Message-Id: <s618ed68.081@YCC.COM>
Date: Mon, 05 Oct 1998 16:01:29 -0500
From: "Bill Gradwohl" <Bill@YCC.COM>
To: lancair.list@olsusa.com
Subject: Soldering wires
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I'm an electrical engineer, and I agree with those advocating soldering 
connections. I plan on soldering all non coax wires.

If you use the right connectors and the proper technique, you can get the
electrical benefits of soldering and avoid the problems associated with the
creation of an inflexible joint. You also end up with a mechanically stronger
connection.

1.) Twist the strands together and insert the end into the connector making 
sure that some of the twisted wire pokes out past the end of the crimp area 
of the connector. Twisting is recommended because it decreases the solders 
ability to wick. Solder prefers to run a straight line.
2.) Crimp the connector on to the wire for a physical bond. I said crimp, not
smash. The crimp tools at Radio Shack or the local auto parts store won't do.
3.) Trim the excess wire in the crimp area so that 1 to 2 mm remains.
4.) Splay the strands of wire in the crimp area to untwist them and put 
some air between the individual strands. Ideally what you want to see is the 
crimp of the terminal with individual strands of wire evenly distributed. You
don't have to strive for perfection, just get the strands separated enough so
the solder has a natural tendency to wick around them. What you want are
strands that want to wick on one end of the crimp and strands that don't
want to wick as much on the other end.
5.) Apply solder only to that side of the crimp and terminal surface away
from the main piece of wire. What you are soldering is the excess wire
sticking out of the crimp area only. 

Don't apply too much solder. Apply only enough to allow the wicking action 
to disperse the solder. If you apply too much you are asking for the solder to
move past the crimp. A good solder joint should be shiny and slightly hollow
in appearance. If you end up with a ball of solder you aren't doing it right. 

When that small area is soldered, the crimp prevents the solder from wicking
back towards the wire segment. If you find that you are getting solder being
wicked past the crimp area to a significant degree, then by definition the
crimp is no good. You may be using the wrong type of connector and crimp tool.
Wires are round, and so should be the crimp. A flat crimp is an invitation to a 
poor joint.

If the strands are sufficiently large to allow a channel to develop that allows
solder to flow past the crimp point, then consider augmenting the twisted wire
with smaller gauge wire in such a manner to fill in the area between the large 
strands. Then crimp. You have now increased the surface area of the 
mechanical bond and closed off the large channels that would allow solder to 
flow past the crimp. Obviously, no one would do this in a mass production
setting in industry, but for our one of a kind creations, we can take the time
and trouble and do it right the few times it may be necessary.

You may also want to let gravity help you. Position the wire and crimped on 
connector so that gravity wants the solder to flow away from the crimp. 
Solder's natural affinity to copper wire will work against gravity to some 
extent. A little experimentation will quickly show you what you need to know.

I plan on using a 2 stage soldering gun for most of the large wires, and a 
soldering pencil for the tiny wires. Battery cables will need a torch. If you
get multi core rosin solder, and thoroughly clean the strands and the 
connector you won't need flux for most situations. Clean only that end of the 
connector where you want solder. Allow tarnish to repel solder where you don't
want it.

I only use solder designed to be used for printed circuit boards. It is very 
thin, heats quickly and contains enough flux per volume of solder. If I have 
an application that needs lots of solder, I just twist several strands of this 
thin solder together. Flux is recommended for really heavy cables, typically 
where a torch is needed.

Anyone that wants to solder well also needs to know how to tin the soldering
tip on a pencil or gun, and how to maintain it. A little steel wool to refresh 
the tip is recommended every so often followed by a layer of solder. Use 
copper tips.

Heat the joint with the heat source (gun, pencil, torch), and then quickly 
apply the solder. The solder should flow from the heat already in the joint, 
not the heat being put out by the heat source at the instant that the solder
is applied. The heat source heats the joint, and the joint melts the solder.If you
apply the solder and it doesn't melt instantly, the joint is too cold. Keep 
applying heat from the heat source to make up for the heat used to melt the 
solder. If there isn't enough heat available to properly melt the quantity of
solder needed by the joint, you end up with a "cold solder joint".

A "cold solder joint" doesn't have the shiny appearance of a 
properly made joint. It also has a significant electrical resistance built in 
and has poor mechanical properties. Definitely something to be avoided.

A 2 stage soldering gun allows you to use high heat to heat the joint, and then
use the lower setting to maintain the heat while applying solder. Too much heat
boils away the flux before it can do its job. Not enough heat leaves the flux
around to assist corrosion.

Pre tinning wire is a good idea if it ends up inside a blind connector such as
the center conductor of a coax connector. If the connector and solder to be 
applied will be visible after the work is done, then tinning isn't usually
necessary. If you find that tinning helps, consider a larger heat source, 
better solder and cleaner mating surfaces.

If you are worried about frying electronic parts use heat sinks such as 
locking forceps. Crumpled up aluminum foil in the forcep jaws also helps in
extreme situations.

I've used the same soldering tools for over 20 years, so I haven't shopped 
for any in a long time. If enough people want tool recommendations, I'll 
shop for some.

Bill Gradwohl
IV-P builder
N858B