What Is Solder Flux? Types of Solder Flux? And How To Use It?

If you desire to make some long-lasting metallic joints, you definitely have to make use of soldering flux. Our goal in the subsequent discussions shall be to aid you in making good use of this item. We shall define it and proceed to know just what you may have to do to make the most of it.

What Is Solder Flux?

In a nutshell, a soldering flux is a chemical cleaning agent. It is added to molten metals to get rid of any impurities which may compromise the quality of final outcomes. They flow faster especially when they are hot, remove oxides, and get rid of other foreign particles from metallic surfaces.

Types Of Solder Flux?

Soldering Flux

As stated above, this cleaning agent comes in many shades and forms. We have devoted this final segment to discussing its various types.


Inorganic Acid Flux

As the name suggests, this kind of soldering flux comprises the inorganic acid as the base ingredient. The agent further comprises stronger acids like ammonium chloride, zinc chloride, and hydrochloric acid. It is mostly suited for handling stronger metals like stainless steel, brass, and copper. This flux eliminates all residual corrosive residues from surfaces.


Organic Acid Flux

Organic acid flux is the exact opposite of its inorganic acid counterpart. This is to mean that it is made of weak acids like stearic, lactic, and citric acids. All these are combined with water, isopropyl alcohol, and other solvents. In most cases, it is used alongside regular water to get rid of unwanted dirt from surfaces that ought not to get wet.


Rosin Flux

Rosin flux is one of the oldest kinds of flux. It is derived from pine sap which is purified and refined. Most modern fluxes of these kinds are blended to optimize their performances. The flux finds applicability mainly in circuits owing to its capability of retaining circuits intact.


Water-soluble Flux

Water-soluble flux, as the name suggests are easily miscible in water. This stems mainly from the fact that it comprises organic materials apart from resin or rosin. Generally speaking, this kind of flux has a good wetting ability. It is pretty effective in getting rid of oxides to prepare surfaces for soldering.


No-clean Flux

Lastly comes the no-clean flux. They are fluxes that require no extra cleaning at the conclusion of the soldering process. This being the case, they are mostly used for light quick fix roles and solutions. Unfortunately, their impacts do not last really long. You have to re-use them every quite often.

How To Use Soldering Flux?


  • Sandpaper
  • Small brush
  • Soldering gun
  • Methylated spirit
  • Power source
  • Piece of cloth
  • Water

Caution Before Using Soldering Flux:

While using this wonderful chemical cleaning agent, you have to adhere to a number of safety tips. Below are the most critical of these tips:

  • Put on the various essential protective gears like overall, apron, face mask, and a pair of gloves. Any direct exposure to the cleaning agent may often end up disastrous to you in the very end.
  • Do not ingest the chemical. That definitely would be a direct ticket to the grave. The chemical is strong and potent enough to inflict bodily harms within the shortest time possible.
  • Cordon off your work area and clearly label ‘Out of Bounds’ or ‘Work in Progress.’ You do not want to endanger the lives of passersby and small children within your vicinity.
  • Work at a generally fast pace. As stated, this liquid oxidizes faster. Any delays may mean it evaporating and leaving behind no meaningful impacts.
  • This cleaning agent comes in many shades and forms. It is hence necessary to match the right soldering flux with the right job to eliminate any unnecessary hassles and inconveniences.
  • While using this agent, ensure that your workshop has adequate ventilation. You should also complement this with an air conditioning unit. This is to keep the interior safe and breathable.

Step-By-Step Procedures:


Clean the two surfaces to be joined

Start off with cleaning the two surfaces to be joined. Your cleaning should be comprehensive and thorough. For these two feats to be achievable, you have to use a multi-pronged strategy. Start off by blowing off all dirt, dust, and debris. This is to make the surfaces ready for the water.

Thereafter, dip some clean piece of cloth in water and squeeze out all the water. Use this damp piece of cloth to wipe the two surfaces. Be sure to get rid of any stubborn stains which may interfere with the final outcomes. Leave to dry for easier applications later.


Apply the soldering flux

After the two surfaces have already dried, apply the soldering flux. You have to make use of a small brush to do the job. In most instances, this small brush is provided for and comes along the flux inside a cap. In its absence, you may make separate arrangements to acquire it.

Use only small droplets of the flux at a time. That is because the flux is generally very fluid. A small droplet will quickly spread out to entire surfaces. You also have to act fast to be able to deter any possible overflows of this cleaning agent.


Leave the Surfaces to Dry

After you have impacted the entire surface with the soldering flux, you have to leave it to dry. Do not put the surfaces out in the open or in direct sun. As stated, this cleaning agent is very viscous. It as such takes shorter durations of time to dry.

By rushing the process, you limit the contact between this cleaning agent and the surfaces targeted. This might compromise its overall efficacy and slow down any impacts on the whole. You should hence insert this agent inside a workshop and let it dry for a longer duration of time.


Apply the solder to the surfaces to be joined

With the surfaces completely cleaned and dry, you may now proceed to apply the electrical solder. Use the soldering gun to heat the copper. Move on to apply the solder to the various surfaces which you intend to join and which you have also already cleaned.

You will observe that the solder is flowing to those portions of the materials onto which you have applied the flux. Do not interfere with this smooth flow. Instead, regulate it to ensure that each portion of the surface concerned has been appropriately targeted. This may require repeated passes and multiple impacts.


Strengthen the Joints

You now have to make your joints stronger. To do this, keep on applying the solder until such a time that you are confident that the joint is now truly strong. You will be able to note this when you hear some sizzling sounds arising out of the liquid flux.

This sound is as a result of the evaporation of the solution in the heat. Make some visual inspections of the joints to ascertain whether you might need to increase the solder or not. If such a need exists in your opinion, consider applying more of the solder until the outcomes are satisfactory to you.


Allow the joint to cool

At the conclusion of this exercise, you are now good to go. Before you go, you have to allow the joints to cool. As stated earlier, do not try to hasten the process. You want nature to take its course and for the outcomes to be as strong and can possibly be.

For this to happen, you are advised to keep the joints inside a properly ventilated workshop and out of the direct sun. Make no attempt to fan any air to the joints. The exercise might take longer but the quality of the joints will definitely be reliable.


Now that you know all about the soldering flux paste, is it not in order to purchase one? Skim the list of the various types of soldering flux to be able to arrive at the most desirable one. Exercise great caution as you use your flux. Remember, these substances are carcinogenic.

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