Solder fumes. Everybody is accustomed to those nasty fumes raising as you are soldering. It’s a bit of a no-brainer that those fumes are bad for us. But how bad are those fumes, and, more important, what can we do about this?
Solder wire: rosin is the main source of fumes
First, we have to take a look at the source for those fumes: the solder wire. Usually, for low-volume soldering jobs, which include makers, hobbyists, as well as low-volume production jobs, the most used is the rosin flux core solder. Think of this solder as a tube made out of a solder alloy, with the inside of the tube filled with rosin.
There are two main types of solder used today: the old model contains lead, with a typical Sn60 – Pb40 composition. Sometimes a small amount of copper and silver can be used too. Note that this proportion between tin and lead is close to the 63/37 eutectic ratio of these metals. The melting point of the typical lead solder used in electronics is 180°C. The rosin content of such solder is around 2.5%.
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| Tin-lead solder used in electronics |
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| Tin-lead solder used in electronics |
On July 1, 2006, the Restriction of Hazardous Substances Directive (RoHS) came into effect prohibiting the use of significant quantities of lead in most consumer electronics produced in the EU. Newer types of solder (also called lead-free) are typical Tin-Silver-Copper alloys, usually marked as Sn-Ag-Cu, or “SAC”. For example, the solder alloy WSW SAC M1 pictured below contains 96.5 tin, 3% silver, and 0.5% copper. These new alloys have a much higher melting point, around 210°C. The solder wire has also a higher rosin content, up to 3.5%.
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| Lead-free solder alloy |
As you can imagine, most of the flux (rosin) content evaporates during the soldering process, turning into fumes. Obviously, more rosin content means more fumes. As such, switching to lead-free soldering also increases the fumes issue. Besides this, there will be a small amount of vaporized metal – lead is the nastier, you don’t want that in your lungs.
Besides this, regardless of which solder alloy you are using, there will be a small amount of vaporized metal – lead is the nastier, you don’t want that in your lungs.
Solder fumes: how bad they are?
The WSW SAC M1 pictured above was not chosen by mistake: I was able to find its safety data sheet. And the safety data sheet contains some alarming data:
This solder wire is classified as R42/R43: it may cause sensitization by inhalation and skin contact.
As statements for health hazards we find:
H317 May cause an allergic skin reaction.
H334 May cause allergy or asthma symptoms or breathing difficulties if inhaled
The manufacturer also indicated the standard precautions to use it:
P261 Avoid breathing dust/fume/gas/mist/vapours/spray.
P280 Wear protective gloves/protective clothing/eye protection/face protection.
P285 In case of inadequate ventilation wear respiratory protection.
As well as the response measures if something goes wrong
P302 + P352 IF ON SKIN: Wash with plenty of soap and water.
P304 + P341 IF INHALED: If breathing is difficult, remove to fresh air and keep at rest in a position comfortable for breathing.
P333 + P313 If skin irritation or rash occurs: Get medical advice/attention.
Not surprisingly, the fumes are harmful by inhalation, in contact with skin and if swallowed. It causes skin problems such as defatting, dermatitis, skin dryness, or cracking. It causes irritation of the respiratory system. Furthermore, it can aggravate problems such as asthma, allergies, chronic or recurring respiratory illness.
Benchtop fume extractors: are they worth it?
Considering the nasty effects of solder fumes, using a fume extraction system becomes a requirement if you care about your health. But choosing a fume extraction system is not easy. There are big fume extraction systems that stay behind your bench, with excellent filtration performance – but they come with a high price tag. And there are the small benchtop units, with nothing but a carbon filter and a fan – and they come cheap.
Today I’m testing one of those cheap units, a model from Duratool. Let’s take a look at it:
What we have here is a 23W fan, with an activated carbon filter sitting in front of it. A small hood helps collecting the fumes from a larger area.
Another similar unit from Weller specifies that the carbon filter contains 9 grams of activated carbon – enough to neutralize 2.5g of noxious components. I expect the same performance from the Duratool unit too. So, for the 250g spool of lead-free solder that I have used as example I would expect some 9 grams of toxic stuff to be released – four filters would be needed to neutralize it.
Some fumes will escape through the filter, as the filter is not so dense. Some consider these desktop units as fume dispersers, as they take the fumes away from the user and mix them with the air in the room. Ventilating the room after use is a good ideea. Also, it’s not so good to stay behind the unit.
As for the fume absorbing capabilities, look at the following pictures:
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| Without fume absorber |
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| With fume absorber |
In the first picture, I did some soldering on a Proto click board. Notice the solder fumes coming right towards me. In the second picture, the fume extraction unit is turned on, and one can see the smoke going towards the unit.
As conclusion, I would say that it’s better to use a cheap fume extractor rather than doing nothing. For low-volume soldering jobs, it performs pretty well, and it moves the fumes away from the person holding the soldering iron.
Filtration is not as good as in professional units. However, the cost is at least eight times lower than of a professional unit. One can still be well by ventilating the room after use, to evacuate the dispersed fumes.
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