If you have ever wondered what clean flux is and whether you should use it, this article is for you. Last year the PCB industry was rocked by reports of various toxic fumes when using fluxing solutions without a ‘clean’ version. However, clean flux has been available for years. Unfortunately, no one realized it until the other sources became less popular. Find out what’s different about clean flux and why we should be using it with every board that we flow solder paste on!
Clean Flux
Clean flux combines organic solvents, wetting agents, and water. As a result, it has improved wetting properties. For example, it flows better over surfaces and easily removes solder paste residues. In addition, the organic solvents are safe, and EPA approved. This is because it is a blend. As a result, it is more consistent than any single solvent alone.
The only ‘downside’ to this flux is that it does not last if no-clean flux. So, the board must go through an extra level of cleaning after reflow. However, this extra cleaning step takes only a few extra minutes. So, if you think about the time, it takes to properly clean a board using IPA or other solvents, the additional time required is negligible.
No Clean Flux
No clean flux is just water and a little bit of a wetting agent. Many reflow stations will not use this flux as a result. This means the boards are going through double the processing time without needing it. It sounds like a reasonable trade-off. But in reality, an extra few minutes can add up to minutes, hours, or even days to your production schedule.
Even if you do not own a reflow oven with a dedicated no clean profile, there are still benefits to using no-clean flux. For example, many new reflow ovens come with an automatic tool changer. This can save time because you do not have to pop the boards out manually and add them to the next panel. However, changing paste often can become very annoying as the tool changer will refuse to cycle if solder paste is on the board.
No clean flux is a very simple product that depends on water and wetting agent. The wetting agent makes the flux flow better compared with the old style. Rayming PCB & Assembly use it to keep the board clean after the soldering process because they don’t want any residue on the board. So, the wetting agent does help the flux flow better or clean the board after the soldering process.
So, what is the best flux for me? Is it clean or no clean?
Whether you use a hot air reflow machine or convection oven, we recommend you use no-clean flux with most boards and components. No clean flux can work well with the most component, not just BGAs. It has a similar effect with hot air reflow machines because their heating element is near the surface. We can keep the board clean after the soldering process. The flux can work well with the surface of circuit boards.
But PCB is different. While wetting agents make flux flow well, you should not use any clean flux with circuit boards. This is because the board has conductors/metal layers and other components in most cases. So, we do not want to put any extra wetting agents on our board. In addition, no-clean flux has organic solvents, which can damage or short out our materials if too much dry out on them.
If it is BGAs and components, we suggest you use no-clean flux to save a few minutes of extra cleaning steps. However, if it is PCBs or any other kinds of boards, we suggest you use clean flux.
What happens if you leave organic flux on a PCB?
We have not seen any harmful compounds on boards with organic flux. However, if you use no-clean flux, some of their components will eventually get damaged. That is why we suggest using clean flux.
We can maximize your board’s life if you use the right tools, solder paste, and reflow profile. We are not suggesting that no one will ever see a PCB with organic flux residue left on it because they may have long-term issues. However, most would be fine. So next time you are soldering a production panel, remember to wash off the flux with a quick blow of compressed air. Your work will be more efficient.
Types of PCB Residues
There are various types of residues on PCB. The most common will be flux that may be on the board. This can happen when you do not blow off all of the paste before you reflow it or if your reflow station does not have any clean profile.
a) Ionic residues:
These residues are the most common. They are not hazardous and will generally dissipate in a few days. If you leave the PCBs overnight, it will be fine in the morning. If you work with sensitive electronics, you should clean out all the flux before putting them back into your product as a precaution.
b) Organic residues:
These residues are not hazardous, but they can cause problems with other components that you put on your board.
c) Inorganic residues:
The residues can cause corrosion, swelling, or even failures in some situations. Therefore, if you are working with extremely high-end electronics, you should take every precaution to remove all the flux. Do this before putting a sensitive component on the board.
What Causes White Residue?
If you have white residue on your board, it could be several reasons. The most common is from the flux that we used previously. If you leave a lot of flux on your board, it will stick to your components and bond to them over time. Any flux can cause this from no-clean flux to any organic on the board.
The other reason for a residue is the substrate material itself. For example, many board materials can have an oxide or residue hard to get rid of. If the oxide particles are big, it will prevent the paste from flowing, and you may see a residue on your board.
Therefore, a dedicated profile for no-clean flux is essential. You want to make sure you are cleaning off all the residue before putting new components down. If it gets under a component, it will prevent it from working properly and not allow your production line to function properly.
How to fix it
If you have white residue on your board, you can take a few steps to get rid of it. First, you can try to use a degreaser. It will remove the excess flux and may dissolve the residue that is sticking to your components. You may need a special chemical made for flux. However, you can try a mild soap or other organic cleaning product if it is not working. Finally, you can remove the residue
What happens if you accidentally leave flux on a PCB?
Working with sensitive electronics, leaving flux on your board can be very risky. The residue can cause corrosion or other problems with your components. Most of the time, it will not cause any harm, but it is better to be safe than sorry.
If your soldering paste remains on the board, you may need to clean it off. The flux is a good conductor and can harm your components. It could increase the time it takes to warm up or cause them not to warm up. This is especially true if you have recently coated a new part that you are trying to use. You do not want any residue getting in between the pads or components on your board, and they should be clean of residue.
Conclusion
Clean flux and no-clean flux off PCB are a big deal. Some people think that we should buy a reflow profile with a no-clean profile and use it with any paste on the board. That is not true. If you are working with sensitive electronics, you should always have a dedicated no, clean flux reflow profile for your board. This will allow you to have the best performance from your circuit and components. In addition, by having a dedicated profile, you will be able to prepare your boards more efficiently.
