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Topic: PCB Routing Tips? (Read 941 times) previous topic - next topic

jerseyguy1996

Well after much moving and re-jiggering of components, followed by vast amounts of wailing and gnashing of teeth, this is as good as I could get things in terms of a rats nest.  Is this normal or is there some trick to getting things to magically line up?


GPS_LOGGER by jg1996business, on Flickr

This is what it looks like after running the auto-router on it:


GPS_LOGGER_AUTO_ROUTE by jg1996business, on Flickr

Is it too ugly to work?
Arduino Uno;
Mega328

JoshD

At the top of the IC on the left side there's some really fine lines that look like nets that didn't get routed.  It's a good start though!

oric_dan

They always look ugly, with more than a couple of traces. However, you should look
at the top and bottom trace layers separately to get a better idea of how the layout
went. Also, the most obvious problem with auto-routing, the way you did it, is that
the power and ground traces are not nice and fat [ie, 30-50 mils], like they should
normally be to handle non-trivial currents.

jerseyguy1996


They always look ugly, with more than a couple of traces. However, you should look
at the top and bottom trace layers separately to get a better idea of how the layout
went. Also, the most obvious problem with auto-routing, the way you did it, is that
the power and ground traces are not nice and fat [ie, 30-50 mils], like they should
normally be to handle non-trivial currents.


So I should change the width to 50 mil and then click on each power and gnd trace?  Is there a quick way to change them all at one time?
Arduino Uno;
Mega328

jerseyguy1996


At the top of the IC on the left side there's some really fine lines that look like nets that didn't get routed.  It's a good start though!


Ya there is a couple that didn't get routed that I will have to do by hand.  I'm just wondering if the liberal use of vias to make things happen is a bad sign regarding my component placement.
Arduino Uno;
Mega328

oric_dan

#5
Dec 29, 2012, 08:50 pm Last Edit: Dec 29, 2012, 08:54 pm by oric_dan(333) Reason: 1
Quote
So I should change the width to 50 mil and then click on each power and gnd trace?  Is there a quick way to change them all at one time?

It depends on your particular CAD program. I never use auto-routing myself, so I cannot tell
you. Auto-routing always creates zillions of vias, like it did on your board. You can make the
layout cleaner and reduce the #of vias by moving and rotating the components, but that takes
practice in visualization, which comes more from manual routing than using auto-routing all
the time. It's clearly a multi-dimensional visualization problem.

bratan

#6
Dec 29, 2012, 08:54 pm Last Edit: Dec 29, 2012, 08:56 pm by bratan Reason: 1
Just like you I also just started to learn routing on PCB.  They way I found best for myself is to use auto-route and then go by hand over power traces and make them from 16 to 24 mils.  I would just I think 50 is overkill, take a look at official Aruduino board, I didn't see any bigger than 34.
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oric_dan

Yeah, 50 mils is probably overkill for most power and ground traces going to single
chips, but I use it a lot for main busses connecting many pads at the same time, eg
o-o-o-o-o-o-o-o

jerseyguy1996

What would we consider to be non-trivial current as it relates to a .008 wide trace?  You can assume I am using the standard board associated with this service:

http://imall.iteadstudio.com/open-pcb/pcb-prototyping/im120418001.html
Arduino Uno;
Mega328

oric_dan

.008 is a teensy trace, barely visible under the solder mask. Not good for a power/ground
traces. Most "signal" traces are 12 mils or so, although .008 is probably common nowadays
with smt parts, and power/ground traces somewhat larger. I recently bought a shield that
uses approx .008 traces, and I hate the darn thing. But then, I like to be able to "fix"
broken boards, and modify the circuitry for my own purposes.

winner10920

My tip would be if you had the time to manually route the whole thing, on my projects I always do that and make every trace basically as big as possible (within reason) , also paying attention to special or sensitive traces or routing noiser ones elsewhere, I actually usually place components not where the ratsnest is easy but where. Its best for electrical reasons, with enough time you can figure out a way to make the most complex ratsnest work, trust me I've done a few where it looks so complex it just increases the cool factor 10x because its less random looking and look very fresh

vasquo

Hmmm I thought connecting traces diagonally to a pad is "bad design practice"... but Eagle's auto-router seems to be doing it.

This is just a small simple board... do it manually.

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