solder with the board or wires moving all over the
place. It may be necessary to use a small vise or
other gripping tool to hold the board or wires steady
while you solder.
Care Is Required
Contact the Author
You can reach James Antonakos at
antonakos_j@sunybroome.edu or visit his website
at www.sunybroome.edu/~antonakos_j.
There are a few problems to watch out for while
soldering. First, you may accidentally create a solder
bridge. This is a blob of solder that fills the gaps
between two different soldered connections. For
example, on a PCB the copper pads where component
leads are soldered are sometimes very close to each
other. If too much solder is applied to one copper pad, it
may overflow and spill over to another pad. The solder
has now made an electrical connection between the
two copper pads. This connection is called a solder
bridge. Unfortunately, this connection is not intended and
changes the circuit. The change may prevent the circuit
from working, create a short that blows a fuse when you
apply power, or have some other negative effect on the
circuit's operation. For these reasons, the solder bridge
must be removed. This is accomplished by reheating
the solder that forms the bridge using the tip of the
soldering iron. Sometimes you can use the tip to gently
push the solder around enough to break the bridge.
Solder — like water and other liquids — has surface
tension when it is molten and will naturally try to bead
together. If there is too much solder in the bridge, this
method will not work and you will have to remove some
of it. This can be done using a solder braid to absorb the
extra solder. A solder braid is a stringy copper mesh that is
heated and placed onto a blob of solder. When the solder
melts, it transfers to the braid, coating it and filling the
gaps in the mesh.
Another way to remove a solder bridge is to heat
up the solder to make it melt and then suck it up with a
solder sucker. This is a small handheld tool that uses a
vacuum to pull the molten solder away from a copper
pad or other connection.
It is important to understand that the solder is not
melted by the soldering iron tip and then dripped onto
the items being soldered. The solder must be melted by
the heat of the items being soldered. Otherwise, you
may encounter another problem called a cold solder
joint. In this situation, the solder has cooled too quickly
and becomes brittle. The solder may actually crumble
when it is wiggled. A cold solder joint typically makes
a poor connection, as well. This may manifest itself as
an intermittent problem that shows up and goes away in
your circuit, especially when the circuit is moved. Unlike
the bright, shiny, smooth surface of a proper solder
connection, the cold solder joint looks flat and pitted. It is
not difficult to make a cold solder joint. Simply blowing on
the molten solder makes it cool quicker. It is best to let the
solder cool on its own.
Protect Your Components!
Sometimes the component whose leads are being
soldered is sensitive to heat. In order to protect it, a
heatsink is used. The heatsink connects to the lead being
soldered, gripping it tightly. If one is not available, an easy
substitute is to take a pair of needle-nose pliers and wrap
a rubber band around the handles. The rubber band will
try to keep the pliers closed. Then, the pliers are used to
grab the lead of the component being soldered. The
better the grip the pliers have on the component lead, the
more heat they will transfer away from it.
When you have finished using the soldering iron, it
should be unplugged and allowed to cool before it is put
away. While it is still hot, it is a good idea to clean the tip
a final time with the wet sponge.
If you have never soldered before, how do you get
started? A trip to RadioShack or some time spent in
an electronics magazine (such as Nuts & Volts) will
present you with an opportunity to buy a soldering iron
kit complete with sponge and solder. And again, you
also need something to solder. Buy an electronic
project kit. Start small with a simple circuit that only
has a few components, such as an LED flasher or a
music board with a single integrated circuit. Build up
your confidence by completing the simple circuit and
getting the satisfaction of seeing it work when you
turn it on. If it does not work, look for unsoldered
leads, solder bridges, or components inserted
incorrectly.
NV
Solder bridge.
66
February 2009
Cold solder joint.
Heatsink.
(shown clipped to body of component)