Why Lead Free Solder Is Better for You

So its 100% better in every way right?

Well of course it isn’t. You need to run an iron hotter, lead-free solder wire tends to have more flux, and naturally that vaporizes a little more flux. There is a lot of FUD put out by what seems to be manufacturers of fume extraction equipment. I’m not going to argue against more fume extraction. You probably need more. However, I haven’t seen any hard data on rosin flux at higher temperatures, just vague generalities. I’d like to see any data on how much of a difference this makes, but all I have to go on is the SDS, which is clearly not worse for lead-free.

You are still vaporizing the same material. Let’s not muddy the water here. Use adequate ventilation and/or fume extraction.

Not All Flux is Equal - Don’t Conflate Flux With Metal

There are a lot of flux options out there. Manufacturers have formulations for all sorts of things, including reflow soldering, wave soldering, and even robotic soldering options. There’s stuff intended for exotic manufacturing processes that don’t involve regular air, or processes sensitive to halogen.

You can find solder wire with various formulations, including non-rosin or no-clean fluxes. These tend to be more hazardous than the rosin-based solder wire.

The flux used in solder paste is different, and there are formulations with nastier stuff. Most seem to be skin and eye irritants, though some formulations even have carcinogens and more serious hazards. Again, browsing through leaded and lead-free options, this seems to be about the flux, and the leaded options have the same hazards, plus those for lead.

In general, you really don’t want to be breathing the smoke from paste or no-clean products.

Read through those SDS documents!

Tips and Recommendations

Not all rosin-core solder wire is equal. The first lead-free solder wire I used was some stuff I got at SparkFun, over a decade ago. It was pretty terrible to work with. The flux would sputter and turn black quickly. If you haven’t had luck switching to lead-free, it’s worth giving another type of solder a try.

I use Kester #48 flux solder wire, with the Sn96.5Ag03Cu.5 alloy, in 0.6mm size. I like it quite a bit. I got a roll back in 2011, and there seems to be no end to the stuff.

For solder paste, I use ChipQuik SAC305 no-clean stuff. It’s full of skin and eye irritants, like all no-clean paste, but lacks the really nasty stuff intended for more exotic manufacturing processes.

When I need lead-free solder to work like buttery magic, for drag soldering or removing bridges, I use some extra flux. The ChipQuik SMD291NL stuff is a tacky flux that is made of pure magic. On the SDS side of things, it has most of the same warnings: skin and eye irritants, avoid breathing, etc.

Prove Me Wrong (or at Least Give Me Data to Look At)

I’m not a materials scientist, and I don’t know everything. I didn’t know most of this stuff before I spent all morning reading those SDS. If you know more, drop a comment or email.

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