replaced 02 sensor - in defense of soldering (long)

[Rocket Science Racing]

>Date:	Fri, 18 Jul 2003 19:06:39 -0700
>From:	Tony Lum <tlum at flash.net>
>
>As SJ correctly describes, a ratcheting crimper is the only tool to use if
you're going to crimp connectors.  The standard crimper you see for >$5 in
hardware stores will NOT do the job correctly.  A ratcheting crimper and the
correct die will cost anywhere from $45-70.
>My company does mil-spec work for aerospace applications and soldering is
not permitted.  Soldering produces a brittle joint right at the end of >the
connector and wire joint that can fracture under vibration and heaven help
you if you use acid core flux solder.  Every type of contact has its >own
specific die and the tools are calibrated and tested at specified intervals.
A pull test is performed where the wire is crimped and then >pulled to test
the quality of the crimp.

Tony hits the nail right on the head. I design and build large electronic
systems for Uncle Sam, and for a long time now. Crimping is the way to go,
primarily because crimped connections are far more vibration resistant than
soldered connections, and, with proper tooling, are much faster in
production. BUT, BUT, BUT, there are a hole host of conditions that must be
met in order to achieve a crimped connection that is actually better than a
soldered connection for most applications:

1. You need to use high quality crimp connectors capable of making gas-tight
connections to prevent corrosion. Radio Shack, NAPA, Home Depot, etc. crimp
terminals do not meet this criteria.

2. You need to use high quality crimp connectors that have strain relief
features, e.g. that grab the insulated wire behind the actual crimp
connection. Again, this is not to found on the average over-the-counter
butt-splice. This is perhaps a crimped connector's most important feature,
without it the connection is only slightly better vibration-wise than a
soldered connection. In military and aerospace connectors, there are usually
multiple, redundant strain relief features, first on the contact itself,
then on the connector body, then on a backshell.

3. You need to use expensive thermal wire strippers and strip them just
right so as not to knick any of the wire strands.

4. You need to use production tooling (i.e. expensive crimp tools and dies)
in order to actually obtain a proper, gas-tight crimp.

5. 100% pull-testing must be performed.

So, my key point is: since most auto mechanics, home or otherwise, cannot
obtain appropriate crimp connectors, or have the appropriate tooling, the
reality is you are going to be able to achieve a better, longer lasting job
with a solder connection vs. using consumer crimp terminals and tooling.

It doesn't need to be neat to work, but wires do need to overlap a good
amount, and the solder does need to flow into the work, something we are all
capable of, I hope! Soldering is more tolerant of wire nicks. Shrink
sleeving is the most important thing you can do because it provides a
measure of strain relief on the soldered joint. If properly and neatly done
(extend the shrink tubing an inch or two past the solder joint on both
sides), it will be more vibration proof than the el-cheapo butt-splice. Good
quality solder, shrink tubing, and cheap tooling (heat gun, soldering iron)
are easily available.

Internal corrosion that might affect conductivity is not an issue with a
soldered joint, as it is inherently sealed. External corrosion is an issue,
but in general the average solder joint on something the size of a wire will
last a long, long time. If you are really worried, smear some RTV over the
ends of the shrink tubing.

Resistance of good solder joint is measurably higher, but not by the average
person with a Radio Shack multi-meter. It's nothing to be worried about.

Finally, the article that shows that solder has a lower melting point is
fun, but silly. If you ever flowed enough current in a circuit to melt the
solder, the fuse would have blown long before the solder even got hot. There
are probably locations in the car where soldering is a bad idea, though,
near hot stuff like turbos and exhaust manifolds. I haven't been faced with
that problem, but it's probably only a matter of time :-)

Personally, I solder and sleeve. I can't get a butt-splice I would consider
good enough. If I'm replacing a terminal in a connector body on my car, I
crimp with my $5 crimp tool, but then solder over that, and sleeve it if it
will fit in the connector body like that. I've never had a sleeved solder
joint fail, on my cars or on my race bikes.

Scott