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 includes 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 a solder is around 2.5%.
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%.
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 defattening, 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.