Hi Mike,
At 11:05 PM 11/6/2012, Mike S wrote:
>Common 60/40 has a tensile strength of around 535 kgf/cm�, 3.5% silver
>solder, about 580. Not that much difference. The important thing is to
>ensure the joint is properly wetted, and keep the joint stationary while
>cooling. Using a eutectic alloy (63/37) almost eliminates the issues
>cause by movement.

I agree that a joint that's moved while in the 
mushy zone is a bad joint, period.
I'm a huge believer in 63/37 solder, wonderful 
stuff.  There's a jeweler's low-temp solder 
called Tix, costs a fortune.  Do you know anything about it?

You have an interesting point about the 
non-eutectic solders needing to have the joint 
mechanically secured while they go through the plastic zone.

>Mechanically, a proper soldered joint of equal overlap (and no twist)
>will be stronger than a non-soldered WU splice with stranded wire, so it
>should be apparent where the strength comes from. WU splices are really
>only effective on solid wire, which shouldn't ever be used in an
>automotive environment.

Yes, I wasn't thinking about how much less 
integrity the WU splice has in stranded wire.

I take your point, I think.  My concern about 
solder joints has never been about tensile 
strength but rather fatigue tolerance.  A prime 
example is in the 022 ECU, where the boards are 
joined by a couple of say 20-pin flattened wire 
interconnects with paper insulation.  The length 
is such that they form an S curve and exert a bit 
of pressure shoving them into their connecting 
through-holes.  I can't imagine these things 
weigh more than a couple grams, but they are 
pulling themselves out of the boards 
nonetheless.  There's no thermal cycling to speak 
of so I can only put it down to vibration.

Now whether this is really an issue with two 
wires soldered together in-line is another 
question and I don't know the answer.  I am 
concerned about it in a high-vibration 
environment like a car, but I'm more concerned 
with the hard spot that the solder leaves when it 
wicks up into the strands.  For these reasons I 
personally am leery of solder joints under these 
conditions, though I'm very fond of solder in 
general.  My habit when working in salt water was 
to seal the ends of crimp connections with 
multiple coats of "Liquid Electrical Tape" which 
is a vinyl compound, and I never had a joint fail 
in many years (whereas every single unprotected 
crimp fitting on the boat corroded completely off 
where the wire entered the crimp. However here is 
an alternate view. 
http://yachtpals.com/marine-electrical-9162   It 
must be stressed of course that a cheap crimp 
connector is useless, and insufficient crimping force likewise.

Yours,
David