What type of solder is safest for home (hobbyist) use?

Question

I'd like to do some hobbyist soldering at home, and would like to make sure I don't poison those living with me (especially small children). Lead-free seems necessary - what other features should I look for in solder? Are the different types of solder roughly the same in terms of safety (breathing the fumes, vapor fallout, etc.)? Is there more I should do to keep the place clean besides having a filter fan and wiping down the work surface when finished?

Answer 1

This advice is liable to be met with doubt and even derision by some - by all means do your own checks, but please at least think about what I write here:

I have cited a number of references below which give guidelines for soldering. These are as applicable for lead-free solders as for lead based solders. If you decide after reading the following not to trust lead based solders, despite my advice, then the guidelines will still prove useful.

It is widely know that the improper handling of metallic lead can cause health problems. However, it is widely understood currently and historically that use of tin-lead solder in normal actual soldering applications has essentially no negative health impact. Handling of the lead based solder, as opposed to the actual soldering, needs to be done sensibly but this is easily achieved with basic common sense procedures.

While some electrical workers do have mildly increased epidemiological incidences of some diseases, these appear to be related to electric field exposure - and even then the correlations are so small as to generally be statistically insignificant.

Lead metal has a very low vapor pressure and when exposed at room temperatures essentially none is inhaled. At soldering temperatures vapor levels are still essentially zero.

• Tin lead solder is essentially safe if used anything like sensibly.
  While some people express doubts about its use in any manner, these are not generally well founded in formal medical evidence or experience. While it IS possible to poison yourself with tin-lead solder, taking even very modest and sensible precautions renders the practice safe for the user and for others in their household.

• While you would not want to allow children to suck it, anything like reasonable precautions are going to result in its use not being an issue.

  A significant proportion of lead which is "ingested" (taken orally or eaten) will be absorbed by the body.

  BUT you will acquire essentially no ingested lead from soldering if you don't eat it, don't suck solder and wash your hands after soldering. Smoking while soldering is liable to be even unwiser than usual.

• It is widely accepted that inhaled lead from soldering is not at a dangerous level.

  The majority of inhaled lead is absorbed by the body.

  BUT the vapor pressure of lead at soldering temperatures is so low that there is essentially no lead vapor in the air while soldering. Sticking a soldering iron up your nose (hot or cold) is liable to damage your health but not due to the effects of lead. The vapor pressure of lead at 330 C (VERY hot for solder) / 600 Kelvin is about 10^-8 mm of mercury.
  Lead = "Pb" crosses x-axis at 600K on lower graph here. These are interesting and useful graphs of the vapor pressure with temperatures of many elements. (By comparison, Zinc has about 1,000,000 times as high a vapor pressure at the same temperature, and Cadmium (which should definitely be avoided) 10,000,000 times as high. Atmospheric pressure is ~ 760 mm or Hg so lead vapor pressure at a VERY hot iron temperature is about 1 part in 10^11 or one part per 100 billion.

The major problems with lead are caused either by its release into the environment where it can be converted to more soluble forms and introduced into the food chain, or by its use in forms which are already soluble or which are liable to be ingested. So, lead paint on toys or nursery furniture, lead paint on houses which gets turned into sanding dust or paint flakes, lead as an additive in petrol which gets disseminated in gaseous and soluble forms or lead which ends up in land fills are all forms which cause real problems and which have led to bans on lead in many situations. Lead in solder is bad for the environment because of where it is liable to end up when it is disposed of. This general prohibition has lead to a large degree of misunderstanding about its use "at the front end".

If you insist on regularly vaporising lead in close proximity to your person by eg firing a handgun frequently, then you should take precautions re vapor inhallation. Otherwise, common sense is very likely to be good enough.

Washing your hands after soldering is a wise precaution but more likely to be useful for removal of trace solid lead particles.

Use of a fume extractor & filter is wise - but I'd be far more worried about the resin or flux smoke than of lead vapor.

Note that there are MANY on we b documents which state that lead solder is hazardous. Few or none try to explain why this is said to be the case.

