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I've been soldering on and off for quite some time, and I've always used whatever Radio Shack had available. Now, I'm about to attempt a bit of SMT soldering (by hand), and I'm having some difficulty sourcing appropriate combinations of diameter and composition.

The general consensus seems to be that Sn63/Pb37 solder is easier to work with than 60/40 solder, and it seems to be widely available. One wonders, in fact, why 60/40 solder continues to be as common as it is today.

When it comes to SMT, the general consensus seems to be "smaller is better", and I'm probably looking for 0.015" diameter solder, if I can get it.

If I wanted to buy in quantities of one pound, I could locate appropriate solder, but it is quite expensive in quantities that high, and I am fairly unlikely to use that much solder in less than a decade or two. I tried Allied, Grainger, Mouser, and even Amazon.com without success.

The closest thing I could find, in fact, ends up being available from Radio Shack: 0.015" diameter 62/36/2 silver-bearing solder.

What I don't know, however, is how this compares to "normal" 63/37 solder. Is this just as good, almost as good, or better? Is it the "right stuff" to use for everyday PTH and SMT soldering (other than it being too small for PTH)?

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  • \$\begingroup\$ FWIW, I use that same 0.015" RS silver-bearing solder for SMD and through-hole work along with a 'no clean' flux pen and have had good results. \$\endgroup\$ – Craig Oct 5 '11 at 17:52
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    \$\begingroup\$ I prefer 0.031" solder for SMT. There is no reason you must use the skinny stuff... Once melted, the solder forgets size of the wire it came from. Flux is more important. \$\endgroup\$ – markrages Oct 5 '11 at 22:28
  • \$\begingroup\$ Solder size does not matter if you are applying it to the iron and wiping it onto the pins, a technique that often does work with SMT. On the other hand, if you use traditional soldering technique - heat the pin and pad and apply solder to those RATHER than the iron, then you need solder that's smaller than the pin pitch. \$\endgroup\$ – Chris Stratton Oct 6 '11 at 15:40
  • \$\begingroup\$ Affordable 63/37 solder: sparkfun.com/products/9161 \$\endgroup\$ – Eric Falsken Dec 5 '12 at 18:05
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    \$\begingroup\$ Just a bit of detail: 63/37 solder is called "eutectic" solder. The reason it's easier to work with is that it does not go through a plastic state when it cools, but goes directly from liquid to solid. It's that plastic state that kills you: if the joint moves while the solder is plastic you get a cold-solder joint that is brittle and doesn't conduct electricity well. \$\endgroup\$ – Pete Becker Apr 25 '15 at 11:47
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I prefer the solder with 2% silver - melting point is lower and joints are shinier. Agree re.flux - you can never have too much flux.

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Personally I use Sn/Ag/Cu solder in a 95.5/4.0/0.5 ratio. I use it for both through-hole and SMD work, and find it perfectly usable for either.

My main reason for using it is it's cheap at about £18 for 100g.

http://www.rapidonline.com/Tools-Equipment/Rapid-Premium-Lead-Free-Solder-22SWG-100G-Reel-85-6612/?sid=45a99737-fdcf-4278-82ef-0af239d9deae

With SMD it's not really the size that matters but what you do with it.

More important than the solder is:

Flux!

Get a decent flux pen and don't worry too much about the solder.

I usually prime the pads with flux, then put solder on the soldering iron's tip, and wipe it across the pads, thus depositing a nice little pillow of solder on each pad. I then add more flux, and place the component in position. Applying the right heat with a hot-air rework station then melts that solder and the component gets sucked into place with the surface tension of the molten solder.

Oh, and if it's a home-made board, invest in some Spot-On solder resist (effectively liquid latex) and some fine paint brushes.

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  • \$\begingroup\$ Why, oh why, doesn't RS carry flux pens? They only have paste... \$\endgroup\$ – Mark Oct 5 '11 at 18:17
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    \$\begingroup\$ It does, but the search is terrible. RS code 425-9379 \$\endgroup\$ – Majenko Oct 5 '11 at 18:24
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    \$\begingroup\$ The point I am making though is that I am using lead free with no issues whatsoever. Yes, the melting profile is slightly different, but that is irrelevant as it's more about the flux when working with SMD as you use such a tiny amount of solder anyway. \$\endgroup\$ – Majenko Oct 5 '11 at 18:55
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    \$\begingroup\$ I agree, it's all about the FLUX. Lead vs RoHS, thick vs thin. None of that matters as much as getting a good flux, and lots of it! I also agree that water soluble is the best-- just keep in mind that most fluxes are CONDUCTIVE and must be cleaned off. This is especially true of the water soluble kind. \$\endgroup\$ – user3624 Oct 5 '11 at 20:19
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    \$\begingroup\$ @Mark - Not a bit. Neither does the lead in the 37/63 leaded solder I use for larger connections to wires: I don't eat it, heat it to its vapor point, or powderize and breathe it. The amount of metal in solder which gets metabolized by the assembler is tiny. RoHS is for reducing the prevalence of heavy metals at landfills, not for protecting engineers and users. \$\endgroup\$ – Kevin Vermeer Oct 6 '11 at 14:31

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