Unless you are getting very expensive extremely high silver content solder, or very special alloy mixes... The difference in electrical conductivity is at best a few percent. (of the IACS standard)

Typical silver solder found in electronics supply shops or online, have only 0.4% better electrical conductivity. They do have increased physical strength, at around 10-15% higher tensile, and can solder to silver plated contacts better. They tend to be eutectic, with formulas around 62/36/2 tin, lead, silver. The cost increase isn't that much, and some may find it worth it for a stronger joint. Lead free formulations are not eutectic, and need around 50-60*F higher temps.

If you are willing to spend 4x as much for solder than the cost of typical 63/37 you can get solder that has 4.5% better conductivity. It's a 96.5/3.5 tin and silver alloy... It has a significantly higher melting point, close to 100*F higher. It is eutectic though. It is stronger than 63/37, but not as strong as common silver solder formulations.

If you want 10% better conductivity, and want to spend around 10x as much on your solder... 90/10 Indium/silver solder will get you there. It is expensive and basically impossible to find outside of industrial supply. Melting temp is over 100*F higher, and it is far from eutectic... With its solidification point about 170*F lower than the melting point. It is also very weak, at about 20% the strength of 63/37 solder.

If you are getting anything other than common silver solder from the electronics store, I question your sanity... The cost and the difficulty in use of those special formulations, plus the potentially damaging levels of heat needed makes them not very viable, especially for the small gains... And the formulation of typical silver solder from the hobby store is so close to 63/37 there is little need to have a dedicated iron, if you clean the tip off well each use.

When it comes to conductivity... we are talking small numbers... Pure copper is 17.2 nano ohms per meter... 63/37 is 145 nOhm/m... Typical silver solder is around 130 nOhm/m... and the indium/silver is 78 nOhm/m...

And considering the thickness of the solder in a typical joint is much less than a millimeter thick... I don't think the conductivity difference between them matters one bit in high energy systems like R/C, where amps are very high. We are not working with small voltages at very small amps, like in an IC chip.


Go buy some 63/37 and be done with it... If you must go lead free, typical lead free silver bearing solder works, if not as easy to use, and needing more heat.