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PICAXE PRIMER
It may seem odd that both
boards in the photo only have two
four-pin headers for insertion into
a breadboard, but for some reason
eight of the DS3231’s 16 pins do
not connect to anything.
After you have finished this
article and practiced a little SMD
soldering on your own, you may
also want to try your hand at
soldering SOIC devices. If so,
there are literally hundreds of
SOIC to DIP adapters available on
eBay. Also, I intend to discuss the
DS3231 in detail in a future
installment of the Primer, and I’ll
add a custom PCB to my site for
use with that particular article.
If you’re familiar with SOIC
chips, you know that the pin
spacing is 0.05 inches, which is
exactly half that of the DIP chips
we’re used to using. Of course,
there are many sizes of SMDs with
pins spaced much more closely
than 0.05”, but soldering those
devices generally requires special
techniques and/or fairly expensive
equipment. We won’t be discussing
those devices, but there’s a wealth
of information online; just search
for “surface-mount soldering
tutorial.”
If you do some online
searching, you will quickly learn
that many people use fairly
expensive equipment, including hot
air rework stations and even
surface-mount reflow soldering
ovens that can cost hundreds of
dollars. However, if we limit
ourselves to SOIC devices and the
larger sizes of passive devices
(resistors, capacitors, LEDs, etc.),
we really don’t need to spend
much at all to get started with
SMDs. The equipment listed here
is all that’s required.
■ FIGURE 2. Tweezers for SMD soldering.
• A soldering iron with a long,
thin tip. I use a Weller WESD- 51
temperature-controlled soldering
station with an ETS long conical tip,
but any soldering iron will work; it’s
the long thin tip that’s important.
• A spool of very thin solder.
Radio.Shack sells a small spool of
0.015 inch diameter solder (catalog
#64-035) that’s perfect for soldering
SMDs by hand. Larger spools of the
same diameter solder are also available
online.
• Desoldering braid. In the event
of an accidental solder bridge between
two pins, it’s helpful to have a roll of
desoldering braid (solder wick) to
remove that bridge. Again, RadioShack
sells a small spool (catalog #64-2090),
and solder wick is also readily available
online.
• Tweezers. Most SMDs are too
small to manipulate by hand or even
with needle-nose pliers, so tweezers
are a necessity. To get started, I would
suggest a pair of regular straight
tweezers and a pair of locking straight
tweezers. (Locking tweezers must be
squeezed to open their points, so they
are useful as temporary clamps to hold
a component in place as it’s being
soldered.)
Figure 3 shows the size
comparisons of the SMDs that
we’ll be discussing in this article.
The decimal rule in the photo is
graduated in tenths of an inch
(with 0.02” subdivisions). In order
■ FIGURE 3. SMD size comparisons.
June 2013 15