2-24
SOLDERING
The following information will aid you in learning basic soldering skills. It should enable you to
solder wires to electrical connectors, splices, and terminal lugs that we have discussed earlier in the
chapter. Special skills and schooling are required for the soldering techniques used in printed circuit
boards and microminiature component repair.
SOLDERING PROCESS
Cleanliness is essential for efficient, effective soldering. Solder will not adhere to dirty, greasy, or
oxidized surfaces. Heated metals tend to oxidize rapidly. This is the reason the oxides, scale, and dirt
must be removed by chemical or mechanical means. Grease or oil films can be removed with a suitable
solvent. Connections to be soldered should be cleaned just prior to the actual soldering operation.
Items to be soldered should normally be "tinned" before making a mechanical connection. Tinning is
the coating of the material to be soldered with a light coat of solder. When the surface has been properly
cleaned, a thin, even coating of flux should be placed over the surface to be tinned. This will prevent
oxidation while the part is being heated to soldering temperature. Rosin-core solder is usually preferred in
electrical work. However, a separate rosin flux may be used instead. Separate rosin flux is frequently used
when wires in cable fabrication are tinned.
Q21.
Why must items to be soldered be cleaned just prior to the soldering process?
TINNING COPPER WIRE AND CABLE
Wires to be soldered to connectors should be stripped so that when the wire is placed in the barrel,
there will be a gap of approximately 1/32 inch between the end of the barrel and the end of the insulation.
This is done to prevent burning the insulation during the soldering process and to allow the wire to flex
easier at a stress point. Before copper wires are soldered to connectors, the ends exposed by stripping are
tinned to hold the strands solidly together. The tinning operation is satisfactory when the ends and sides
of the wire strands are fused together with a coat of solder. Do not tin wires that are to be crimped to
solderless terminals or splices.
Copper wires are usually tinned by dipping them into flux (view A of figure 2-25) and then into a
solder bath (pot) (view B of the figure). In the field, copper wires can be tinned with a soldering iron and
rosin-core solder. Tin the conductor for about half its exposed length. Tinning or solder on the wire above
the barrel causes the wire to be stiff at the point where flexing takes place. This will result in the wire
breaking.
