BEAM Techniques is a BEAM
SMT assembly techniques
Building small stuff from smaller
When you're ready to build a circuit using SMT parts, there
are 4 different ways (that I'm aware of) to get your surface
mount components actually soldered to a PCB.
Mind you, I haven't done this (yet) myself, so here I'm just
passing along information from folks who actually have done
- Discrete pin soldering by hand
You'll need a needle tip on your soldering iron, SMT
solder (low melting point solder in a very fine
diameter), a water-soluble solder flux pen, a steady
hand, and some sort of magnifier (to see what you're
doing on such small things).
Start by laying down a thin layer of solder flux on the
pads. Place the chip on the pads (watch the alignment!)
and gently press it in place. The flux should have just
enough "stick" to it to hold the chip. Carefully solder
one pin on one corner, then verify the chip's alignment.
Now solder one pin on the opposite corner, then verify
If all is well, carefully solder each pin in order,
working your way around the device. Use the iron to heat
the pad, then flow the barest amount of solder from the
pad under the pin. Watch for solder bridges; if you get
any, use a very fine solder wick to remove the
One version of this is as follows: lay a piece of solder
across the ends of the pins (so it touches both the pins
and the pads) along one side of the chip. Touch the
solder with a hot iron at the end of the solder. It will
melt onto the pad and pin. Without moving the solder, do
the next pin, and the next, till the side is done. Each
time you touch your iron down, the end of the solder will
be perfectly placed for the next joint.
- "Painting" pins
Use a large tip (1/8th inch wide or more) soldering iron.
Stick the chip onto the layout using the flux technique
given above. Tack one lead in place at each of two
opposite corners, to hold the chip in position. Coat a
fair amount of solder onto the iron's tip then, in one
smooth stroke, paint all the leads on one edge by wiping
the iron's tip down the length of the chip. Repeat for
- Hot air stream -- reflow "pen"
Here, you'll need water-based solder paste, an iron or
hot-plate and frying pan, and some sort of gizmo that can
produce a thin stream of very hot air (you can spend
about $700 US on a commercial one, or see here
for a way to build one for about $20). For SO
components, put a dab of solder paste on each pad. For
TSSOP components, put a thin line of solder paste
across each row of pads. Put the chip on the pads and
push it down. Preheat the board with components on an
inverted (flat side up) clothes iron, or an old frying
pan on a hot-plate. Carefully "spray" the pads with the
hot air to melt the solder.
- Toaster oven
Here, you need water-based solder paste and a toaster
oven. Note that the oven needs to be "dedicated" to this
use; small bits of lead will (at least potentially) move
around while you're heating boards, so you won't want to
use this oven with food after using it for circuit
boards. For SO components, put a dab of solder
paste on each pad. For TSSOP components, put a
thin line of solder paste across each row of pads. Put
the chip on the pads and push it down gently. Put your
board into the oven, heat it up to melt the solder, then
turn off the oven and open the door. Wait for the solder
to cool and solidify before you take the board out of the
This is essentially an at-home version of commercial
"reflow" soldering. The Seattle Robotics Society has
details on this method (oven temperature profile,
pictures, etc.) here.
For more information...
You can learn how to build your own SMT reflow air
Another neat trick for getting surface mount
ICs lined up
correctly is here.
For another take on working with SMT parts, I
found "Steve"'s description
of making a solar
engine with them.