Lead free
solder is being required for the electronics industry, but not yet for the
stained glass industry. However, some
people are beginning to use lead-free solders for other reasons. In general, it is reported that it is harder to
get smooth beads. Some reasons may
relate to the physical properties of the material being used.
Lead free
solder solidifies at a higher temperature than the common tin/lead solder
compositions although the common lead free solders melt at slightly lower
temperatures. For comparison purposes
characteristics of some common lead free solders are given with the common
tin/lead solders.
Sn =
Tin, Ag = Silver, Cu = Copper
Pb = Lead
Solidus =
solidification temperature. Liquidus =
Melting temperature
96%Sn, 4%Ag
which has a Solidus of 221C and Liquidus of 229C
95%Sn, 5%Ag
which has a Solidus of 221C and Liquidus of 254C
Slightly less
commons is
96.5%Sn,
3.5%Ag which has a Solidus of 221C and Liquidus of 221C, but has poor wetting
properties except on stainless steel.
Other solders
are available up to 7% silver, but these are increasingly expensive and have
much higher liquidus points.
A truly
eutectic lead free solder can
be produced with 95.6%Sn, 3.5%Ag, and 0.9Cu, which has a Solidus and Liquidus
temperature of 217C
For
comparison:
63%Sn, 37%Pb
has a has a Solidus of 183C and Liquidus of 183C
60%Sn, 40%Pb
has a has a Solidus of 183C and Liquidus of 188C
50%Sn, 50%Pb
has a has a Solidus of 183C and Liquidus of 212C
40%Sn, 60%Pb
has a has a Solidus of 183C and Liquidus of 238C
The solidus
temperature of lead free solders is almost 40C above the tin/lead solders. This may be the reason people find the need
to turn up the heat of their soldering iron when using lead free solders. The difference in the Liquidus and Solidus
points for 4%Ag is very similar to that for 60%Sn/40%Pb. So with enough heat should behave similarly.
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