Is Solder Flux Conductive? Here’s the Truth!

With vital electrical equipment, it is crucial to keep circuits from faulting and to keep the machine at an optimal production level for as long as possible. That’s where solder flux comes in. Solder flux works to reduce oxidation during the soldering process and improves electrical contact.

Solder flux can be conductive depending on the type of flux used. Since conductivity lowers your device’s performance, it is crucial to remove the flux residue after applying it.

In this article, we will learn about the different types of solder flux, why solder flux application and cleaning is so essential, the dangers of conductivity, how to apply and remove flux, and more below.

Why is Conductivity an Issue With Solder Flux?

Solder flux works to eliminate metal oxides using acid—acidic items, like solder flux, consist of both hydrogen ions and negative ions. Ions are conductive, so the solder flux carries these conductive ions over to the component being soldered. 

When solder flux leaves a residue, the conductivity disperses and lowers the effectiveness of the electric currents. Furthermore, a high amount of conductively will make your electronics very unstable.

Other issues you may experience with conductivity include:

  • Reduced battery life
  • “Glitchy” components
  • Electronics completely shutting down 

Can You Solder Something Without Flux?

While it is tempting to try to find an alternative way to solder without adding excess conductivity, the fact of the matter is, while it is possible, it is challenging to solder something without flux. This is especially the case with electronics. 

Furthermore, when you attempt to solder without solder flux, you will put the long-term integrity and durability of that product at risk. Another important thing to know is that you most likely will not be successful in conjoining two pieces in the first place.

The reason is that the solder flux removes the oxides, which allow the two materials to mold together. In a perfect scenario where no oxides are present in the environment, only then may soldering be possible.

Conductivity and Benefits of Different Types of Solder Flux

The types of solder flux can be broken down into three different categories. The solder flux category is determined by three things: activity, material type, and solids content. Each type of solder flux provides different levels of conductivity. These three solder flux categories include low-solids/no-clean solder flux, rosin-based solder flux, and water-soluble solder flux.

Low-Solids/No-Clean Solder Fluxes

Low-solids/no-clean solder fluxes are usually non-conductive because of their low activity levels.

Typically, low-solids/no-clean solder fluxes provide a low to medium level of active chemistry. 

Additionally, no-clean solder fluxes get their name because they generally require no cleaning once applied (however, there are always exceptions), so you can leave it on the board without worrying too much about conductivity causing issues. Because this type of solder flux is non-conductive:

  • It works on many different types of surface finishes and textures. 
  • It also can withstand a vast temperature range.
  • No harsh cleaner is needed, unlike some rosin and water-soluble solder fluxes.

Rosin Solder Fluxes

Rosin solder flux is usually not conductive. However, if it is exposed to extremely high temperatures and turns dark brown or black, that is a sign that it can be conductive. Therefore, it is very important to clean the rosin solder flux residue off after the soldering process. Some rosin solder fluxes may require a specific cleaner to effectively remove the residue. 

While the rosin solder fluxes can be conductive, they offer many benefits. Firstly, rosin solder fluxes are significant at soldering and are effective at cleaning the soldered metals. Also, like water-soluble solder fluxes, rosin solder fluxes are highly reliable. 

However, unlike water-soluble solder fluxes, rosin solder fluxes are not strong enough to corrode the pipe or wire. Instead, rosin solder fluxes protect the material during the soldering process by keeping ionic residues from moving and destroying the product. 

Water-Soluble Solder Fluxes

Water-soluble solder flux is highly-conductive because of its high activity. Because of its high conductivity and other potential issues that may arise, water-soluble flux residue needs to be cleaned within a strict time-frame. It also may require a specific cleaner with harsh chemicals that can damage your components if not used correctly. While the majority of water-soluble solder fluxes must be cleaned due to the conductive residue they leave, this type of solder flux has many benefits: 

  • Water-soluble solder fluxes are the strongest out of all the solder flux types. 
  • This type of flux is the most effective at soldering.
  • This solder flux is highly active, resulting in the cleaning of the soldered metals.
  • Water-soluble solder fluxes do well in high temperatures.
  • This type of flux is highly reliable when application and cleaning are done correctly.

Proper Flux Application to Reduce Conductivity

It is essential to learn how to apply solder flux correctly, as it is exceptionally abrasive when heated. What’s more, when you know how to use it the right way, your soldering will be more durable for longer. Below are step-by-step instructions for applying solder flux in order to reduce conductivity: 

  1. Choose the right type of solder flux for your project. For example, a water-soluble solder flux may be better suited for heavy-duty electronics that need a long-term, durable hold. Keep in mind though, the type of flux you use will determine the conductivity.
  2. After you solder your wires or pipes, coat the intended surface with the solder flux with a paintbrush. Be sure that the entire surface is covered with the solder flux, yet try to avoid using an excess amount. While you will most likely be required to clean the solder flux residue off after, it is still helpful to be proactive in preventing conductivity as well. 
  3. Then, use your soldering gun or blowtorch to heat the solder flux until it turns into a liquid. Make sure that everything stays in place while this is happening.
  4. Lastly, let the solder flux cool and harden. 
  5. Once the solder flux is cooled, be prepared to clean the solder flux residue in an appropriate time-frame. 

How to Clean Solder Flux Residue

In most cases, it is imperative to clean the solder flux residue once finished with soldering. This is because excess solder flux residue can cause conductivity, low voltage insulation short, and has the potential to damage other parts of the device. What’s more, additional solder flux residue causes current leakage, which makes your electronics less effective. 

While water-soluble solder flux residue can be cleaned with hot water (when done so quickly enough) and a rosin-based solder flux may require a special cleaner, in general, solder fluxes can be cleaned as follows: 

  1. Take an unused toothbrush and dip it in either acetone or isopropyl alcohol. Wipe away any excess on the toothbrush. 
  2. Brush the alcohol- or acetone-covered toothbrush across the solder flux. Be careful not to do this too roughly since doing so can break the solder point. 
  3. Repeat step number two until the solder flux residue is completely gone. 
  4. Lastly, use a clean napkin or wipe down the area and allow it to dry. Make sure there is no solder flux dust present by using canned air. 

Conclusion

While solder flux is conductive, the conductivity levels highly depend on the type of solder flux and the care taken during and after the soldering process. Therefore, by choosing the right solder flux for your product and ensuring that you clean the solder flux residue up promptly, your device will have improved electrical contact and a longer lifespan.

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If you liked this article, have a look at my other articles I wrote about the topic!

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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