Soldering
Techniques
Soldering
- how it works
Soldering
is a well known and widely used process where two or more metal items
are joined together using a fusible alloy with a melting temperature
that is lower than their own. The most commonly used solder is a
fusible alloy consisting essentially of a tin and lead mixture.
The
solder actually dissolves a small amount of the metal’s surface, at
a temperature that is well below its melting point and joins with it.
It is this solvent action of the solder alloy that causes it to fuse
with and attach to the surface of the metal items being joined.
The
solvent action that takes place, between the solder and the metal,
makes the joint chemical (not just physical) in nature and causes the
properties of the joint to differ from the original solder’s
properties and from those of the surface of the metal items being
joined. When metal parts are joined by solder, a metallic continuity
is established as a result of the interfaces where the solder is
bonded to the metallic surfaces.
Courtesy
of American
Beauty Tools
Soldering
vs. Welding
The
metal joining process that is generally referred to as soldering (or
soft soldering) requires temperatures between 183 to 445°C. The
joining of metals at temperatures above 445°C (and below the melting
point of the metals being joined) is more commonly referred to as
brazing (or hard soldering). The actual melting and fusing of the
metal items that are being joined together is considered welding.
There are, of course overlapping situations that may occur when
classifying a process.
The
actual joining characteristics that take place are physically
different in each of these processes. Soft solders attach to metals
by what is referred to as a solvent action that takes place at
relatively low temperatures. Hard solders, or brazing alloys contain
metals that require higher temperatures to cause the solvent action
to take place and fuse the alloy with the metal being joined. Because
welding involves actually melting and fusing the surface of the
metals that are being joined together, a filler, or fusible material
is not always used.
Courtesy
of American
Beauty Tools
Creating
a Quality Solder Joint
Soldering
is the process that uses solder (a metal alloy usually consisting of
tin mixed with other metals) for the metallurgical joining of metal
components to form an electrical, mechanical or hermetically sealed
bond at temperatures (less than 449°C) that are well below the
melting temperature of the individual components that are being
joined. The soldering equipment used to create the required heat and
other materials (solder, fluxes, heat sinks, fixtures, etc.) should
always be properly matched to the intended soldering application. The
equipment and materials used may vary, but the basic soldering
techniques that are required will usually remain the same.
One
of the most important rules to remember about soldering is "keep
it clean". This includes, not only the items being soldered, but
also the materials used. Choose quality solders and fluxes without
unnecessary impurities. Surface oxidation, contaminants and other
impurities are some of the most common reasons for poor quality
solder joints. The use of fluxes does not eliminate the need for
pre-cleaning the surfaces you are joining, especially if heavy
oxidation or large amounts of grease, oil or dirt are present. The
stages of soldering are:
Clean:
Thoroughly clean all surfaces to be joined, removing any dirt,
grease, oil, oxidation, paint, coatings or other impurities that may
exist before attempting to solder. Proper wetting can only occur when
the intended solder joint area has been properly cleaned. Soldering
should be performed as soon as possible after cleaning to eliminate
the possibility of re oxidation or contamination of the items being
soldered. [So leaving pieces fluxed overnight is not good practice.
Flux only the area that can be soldered in the next few minutes.]
Flux:
Apply flux sparingly to each of the intended joint surfaces. Flux is
primarily used for the removal of light oxidation and to protect
against re-oxidation during the actual soldering process. Make sure
you have the right flux for the application being performed.
Heat:
Apply heat directly to the intended joint area. The correct
application of heat is important and should be consistent with the
operating requirements determined by the type of equipment being
used. Fast and accurate heating will minimize the risk of thermal
damage.
Solder:
Add solder to the heated surfaces you are joining (do not apply
solder directly to the tip, or other heat source being used). The
solder should flow uniformly over all of the surfaces that are being
connected. Stop feeding solder as soon as you have applied an
adequate amount and then remove the heat source. The amount of solder
is important because too much will create unnecessary waste, while
too little can affect the mechanical strength and conductivity of the
finished solder joint.
Cool:
Allow the finished solder joint to remain undisturbed until it has
completely cooled. You should never attempt to speed up the
cooling process by blowing on the solder joint. Even minor
vibrations or disturbances during cooling, can cause micro fractures
or other types of damage that may severely weaken the solder joint.
Inspect:
Check all finished joints for proper wetting, the right amount of
solder, a good physical appearance, and the required mechanical
strength.
Skills
A
quality solder joint is not achieved solely by the equipment and
techniques being used, but also by the operator being trained to use
them properly. An operator should know how the physical appearance of
a finished solder joint helps to determine possible flaws that may
exist.
A
quality solder joint appears bright, shiny and smooth with all
components appearing well soldered. The surface of a finished joint
should never look rough, grainy, dull, or flaky (these are signs of
what is commonly referred to as a cold solder joint). Problems with
proper wetting (solder balling up and not adhering to the components
surface) are sometimes associated with too much heat, but are more
often related to cleanliness issues.
Courtesy
of American
Beauty Tools
Exhausting
Soldering Fumes
Making
a fan
Exhausting
fumes while soldering is a safety issue of some importance. If you
happen to have an outdoor screened-in studio a simple fix can be had
with a computer fan You can scavenge such a fan from an older used
computer ready for disposal. Simply cut four timbers 50mm square or
25mm x 100mm to fit around it as a box. Attach a long electrical cord
to it with an approved plug;. Attach a screen to both sides. Plug in.
An additional feature is to attach an activated carbon filter (as
used for cooker hoods) to the front of the fan. This removes
particles and some fumes.
Positioning
Always
set it to draw fumes away you, generally pointing it so that it is
blowing the fumes in the same direction as the larger air flow in the
studio. In general a very large fan doesn't always do the job alone,
since the fumes always seem to rise up and find your nose. However,
with the additional tiny computer fan sitting right next to where you
are currently soldering, the fumes just move away.
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