Lets make rosin soldering flux.

From Wikiless: "Rosin, also called colophony or Greek pitch, is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene components. It is semi-transparent and varies in color from yellow to black. At room temperature rosin is brittle, but it melts at stove-top temperature. It chiefly consists of various resin acids, especially abietic acid."

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Some commercial flux variants contains a lot of chemicals that evaporates when heated, that again could leave toxic gases in the work environment and bad chemicals in the nature.  I am not saying gases from rosin flux is harmless, but I really think they are less harmful than most of the products in the store.

You should always use proper ventilation when soldering -Anyhow, this is how you make your own flux using only natural ingredients.
All you need is the pine resin itself and some alcohol (rubbing alcohol/ surgical spirit/ ethanol, 80vol% or stronger), I guess other solvents works as well but alcohol (at least ethanol) does not make any toxic gases.

My recipe here is basically the same as the rosin flux you could by in the store back in the days. Biggest difference being this have alcohol added making it liquid as opposed to the old type being solid. The old timers would probably recognize the smell of this flux. It works with both leaded and lead-free solder.

If you live in urban areas or are too lazy to get out in the woods to get pine resin you can buy ready made rosin in your local music instrument shop. Rosin helps to create friction between the bow hair and strings on violins and cellos. Just crush it and dissolve it in alcohol.

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1: Gather some pine resin, this could be resin that have oozed out of a wound on a tree, it does not matter if it is old and dry and full of dead ants. the important thing here is to not kill the tree, we need them for more important stuff, like transforming CO2 to oxygen.

 2: Do some mechanical cleaning, try to remove some of them dead ants and most of the tree bark.

3: Put the resin in a glass jar and fill just enough alcohol so that all resin is covered in alcohol.

 4: Stir or shake until the resin is completely dissolved. It's ok to leave it overnight if you don't want to stir so much, do not use the oven to heat it up as the liquid and the gasses is extremely flammable at this point.

5: Use a coffee filter or similar and filter the liquid over in a clean glass jar, add more alcohol if you are having problems with the liquid being to viscous to pass trough the filter. Repeat the filtering process if necessary.

6: Now you can adjust the viscosity to your liking, for a thicker product you just leave the jar without a lid so that the alcohol evaporates, and if you like it thinner just add more alcohol, just remember that by adding alcohol you also thin out the active ingredients, so don't add to much. Some like it being very syrupy so that one can use it to tack down smd components to the pcb. For hot air soldering maybe it's better with a thinner product. Make a little of both and try to see what you like the most.

 7: Now you can solder together your time machine using a more environment friendly flux.

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I have made flux both by heating the resin, and also without using heat at all, and I can't say I have noticed any difference in the quality of the end product. Maybe someone with more experience and/or education can comment on this matter. Just remember that both the resin itself and also the alcohol is extremely flammable and may self ignite on relatively low temperatures, use proper ventilation and take precautions if you are going to heat it up.

This type of flux leaves a thin layer of residue on the pcb that can be easily cleaned off with a brush and alcohol. It have isolating properties so for home use it's not necessary to clean the pcb after soldering, at least I don't do it myself.

Happy soldering!

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