_____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
_____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!"
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