On 2007-12-05, bigorangebus wrote:

Soldering larger QFP type devices: ...

I would add that QFP devices (especially the 0.5mm pitch types) have the
most fragile leads of any package type I've worked with. You can easily
bend the leads if you jostle an open tray of QFPs. If you do, you have
to fix them all before soldering, because there's almost no room for
error and nothing to guide the pins on the board. It takes an xacto-
knife blade (the sharp edge!) to get in between the fine pitch leads and
straighten them.

Once the part is positioned and tacked, go over the pins with the flux
pen.

Gently! See above.

Small devices like 0602, 0805 components:

Tin one pad, then hold the component and reflow that end to tack the
part down. Then do the other side. Do the steps in batches (go around
and put a bit of solder on one pad (NOT BOTH) of lots of components,
then tack them, then finish them).

I've also seen a neat homemade tool for small SMT parts which looks like:

,---------------|
| |
O PART

It's an arm that rests to the side of the board, with a vertical pin
to hold down the parts (eg a sharp toothpick). A tiny finger holding
your smt part in place.

--
Ben Jackson AD7GD

http://www.ben.com/