Originally Posted by compuryan
Solder with silver has better conductivity than solder without, simply because silver is much more conductive than the tin and lead which usually makes up solder. Its the same difference you'd hear upgrading your $.50 steel rca cables to copper ones, or copper ones to silver plated copper ones.
In most cases the silver content is 2%, so the analogy comparing steel and copper cables doesn't really apply. I'm also not convinced that silver plated copper cables are better than pure copper. That being said, here is an excerpt from a how to solder tutorial:
"Silver bearing solder: (that is, contains silver, not for roller bearings) Silver is used in one of the leading alloys for lead free solder (An96.5% Ag3.0% Cu.5%) and also as an addition to tin-lead solder, usually in the 2-4% range (when you se 62/36/2 this means Sn64Pb36Ag2).
People claim that it flows better, has a lower melting point, is stronger, and has a higher conductivity. According to Indium's solder wire data sheet, their 2% silver solder has an electrical conductivity that is 11.9% of Cu compared to 11.5% of 63/37 tin-lead solder, a shear strength of 7540psi vs. 6200psi, and a tensile strength of 7000psi vs. 7500psi for 63/37. So, yes, the claims are true, and also mostly insignificant. Silver was initially added to solder to prevent silver platings on component leads from dissolving into the solder ("silver migration") and forming brittle joints. Having silver in the solder reduces migration, so you may want to use it on silver joints. (Note: this logic doesn't entirely make sense to me. If silver getting in the solder caused embrittlement, how does adding more silver prevent this?)"