Parts Express Sound Solutions V1 - page 18

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18
Soldering is superior to using connectors
because it creates a “gas tight” seal at
the point of contact. Excluding oxygen,
moisture, and contaminants from the
point of contact prevents the possibility
of corrosion creating a resistive path to
current flow.
Modern solder used for electronics is most
commonly a mixture of 60/40 lead and tin,
melts at no less than about 360° F, and
has through its center a “rosin core”—
a substance known otherwise as flux. This
rosin flux melts and flows onto the metal
being soldered, removing oxidation from it.
In years past, flux was a separate product
that had to be applied prior to melting the
solder.
Solder intended for plumbing work or
other purposes should never be used
for electronics! Its flux is highly acidic
and will corrode leads and connections
very quickly. There are other electronic
“specialty” solders such as lead-free
or silver-bearing solder for critical
applications such as CMOS digital
integrated circuits. For the majority of
applications, standard solder is more
than adequate.
Soldering is not at all difficult to
do, but it does take a little practice
to get a consistent, reliable
solder joint every time. Don’t
think of solder as a “hot melt”
glue—it’s not intended to be
load bearing or structural. For a
reliable connection, the solder
joint should not support weight or
hold parts together. Once solder
is melted and applied, it transforms
from soft and flexible to hard and
somewhat brittle.
Allow your soldering iron enough time to
reach full temperature, usually about five
minutes. Keep the iron’s tip clean by using
a damp sponge or stranded brass pad.
Start by heating one of the conductors
to be soldered while holding solder in
contact with it. As the metal reaches the
melting point of the solder, the solder will
begin to melt into a bead or drop.
It’s important to heat the solder via the
conductor, not the soldering iron’s tip.
When the metal exceeds the solder
melting temperature, it will “flow” onto
the surface or
“wick” into the
strands of wire.
If it continues
to stand like a
bead of water,
the metal is not
yet hot enough
for a good
connection, or the surface is
contaminated in some way.
Once the solder has begun to flow, bring
the other part to be soldered into contact
with the melted solder and iron tip. The
melted solder will transfer heat quickly
as it contacts the surface of the metal.
Continue to apply heat until the solder
flows onto the second part and takes on
a shiny appearance. Remove the solder
and iron. If any portion of the solder joint
appears beaded or standing on top of the
metal, reheat until it flows properly.
When soldering on printed circuit boards
(PCB), take care not to overheat the
solder “pad” as it may delaminate from
the PCB. Do not push or pull on leads.
Never attempt to solder together a broken
trace on a PCB. The best repair is to use
hookup wire (22 gauge solid wire is good)
as a jumper around the break.
It is always a good idea to test a new
solder connection with a continuity
tester or volt-ohm meter before moving
on. A proper-looking solder joint may
not actually be good, and could be very
difficult to locate later on as an open
or intermittent in the circuit. Re-melting
the solder on the connection will usually
correct a “cold” solder joint. A pocket of
flux or a connection not heated enough is
usually the culprit.
Mark Parson is a Product Line Manager
at Parts Express
SOLDER LIKE A PRO!
Some helpful soldering tips—besides the one that’s on your iron
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By Mark Parson
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