How to Solder
April 1955 Popular
soldering is almost as much of an art form as it is a technical
skill. Having been through numerous soldering classes in my career,
starting with electrical vocational courses in high school, then
again in USAF technical school, and other times while working as
a technician and engineer, I always exercise care in making solder
joints. Proper preparation - including both tinning of mating surfaces
and a means to prevent the joint members from moving during cool-down
- is of utmost importance for assuring a nice, smooth, shiny joint
with just the right amount of solder. Lead-free solders do not tend
to produce the level of shininess as do the good old 60-40 type
tin-lead solders, but you can still make a nice looking joint. This
might be more information than you want to know about me, but I
even strive for perfection in solder joints in copper pipes and
fittings used in plumbing work. Call me a masochist, eco-villain,
or worse, but I still use PbSn solder for plumbing joints just to
get the beautiful joints!
April 1955 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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How to Solder
Poorly soldered connections are often responsible for poorly functioning
and inoperative equipment. Since good soldering is actually easier
to do than poor soldering the amateur should do three things: he
should follow the basic rules of good soldering, he should learn
the difference between a poorly soldered joint and a good one, and
he should practice soldering different types of connections until
he acquires the "feel" of his iron.
Soldering "gun" and two types of irons, along with "accessory"
The ten rules for good
Select the right equipment for the job: Essential
soldering tools include a soldering "gun" or soldering iron and
stand, solder, paste flux, and a file.
Care should be taken
to select an iron suited to the work. Too large an iron may be hard
to handle and may deliver too much heat, burning the insulation.
Too small an iron, on the other hand, may not deliver enough heat
to the work, making it impossible to flow solder into the joint.
A 60 to 100 watt iron with a 1/4" to 3/8" pyramid tip is best for
most radio and electronic work. However, for work with hearing aids,
miniature radios, remote control equipment, and similar small items
using fine wire, a 25 to 50 watt iron or soldering "pencil" is preferred.
On the other hand, for work involving large wire and considerable
soldering to a chassis, a 150 to 250 watt iron may be required.
Soldering "guns," while more expensive than irons, are easier to
use, use less power since they consume power only when in actual
use, require virtually no warm-up time, have a small tip suitable
for radio wiring, and, generally, have small lamps which spotlight
the work. A 100 to 150 watt soldering gun is a good choice for electronic
Correct soldering technique. The iron is held against part
until hot enough to melt solder when applied to heated junction.
The three types of mechanical connections used in soldering.
(A) For permanent installations. (B) For work where some
changes may have to be made. (C) A "lap" joint for temporary
Correctly (right) and incorrectly (left) soldered connections.
The latter type can cause electrical and mechanical troubles.
Solder is available in many grades and in two types,
wire and bar. The most popular grades are 40-60, 50-50, and 60-40.
The first figure refers to the percentage of tin and the second
to the percentage of lead in the alloy. In general, the higher the
percentage of tin, the lower the required soldering temperature.
For radio and electronic work, 50-50 or 60-40 wire solder with a
rosin core is recommended. Never use acid core solder in electronic
Fluxes are used to remove the thin film of oxidized
metal that forms on the surface of the work as well as to prevent
additional oxidation when the metal is heated prior to soldering.
Although flux core solder is used for most wiring, a small can of
paste flux is handy to have around for tinning leads, tinning the
iron tip, and similar work. Use a non-corrosive flux.
fine-cut file should be available for removing pits and smoothing
the tips of soldering irons. The file should not be used unless
the copper tip of the iron is pitted and then only enough of the
metal should be filed away to leave a smooth, shiny surface.
Clean the metals to be soldered: All grease, dirt, corrosion, or
enamel must be removed from the surface of the metal prior to soldering.
Use steel wool, sandpaper, a file, a knife, wire brush, or any similar
tool to remove the dirt and grease.
For tight spots, an "extension" can be added to soldering
iron by means of copper bus bar.
Keep the soldering iron
tip clean and well tinned: If the tip of the iron is not clean,
the film of oxidation formed will act as insulation and prevent
the proper conduction of heat to the joint. To tin an iron, first
make sure the tip is free from corrosion and pits. If the tip is
badly pitted, it will have to be filed. Allow the iron to heat until
its tip is hot enough to melt solder then flow solder over the end
of the tip. In some cases it may be necessary to rub the tip against
a metal plate (such as the top of a tin can), applying a little
solder as this is done. Finally, wipe off excess solder with a heavy
cloth, leaving the tip bright and shiny.
Don't tin the entire
tip: When using the iron, occasionally check for proper tinning.
Try to keep a thin film of solder on the tip of the iron at all
the joint, not the solder: To solder a joint, hold the tip of the
iron against the joint until the joint is hot enough to melt the
solder - then apply the solder to the joint.
Don't try to
solder unless the iron is really hot: Make sure the iron is hot
enough to melt solder instantly when it is touched to the tip before
trying to solder a joint. Let the heat do the work. Apply only enough
pressure to the work so that good contact is made between the iron
tip and the joint. Then solder quickly.
Posted October 11, 2013