SURFACE MOUNT SOLDERING
1. Add flux to the pads (Figure A). This may not be
necessary for 1206s, but is helpful for 603s and
402s, where melting solder wire directly on the
connection will likely deposit too much. A lightly
tinned tip may provide all the solder necessary. As
a rule, if you’re melting solder wire directly onto a
connection, you don’t need additional flux, but if
you’re carrying solder to the joint with an iron, you do.
2. Add a small amount of solder to 1 of the 2 pads
3. Use tweezers to hold the 1206 in place while
touching the junction between chip and pad with
the iron. You should feel the chip drop into place
as the solder liquefies underneath (Figure C).
4. Solder the other side by holding the iron so it
touches the chip and board and adding a small
amount of solder (Figure D).
Install a QFP (Quad Flat Package)
QFPs are square IC packages with leads all around.
The distance between the leads, called the pitch, is
typically 0.5mm or 0.8mm, but some are 0.4mm.
1. Flux the pads (Figure E).
2. Align the QFP over its pads with tweezers or
dental picks (Figure F).
3. Add a small drop of solder to the tip of the iron.
This part is key: you want a small drop to hang off
the end (Figure G).
136 Make: Volume
4. Tack 1 corner by sliding the tinned tip up against
the toe of the lead (Figure H). The solder should
quickly wick under the lead. Check alignment and
tack an opposite corner. Sometimes I add more flux
on top of the leads after tacking.
5. Continue touching the toes of the leads with the
iron to complete the chip. You should be able to solder several leads with 1 load of solder on the tip. With
practice, you can slowly drag the tip over the feet and
“drag-solder” an entire row with 1 pass (Figure I).
6. Use the loupe to check for bridges and sufficient
solder (Figures J and K).
7. Remove any shorted or bridged connections by
touching the leads with a clean iron tip or applying
solder wick (Figure L).
Alternately, there’s the “flood and wick” method,
which involves flooding all the leads with solder
and then removing the bridges with wick. Surface
tension holds some solder under the leads even
after wicking. I hate to argue against something that
works, but folks in the industry don’t recommend
this technique because it can overheat the board or
component, and the wick might detach pads.
Install a PLCC (Plastic Leaded Chip Carrier)
PLCCs have legs that fold back under the package
rather than sticking outward. The steps are similar
to soldering a QFP: flux the pads (Figure M), align
the part, tack some corners, flux some more, and
solder. Keep the iron in contact long enough for the