Mitsubishi WD-52627 Training Manual page 34

Also, Lead-free solder does not "wet" as well as leaded
solder. That means it has trouble adhering to both the
soldering iron tip and the surface being soldered. To
counteract this, the flux used is more corrosive. Lead-
free solder also does not change from solid to liquid or
back again all at once. It passes through a soft state.
So, the melting process actually occurs through a range
of temperatures.
This makes a significant impact when repairing PCBs
using Pb-free solder. Problems that can be encoun-
tered working with Pb-free solder are:
• Excessive heat can cause the PCB to warp,
detaching surface mount components.
• Excessive heat may cause thermal damage to
components.
• Excessive heat can cause plastics such as
connectors, relays, LEDs, electrolytic capaci-
tors, etc. to melt or warp.
• Higher temperatures can cause surface oxida-
tion resulting in poor solder spread-ability and
wet-ability.
• The flux is more corrosive.
• The time required for a good solder connection
may be longer.
• Poor wet-ability can cause solder balls.
• Higher temperatures can cause flux spattering.
• Soldering iron tip life is shortened.
• Duller finish solder joint can appear to be a
"cold" solder joint.
Pb-free Hand Soldering
Hand soldering with lead-free solder doesn't necessar-
ily require higher soldering temperatures. The melting
time will be slightly slower than with leaded solder, re-
quiring an increase in contact time. The solder joint will
also look different. It will have a dull finish that is similar
in appearance to a "cold" solder connection when using
leaded solder.
To help eliminate problems working with lead free sol-
der, consider the following points.
Temperature... Use the same soldering temperature
as you would with tin-lead solder, about 700 F. If hot-
ter, you may be making it more difficult to solder. The
higher temperature causes oxidation to form faster, mak-
ing wetting even more difficult. Excessive temperatures
can also lengthen the cooling time, allowing micro-cracks
to form within the joint.
Thermal Recovery... Use a soldering iron with good
thermal recovery. When the iron is first applied to a
cool joint, the heat transfer causes the tip temperature
to drop. A higher powered iron will bring the tip back
up to the proper temperature faster. Using a shorter tip
will also improve thermal recovery.
Thermal Conduction... Use the widest tip possible in
relation to the joint being soldered. This will allow the
heat to conduct to the joint better. Also keep the tip
wetted for better heat transfer.
Tip Cleanliness... Important! Keep the soldering
iron tip clean at all times using a damp sponge. Re-tin
the tip before returning the iron to its stand. To extend
the tip life, do not leave the iron on when it is not being
used for longer periods of time.
De-soldering... For the same reasons as soldering,
increasing the temperature for de-soldering is not desir-
able. However, if a vacuum de-soldering tool is used,
the solder must remain molten from the tip, all the way
to the entrance to the filter. If the solder hardens along
the way, it can clog the tool.
Solder
When performing repairs, it is necessary to use solder
as that is compatable with that used in the original manu-
facture. Leaded solder cannot be used when soldering
PCBs manufactured with Pb-free solder. And, Pb-free
solder cannot be used on PCBs manufactured using
leaded solder.
The Mitsubishi standard for service requires the use of
Tin-Silver-Copper ( Sn-96.5, Ag-3.0, Cu-0.5) solder.
It can be obtained through the Parts Department.
Order part number: PB FREE SOLDER
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