In article ,
Roy Lewallen wrote:

The eutectic combination of tin and lead is 63% tin, 37% lead. 60/40 has
a slightly higher melting point, and unlike the eutectic alloy, has a
plastic stage between liquid and solid. Consequently, 63/37 is a better
choice for solder.

I understand that there's a tradeoff involved. The 63/37 eutectic has
a lower melting point and no plastic stage, and some people feel that
the latter reduces the risk of 'cold' solder joints somewhat. On the
other hand, I've read that the 60/40 alloy is somewhat superior in its
"wetting" property - it adheres and bonds to some base metals better
than the eutectic does, and might make superior joints as a result.

I tend to prefer the eutectic, or a eutectic modified with 2% silver.

--
Dave Platt AE6EO
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