CONSTRUCTION HINTS
_____This information had originally appeared in
the SM-2 planspec. Because so many newcomers said that it had
really helped them to succeed in their attempts to acquire new
skills, I opted to present it again in the RF-V series. It's just
some general tips that may help some to make the transition from
through-hole assembly into the smaller, more densely populated
constructions using SMT components. Once you get the hang of it,
it's very satisfying to be able to re-do the layouts into smaller
and smaller configurations.
_____If you're an old hand at SMD work, the
following suggestions will ring very true. If any of this is new
to you, don't fret! SMD work does require attention to detail,
but it is not all that arduous, and the rewards are big. So
accept this as a learning tool.
_____1.) Spacious work bench with
adequate lighting. You don't want things piled up on top of one
another. Each part should be in a separate container and spread
out so it can be immediately identified without having to dig for
them. When you handle these little creatures, they have an
uncanny ability to 'fly'. So you need a large work surface to
retrieve them, lest they fall into a sea of carpet or leap into
hyper-oblivion.
_____2.) Non-magnetic tweezers. Use
stainless steel or plastic forceps. Eyebrow tweezers or the like
have enough rententivity to cause the component contacts to
'cling'. It is exasperating to try placing the SMDs on the board
only to have them follow your tools around. Or you can use a
toothpick to hold them in place while soldering.
_____3.) Miniature bench vise or some
other small board holding device. Else you'll have to put a loop
of tape on the back of the board to secure it to the bench while
soldering on it. It's best to be able to reposition the board
easily for best angle of attack.
_____4.) Magnifying Lens is a must unless
you have bionic eyes. A five inch diameter lens with a three
diopter (13" focal length) and >1.75 power is a good
bench lens to have around, but in a pinch, a high power hand-held
magnifier will suffice. It's also 100 times less expensive.
Without the lens to increase your apparant field, you will
probably use too much solder, misalign some parts, and develop
eye strain.
_____5.) Low wattage soldering pencil or
temperature controlled iron that has a #7 ,i.e. a small long
conical tip. You have got to be able to maneuver the tip in
between some tight spots. Question: How often should you tin your
soldering iron? Answer: EVERY TIME YOU USE IT! When you solder
SMD components it is imperative that you transfer the necessary
heat to get the job done within the least amount of time as
possible. If the tip is not well primed, then an inefficient
surface area is not allowing enough heat flux to be transferred
to the pad and component contact. The end result is that while
the surfaces are slowly absorbing enough energy to cause the
rosin and solder to run, the SMD chip itself is 'internally
hemorrhaging' and rapidly on its way to becoming a charcoal
briquette. It's a good idea to use Sn63 solder instead of 60/40
because it is a true eutectic alloy, that is it melts and freezes
at 185 degrees Celsius. Also use .01 to .02 diameter solder for
the board work and use .03 to .06 diameter multicore rosin for
tinning your iron. If you do nothing else, follow the tips in
this step.
_____There are probably many other tidbits that
the old-timers would consider to be crucial advice, but
eventually you have to test the water on your own. The best
thought that I can leave you with is this: When you start to
become tired, stop working! Don't go on to make an irrevocable
mistake. Remember, "Tomorrow is another day!"