Author Topic: Routing 4 layer boards  (Read 9734 times)

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Offline Neilm

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Re: Routing 4 layer boards
« Reply #25 on: May 09, 2017, 04:11:17 am »
I have worked passing IEC61326 for years and have always gone signal-0V-Vcc-signal for a 4 layer board.

There are a very good series of articals on PCB layout by Keith Armstrong look at https://www.emcstandards.co.uk/ You will have to log in, but I found his articles easy to understand and without all the transmisstion theory maths that some people insist on putting in articles on EMC.
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Online mikeselectricstuff

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Re: Routing 4 layer boards
« Reply #26 on: May 09, 2017, 05:40:15 am »
The only time I've seen a production 4L PCB with planes on the outside was on an extremely dense design on a large PCB, where it was done to prevent having to go to 6 layers - I think it was a predominantly through-hole design, so theer is more clearance between TH pins on inner layers than on the surface, as pads weren't needed on the inner layers.. 
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Online Simon

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Re: Routing 4 layer boards
« Reply #27 on: May 09, 2017, 07:23:24 pm »
Well I'm going with GND-signal-GND-signal + SMD, my board is layed out in functional blocks anywhere and many traces would take as much length if not more to bury than route directly.
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Offline NANDBlog

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Re: Routing 4 layer boards
« Reply #28 on: May 09, 2017, 08:14:48 pm »
Well I'm going with GND-signal-GND-signal + SMD, my board is layed out in functional blocks anywhere and many traces would take as much length if not more to bury than route directly.
So, you are not listening to us.
 

Offline timb

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Routing 4 layer boards
« Reply #29 on: May 09, 2017, 08:50:39 pm »
Well I'm going with GND-signal-GND-signal + SMD, my board is layed out in functional blocks anywhere and many traces would take as much length if not more to bury than route directly.

OP: "Hey guys, how should I blah blah blah?"

Everyone: "X is the correct way to do it in your case, not Y."

OP: Thanks guys, I'll go with Y!

Everyone: :palm:
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Online Simon

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Re: Routing 4 layer boards
« Reply #30 on: May 09, 2017, 09:36:22 pm »
Well I'm going with GND-signal-GND-signal + SMD, my board is layed out in functional blocks anywhere and many traces would take as much length if not more to bury than route directly.
So, you are not listening to us.

err i am
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Online Simon

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Re: Routing 4 layer boards
« Reply #31 on: May 09, 2017, 10:07:07 pm »
Well I'm going with GND-signal-GND-signal + SMD, my board is layed out in functional blocks anywhere and many traces would take as much length if not more to bury than route directly.

OP: "Hey guys, how should I blah blah blah?"

Everyone: "X is the correct way to do it in your case, not Y."

OP: Thanks guys, I'll go with Y X !

Everyone: :palm:
https://www.simonselectronics.co.uk/shop New stock now in of EEVblog Brymen 235 and uCurrent Gold, Now selling a selection of Probe Master probes
 

Offline timb

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Re: Routing 4 layer boards
« Reply #32 on: May 09, 2017, 10:15:13 pm »
Well I'm going with GND-signal-GND-signal + SMD, my board is layed out in functional blocks anywhere and many traces would take as much length if not more to bury than route directly.

OP: "Hey guys, how should I blah blah blah?"

Everyone: "X is the correct way to do it in your case, not Y."

OP: Thanks guys, I'll go with Y X !

Everyone: :palm:

You said you're going with GND-Signal-GND-Signal (which wasn't even one of the recommended methods). Recommended was Signal-GND-Power-Signal (with short runs of signal being OK on the power plane if required). ;)

Anyway, I was just messing with you; your method will work, but is still non-ideal. You need to make sure you have *plenty* of via stitching between GND planes otherwise you'll end up with your two GND planes at different potentials, which wouldn't be good.
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Online Simon

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Re: Routing 4 layer boards
« Reply #33 on: May 09, 2017, 10:23:26 pm »
I see the suggestion was power be a plane instead of two grounds, in that case it makes lots of sense to have a top plane for power There is only 5A in the board and with 2 TO220 packages with a ton of vias full of solder under their heatsinks that will be plenty.
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Offline noname4me

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Re: Routing 4 layer boards
« Reply #34 on: May 23, 2017, 03:45:17 am »
Please let us know how you get on at EMC testing.

