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What is Flux and Why You Need It

What is Flux and Why You Need It

Flux is a chemical cleaning agent that is used to clean and join metals. Flux contains an acid activator and sometimes a wetting agent to prepare surfaces for joining metal.  These activators are blended into a chemical carrier which is typically a solvent, thickening agent or even water.  

Why Do You Need To Use Flux?

Flux is used for different functions in the soldering process:  It cleans the metal by removing the contaminants and metal oxides; it keeps the surfaces oxide-free until the melted solder is covering the attachment area; and it acts as a wetting agent so that the solder spreads correctly on the surfaces.

Choosing the right chemical flux is critical to making a good solder joint. Flux can come in different forms: organic or inorganic acid water-soluble, no clean or rosin.

Flux is Necessary for Soldering

Flux is a necessary element of soldering.  Soldering fills the gaps between electrical or mechanical workpieces so that a mechanical, thermal or even electric connection is created.

Flux removes the oxide layer so the solder can bond to the surfaces.  Flux not only aids in the soldering process by removing dirt and films, but it also increases the wetting of the solder which can help it flow more smoothly.

What Are the Different Types of Flux?

1. Rosin Flux

The most basic soldering flux is the natural rosin that is derived from pine tar resin. Rosin is a collection of naturally occurring acids. When used for soldering, the clear rosin is dissolved in a solvent such as rubbing alcohol (isopropyl).  This is called type R rosin flux.

2. No-Clean Flux

No-clean fluxes are usually made from natural rosin or have some synthetic resins. No clean fluxes are great for hand-soldering projects or any job when there won’t be any cleaning done which can save time and money.  The benefit of a no-clean flux is that it won’t leave as much residue as most of the conventional R type flux and allows it to operate more smoothly without any corrosion.

3. Water Soluble Flux

Water soluble fluxes typically have water-soluble resins which should be removed using a water rinse. Some water-soluble fluxes are water-based solutions and therefore you won’t need an alcohol-based flux solution.  All water soluble flux residues are corrosive and should be removed whenever used to ensure long-term reliability.

How Do You Choose The Right Flux For Your Job?

All fluxes have some acids and some of the flux will need to removed or cleaned off after you’re finished soldering.  Make sure to pick a flux that is strong enough to clean off the oxides but not attack the parts afterwards.

  • For soldering electrical or electronic parts, you will want to use a rosin flux, resin or no-clean flux, or a water-soluble flux (which should be completely removed after with water).
  • Rosin soldering fluxes contain natural gum rosin from pine trees and are safe to leave on electrical parts after soldering and are like a no-clean flux.
  • No-clean fluxes are synthetic rosins known as resins; they are similar to natural rosin but will leave less residue.
  • Organic acid fluxes can be used on electronics or some industrial metal parts but need to be completely removed after soldering with water.
  • Cored wire solder containing just the right amount of flux is preferable to using a liquid external flux if the soldered area is small enough.
  • Inorganic acid fluxes are used for joining metal parts like sheet metal.

Our classic 100 gel flux is excellent for soldering stained glass copper foil as well as copper sheet metal.

The best flux for your particular project depends on the metal surfaces you are trying to connect and what you want to achieve from the flux.  Use a flux strong enough to remove the surface oxides, but is able to be cleaned off if required.


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