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Solder Selection
The selection of a specific solder is
made easier by understanding the melting characteristics
of metals and alloys. Pure metals transform from solid to
liquid at one temperature. Alloys melt over a temperature
range. Solders are selected to:
- provide good flow
- penetration and wettability
- desired joint strength.
Because solders have low strength compared to the metals
that are being soldered, the joint should be designed so
as not to depend on the strength of the solder.
The solderability of the base materials must also be
considered. The selection of flux and surface preparation
will be affected by the solderability of the base materials
to be joined.
Solders generally have melting points below 840°F (450°C).
Tin-lead alloys are the most widely used solder filler
metals, except for potable water systems, as they bond
with most common metals-such as copper, brass, steel,
iron or nickel. Most commercial fluxes, cleaning methods
and soldering processes can be used with tin-lead solders.
Torch soldering & dipping are widely used.
In describing tin-lead solders, it is customary to identify
the tin content first; i.e., 40/60 solder is 40% tin and
60% lead. The higher the tin content, the better the joint.
Tensile strength of tin or lead is approximately 2000 pounds
per square inch; when alloyed, the strength of the two
metals increases. In general, the strength of the joint
is somewhat higher than the strength of the solder.
Quick Tips...
“Wiping solders” usually contain between 30-40% tin. The
combination of good plasticity and moderate melting range
is ideal for wiping solders.
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