[Elecraft] Solder Question

[Rich Lentz]

From a Navy Training publication for electronic Technicians:

"Solder is a metal alloy used to join two or more metals with a metallic
bond. The bonding occurs when molten solder dissolves a small amount of =
the
metals and then cools to form a solid connection. The solder most =
commonly
used in electronic assemblies is an alloy of tin and lead. Tin-lead =
alloys
are identified by their percentage in the solder; the tin content is =
given
first. Solder marked 60/40 is an alloy of 60 percent tin and 40 percent
lead. The two most common alloys used in electronics are 60/40 and =
63/37.=20

The melting temperature of tin-lead solder varies depending on the
percentage of each metal. Lead melts at a temperature of 621 degrees
Fahrenheit, and tin melts at 450 degrees Fahrenheit. Combinations of the =
two
metals melt into a liquid at different temperatures. The 63/37 =
combination
melts into a liquid at 361 degrees Fahrenheit. At this temperature, the
alloy changes from a solid directly to a liquid with no plastic or
semiliquid state. An alloy with such a sharp changing point is called a
EUTECTIC ALLOY.=20

As the percentages of tin and lead are varied, the melting temperature
increases. Alloy of 60/40 melts at 370 degrees Fahrenheit, and alloy of
70/30 melts at approximately 380 degrees Fahrenheit. Alloys, other than
eutectic, go through a plastic or semiliquid state in their heating and
cooling stages. Solder joints that are disturbed (moved) during the =
plastic
state will result in damaged connections. For this reason, 63/37 solder =
is
the best alloy for electronic work. Solder with 60/40 alloy is also
acceptable, but it goes into a plastic state between 361 and 370 degrees
Fahrenheit. When soldering joints with 60/40 alloy, you must exercise
extreme care to prevent movement of the component during cooling. "


A search on the WEB  for the words eutectic and solder provides a wealth =
of
information on this topic.=20

Rich
KE0X