> I've made a PCB for the DIP version of the PIC18F4550, but now I'm trying=
 to
> make a board for the TQFN package of the 4550. I was wondering if you guy=
s
> would mind checking out my schematic and layout below and let me know if =
it
> looks alright?
>=20
> Schematic:
> http://www.roboticsguy.com/images/misc/pic18f4550_tqfn_schematic.png
> Layout: http://www.roboticsguy.com/images/misc/pic18f4550_tqfn_pcb.png
>=20

My suggestion is to use SMD parts for everything except the connectors and =
the=20
LEDs (since they are going to be placed on the top side). It really is not =
very=20
hard to mount the SMD components if you have a decent solder iron and some =
good=20
tweezers. In fact it might even be easier than to use TH parts since you do=
n't=20
need to drill holes for them.

Use a through hole connector instead of just pads for the external connecti=
ons.=20
If that messes up your layout, use two or more. This way the board can be=20
easily switched between projects without desoldering/soldering. Bare wires =
also=20
have a tendency to get broken off at the board surface. Don't forget power =
and=20
ground in the connectors. Flat ribbon ICD type connectors usually works goo=
d=20
for this. If you don't go with the connector idea, you still will need some=
=20
pads for ground and power.

The groundplane - Use a two sided board instead and use all the top layer a=
s=20
the ground. Just make clearances for the TH component pads on the top side.=
 If=20
this is a hobby project with a few home made boards, then make solderpads=20
(vias) besides the ground pads for pins that should be grounded but not=20
directly under the component and connect the top and bottom side with a bar=
e=20
wire through the via pads. This way you can remove the ground traces on the=
=20
bottom side and make better room for connectors for the external signals. I=
f=20
you really, really want to stick to a single sided board you can use jumper=
=20
wires on the top side to connect all ground islands on the bottom side so i=
t=20
more closely will resemble a ground plane - the more jumper wires, the bett=
er.

Make room/pads for test points and ground connection for a oscilloscope.=20
Sometimes it may be hard to find a good connection for the probe ground. (U=
sing=20
a ground plane will make it easy - just solder a short piece of bare wire o=
r a=20
cut of resistor leg to the ground plane.)

Good luck with your project / Ruben

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

--=20
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