Soldering is your best friend when making stuff. But are you doing it right? Probably not!

Leaded solder vs lead-free solder.

When you are a company and want to sell (or give away) a product, it must be RoHS (lead-free).
When you are a hobby enthusiast and want to make stuff for yourselves, there is no reason not to use lead containing solder. Lead-free has a higher melting point and you probably need flux to get things done properly. Also, you need a soldering iron which can be set to a higher temperature to do the job. Soldering lead-free is more difficult and can result in a bad connection when not done well.

Eutectic solder

Huh, what’s that? Solder can be solid, something between solid and liquid and it can be liquid. Some types of solder are completely solid or completely liquid. Nothing in between. This is the most ideal solder to work with. You see it when you see it shine and then BANG in an instance it becomes solid.

AlloyTemperature (range)EutecticLead-free
Sn62/Pb36/Ag2179YES 🙂No
Sn63/Pb37183YES 🙂No
Sn96.5/Ag3/Cu0.5221YES 🙂Yes
Sn99.3/Cu0.7/Ni0.06/Ge0.005227YES 🙂Yes (contains Nickel)

Sn: Tin
Pb: Lead
Ag: Silver
Cu: Copper
Ni: Nickel (Some people are allergic to this)
Ge: Germanium

When you hace the old fashioned solder Sn60/Pb40 it is solid below 183 C. Between 183C and 190C it is a bit pasty. Above 190 it is completely liquid. In those seconds between 190C and 183C, when you move the components in the connection it can result in cracks in the soldering. This results in a cold solder joint (very unreliable).

The conslusion is, do not use Sn60/Pb40. You could use Sn63/Sn37, which has a low temperature, is eutectic, but is a bit more expensive. However, it is harder to find this alloy of solder these days. Sn63/Sn37 has one specific temperature where it goes from fully solid to fully liquid. On the other hand, it also goes from completely liquid to fully solid.

First of all. Should you use lead-free solder? When you are a hobbyist like me, the answer is probably NO. When you are running a business you have no choice other than to comply with RoHS (thus using lead-free solder).

Why shouldn’t you use lead-free? The temperature needed is significantly higher. Also lead-free you probably need to use flux.

When you want to remove a component from an already soldered PCB there is a high chance that lead-free is used. In that case, I would suggest soldering the connection again with leaded solder. This will add resin and it will change the alloy. The resulting alloy probably has a wider temperature range where the solder is liquidous.

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