[sitharus]

Leaded solder is not a big health risk for hobbyists as long as you have proper fume extraction. Metallic lead is poorly absorbed through the skin (it _is_ absorbed from what I can find, but very very slowly), the major risk is from lead vapour and at normal soldering temperatures that’s very minimal.

However, lead free tin-silver-copper (SAC) solder is fairly easy to work with. You need a hotter soldering iron at around 300°C, and if soldering PCBs preheating the board to 80-100°C may be needed for good results. It may also take a bit longer for the solder to propagate flow and wet, since the surface needs to be hotter.

If you’re using additional flux or non-fluxed solder you’ll need to check it for compatibility, that should be on the data sheet. Most fluxes are fine, but I’ve seen a couple that say not to use with some lead free solder formulations.

The main downside to SAC lead free solder is the higher temperature required which can overheat some components, particularly capacitors and ICs in my experience. It’s a case of being careful to keep the heat duration as short as possible.

Personally I went back to lead solder and manage my exposure with ventilation and HEPA filters.

[zrobotics]

One thing I didn't see brought up in the sibling comments about vapor is that the real hazard of using leaded solder is small particles which can end up on clothing or your hands and later ingested. It is definitely a hazard to be aware of, you want to wash your hands after working with it and keep your workspace cleanliness in mind.

For hobby work, I've switched to lead-free simply because that's what 99% of the boards I work on we're originally soldered with, but I still have some leaded solder around. That being said, it can be used safely, I cast my own bullets which generates a far larger amount of lead particulate and my blood lead levels were not at all elevated when I had them checked 2 years ago. But since it bioacumulates, you do want to keep exposure in mind.

[sitharus]

Good point, I totally forgot that because cleaning my workbench and hand washing after work is just second nature to me now.

Metallic lead is dangerous if inhaled or ingested, but not a big concern for momentary contact with your skin as metal, especially given most modern solder is only 40% lead.

Your body will remove a small amount of lead, so hobby soldering is unlikely to cause long term problems.

[TheSpiceIsLife]

You can also take lipoic acid, methionine, and n-acetyl-cysteine, to help the body remove bioaccumulated heavy metals.

This is proven to work via hair-tissue mineral analysis before starting therapy, during, and after.

[BasilofBasiley]

I cannot imagine anyone soldering with SAC at 300ºC. Not even leaded solder with pre-heating as merely an option. But somehow those values crop up from time to time.

I'm not going to debate them though, I'll just dump my values, it might help someone.

My job involves soldering at least once a week from through-holes to SMDs(mostly), 1.6mm to 0.8mm pcb thickness, from 1206 smd to 0402 (imperial) sizes. From flimsy 0402 resistors to beefy 1cm² all metal casing inductors from hell.

To do all this I use a JBC soldering station with C245 and C210 tips. I also use a non-brand hot-air station for TSSOP ICs with exposed pad on the underside for heat transfer. Sometimes I use a hot-plate as well, and a reflow oven while we're at it.

On the JBC:

For leaded solder: 350ºC on both C245 and C210 tips. I do increase it to +/- 360ºC on occasion to solder near big stubborn ground planes on the pcb. Less than that is impossible without pre-heating because I can't afford to spend more than a few seconds on each soldering op, both because have other things to do and because I can't overheat components. Overheating is also dependent on the time you spend on each component. Might bump it up to 380ºC on those inductors and switch the tips to beefier ones like the chisels and the knives.

For unleaded SAC: 360ºC to 380ºC on those same tips, and I might bump it up to 400ºC again on those inductors.

On the hot-air station:

For leaded: 275ºC

For SAC: 282ºC

On the hotplate: 240ºC for both SAC and leaded. (Mostly repair work after pcbs come out of the oven.)

On the oven: It's a temperature curve and I only use leaded solder paste. Peak at 240ºC.

NOTE1: All the soldering wire I use is flux cored. I tend to use extra flux a lot (Chipquik SMD291), even if it's not really necessary. But on lead-free SAC it's always obligatory.

NOTE2: We don't have any fancy setup where I work and it's overall barely professional in my opinion. Pre-heating is not used much if at all so, I don't have any temperature values to share in that regard.

NOTE3: The SAC solder wire I use is Sn99Cu0,7Ag0,3 EVO11 from CYNEL. I like the brand but I feel the need to try other formulations for different use-cases so I can get away with using lower temperatures on specific temperature sensitive components. On leaded I don't feel that need at all.

[stavros]

I have my Pinecil set to 320 C and it works beautifully for leaded solder. I momentarily bump it up to 400 for big ground planes, but rarely.

