inductor for HV flyback supply

I have been dicking around with magnet wire for around four decades, and I've never heard a hint of that trick. Wow.

Is it just the fact that it's an acid that melts at soldering temperatures that does it (like, could I use some other flux)? Or is the fact that it's asprin that's special?

Yes and yes. First, an organic melt helps to dissolve and loosen things (it's a solvent). An acid helps, combining with oxides (and carrying them away in the liquid). Acetylsalicylic acid will help further because the acetyl- part hydrolyzes relatively easily (even if you're not putting water into it, it's probably a prime part of decomposition products), giving a much stronger acid to dissolve crusty deposits. (Acetic acid also forms a complex with copper ions, giving extra solubility over, say, nitric acid. Not that you'd use that for soldering.)

The boiling/decomposition temperature sounds a little low, though, if it's sputtering and boiling away immediately.

That's a downside to ~pure organic compounds: the melting and boiling points are sharp. Rosin is a mixture of heavier organic acids, so it's a bit milder (depending on "activation"), and different compounds evaporate first, leaving the metal protected even if the remaining goo isn't very active.

Tim

Me too. (Years ago I used this awful black gunk that you let sit on the insulation and it would slowly eat it away...) Now we just use a coating that melts in the solder pot.

I'll give it a try on some other wire.

George H.

This is 30 gage Beldsol, from ebay. It helps to scrape away a bit of insulation before soldering, but with a hot tip it's not necessary. I used a Metcal iron here with a cheapish Thermaltronics S75C clone tip, rated 350-398C.

Brand names "Soldereze" and "Thermaleze". Apparently this uses a polyurethane-base enamel.

I've done a couple of projects using it... something akin to "wire wrap" construction, but you connect-and-wrap using Soldereze wire and then do the soldering using an iron with an 800-degree-F tip. Unlike normal wire-wrap you don't have to either strip or slit the wire in advance, or wrap only onto sharp-cornered square pins that can penetrate the insulation.

One disadvantage is that you need a fairly hot iron to get the insulation to melt/burn off properly, and this may be too hot for certain components, nylon bobbins and connectors, etc.

Den tirsdag den 3. januar 2017 kl. 22.27.57 UTC+1 skrev Dave Platt:

as long as you start from the wire end where the solder can get in direct contact with copper and sorta creep under the insulation it doesn't need to be that hot

Also, in cases where you expect problems you can just start putting solder on just the end of the wire, and when it has cleaned the isolation and flowed the solder you put the end of the wire on the component and solder it the normal way.

it is different from what I used, in my case the isolation had a more neutral color so the wire looked like bare unoxidized copper.

You lay the wire down on the aspirin tablet, then touch it with iron, and apply solder. The aspirin melts a bit. Just try it, it is so easy it is hard to explain.

P.S. I only ever did this with classical Pb/Sn solder.

Groetjes Albert

By far the most important aspect is that the enamel has affinity with the aspirin, dissolving in it. The pristine copper layer underneath the enamel then takes up solder like the best. On the other hand with rosin you can't get through the enamel.

Having done this time and again, I can't see what you mean. Are you arguing that a tried and proven method doesn't work on theoretical grounds?

You still need rosin. The aspirin takes care of the enamel that is hard to remove mechanically, especially on the 0.1 mm (that is 4 mil for those imperialist) wire.

P.S Oops, imperialist don't measure wire in inches, they use wire gauge like #34.

Groetjes Albert

Duh. Theory is always right. You dare argue that? :^)

That was more about the observation that someone else had. Which was probably the wrong technique. Your mention above (just tapping it briefly) sounds more plausible.

FWIW, I've soldered steel using ZnCl2 and HCl before -- they evaporate rapidly, but the metal remains clean long enough to be wetted. Similar idea!

If you didn't buy Soldeaze (or whatever), I don't really know what to say; it's your own fault. :-p

I've never had a problem with the #37 (uh, 4.5 mil?) wire I've got, which is of the solderable kind.

I've also used molten potassium nitrate or chlorate, to burn away some rather more annoying enamels. I think that wire is so old, it's from the days when they used literal enamel.

You melt some salt in a spoon, dip the wire, then quench the wire in water to freeze and dissolve the salt immediately. Shiny pink copper remains!

Oh, and just don't get anything even marginally organic in the molten salt. Or even just a catalyst (like MnO2), in the potassium chlorate case.

Tim