DIY Liquid Flux (Using Rosin)

Flux is a chemical that’s an essential part of soldering, as it’s used to clean surfaces and remove oxidation and allow solder to flow freely. Most electronics repair is done using liquid flux, that’s bought separately (in syringes or pens) but can also be made using rosin flux, solid tree sap (resin) chunks that are normally included with solder (pictured). In this relatively short tutorial, we’ll be doing just that!

Its best you follow this tutorial in your kitchen instead of your electronics workshop.

⚠️ Hazard Warning ⚠️

Alcohol is flammable so PLEASE do not bring it near any heat.

1. Rosin Flux
2. Isopropyl Alcohol (Ideally 99% — 70% will also do)
3. Glycerin Oil
4. Syringe and Needle (to store)
5. Kitchen Balance
6. Pestle/Mortar
7. Glass Cups
8. Sieve or Coffee Filter
9. Cutting Pliers (optionally)

Use the pestle/mortar to crush the rosin flux into fine powder for easy dissolving and measure its mass accurately using the kitchen balance.

Isopropyl alcohol is our solvent and must be added in a 2:1 ratio of alcohol to rosin by mass. (My rosin was around 10 grams so I added around 20 grams of alcohol). Add these together and stir throughly and vigorously.

As this reference page puts it,

The glycerin is to inhibit polymerisation and retard decomposition, all of which is aimed at preventing any charred residue. The residue that does remain is so non-corrosive that it can be left on the soldered part. Chemical and corrosion analysis have shown no harmful effects from the residue.

Add a very small amount of glycerin (normally sold as natural glycerin oil). Half of a tablespoon (roughly 3-6 grams) is plenty. Stir well, once again.

Use the baking syringe (hopefully you have a big one!) to withdraw and store the liquid flux. You may need to filter the liquid to remove any remaining residual particles of rosin.

And that’s it! You’ve just MacGyver-ed some basic flux that can (hopefully) be used for crude repairs.

As a quick ending tip, rosin is hydrophobic (repels water) and hence the white sticky residue it leaves on your cups, spoon and fingers cannot be cleaned with just water and soap. Use the same isopropyl alcohol to dissolve the residue. If that doesn’t work, try acetate or nail polish remover. Alcohol will also strip your skin of its own natural oils for a bit, so do moisturize with some cream or vaseline!

Happy tinkering! 💟