[BasilofBasiley]

It's curious how you use such a big temperature range. I've never used a pinecil despite having friends telling me very good things about it, which picked my interest a bit.

Can you tell us what exactly do you solder at 320ºC and what is the exact type of solder you use and/or Pb and Sn percentages?

Also, is your pinecil calibrated? And which tips do you use at that temperature?

Anecdotally, what usually happens to me at lower temps is the tip and/or the solder wire sticking a bit while I'm soldering which I take as a sign that the liquid solder won't flow correctly and that I have to spend more time giving it heat from tip, than I should.

[stavros]

I use 63/37 solder with a flux core. The Pinecil is amazing, it holds heat really well and gets to 320 C in eight seconds. I didn't calibrate my tip in boiling water, and I don't remember which tip I use now, it's the one that comes by default (B2?).

I only bump it up to 400 C because that was the default, I never use it for more than two or three seconds so the temperature hasn't mattered much. I haven't noticed solder stick, it just sometimes fail to melt properly with large ground planes, so that's when I bump the heat.

[sitharus]

That is indeed a typo, it's supposed to be 400°C.

[oasisaimlessly]

You can (/ should) edit your original comment.

[sitharus]

It was too long since I’d posted and I couldn’t edit it, otherwise I would have.

[BasilofBasiley]

Got it. Cheers.

[TheBigSalad]

I've heard that the soldering temperatures aren't nearly enough to make the lead a gas and the fumes from the flux are what can kill you. I suppose the same advice applies in that case, but is that accurate?

[sitharus]

Yes that’s accurate for hobbyist work. There will be some lead vapour, but at the temperatures used for soldering we’re talking a few atoms. The flux is much more of a risk, and both are mitigated with proper fume extraction.

Lead does bioaccumulate so continual exposure to low levels is dangerous, but unless you’re soldering all day every day it’s not likely to be dangerous.

If you’re a factory and have multiple wave soldering baths operating it’s a different story.

[IgorPartola]

Lead has a boiling point of 1749 degrees C. That is at least 1200 degrees higher than your typical soldering temperature. If you use a propane torch you’ll almost touch that temp.

[sitharus]

Correct, but all materials have a vapour pressure so there will be a very small amount of lead vapour when soldering. Based on lead’s vapour pressure it’s in the range of a few atoms, I haven’t done the math though.

I mentioned it for completeness because someone else would if I didn’t.

[IgorPartola]

Quick math shows that vapor pressure of lead at 500 degrees C is 1/7,600,000 of an atmosphere. I don’t know how to calculate the rate of sublimation but this does seem pretty negligible.

[Aldipower]

Did you ever forgot a cup of water somewhere? It fumed away after 2 weeks! All without boiling it. :-O Same applies to lead, especially if you heat it to 360 C.

[IgorPartola]

I mean you can do an experiment: put a gram of lead onto a hotplate at 360C, then weigh it after 2 weeks. I would really love to see your results.

[hooli_gan]

Do you know how dangerous new vs old flux is? I'm using some old Канифоль from the USSR and get headaches while soldering. Fume extraction would probably be a good idea, but I solder no more than 4h a year

[sitharus]

It really depends on the flux, even modern fluxes have a range of toxicity. The only way to know is to check the MSDS.

I use Канифоль/rosin flux as well and use a fume extractor. Rosin flux is the most common for flux-cored solder in my experience.

But a few times a year is unlikely to be an issue, soldering health effects are in people who do it for work.

[IgorPartola]

There is a technique where you breathe out as you solder. No idea if канифоль is toxic or not but honestly if it gives you headaches why not try another type? Or wear a respirator?

[hooli_gan]

The answer is laziness

[jdietrich]

Most electronics fluxes aren't particularly toxic, but rosin is a sensitiser - repeated exposure will cause an increasingly severe allergic reaction. Working in a well-ventilated room is probably fine if you only solder occasionally, but anyone who is soldering regularly should be using a good fume extraction system.

https://www.hse.gov.uk/pubns/indg249.pdf

[moffkalast]

Yeah I've found that SAC solder typically doesn't contain nearly enough flux to get the job done (just 2% at most, seriously?!). Small joints like really tiny wires work great at something like 370C so I can just touch it for a split second and it's instantly done, for anything else it's dripping into flux paste time and it works almost as good as leaded used to. Would've been easier to streamline the process if the rosin core was like 10% or 15% instead.

Not all types of flux work well though, my local store sells something that has no labels but seems to be very aggressive and works exceptionally well, the more common no clean types don't do anything at all.

Tips are definitely eaten a lot faster than leaded, but it's not exactly a huge expense when they're like a dollar or two for a 10 pack on aliexpress.