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Online Simon

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Re: Routing 4 layer boards
« Reply #35 on: May 30, 2017, 06:49:25 am »
Well I spoke to the guy that suggested the idea to me and it's ground - signal - signal - power.
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Offline dmills

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Re: Routing 4 layer boards
« Reply #36 on: June 08, 2017, 01:30:11 am »
So coupling between the two signal planes, and big loops for the current in the lower signal plane trying to return on the nearest plane which is power and needing to find a decoupling cap and making the thing a right `mare to debug then, also long vias adding inductance to your power connections?

The thing to remember is that the significant fields in modern electronics are usually magnetic, not electric. This did not used to be the case back in the valve era when everything was high voltage and high impedance, but is very much the case these days.

Both radiation efficiency and susceptibility to magnetic fields is largely driven by loop area, so having a reference plane that is both unbroken and **close** to your signal layer serves very much to minimise radiation, there is a reason almost everyone uses S-P-P-S for 4 layer.

73 Dan.
 

Online Simon

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Re: Routing 4 layer boards
« Reply #37 on: June 08, 2017, 03:10:43 am »
But if you have power traces that are negative and positive shifting the same current you can put then on top of each other, much as we use twisted wires in cable bundles to keep opposing conductors close.
I'm in the middle of getting into ARM and learning circuit studio as I have given up on proteus.
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Offline Rerouter

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Re: Routing 4 layer boards
« Reply #38 on: June 08, 2017, 09:38:05 am »
By having signals on the outside, all vias can be impedance compensated without stubs for high speed signals that traverse the outer layers.

With signals in the middle any high speed nets need to be back drilled, which ends up expensive. Or your left with many stubs radiating noise
 

Online Simon

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Re: Routing 4 layer boards
« Reply #39 on: June 09, 2017, 04:13:05 pm »
So your referring to tiny un-terminated spurs in the form of a via extension that does not make up part of the main path ? I expect at high frequencies that would be a problem. Well I am a long way off a redesign as I'm back to the drawing board anyway.
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Offline electrolust

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Re: Routing 4 layer boards
« Reply #40 on: July 12, 2017, 04:53:57 am »
I am trying to do my first 4 layer board in Proteus. This is proving to be a bit of a nightmare.
...
I’m also at a loss as to how I would choose to use a specific via while I am manually routing. Or indeed how do I choose which layer I am going to switch to.

This is pretty simple.  The configuration you are looking for is "drill spans", part of the layer stackup definition for your board.



I'm in the middle of getting into ARM and learning circuit studio as I have given up on proteus.

That's unfortunate, as you've barely learnt how to use Proteus.  I also gave up due to library frustrations, and took the plunge @ $500 for CS, but now I'm back to Proteus ...
 

Online Simon

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Re: Routing 4 layer boards
« Reply #41 on: July 12, 2017, 05:06:32 am »
both programs have pros and cons, proteus is more stable and mature, but CS is actually intuitive enough to use without trying to use hopeless documentation.
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Offline electrolust

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Re: Routing 4 layer boards
« Reply #42 on: July 12, 2017, 05:30:46 am »
I agree CS is more intuitive so to do simpler things you can get there quicker from ground zero.  But you still have to learn it to do anything beyond "my first circuit".  It's not fair to compare the first-pcb experience, you have to compare the 2 as if you are reasonably experienced with both packages.  I hit 2 fatal bugs within my first hour of using CS.  I've yet to find a fatal bug in Proteus.  But what really kills CS for me is 1, the lack of win 10 high res (retina) display support.  It makes many essential dialogs unusable -- either too small to read or too big to fit the screen.  And 2, the complete lack of support.

You aren't reviewing Proteus fairly if you're not willing to even read the documentation.
 

Online Simon

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Re: Routing 4 layer boards
« Reply #43 on: July 12, 2017, 05:35:29 am »
I have used proteus for 1 year, more infact now and done a few designs in it two of which were manufactured. I don't find it easy to use and the documentation is not comprehensive and considering they seem to have gone to extreme lengths to complicate everything or find the weirdest way of doing it I have given up. Support is a big issue with CS and with proteus for £210 less you do get instant phone support and if they can reproduce a bug they will take it seriously I think.
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