Soldering precautions sheet. They note:

• Potential exposure routes from soldering include ingestion of lead due to surface contamination. The digestive system is the primary means by which lead can be absorbed into the human body. Skin contact with lead is, in and of itself, harmless, but getting lead dust on your hands can result in it being ingested if you don’t wash your hands before eating, smoking, etc. An often overlooked danger is the habit of chewing fingernails. The spaces under the fingernails are great collectors of dirt and dust. Almost everything that is handled or touched may be found under the finger nails. Ingesting even a small amount of lead is dangerous because it is a cumulative poison which is not excreted by normal bodily function

Lead soldering safety guidelines

Standard advice Their comments on lead fumes are rubbish.

FWIW - the vapor pressure of lead is given by

• log10p(mm)=-10372/T-log10T-11.35

  Quoted from

More on soldering in general. Better soldering

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Lead spatter and inhalation & ingestion

It's been suggested that the statement:

• "The majority of inhaled lead is absorbed by the body. BUT the vapor pressure of lead at soldering temperatures is so low that there is essentially no lead vapor in the air while soldering."

is not relevant, as it's suggested that

• Vapor pressure isn't important if the lead is being atomized into droplets that you can then inhale. Look around the soldering iron and there's lead dust everywhere.

In response:

"Inhalation" there referred to lead rendered gaseous - usually by chemical combination. eg the use of Tetraethyl lead in petrol resulted in gaseous lead compounds not direcly from the TEL itself but from Wikipedia Tetraethyllead page:

• The Pb and PbO would quickly over-accumulate and destroy an engine. For this reason, the lead scavengers 1,2-dibromoethane and 1,2-dichloroethane are used in conjunction with TEL—these agents form volatile lead(II) bromide and lead(II) chloride, respectively, which are flushed from the engine and into the air.

In engines this process occurs at far higher temperatures than exist in soldering and there is no intentional process which produces volatile lead compounds. (The exceedingly unfortunate may discover a flux which contains substances like the above lead scavenging halides, but by the very nature of flux this seems vanishingly unlikely in the real world.).

Lead in metallic droplets t soldering temperatures does not come close to being melted or vaporised at anyhing like significant partial pressures (see comments and references above) and if any enters the body it counts as 'ingested', not inhaled.

Basic precautions against ingestion are widely recommended, as mentioned above.
Washing of hands, not smoking while soldering and not licking lead has been noted as sensible.

For lead "spatter" to qualify for direct ingestion it would need to ballistically enter the mouth or nose while soldering. It's conceivable that some may do this but if any does the quantity is very small. It's generally recognised bothe historically and currently that the actual soldering process is not what's hazardous.

A significant number of webpages do state that lead from solder is vaporized by soldering and that dangerous quantities of lead can be inhaled. On EVERY such page I have looked at there are no references to anything like reputable sources and in almost every such case there are no references at all. The general ROHS prohibitions and the undoubted dangers that lead poses in appropriate circumstances has lead to a cachet of urban legend and spurious comments without any traceable foundations.

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And again ...

It was suggested that:

• Anyone who's sneezed in a dusty room knows that it doesn't have to enter the nose or mouth "ballistically". Any time solder splatters or flux pops, it creates tiny droplets of lead that solidify to dust. Small enough particles of dust can be airborne and small exposures over years accumulate in the body. "Lead dust can form when lead-based paint is dry scraped, dry sanded, or heated. Lead chips and dust can get on surfaces and objects that people touch. Settled lead dust can re-enter the air when people vacuum, sweep or walk through it."

In response:

A quality reference, or a few, that indicated that air borne dust can be produced in significant quantity by soldering would go a long way to establishing the assertions. Finding negative evidence is, as ever, harder.

There is no question about the dangers from lead based paints, whether form airborn dust from sanding, children sucking lead painted objects or surface dust produced - all these are extremely well documented.

