Homemade fluid solder flux

When I tried to solder IC components for the first time one of the mistakes I made was that I did not use solder flux during soldering. The results (inevitable failure) can be read in the correstponding blog post.

Nevertheless when I tried to find out which solder flux to buy I realized that this was a pretty expensive attempt as commercial solder fluxes sell in almost unrecognizable tiny quantities at extremely high prices. Think of something like 10EUR for just 10ml and then this stuff is often extremely poisonous and should only be handled with good ventilation. The one I had a look at initially had three pages of health-instructions in its data-sheet. Inspiring confidence.

Well, I decided to don't go that route and pick up good old colophony ('rosin') which was the primary flux component for decades. What has been good in electronics 20 years ago should be more than sufficient for my purposes. And it's pretty cheap, I could pick up 20g for just 2EUR. I tried soldering SMD again using colophony and of course that time was a success (granted, also using a clean solder tip that time). But it was a bit cumbersome as colophony is in cristaline form and I had to scratch a bit of it for usage which also involved tiny bits and pieces flying off in all directions.

So I decided to take a hint from somewhere (don't remember where), solve it into some isopropyl alcohol and fill it into a small flask with a pipette I still had at home from some overdue nosedrops. This should make a decent selfmade liquid solder flux for hobby purposes. Picking up IPA was no problem, I got 100ml for 3.85EUR at the local drugstore.

From Homemade liquid solder-flux
From Homemade liquid solder-flux

Then I scratched up a larger portion of the colophony so that it was in tiny chips and dust...

From Homemade liquid solder-flux

...and poured it into the flask which was half-filled with the IPA. The larger parts of the colophony took some time to dissolve (barely visible in the photo). I added colophony until the solution had a viscosity which was good to use on PCB.

From Homemade liquid solder-flux

Using a drop of this solution on the IC pins before soldering worked like a charm and I was able to solder the IC onto the PCB without much hassle (can be seen in my first test posting).

One note though, the usage of colophony leaves back some light brownish residues after solding. Those are completely inert, do not interfere with the circuit and cause no harm. To the contrary it has even a certain conservation effet. If desired those residues can be removed also with isopropyl alcohol (still got plenty of it left from the purchase, remember?) but I decided to leave it on for the nostalgic effect ;)

Some warning notes: Although colophony is far from being as poisonous as other fluxes, the fumes should not be inhaled and skin contact should be avoided as it can cause allergies. Make sure the soldering place is properly ventilated and do not touch the fluids. If it comes onto your skin, wash it off with lots of water and soap.


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