Arduino Forum

Using Arduino => General Electronics => Topic started by: jerseyguy1996 on Dec 29, 2012, 06:37 pm

Title: PCB Routing Tips?
Post by: jerseyguy1996 on Dec 29, 2012, 06:37 pm
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?

(http://farm9.staticflickr.com/8495/8322706616_1dbceb809f_b.jpg) (http://www.flickr.com/photos/8446055@N05/8322706616/)
GPS_LOGGER (http://www.flickr.com/photos/8446055@N05/8322706616/) by jg1996business (http://www.flickr.com/people/8446055@N05/), on Flickr

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

(http://farm9.staticflickr.com/8492/8321647891_1bf153c91e_b.jpg) (http://www.flickr.com/photos/8446055@N05/8321647891/)
GPS_LOGGER_AUTO_ROUTE (http://www.flickr.com/photos/8446055@N05/8321647891/) by jg1996business (http://www.flickr.com/people/8446055@N05/), on Flickr

Is it too ugly to work?
Title: Re: PCB Routing Tips?
Post by: JoshD on Dec 29, 2012, 07:52 pm
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!
Title: Re: PCB Routing Tips?
Post by: oric_dan on Dec 29, 2012, 07:53 pm
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.
Title: Re: PCB Routing Tips?
Post by: jerseyguy1996 on Dec 29, 2012, 07:59 pm

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?
Title: Re: PCB Routing Tips?
Post by: jerseyguy1996 on Dec 29, 2012, 08:00 pm

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.
Title: Re: PCB Routing Tips?
Post by: oric_dan on Dec 29, 2012, 08:50 pm
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.
Title: Re: PCB Routing Tips?
Post by: bratan on Dec 29, 2012, 08:54 pm
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.
Title: Re: PCB Routing Tips?
Post by: oric_dan on Dec 29, 2012, 08:58 pm
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
Title: Re: PCB Routing Tips?
Post by: jerseyguy1996 on Dec 29, 2012, 11:10 pm
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
Title: Re: PCB Routing Tips?
Post by: oric_dan on Dec 29, 2012, 11:19 pm
.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.
Title: Re: PCB Routing Tips?
Post by: winner10920 on Dec 30, 2012, 08:09 pm
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
Title: Re: PCB Routing Tips?
Post by: rvasque on Dec 30, 2012, 09:42 pm
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.