Good soldering skills are imperative to the proper
circuit. This is intended as a quick and handy guide to show people how
Tools and Materials
I really can't overstate how important a good soldering
you're using a cheap or underpowered soldering iron you'll end up with
a lot of unreliable cold solder joints, which will hold for a while but
fail when moisture causes corrosion inside the joint or shock/vibration
mechanically loosens it. I have loads of soldering irons, but I have
two favorites that I use for almost all of my projects. For most
projects I use a big Craftsman 100/140 watt dual heat soldering gun (Sears model no. 113.540450). This type of
iron heats up quickly and the gun shape makes it easy to handle. Most
importantly, it provides plenty of heat to melt pretty much any type of
solder. It's perfect for projects where you'll be using physical wires,
speakers, tube amps, connectors, and general point-to-point wiring. My
other favorite is a little 15 watt soldering pencil from Radio Shack (Cat #64-2051B). This
one is great for smaller conductors that might be burned away by too
much heat like the hair-thin wires inside tonearms and the thin copper
foil on PCBs. A small iron like this is essential when working with
surface mount components, especially small SOIC, SOP, and TSOP
Since solder doesn't just melt, but forms what is called
bond with the surface metal, it's important to choose a solder that's
compatible with the metal you're trying to bond. Common electric solder
is composed of 60% Sn and 40%
usually referred to as 60/40. This
type of solder is OK, but my personal favorite is 62% Sn, 36% Pb, 2% Ag.
Adding a noble metal like silver increases the electrical as well
as thermal conductivity, which seems to make the solder melt and flow
more evenly, especially over metals other than copper, and imparts some
corrosion resistance. Electronics work calls for fine solder with a
diameter of around 0.022" to 0.032". A good solder I use often is Radio
Shack #64-013 (62/36/2, rosin core, 0.022" dia), but if you're worried
about the lead, then Sears Craftsman
#980061 (96/4, flux
core, 0.032" dia) is a great lead-free substitute.
Flux "wets" the metal and helps the solder flow more
over the surface. Most solders these days use a flux core, usually
rosin. For large joints, or joints where a good quality connection is
extremely important you should consider using a brush-on flux as well.
Radio Shack #64-022 is a good choice. Crusty black stuff called dross
builds up on the tip of a soldering iron when it's hot, so you should
have something to clean it off. Radio Shack sells a compound
specifically for this (Cat #64-020) that works very well, but it's kind
of pricey. If you don't want to spend the money, a dampened cellulose
sponge or paper towel will do in a pinch.
You will invariably screw up some time, and for that you
need de-soldering equipment. The only thing you'll really need for this
is a little solder sucker like Radio Shack #64-2086. Don't bother with
fancy spring operated pumps and desoldering irons, that's really not
necessary. If you need to de-solder something really small, like an
integrated circuit, you may also want to consider a de-soldering braid
(Radio Shack Cat #64-2090).
You should invest in a good set of small pliers.
minimum you should have one pair of needle nose pliers and one wire
cutter. Sears sells sets of these, with varying lengths of needle nose
pliers, wire cutters, and a wire nipper for around $20. My favorite is
the little spring loaded Craftsman Professional deal pictured at right,
which has a built in wire cutter.
For general wiring, I suggest solid core "hookup wire".
Shack sells 100' spools in a variety of colors. Stranded wire is harder
to use, but comes in handy for applications where vibration or movement
over time might cause solid wire to snap. The best size for general
elecronics use is around 22 AWG, for both solid and stranded wire. When
a smaller wire is needed, you can remove the conductors from phone or
The tip of the iron should be "tinned" by wetting it
small amount of flux and solder, or the tinning compountd mentioned
earlier. Always keep a small amount of solder on the tip of the iron,
but wipe it off whenever too much of it builds up. "Tin" any stranded
conductors by coating them with a small amount of solder to keep the
strands in place.
Make a good physical connection. For wires, twist them together.
For components with leads, use small needle-nose pliers to wrap the
leads around what your connecting it to. For things with solder lugs,
thread the wire through the hole in the lug and wrap it around the lug
at least once. When mounting components to PCBs, bend the leads outward.
Heat up the joint for a few seconds by holding the soldering iron in
the same spot, don't move it around, just let the metal conduct the
heat. Try to touch both wires with the tip of the iron at the same
time. For small surface mount ICs, solder pin 1 first, then solder the
pin in the opposite corner, then solder each pin individually.
Feed the solder in where the tip of the iron meets the conductor. The
solder will melt and help conduct heat into the joint, allowing more
solder to flow. Be careful not to heat components like capacitors and
ICs any longer than necessary. Use the right size iron: too small and
you'll be heating the joint for an extended period of time, too large
and you'll overheat the component - too much in either direction and
you're likely to damage something. Things like tube sockets and wires
are unlikely to be damaged by any amount of heat.
For larger joints, move the iron slowly down the joint while continuing
to feed in solder at a steady rate. Only use enough solder to cover all
of the conductors, you don't want big blobs hanging everywhere. Don't
move any of the wires while the solder cools.
Once you're done, inspect the joint. Make sure there are no solder
"bridges" between other nearby conductors, which happens quite easily
with surface mount components. Use a solder sucker and/or de-soldering
braid to remove excess solder if this happens.
The joint should be smooth and shiny, and the flow of solder should be
evenly and seamlessly flowed around both conductors. If it's dull,
you've moved it while it was cooling, and should re-melt it to ensure a
If it's formed a rounded bubble, you've not applied enough heat to melt
the solder over both wires and should re-melt it to flow the solder
evenly onto both conductors.
This isn't as hard as it sounds. Heat the solder joint
it melts, then use a solder sucker, which should remove most of the
solder, leaving only a thin plating still on the part. You can then use
a small pair of needle nose pliers to unwrap the lead. When removing
through-hole components from PCBs, you may need to continue heating the
part as you pull the leads out. Removing surface mount components is a
little trickier, and there's no good way to do it without destroying
the part you're removing. Use needle nose wire cutters to snip off each
lead, being careful not to tear the foil off of the PCB, and remove the
IC. Use a de-soldering braid to remove the solder and pin remnants
still stuck to the board.