Assembly:
●Your work area should be reasonably clean and uncluttered. Good lighting is a must.
●Empty the packets containing the parts into small paper bowls. This will ensure that they do not get
lost. Some people like to do the assembly over a cookie sheet as the lip around the edge helps to keep
parts from going far. The metal sheet also provides some measure of static control, especially if you
ground it. A white sheet under your work area could help in finding a part which might get away from you.
●A very thin 0.015”) solder is supplied for soldering the surface mounted parts. Very little solder is
need for each connection. Ideally, you want a little convex fillet at the end of chip resistors and
capacitors. Try not to end up will a ball of solder at the end of the part.
●Do not use liquid solder flux. It simply makes a mess and is difficult to clean off the board and get out
from under parts. If not completely removed from the board, it can cause problems.
●Before placing a part, lightly tin one pad for where it will go. You can speed assembly by tining one pad
at all the locations for which a particular value of part will go. There is no need for a low wattage
soldering iron. It is best to have a hot tip which will let you get the job done quickly. You will need
a small tip on the iron, 1/32” to 1/16” chisel or round is best.
●Most of the surface mount parts come in part carriers. To remove the part s), hold the carrier close to
the work surface and carefully peel back the clear plastic covering the part. This can be done with the
tip of a sharp hobby knife such as a #11 Xacto blade or pointy tipped tweezers. Once you remove the
clear plastic strip, dump the part out of the carrier and onto your work surface.
●If you use tweezers to handle the parts, be very careful you don't grab onto them too tightly. These
little parts have a way of flying out from between the tips of the tweezers, never to be seen again.
Apparently, they go into the twilight zone, along with all the pens, small parts and hardware which
falls off the bench. They must go someplace since its never anywhere I can ever find them again!
●An alternative to using tweezers to handle the parts is to use a tooth pick or chop stick with the end
rubbed into a little bees wax. The bees wax makes the end sticky so the part will stick to it. For the
smaller IC's I grab them length wise with the tweezers.
●Tack the end of a part in its place by applying heat to the end of the part over the tined circuit board
pad, while applying a little pressure to make sure it lays flat to the board. Be sure to heat both the
pad and the end of the part. Generally, you will not have to add any additional solder to this
connection. Then solder the other end of the part. If you don't do this right away and go onto tacking
down some more parts, there is a good chance you will forget to go back and solder all the parts which
require it.
●It is nearly impossible not to make solder shorts between pins on the DDS chip, due to the close pin
spacing. Remove any shorts with solder wick.
Using solder paste:
Using solder paste is the ideal way to build the board. Small amounts of solder paste in an application syringe
can be bought for about $5.00 from Cash Olson over the internet. Also needed is a warming plate to preheat the
board to about 200 degrees and a low power heat gun. An “Embossing” heat gun is commonly used found at craft
stores), though a hair dryer on low setting might work. A soft air flow is required as to not to blow parts off
the board.
For chip caps and resistors, a very small dab of solder paste is put on the pads and then the part placed
over the pads. The parts will slide around very easily, so one must be careful not to nudge them. For IC's,
placing the IC down first, then putting a bead of paste along the leads looks to be a better method then putting
the paste on the pads first, then the IC.
The LED display should be hand soldered, along with all the through hole parts. Start with the side of the board
with the most parts first bottom in the case of the MTR).
Once all the parts have been placed, put the board on the warming plate and heat to about 200 degrees.
Then slowly heat the top of the board with the hot air gun. When the solder paste reaches its melting point, you
will see it liquefy and the parts snap into alignment to the pad. This is when the solder paste turns from a dull
gray to shinny. Be on the look out for “tomb stoning” which is when a chip cap or resistor will stand up on one
end. Once all the solder has reflowed, remove the power to the heating plate and let it cool down.
I have a youtube video showing how to solder SMT parts, both by hand and using solder paste.
http://youtu.be/Ah5HEjDTHUo You may want to watch some of the other suggested videos on SMT soldering which are
done a bit more professionally then mine.
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