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I've searched Google and couldn't find a simple answer to this question. I'm guessing the only limiting factor is the solder's melting temperature? I don't think I should have a problem with < 20A, but now I'm just curious about this. I know the resistance of solder is calculated from its total area, but that isn't exactly easy to calculate. So I guess I'm going for more anecdotal evidence.

Anyone have experience using solder joints for high currents?

edit: Sorry, I meant for longer tracks of solder (oops)

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    \$\begingroup\$ Your solder joints are almost always larger than the pins or wires you're soldering together. They are very likely not the weak point in your design. \$\endgroup\$
    – Samuel
    Commented Mar 31, 2015 at 19:33
  • \$\begingroup\$ When I solder together arm thick bars of copper, then I can run thousands of amps through it... and even if the solder there has a higher resistance and is getting hot, the copper transports the heat quite well \$\endgroup\$
    – PlasmaHH
    Commented Mar 31, 2015 at 19:38
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    \$\begingroup\$ "tracks of solder"...? What are those? \$\endgroup\$
    – Majenko
    Commented Mar 31, 2015 at 19:42
  • \$\begingroup\$ @wildwood A picture of what you have in mind would make this question clearer. \$\endgroup\$
    – Nick Alexeev
    Commented Mar 31, 2015 at 19:49
  • \$\begingroup\$ I'm having a brain fart right now... I mean any longer sections of solder. I don't have the materials to make PCB. I could just solder thicker wires to carry the current, but I like the look of solder better. I don't have pictures but an example would be a very high current motor driver circuit, but with all the copper traces replaced with solder. \$\endgroup\$
    – wildwood
    Commented Mar 31, 2015 at 19:53

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I honestly don't know the answer to your question but I can point you in one direction.

I see circuit boards in commercial equipment where the traces have to handle significant current. What the manufacturers seem to do is to have a bead of solder down the middle of each high-current trace. The solder is usually not the full width of the trace but covers most of it (anywhere from 50% to 80% of the trace width).

What this does is improve the heat dissipation of the copper trace. It doesn't actually reduce the trace resistance very much - copper is a far better conductor than solder - but it gives both more surface area as well as more thermal mass.

As a production technique, it seems to work well. I rarely see damaged or destroyed traces unless the whole board section is blown up (including exploded relays) because of catastrophic shorts at the load terminals.

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