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I'm thinking of changing to lead-free solder. I've heard some people prefer a traditional Pb/Sn solder, but haven't heard any specific reasons why.

I'm mostly doing through-hole work, and I have a decent temperature-controlled iron.

So, are there any issues I might encounter with changing over? And are there any situations where I'd want to use a particular type?

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Workmanship is more challening with Pb-free solder, due to degraded wetting and a higher melt point. It is often more difficult to visually verify a cold-solder joint by visual inspection, because most Pb-free solder joints 'look' cold if you judge with the same criteria that is normally used to judge conventional solder joints.

Also, Pb-free is much more prone to tin whiskers than conventional solder - in fact, way back in the day (decades ago) this was one of the reasons lead was added to solder (it's the most effective whiskering inhibitor known). Tin whisker-induced failures are more common with dense layouts and usually happen months or years after assembly.

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  • \$\begingroup\$ +1 for tin whiskers; I had never heard about them before. \$\endgroup\$ – Steven T. Snyder Oct 23 '12 at 21:53
  • \$\begingroup\$ @Series8217 It's a huge, scary problem - one that you don't want biting you in the behind, as it's notoriously difficult to prove, and even harder to solve sometimes. \$\endgroup\$ – Adam Lawrence Oct 24 '12 at 0:04
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DO not use lead free unless you really really need to. And even then consider if anyone's going to find out it's not leadfree. Temeratures are higher, so more risk of part & PCB damage, and it doesn't flow as nicely. Desoldering through-holes with leadfree is a bitch, to the extent that it's easier to first flood it with leaded. It also eats through tips way faster than leaded. The flux fumes are also more unpleasant than leaded fluxes. If you really must do leadfree, use the stuff with 2% silver as this has a lower melting point and produces nicer joints.

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Well... try by yourself and you'll discover the reason why peoples don't use lead free solder unless they're forced to.

My supplier, when I go buy solder, always asks me "Do you need lead-free solder or do you want the working one?" :-)

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