The Art and Science of Soldering
Very Little has been written in the general audiophile
press on the subject of soldering. This is unfortunate,
as many of us are required to perform the task from time
to time, and should know how it is done. Like anything else,
there is a right way and a wrong way to go about it. Since
a poor solder joint can do much to undermine the quality
of the signal attempting to pass through it, it is important
to insure quality whenever we tackle a soldering job. I
hope that this brief introduction will give you the information
you need to make minor repairs or modifications. Or, in
the case of the more ambitious hobbyist, become proficient
at making ultra-high quality solder connections for more
The object in soldering is to join two metal conductors
by flowing molten metal across their surfaces. Sounds easier
than it really is. In a proper joint, the solder molecules
actually combine with those in the metals being joined.
The term applied to this action is wetting.
Proper technique requires proper tools, and this begins
with a good quality iron of the right temperature for
the job. Fixed temperature irons come in various sizes
or wattage's and cost between $15.00 and $50.00, depending
on quality. Fixed wattage irons are the most common types,
although variable heat devices are the choice of most professionals.
These units allow the user to select a variety of temperatures,
one that will be correct for the task at hand.
The next most important element of the equation is the
solder itself. For audiophile quality work this will normally
be a solder containing a small percentage of silver. Most
all solders contain a small inner core of flux. Flux helps
the solder adhere to the work by removing oxides from the
surfaces of the metals. For electronics application, only
resin core solder should be used.
To begin, be sure that the metal surfaces of the work are
clean, free of oils and debris that could reduce the ability
of the solder to adhere. Also be certain that the tip of
the soldering iron is clean and properly tinned. Place the
tip of the iron at the junction of the two pieces being
joined, this will insure that even heat is applied to both.
After the metal has been sufficiently heated, apply the
solder at the junction of the two pieces. Do not apply solder
to the tip of the iron itself. The solder will flow to the
hottest part of the connection, the point of iron contact.
Withdraw the iron as soon as possible and let the joint
cool. It is important to heat the connection for as little
time as possible to avoid undue stress to the conductor
and/or insulation or dielectric. Avoid disturbing the completed
joint during cool-down. Finally, de-flux the area
with an appropriate solution to remove unwanted traces of
the resin flux. Your labor should have resulted in a bright,
shiny, smooth surface.
A dull, rough or grainy surface texture is indicative of
a solder job gone wrong, a cold solder joint has
been produced, and is unacceptable. Either too little heat
was used or too rapid cooling has occurred. Reheat the joint
to see if you can restore the connection. If that fails,
remove the old solder and start over.
Certain more specialized jobs, such as soldering components
on a printed circuit (PC) board, require additional knowledge
and care. The component parts themselves (especially sensitive
transistors and integrated circuits) can easily be damaged
with excessive heat. When installing these sensitive parts,
one must be sure that an iron of the proper heat (wattage)
has been selected. Small heat sinks designed especially
for the job (or alligator clips) may be attached to the
parts themselves to help dissipate damaging heat.
If you need to repair a poor solder joint, or replace a
component soldered to a PC board, you must first remove
the old solder. This may be accomplished using a variety
of methods. Solder removal wick or braid is the most common.
This product consists of resin coated copper that attracts
molten solder. After the old joint has been reheated, the
wick is applied to draw the solder off the connection. This
procedure requires a bit of practice to master. Another
common means of removing solder employs a tool affectionately
known as the "solder-sucker." This little device
consists of a spring loaded plunger inside a tube. Pressure
on the trigger releases the plunger, creating a suction
or vacuum at the tip. Simply heat the connection, melt the
solder, put your "solder-sucker" in place and
viola, clean surface! Concerning costs, a roll of solder
wick sells for a few Dollars, the vacuum tool commonly sells
for about ten.
It takes practice to produce a good solder joint. I recommend
that you spend some time honing your skills before attempting
more important work.
Dr. A.J. van den Hul has put together what he calls "The
Commandments for Optimal Soldering. " While these recommendations
were originally targeted for implementation with van den
Hul products, the general guidelines put forth aptly apply
is most cases. Although some of the suggestions are a bit
esoteric for the average hobbyist, much can be learned from
the basic techniques. It may also help you to understand
some of the reasons behind the high termination costs of
some of the more exotic, difficult to work interconnects
and speaker cables. What follows is an amended version of
1) Properly prepare the surfaces for soldering
by thoroughly cleaning them with a non-residue product such
as Freon TF. It is especially important that any oils or
grease be removed from the surfaces to insure proper solder
2) Stripping of the insulation or jacket, should
be done with a thermal stripper or very exact mechanical
unit. It is very important to prevent the all to common
surface damage inflicted by careless stripping. Significant
sonic degradation may result from this type of conductor
3) Soldering should be done with a silver-saturated
solder or soldering device with a silver tip. The silver
will improve the conductivity of the connection and decrease
the tendency to oxidize over time.
4) The temperature of the iron should be around
300'C (approximately 550° F). This range may vary depending
on what you are soldering. Lower temperatures may be recommended
for more delicate operations involving IC's and transistors.
Our note: It may be difficult to find a temperature specification
for some irons. More common is a wattage rating. As a general
recommendation, I find that a 25 to 40 watt iron is ideal
for most audio work.
5) A light flow of N2 or C02 during soldering is
strongly recommended. The gas is to be blown over the joint
being soldered through a small orifice. Our note: Obviously
this step is not practical for the average audiophile, but
is another reason I always recommend factory termination
of the more exotic cables.
6) The use of a heat-sink during the soldering process
is highly recommended. This will draw heat away from delicate
parts or conductors. Our note: According to Mr. van den
Hul, the signal transfer quality of the cable is preserved
if excessive heat build-up in the conductor material is
7) De-flux the joint with a suitable solvent to
remove all traces of resin. A cloth or small brush may be
used to help remove stubborn resin deposits. The completed
joint should exhibit a bright, clean appearance. A dull
or uneven surface indicates a cold solder joint and will
not be conducive to optimum signal transfer.
8) Cover the completed joint with a flexible coating
of enamel (Our note: fingernail polish works well) to prevent
airborne contamination or oxidation. Our note: While
not necessary on most connections, this procedure is vitally
important when terminating some cables to prevent air migration
into the jacket opening. In these situations it is important
to close this entry-way by sealing the jacket opening at
the point where the conductor exits.
9) Conductive parts of the connector should be treated
with an oxidation inhibitor. Silicone oil with a viscosity
of between 150 and 200, diluted 1 to 25 with acetone, may
also be used.
CARE AND FEEDING OF THE SOLDERING DEVICE
1) Always keep the tip properly tinned. A well
tinned tip should exhibit a bright surface, with no dull
or discolored areas.
2) To properly tin the tip, proceed as follows:
A. Heat the iron to operating temperature.
B. Apply a liberal amount of solder to the
tip and let stand for one minute.
C. Apply more solder to the tip, allow to
stand for two minutes then wipe lightly on a dampened
sponge. Wipe off only the excess and try to wipe melted
solder onto non-tinned areas.
D. Always add additional solder to the tip
before returning the iron to its rest.
3) For maximum tip life, apply solder to the heated
joint, not to the tip itself. Repeated application of solder
directly to the tip will significantly reduce tip life expectancy.
I hope that the information we have provided here will
further your understanding of the soldering process. Good
luck, and don't burn your fingers!