On 11/2/15 6:05 PM, J. Hunt via TowerTalk wrote:
Pb free solder.
I'm not sure I see a good reason for RoHS solder on connectors,
particularly for hand assembly. The advantage of classic tin/lead,
especially the eutectic SN63, but pretty much for the Sn60 too, is that
there's a nice sharp transition from solid to liquid, so if you jiggle
it a bit, you're less likely to mess up the joint. The other alloys
have a longer transition zone from solid to liquid, and you can easily
get that classic "cold solder" joint if something moves while it's
cooling. I once was desperate and assembled a circuit with 50/50
plumbing solder, and that was a nightmare.
I also like the low melting point, since you're always worried about
melting the dielectric (solder gods help you if you're soldering foam
polyethylene dielectric.. just get a crimper and don't bother)
most lead free solders melt around 230C and lead/tin melts around 180C.
PTFE starts to lose its mechanical properties around 200C, although it
doesn't melt til over 300 somewhere, so that's another reason why
lead/tin is nice.
One can probably find low melting lead free alloys with indium or
something in them.
Lead-free RoHS is fine in mass production, where you can work your
process controls to deal with the generally less convenient properties
of lead-free alloys. If you're doing reflow, you can figure what works,
and most all components will tolerate the higher solder temperature.
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