There are many different types of solder being used
by industry. Solders are available in various forms that
include bars, wires, ingots, and powders. Wire solders
are available with or without a flux core. Because of the
many types of solder available, this chapter only covers
the solders most commonly used by Steelworkers.
TIN-LEAD SOLDER. The largest portion of all
solders in use is solders of the tin-lead alloy group. They
have good corrosion resistance and can be used for
joining most metals. Their compatibility with soldering
processes, cleaning, and most types of flux is excellent.
In describing solders, it is the custom of industry to state
the tin content first; for example, a 40/60 solder means
to have 40% tin and 60% lead.
Tin-lead alloy melting characteristics depend upon
the ratio of tin to lead. The higher the tin content, the
lower the melting temperature. Tin also increases the
wetting ability and lowers the cracking potential of the
The behavior of tin-lead solder is shown by the
diagram in figure 6-8. This diagram shows that 100%
lead melts at 621°F and 100% tin melts at 450°F. Solders
that contain 19.5% to 97.5% tin remain a solid until they
exceed 360°F. The eutectic composition for tin-lead
solder is about 63% tin and 37% lead. (Eutectic means
the point in an alloy system that all the parts melt at the
same temperature.) A 63/37 solder becomes completely
liquid at 361°F. Other compositions do not. Instead, they
remain in the pasty stage until the temperature increases
to the melting point of the other alloy. For instance,
50/50 solder has a solid temperature of 361°F and a
liquid temperature range of 417°F. The pasty tempera-
ture range is 56°Fthe difference between the solid and
Solders with lower tin content are less expensive
and primarily used for sheet metal products and other
high-volume solder requirements. High tin solders are
extensively used in electrical work. Solders with 60%
tin or more are called fine solders and are used in
instrument soldering where temperatures are critical.
TIN-ANTIMONY-LEAD SOLDER. Antimony
is added to a tin-lead solder as a substitute for some of
the tin. The antimony, up to 6%, increases the strength
and mechanical properties of the solder. A word of
caution, solders having a high antimony content should
not be used on aluminum, zinc, or zinc-coated materials.
They form an intermetallic compound of zinc and anti-
mony that causes the solder to become very brittle.
Figure 6-8.Tin-lead alloy constitutional diagram.
TIN-ZINC SOLDER. Several tin-zinc solders
have come into use for the joining of aluminum alloys.
The 91/9 and 60/40 tin-zinc solders are for higher tem-
perature ranges (above 300°F), and the 80/20 and 70/30
tin-zinc alloys are normally used as precoating solders.
LEAD-SILVER SOLDER. Lead-silver solders
are useful where strength at moderately high tempera-
tures is required. The reason lead by itself cannot be used
is that it does not normally wet steel, cast iron, or copper
and its alloys. Adding silver to lead results in alloys that
more readily wet steel and copper. Flow characteristics
for straight lead-silver solders are rather poor, and these
solders are susceptible to humidity and corrosion during
storage. The wetting and flow characteristics can be
enhanced as well as an increased resistance to corrosion
by introducing a tin content of 1%.
Lead-silver solders require higher soldering tem-
peratures and special fluxing techniques. The use of a
zinc-chloride base flux or uncoated metals is recom-
mended, because rosin fluxes decompose rapidly at high
TIN-ANTIMONY SOLDER. Tin-antimony
solders are used for refrigeration work or for joining
copper to cast-iron joints. The most common one is the
TIN-SILVER SOLDER. Tin-silver solder (96/4)
is used for food or beverage containers that must be
cadmium and lead-free. It also can be used as a replace-
ment for tin-antimony solder (95/5) for refrigeration