Lead in a metallic alloy for soldering is an entirely different animal.
I have many decades of personal soldering experience experience and a reasonable awareness of industry experience. Dusty rooms we all know about, but that has no link to whether solder does or doesn't produce lead dust. Soldering can produce small lead particles, but these appear to be metallic alloyed lead. "Lead" dust from paint is liable to contain lead oxide or occasionally other lead based substances. Such dust may indeed be subject to aerial transmission if finely enough divided, but this provides no information about how metallic lead performs in dust production.

I am unaware of discernible "Lead dust" occurring from 'popping flux', and I'm unaware of any mechanism that would allow mechanically small lead droplets to achieve a low enough density to float in air in the normal sense. Brownian motion could loft metallic lead particles of a small enough size. I've not seen any evidence (or found any references, that suggest that small enough particles are formed in measureable quantities.

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Interestingly - this answer had 2 downvotes - now it has one. Somebody changed their mind. Thanks. Somebody didn't. Maybe they'd like to tell me why? The aim is to be balanced and objective and as factual as possible. If it falls short please advise.

Answer 2

You're making a big deal out of something small. Lots of things you have around your house and handle regularly are poisonous. Solder isn't even high on the list compared to cleaners and stuff in your medicine cabinet. As long as you take common sense precautions and don't stir your coffee with a solder lead, there won't be any problems. Reasonable precautions of course includes keeping things away from little kids, just like all the much more dangerous things in your house.

Answer 3

As mentioned above the metal isn't a big deal - I find the flux fumes from leadfree to be significantly more unpleasant than leaded - I don't know how much difference there may be between different brands. Leaded is nicer to use anyway, so unless you really need to I'd avoid leadfree whenever possible.

Answer 4

I have been using leaded solder since a very early age (early teens), so for more than half my life. I am not aware of it having any form of an adverse affect on me.

The fumes you get from the solder is purely from the flux. Getting lead to vapourise at anything even vaguely approaching dangerous (or even noticeable) levels would take an awful lot more heat that a soldering iron can produce. It would also make soldering impossible as the lead wouldn't stay on the board ;)

The sole reason for switching to lead-free solder is purely from a reclamation and recycling point of view.

As they all contain the same flux (near enough - Rosin, etc), the fumes will all be pretty much the same. Just avoid the acidic fluxes used in automotive work as this is unsuitable for the delicate electronic work.

The only other consideration is the alloy mix. Different mixes will have different melting / cooling profiles, and it's really a matter or personal choice and what performs best with your soldering iron. Try a few out until you find one you like.

Personally I have recently switched to lead-free solder purely so I can re-sell my products and adhere to the RoHS standards.

Answer 5

I find this a curious question as people are always questioning the fumes from solder. Sure some soldering processes are worse than other (car radiators) but for home electronics As the soldering temperature is below the fuming temp for lead. I am more worried about the person holding the solder in their bare hand and not washing their hands before breaks for lunch or toiletry. You should analyse the whole process when you make your decision not just one part of it.

Answer 6

The only real way to know would be to test the rosin smoke and surfaces in areas where soldering with lead-tin alloys occurs.

The burning rosin is intended to prevent oxides from accumulating on the solder surface. Some articles have noted that this smoke will take fine aerosols of lead away from the solder surface, into the air where it can be inhaled. This creation of fine lead oxide particles in the the smoke can occur even at temperatures where the vapor pressure of lead is very low.

Another possible route of exposure: Many solder irons do not have sophisticated temperature controls, so the tip, "tinned" with a thin layer of solder, may get much hotter than the typical soldering temperature, especially whenever the tip is not in contact with anything. It could reach temperatures where the vapor pressure of lead is much higher. Any lead vapors would immediately cool back down into find lead dust.

Again, the only real way to know whether lead contamination is a problem in a typical home solder operation would be to conduct testing. I understand the lead-free solders are harder to work with because they don't wet as well and require more heat, but those problems can be overcome in most situations with practice. For what it's worth, a lead-free solder joint can potentially be stronger than the tin-lead solders.