trying to scrape away using a toothbrush alone probably won’t do you much.

This is why you need to include a cleaning agent in the process. Among the many products you can use, the isopropyl alcohol is probably the most accessible and affordable cleaning solution you can use.

Simply dip the toothbrush in the cleaning agent for a few seconds and brush the flux residue away from your PCB. Once you think that you are done with the brushing, you can grab a paper towel or rag fabric to wipe the area.

The issue with using isopropyl alcohol and toothbrush to remove PCB flux is that this combination lacks the muscle power to scrap away stubborn residue kinds, just like the one left by the no-clean flux. It means that you may need a stronger cleaning solution if you face such flux residue.

Another issue with using isopropyl alcohol is related to the hygroscopic characteristic of the substance. The alcohol will attract the surrounding moisture content in the atmosphere, which will decrease the alcohol’s cleaning capability. This is the explanation for why you feel that the alcohol no longer cleans well after a few brushing motions.

Using A Dedicated Flux Remover

Getting a ready-to-use flux cleaning kit is undoubtedly a better and more effective option than that good old’ combo of toothbrush and isopropyl alcohol. Still, you need to really understand what kind of flux and PCB components you are working with so you don’t waste your money on an excessively strong cleaner solution.

Using a dedicated flux remover is a great alternative, especially if you are working with a lot of PCBs.  It removes flux more effectively than the isopropyl alcohol solution and the process is done considerably quicker, allowing you to cut down your working time on each PCB. You may not feel much time difference when working on a single PCB, but imagine if you must work with more than 20 PCBs in a day!

Each flux PCB cleaning kit product on the market will have different instructions. However, many of them typically include three processes: dip, cleanse, and heat. This means you only need to dip the PCB in the cleaning agent, cleanse any remaining residue by brushing, and then dry the PCB using a heat gun.

Whatever method you choose, you must ensure that you have thoroughly cleaned your PCB from any flux residue. Once your PCB is free of excess flux residue, you can have peace of mind knowing that you have minimized the risks of dendrite growth, shorting, and electrochemical leakage.

The Do’s and Don’ts in Cleaning Flux Off PCB


The number one mistake you can make when it comes to cleaning flux off a PCB is trying to avoid the issue by using “no-clean” flux. Despite the name and the popular belief, this one is actually the worst kind of flux to clean. It will leave a stubborn and hard-to-clean white residue that may interrupt signal transmission.

Another thing you should remember is that a stronger flux cleaner does not always work better for your PCB. If you choose one that is more potent than what you need, it may actually damage the delicate metals and fragile coatings on your device.

The Takeaway

Yes, using flux and making sure that you are using enough of it is essential during the PCB manufacturing process. Even so, believing that it is okay to not clean the excess flux off your PCB is a big mistake!

It can actually lead to all sorts of problems from electrochemical migration to delamination to costly board failures. This is one of the reasons that it is crucial for you to learn flux cleaning techniques as well as the tools you can use during the process.

Whether you run a PCB manufacturing company or an electronic device service facility, you can use the tips above to guide you in your flux cleaning journey. Of course, to get more thorough guidance, you can ask a pro near your area that is experienced with PCBs and their cleaners.




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