The most common lead free electrical solder alloys are SAC305 (96.5%Sn, 3.0%Ag, 0.5%Cu) and Sn99 (99.3%Sn, 0.7%Cu), especially for hand soldering wire.
Small amounts of antimony (Sb) have been shown to improve the properties of tin-based solder. Most of these are mechanical (strength) benefits, similar to the benefits of silver while being cheaper. The most common electical solder alloy with antimony is Ag03A (96.5%Sn, 2.5%Ag, 0.8%Cu, 0.5%). It's still not as common as the above mentioned alloys in mass production, and is almost nowhere to be found for hand solder wire. So I question why this is.
Here are some advantages I see of the Ag03A alloy vs SAC305 (due to the antimony):
- Increased wetting (probably, although 0.3% is more optimal for this)
- Increased thermal fatigue resistance. [1]
- Inhibits tin pest and other undesirable compounds.
And here are some more advantages that come specifically from replacing some of the silver with antimony:
- Lower cost
- Less silver oxide (which ruins the solder when heated for too long)
- Reduced cracking
So why is this alloy not more common?
Some sources say that AIM has a patent on it, but according to this it only applies in USA and Japan. But isn't SAC305 also patented?
Best Answer
Because hobbyists and plumpers may be tempted to use zinc chloride as a soldering fluid with antimony solders. That produces stibine, a very poisonous gas. At least it smells like hell so you have a chance to flee.