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EEVblog #319 - Lead Free PCB Tinning

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EEVblog:


Dave.

Psi:
Next up... Silver solder :D

naimis:
Based on my fairly limited education in chemistry I would think the lead would actually be more conductive.  Lead and tin have the same number of electrons in their outermost shell but lead, being one period down on the table has a "less tight grip" on its outer shell of electrons... and as such the electrons in a lump of lead ought to move more freely than in a lump of tin (or to take the same argument even further, in a lump of germanium or silicon or carbon).

But I'm probably talking out of my ass.

PeteInTexas:
Do wave solder machines use solder with some other composition Dave/Mike tested?  I'm thinking it might be different because the process is very different from hand soldering.  And if its different, somebody will need to test that to satisfy the forum.  ;D

amspire:

--- Quote from: naimis on July 22, 2012, 03:01:34 am ---Based on my fairly limited education in chemistry I would think the lead would actually be more conductive.

--- End quote ---
Lead has over double the resistance of tin, and the 60/40 solder has about 25% more resistance then the Tin solder.

I do not think the 0.7% copper content in Dave's lead-free solder is anything to do with lowering the resistance, as Dave suggested. I think it helps prevent copper ions diffusing into the solder which can cause the solder to become brittle.  This makes it liable to fracture and turn into an intermittent joint. That is something I heard decades ago, so if the explanation is wrong, I hope someone can correct me.

Richard.

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