TM 9-243
SOLDERING
Soldering that will meet Air Force requirements of no
more than 1 error out of each 500,000 soldered
connections requires skilled application and integrity.
The success of IBM's reliability factor may depend on a
satisfactory soldered connection. Consider this down-
time comparison. The time spent to find a defective
tube, resistor, transformer, or other component part
averages half an hour. Isolating a poor soldered
connection can take eight hours or longer.
Solder is one of the oldest and most useful of alloys.
Because of the ease with which it has been used, few
people have bothered to acquire the basic, but
necessary, background for good soldering techniques.
Soft solder is a fusible alloy mainly composed of tin and
lead.. This alloy makes it possible to join two or more
metals at temperatures well below their melting point.
The solder-to metal attachment is formed by an inter
metallic
compound
phase
which
takes
place
at
comparatively low temperatures . The solvent action of
hot solder on copper or steel resembles the action of a
few drops of water on salt. The solder dissolves
microscopic particles of the copper or steel, forming a
chemical attachment instead of physical adhesion.
Therefore, heating the soft flexible solder during the
soldering act causes a chemical change to take place
which results in a hard metal alloy. Thus when two or
more pieces of metal are soldered together, a joint is
formed which acts like one continuous piece of metal.
(This is not true of a pure physical connection, such as a
bolt or spring, because a layer of oxides always remains
between he surfaces.) In addition, the solder alloy
withstands the stress and strain of the temperature
changes without rupture of the joint.
The primary purpose of a soldered joint is to achieve an
airtight metallic connection by means of a film of solder
alloy, varying in thickness from 0.002 to 0.004 inch
between the metal parts; i.e., wire and terminal. When
such a connection has been made, It is a waste of time
and material to add solder just to improve its
appearance;
the
electrical
conductivity
has
been
established with the original bond and will be unaffected
by the addition of solder.
SOLDERING TOOLS
Five different soldering irons with interchangeable tips,
transformers (6.3 VAC), heat shunts, soldering iron
holders, soldering aids, and electric solder pot comprise
the soldering tools stocked at field locations. The
6.3VAC soldering irons are to be used with the
transformer which has four wattage tips: 26, 29, and 35.
Always use the lowest wattage necessary for the work.
In most cases 26 watts will be sufficient for electrical
soldering.
53-8 Change 3
