How To Solder:

When soldering, NEVER apply solder directly to the soldering iron
(except when "tinning" the tip of the iron). Solder is not applied directly
from the iron to the electronics. In fact, touching the actual solder site
with the soldering iron is often the worst thing you can do. This is
because, irritatingly, the solder is very often more attracted to the
soldering iron than the spot where you actually want the solder to go.
The iron seems to have an almost magnetic attraction for the molten
solder, and when this happens, touching the iron directly to the soldering
point will result in nothing more than a rounded blob of solder collected
on the tip of the iron, with no solder actually on the joint. Attempting to
add more solder will only increase the size of the blob on the iron, until
gravity finally takes over when the blob becomes so huge that its surface
tension cannot keep it on the tip of the iron any longer. When this
happens and the blob falls onto the solder joint, it is usually so huge that
it floods the surrounding area, usually creating a short with some other
part of the circuit. The reason this happens is because solder is most
drawn to the hottest thing it touches. Since the soldering iron will always
be hotter than the components you are trying to work with, the solder
will always tend to stick to the iron. This is why you do not actually
touch the iron directly to the solder. If you find your solder begins
sticking to the iron, wipe the tip of your iron off on a moist sponge or
piece of paper towel, and start over. The instinct is to get the solder on
the iron, then wipe it on the solder joint, just as you would do with a
paintbrush. That is the wrong way to solder. You solder by holding the
iron near the joint (but not actually touching the joint) so that the joint
itself becomes hot. Then you touch the solder to the joint, which will
melt the solder around itself when it is hot enough.

Also note that solder should never be used for physical connection
strength. The connection should already be physically made with screws,
crimping, or some other mechanical means before solder is applied.
Soldering is done simply to create a better electrical connection (because
solder itself is conductive), but solder should NEVER be used for
physical strength. This sometimes creates confusion, because in fact
plumbers do use solder to physically connect pipes; Understand that
plumbers use a different composition of solder (and different flux, as
well) than the solder that is necessary for electronics work. Typically,
plumbing solder is 50% lead and 50% tin, and plumbers use acid flux.
Electronic solder is 60% lead and 40% tin, and uses rosin flux. (Rosin
being, essentially, hardened tree sap.)

Once you understand these key soldering concepts, you can follow these
steps to soldering:

1. Take health precautions before you start. People who solder all day as
a job usually set up a small fan blowing away from their workspace,
which helps to carry away the fumes from the burning flux and molten
solder. You might also want to use needle-nosed pliers to hold the actual
solder instead of keeping it in your hand, so your skin isn't in constant
contact with it. Remember, the solder used with electronics is about 40%
lead.

2. Prepare the parts to be soldered. If necessary, clean the components
to be soldered with sandpaper, a file, or a wire brush, to remove oxide
coatings or other dirt which might reduce the quality of your solder. If
you are soldering a wire, ensure that you have stripped enough insulation
off the end of the wire to allow for a proper solder joint (usually about
half an inch). Make sure the component(s) to be soldered are held in
place firmly so they don't move around while you're soldering.
Remember: DO NOT use solder for physical connection strength!

3. Apply flux. Solder flux is the semi-secret ingredient of soldering that
makes everything run much smoother. Flux serves two purposes: It
cleans the area to be soldered, and it helps the solder flow more freely
over the surface instead of having the solder just stick to itself in a ball.
Both of these will make for a much better solder joint. Put a little flux
on the area to be soldered and leave it for a moment, then proceed. It should
be mentioned, in fact, that the most common cause of so-called "cold solder
joints" (in which the solder is dull and brittle instead of shiny and smooth)
is NOT insufficient heating, as many supposed soldering experts claim, but
quite the opposite: Too much heat applied for too long, which burns off the
flux inside the solder. When solder has lost all its flux, no amount of
heating will make the joint smooth. You could turn up the heat on the
soldering iron and hold it to the joint for 10 minutes; it won't do a bit of
good without flux. If you are faced with this kind of joint, the ONLY way to
fix it (besides removing the solder and starting the joint over) is to apply
some flux. This becomes especially important when soldering using lead-free
solder, which has a higher melting point and so is more prone to having all
its flux burn away before the solder has melted into a reliable joint.
Soldering lead-free solder without flux is practically impossible, and
attempts to do so will usually ruin both the joints and the soldering iron
tip, since a long-term lack of sufficient flux on the soldering iron tip will
cause the tip to oxidize to the point of uselessness.

4. Pre-heat the soldering iron to operating temperature for a few minutes.
If the iron does not already have a coating of solder on its tip, "tin" the
iron by applying a very small bit of solder to the end of it. This will
maintain a thin film of molten solder on the tip of the iron, which creates
better heat conductivity.

5. Place the tip of the iron against the component to be soldered and hold
it for a few seconds to heat it up. Do not apply the solder without first
heating up the component to be soldered (this makes for a much better
solder and helps prevent "cold solder joints").

6. While still holding the hot iron against the electronics, bring in the
solder, and lightly touch it to the soldering point. Rather than pressing it
into place, simply allow the solder to run off and settle into a tiny
puddle.

7. Remove the solder, and remove the soldering iron a few seconds later.
A smooth, even coating of solder should remain. Let the solder cool and
harden for a while before you stress or move the new joint.

Being able to solder effectively takes some practice. Be sure to try
soldering some "test" joints on cheap components before you do real-
world soldering.