12 ELECRAFT
Integrated Circuits and ESD
The K2 transceiver uses integrated circuits and transistors that can
be damaged by electrostatic discharge (ESD). Problems caused by
ESD can often be difficult to troubleshoot because components may
only be degraded, at first, rather than fail completely.
To avoid such problems, simply touch an unpainted, grounded
metal surface before handling any components, and occasionally as
you build. We also recommend that you take the following anti-
static precautions (in order of importance):
Leave ESD-sensitive parts in their anti-static packaging until
you install them
Ground yourself using a wrist strap with a series 1 megohm
resistor (do NOT ground yourself directly, as this poses a shock
hazard)
Make sure your soldering iron has a grounded tip
Use an anti-static mat on your work bench
IC Sockets
Sockets are used for only the largest ICs. You should not use
sockets for the other ICs because they tend to be unreliable and can
cause problems due to added lead length. Since sockets are not used
in most cases, you must double-check the part number and
orientation of each IC before soldering.
Soldering, Desoldering, and Plated-Through Holes
CAUTION: Solder contains lead, and its residue can be
toxic. Always wash your hands after handling solder.
The printed circuit boards used in the K2 have circuitry on both
sides ("double-sided"). Boards of this type require plated-through
holes to complete electrical connections between the two sides.
When you solder components on these boards, the solder fills the
plated holes, making excellent contact. This means that you do not
need to leave a large "fillet" or build-up of solder on top of the pads
themselves. A small amount of solder will do for all connections.
Unfortunately, removing components from double-sided PC boards
can be difficult, since you must get all of the solder back out of the
hole before a lead can be removed. To do this, you'll need solder
wick and a vacuum desoldering tool (see techniques below).
The best strategy for avoiding de-soldering is to place all
components properly the first time. Double-check values and
orientations, and avoid damaging parts via ESD.
When removing components:
Don't pull a lead or pin out of a hole unless the solder has been
removed, or you are applying heat. Otherwise, you can literally
pull out the plating on the plated-through hole.
Limit soldering iron contact to a few seconds at a time.
Use small-size solder-wick, about 0.1" or 2.5 mm wide. Use the
wick on both the top and bottom pads when possible. This
helps get all of the solder out of the hole.
Buy and learn how to use a large hand-operated vacuum
desoldering tool, such as the "Soldapullt," model DS017LS.
Small solder suckers are not effective.
With ICs and connectors, clip all of the pins at the body first,
then remove all of the pins slowly, one at a time. You may
damage pads and traces by trying to remove a component
intact, possibly leaving a PC board very difficult to repair.
Invest in a PC board vice with a heavy base if possible. This
makes parts removal easier because it frees up both hands.
If in doubt about a particular repair, ask for advice from
Elecraft or from a someone else with PCB repair experience.
Our e-mail reflector is also an excellent source for help.
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