Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

In theory, you should be able to do 0.5mm pitch QFN with TT - 0.25mm is
about 10 mil, which is "in range" for TT, assuming your process is
accurate enough. You'll probably want to use 1/2 oz copper though.

What I've found is that you need to extend the copper away from the qfn
chip far enough to be able to hand solder it ∗also∗ - even with a
hotplate, it's likely you'll need to fix the joints, and that's a lot
easier if the pads are accessible next to the chip - lets you drag
excess solder away from the chip, for example. To fix, use a flux pen
along that edge, add a little solder to your iron, and TAP it along the
edge. you don't want to drag solder along the edge, you want to drag
extra solder away from it.

If your QFN also needs a center pad, be careful to make it small enough
to avoid solder bridges - you won't be able to see or fix those. If
your center pad need electrical connectivity, either tie it to a pin or
drill a big hole through the center so you can manually solder it from
the other side.