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| Restoring dried solder flux paste |
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| tooki:
--- Quote from: SilverSolder on February 16, 2021, 02:20:28 pm --- Who knew flux was so complicated! :D Presumably the recipes for some old school fluxes are more realistic to execute at home? --- End quote --- Not necessarily. If you can get the ingredients, many modern fluxes are very easy to mix, though it hardly makes sense given how cheaply flux can be purchased. |
| jpanhalt:
Sorry for the delayed response. I had to order some "stuff" (rosin, beeswax, petroleum jelly (Walmart), and stearic acid). I spent a little time searching for formulations on the web and much less time experimenting. My control/comparison standard is Kester SP-44 flux (I still have half a tin) and Kester 63/37 solder with SP-44 flux. The MSPS/SDS for SP-44 shows: Rosin: 30% Petroleum jelly (PJ): 40% Stearic acid: 10% Another SDS for the same thing is similar but shows a few percentage of benzoic acid and ethanediol + "nonhazardous additions" (presumably petroleum jelly). My first experiment was to test a simple mixture of rosin and petroleum jelly in the ratio of 8g PJ and 6g rosin (43%). On heating they dissolved each other to give a clear, light amber color. On cooling there was no separation of phases. Although, it was cloudy. A small amount (0.5g) was removed to test as a solder flux. With arrival of my stearic acid, I added 1g to the mixture, heated and let cool. The product looked the same as the one without stearic acid and was maybe just a little more stiff (no picture). Final composition: Rosin: 39.9% Petroleum jelly:53.2% Stearic acid: 6.9% I wanted to oxidize the surface of some PCB without adding halides or sulfates. I simply used a flame to get a little disolaration. I then tested the strips using 63/37 leaded solder without flux core. Here are the results: #1: No flux, solder simply balled up and didn't stick. #2: Rosin+PJ only -- almost as bad as #1, ball fell off and was lost. Some solder stuck to board. #3: Rosin/PJ/Stearic acid -- Good adhesion #4: Control (Kester 63/37 w/SP-44 flux |
| SilverSolder:
Interesting experiment! - does there always has to be some kind of acid in a solder flux, even if it is a mild one, to cut through the oxide layer? |
| jpanhalt:
The principle component of rosin is a tertiary carboxylic acid (abietic acid). So, I'd say, "yes." Stearic acid is not that much different, but is softer than rosin. It has fewer carbons (18 vs. 20) and is a primary carboxylic acid. I suspect there could be a lot of changes in the formula without affecting performance. SP-44 flux has a distinct odor that reminds me of iso-amyl alcohol. I suspect there are other GRASS (generally regarded as safe) components that aren't on the label. |
| T3sl4co1l:
Possibly it could be a complexing salt, or amine, but this would work more on the copper than the solder (tin and lead form fewer complexes, AFAIK), and probably slower anyway. This is why, for example, copper (as salts, or slowly with exposure to air) can dissolve in ammonia solution, forming the deep blue tetraamminecopper(II) hydroxide. There is stannate, and plumbate maybe not so much I think; that is, the metals are amphoteric, meaning they can be dissolved in acid or base. Lead I think requires high oxidation state (not going to happen in contact with bare metal), tin may be happy enough, not sure. No idea if these are stable and soluble in organic substances, at soldering temperatures. Whereas the carboxylic acid complexes, of all the above metals, are pretty simple (in any oxidation state, besides metal of course), and reasonably stable. Tim |
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