Make Your Own Solder Flux


I found this great video on making your own flux for soldering. Flux is a must have product when doing any electronics work, especially for surface mount parts. It helps to clean dirty parts and improves the surface tension of the molten solder so it stays on the pads instead of running between them (called bridging).

One would think that making your own solder flux wouldn’t be as good as the real thing. That may be true in some cases, but for most this at-home method is not only inexpensive but allows you to vary the thickness of the flux. Commercial flux comes in viscosities ranging from a watery liquid to a waxy paste. To understand how to create your own viscosity, let’s look at the recipe:

  • Isopropyl alcohol – the kind in your medicine cabinet
  • Pine Rosin – thickened sap from trees. Used to make violin bow hairs grab the strings and make them sing. Search for violin rosin on e-bay, and buy for a few bucks.
  • Glycerin – just a drop or two per batch (2-3%). Buy in drugstores.

To make a batch, simply crush the rosin into a powder with a hammer (put into an envelope first before pounding). Next, stir into the alcohol and let sit overnight. When stirring it in, some will clump and not dissolve. Let time finish the job. Add a drop or two of glycerin (this step is optional – it will still work without it).

As far as how much rosin to alcohol, that ratio is up to you. You can vary from as little 40% rosin (by weight) to 80% (by weight), or anything in between. You can dispense the thin stuff with a dropper, the medium stuff (65% rosin or more) with a syringe, and the thick stuff with a toothpick. To get a handle on using and choosing the viscosity, this video comparing some commercial fluxes will be helpful.

Concluding Thoughts

If you watch the last video, he discounts the Kester 951 flux. It is a really inexpensive liquid flux you can buy on e-bay for just a few dollars. It lasts a long, long time and I find it useful myself. I like the fact that it is a no-clean flux. It efficacy may be mild, but I have found it helpful for most cases.

For more difficult cases, a better flux is called for. The second video recommends this particular commercial flux in a syringe. I priced this flux, and it is $25. While it lasts a long time, and if you you do a lot of surface mount work it would be worthwhile. For the occasional hobbyist, it is kind of pricey – you can almost buy a temperature controlled solder station for that amount! 

Instead of buying an expensive commercial flux, I recommend using the Kester 951 most of the time – due to its no-clean traits, and making your own flux for more difficult problems.

Desoldering tip:  I am looking forward to trying some out by applying it to some desoldering braid. I have always had difficulty getting the solder to wick up into it. I have tried the Kester 951 with poor results. A strong paste wouldprobably do the trick.

One last thought – clean-up. With rosin based flux, it will leave a sticky residue behind. For a commercial product, some clean-up will be necessary. I would expect some more isopropyl alcohol would work nicely. For your own boards, the rosin will eventually dry out and no longer be sticky. You can just leave it on if you like. It won’t hurt anything.

Please share your own tips and experiences in the comments below.

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