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Dear fellow users of Electronics StackExchange,

I'm in the process of trying to upgrade my electronics lab to be able to comfortably drag-solder dense SMD packages (SO's and PLCC's) and I'm wondering what flux paste or liquid to use. My part of the world (Europe) is specific in that electronics repair gear and materials seem pretty expensive, and the domestic brands seem different from the "U.S. and global golden standard" :-)

I've noticed some reasonable-looking flux pens in the shop of a friendly nearby distributor. The trouble is: there are two models and mine is the difficult freedom of choice! :-) Please help :-D

The dispenser pen by Stannol is probably a pretty standard job, but speaking about the liquids inside, I'm painfully undecided between the X33S-07i and the X32-10i. Any German hackers around, with practical advice? :-)

I mean are there any practical differences for my purpose? Does one drag better than the other? Does one smell worse than the other? Both are no-clean non-corrosive halide-free liquids, supposed to leave an alcoholic smell, and both pens cost the same. The X33 is also specified to be resin-free (synthetic? inorganic?), while the X32 does not have that note in the datasheet = apparently resin-based. As for "intended application" and practical properties, the datasheet texts are almost the same (except that they're not copy+paste).

Hmm. They look the same, they're supposed to smell the same, they cost the same, the declared application is the same... so I guess either will probably work fine for me :-) Any comments welcome.

I do not expeect to use the flux pen every day. Should I be worried that the solvent in the liquid dries out over time? Should I rather just get some paste in a can (a thick resin-based oily emulsion) and just work with that? :-) Note that Stannol have a "contact soldering paste" in a can, for electronics, that is not acid-based / corrosive...

References to further reading:

Gosh this whole post looks like a Stannol ad. In that context I'd like to declare that I am not in any way affiliated to Stannol. I'm just googling around for some information on Flux pastes/liquids and I find their papers pretty educational and well explained. Even if they don't go into sweet details about the chemistry of the various ingredients and additives, it's difficult to find such public information elsewhere. Should the moderators find my text "over the top", I welcome their wise verdict and action.

Note that Stannol is a traditional German brand and the papers have their originals in German. Thus, some cultural references may not ring a bell to English speakers around the world ("the one traditional solder paste in a blue can" etc).

===== EDIT =====

Based on the answer by Spehro Pefhany, I googled some more and found further interesting reading. Hence this edit.

...or maybe I should just say Google "RMA flux" :-)

And I also found other, cheaper local brands of flux pastes and liquids, which I'm now able to understand better even without a detailed "application information". Next I actually have to try some :-)

==== EDIT ====

In case someone was interested in a more thorough reading on various Flux ingredients and the chemistry background, there's a book called the Handbook of Lead-Free Solder Technology for Microelectronic Assemblies - the chemistry is concentrated in maybe 20 pages around page 400.

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  • \$\begingroup\$ You might want to single out your questions a bit better, not everyone will read the whole post because of it's length and a bit of a chatty nature. So condensing the questions for TL;DR comments might be helpful. Can't answer your questions though. \$\endgroup\$ – Arsenal Apr 5 '18 at 9:52
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Neither German, nor a 'hacker', but I wouldn't use either one of them.

They contain "no clean" type flux, which is okay for digital circuits but can cause issues with sensitive analog circuits. Also very hard to clean the (non-visible) residue when you have to clean.

I suggest RMA liquid flux if you can't find it in pen form. There may be some refillable pens available that you can put whatever flux you like into them.

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  • \$\begingroup\$ Thanks for the recommendation :-) I can see RMA04 also from Stannol within my reach, in a syringe apparently. At least twice as expensive as the "no clean" pens for the same qty of the stuff, but you've probably just told me the reason. \$\endgroup\$ – frr Apr 5 '18 at 14:26

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