Overview
What Is Flux Remover or Flux Cleaner?
Flux remover, or flux cleaner, is a type of product made to clean soldering flux from surfaces. Choosing the right product for the job can be a daunting task when there are so many products on the market to choose from. Let this article be your guide to finding the right tool for the job.
Why Do So Many Types of Flux Removers Exist?
Soldering flux has many different chemical composition types. This means you need to pay attention when picking the right flux remover.
People wouldn’t use window cleaner to wash the kitchen floor, so using the right product is important. The best results come from using solutions made for specific tasks. These purpose-built products work best when users use them as intended.
Flux Type
The type of flux being removed is an important consideration, as some are more difficult to remove than others. A common rosin flux on your workbench can be removed easily.
You can use any flux remover product or just some IPA and a little effort. Industrial wave or reflow soldering and No-Clean products may need a special flux remover. This is important if there are extra requirements to meet.
Why Do I Need to Remove Flux?
Several reasons exist for removing flux after completing the soldering process.
One function of flux during soldering is to remove the oxide layer on most metals. This oxide layer resists solder flow and makes it much harder to achieve reliable, electrically conductive connections.
Flux can remove oxide layers thanks to its corrosive nature. Not removing flux from metals can cause a circuit to fail early. It keeps wearing away the conductive metals on the board’s surface.
Some types of fluxes, including No-Clean types, can be electrically conductive or even become conductive over time. This is a serious problem. It can cause short circuits and, in severe cases, damage sensitive parts permanently.
Also, any kind of flux residue can cause problems with later processes. For example, it can affect the application of conformal coating. The residue changes the surface energy of the PCB substrate. This change can lead to poor coating coverage.
Figure 1: How flux can interfere with coatings
Figure 1 shows an acrylic conformal coating with a UV indicator. This coating is applied over a traditional rosin-based flux and a modern No-Clean liquid flux. The sample marked “none” was applied directly to a clean copper surface.
Visible blemishes shown by the UV indicator mean the coating did not stick to the board well. This will hurt the coating’s performance.
Cleaning No-Clean Flux
In 1987, the introduction of the Montreal Protocol banned the use of many ozone-depleting substances of the time. Researchers found these environmentally damaging substances everywhere, including in refrigerators, air conditioners, aerosols, and flux removers.
The introduction of new restrictions prompted the development of next-generation soldering materials known as no-clean fluxes. These fluxes are designed to leave minimal or no visible residue.
When residue is present, it usually gets trapped during soldering. This creates a “benign glassy layer” that protects the ionic material underneath.
If this layer sustains damage, ionic contaminants can expose themselves. These contaminants can create conductive dendrites through electrochemical migration. This may lead to shorts or circuit failures.
Additionally, research has shown that no-clean fluxes can contribute to corrosion under certain conditions. These products can help reduce cleaning needs in some cases. However, the best practice is still to remove all flux residues for the best reliability.
Choosing a Solder Flux Remover
Overview
Choosing the right flux remover depends entirely on the task at hand. Whether you are a hobbyist or a large manufacturer, you need to think about the type of flux to remove. You also need to consider the surface it is on.
On a microscopic level, covalent or ionic bonds hold the atoms in flux together. The best remover will share similar chemical bonds with the targeted flux. Therefore, an ionic flux is best removed by a cleaner designed to target ionic substances.
You should also think about other factors. These include the surface being cleaned and the environment where the flux remover will be used. You might need a good flux remover that is safe for plastic surfaces on food processing equipment. Though that sounds like a niche request, MG Chemicals has a few products to offer (see table 1 in the next section).
Heavy Duty Flux Remover
As we mentioned earlier, some flux residues are difficult to remove. Cleaning here requires aggressive solvent blends that can subsequently potentially damage plastic. Heavy-duty flux remover users should test compatibility between the cleaner and substrate for the best results.
Safe for Plastic and PC Boards
Consider the materials where, the flux remover will be applied to. If plastic is present, an aggressive flux remover may cause damage. Manufacturers make PCBs from a material called FR-4. This material is a mix of fiberglass and epoxy resin, which is a type of plastic.
It is wise to be careful and use a flux remover that is safe for plastics when working with PC boards. Many transistors and ICs also use plastic packaging. If plastic will be on the board or anywhere near it, look for a product that is safe for plastics.
Safe for Use in Food Facilities
If you need to use the flux remover near food or food equipment, MG Chemicals has NSF registered products.
Aerosol
Some flux removers are available in aerosol form. Flux remover spray is often easier to use than a liquid flux remover. It is simple to apply.
| Comparison of MG Flux Removers | ||||||
|---|---|---|---|---|---|---|
| Flux Type | 413B | 413C | 4140 | 4140A | 4050 | 4050A |
| Heavy duty? | Yes | Yes | No | No | No | Moderate |
| Safe for plastic? | No | No | Yes | Safe for most plastics | Yes | Yes |
| Safe for use in food facilities? | No | No | Yes | Yes | No | Yes |
| Residue? | None | None | None | None | None | None |
| Aerosol available? | Yes | No | Yes | No | No | Yes |
Table 1: A comparison of MG flux removers
How to Clean Flux Off a PCB
Manufacturers design flux remover to dissolve flux. It helps carry the flux away from the board and into disposal. There isn’t truly a “correct” way to use flux remover, but there are common methods.
Some may opt to apply the remover to a cotton swab or paper towel and rub it into the surface. Some people may use the flux remover as a rinse. They pour it over the board and let gravity help. No matter what method you use, always wear the right PPE for the product you are using.
Proper Disposal
Most flux removers contain a solvent as the main ingredient. This solvent will evaporate, leaving nothing to dispose of. If you find yourself with a lot of flux remover to dispose of, don’t pour it down the drain.
The ingredients of some flux removers can irreversibly damage aquatic, environmental, and human health – including yours. Many municipal waste management centers will take hazardous materials for free, but always check with your local law and legislative conduct for how and where to dispose of hazardous materials.
