[TowerTalk] Solder For Connectors

[Jim Lux]

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.