Solder flux Types and Soldering Flux Alternatives

Soldering flux is a chemical that helps the solder flow and fills gaps when soldering. Flux can be liquid or paste; its use depends on the solder type (resin, rosin core) and metals being soldered. This blog post will cover three common types of solder flux: rosin core, No-clean flux, and water-soluble liquid fluxes. Here also talk about some solder flux alternatives as well as give you some tips on how to use them effectively! 

What is soldering flux?

Flux is a chemical used to remove metal oxide and clean the surface while soldering and PCB assembling. Besides removing the metal oxide, it also helps to remove other impurities and to wet the surface to make a strong joint.

Why Do You Need To use flux During soldering?

Here are the uses of soldering flux;

  1. While Soldering pre-cleaning is not enough. Cause When the solder flow reaction between the flowing solder and oxygen in the air creates oxidation problem which prevents solder wetting and bonding the joint. In this situation, flux reacts with metal oxide and converts this oxide to metal salt and water, which is generally harmless.

2. Remove the oil and other dirt from the surface by transferring them into salt and water; thus, solder sticks to the joint metal at the first attempt.

3. It does not only prevent reforming oxidation but also corrosion and other residue producing while soldering.

4. Help to maintain correct viscosity and adhesion while molting.

5. Protect surface metal and solder parts from damage.

6. The adhesion property of molten flux helps solder to flow.

Types Of Flux:

There are mainly three types of flux;

Flux TypeActive IngredientSolvent ratio
Rosin FlufAbietic Acid15%-45%
Water-soluble FluxCitric, Lactic, Stearic acid11%-35%
No clean fluxHCl, ZnCl2 ,NH4Cl1.5%-8%

1. Rosin Flux

Rosin flux made from the sap oozes from the pine trees. It is a solvent-based flux that contains 15%-45% solid content.

  • Give more powerful Joint Than Other types
  • expensive
  • cleaning needed

There are three types of rosin flux;

  1. Rosin Flux
  2. Rosin Mildly Activated (RMA)
  3. Rosin Activated (RA)

2. Water Soluble Flux / Organic Acid Flux

Water-soluble flux is a mixture of some common weak acids such as citric, lactic, and stearic acid. The percentage of solid content is 11%-35%.

  • uses in electric assembly work and other electrical work

No-clean Flux/ Inorganic Acid Flux

No clean Flux is composed of some strong acid such as hydrochloric acid, Zinc Chloride, and ammonium chloride. The percentage of solid content is 1.5%-8%.

  • Uses in selective soldering method
  • Uses in Copper, Brass, Stainless steel soldering and cleaning work

Solder flux Alternatives

You don’t need to use always commercial flux. There are some solder flux alternatives effective as commercial flux.

Petroleum jelly as a Soldering Flux

Petroleum jelly is the best effective alternative to commercial flux. Its waxes and mineral water ingredients make it antioxidant thas why you can easily use it as a soldering flux.

  • effective as commercial flux
  • cheap than any other alternatives and commercial flux
  • Anti-corrosive
  • always handy when need

Lemon Juice As a Flux alternative

If vaseline and other fluxes are not available and you have to continue your soldering immediately, you can use lemon juice as a soldering flux alternative. 

How to use Lemon as a soldering flux alternative

  • First, squeeze the juice from slice lemon
  • To remove seeds and other substances from juice strain it
  • Stir the liquid for 20-30 sec
  • Again Strain the juice
  • Use at a time can save for later
  • Don’t refrigerate; it will damage the flux quality

Lemon juice may be expensive for long-term use and need a large amount to complete a comparatively large job.

 Homemade Rosin Flux From Crystalised colophony Rosin

If crystalized colophony rosin is available at home, you can easily make your homemade rosin flux. You just need a solvent to dissolve. For This, you need 2 Ingredients;

  • One teaspoon crushed rosin
  • 20ml Isopropyl alcohol
  • Don’t have alcohol; you can use nail polish remover as a solvent
  • Place the crushed rosin and solvent in a container
  • cover it for some time to dissolve

Homemade rosin From Pine Trees

 Preparing rosin from pine trees is a conventional way. It’s as powerful as commercial flux. Here are the steps;

  • Find out an injured part of the pine trees, collect the oleoresin/ sap oozes from the wound with a butler.
  • Collect your raw resin into a glass or HDPE plastic container.
  • Add A small amount of anhydrous magnesium if possible.
  • Cover the resin with acetone to dissolve.
  • Use 5/6 milliliter per gram of raw resin.
  • Stir it. It takes a few minutes to dissolve.
  • Strain the liquid solvent
  • Store in a glass or HDPE container
  • Complete these stages in a well-ventilated place; otherwise, acetone is volatile, and produced vapor is toxic and flammable.
  • Wear gloves and maintain other safety precautions

Final Thought

Using flux is essential for making strong joints. Though nowadays, most solder is rosin core. This type of solder has its own flux. But solid core solder still needs flux to clean the surface. Of all the alternatives above there vaseline is the best among them.

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