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'[EE] PCB Layout - Dos and Do nots'
2006\01\27@161812 by Shawn Wilton

picon face
Does anyone have a list of potential dos and do nots for PCB layouts
involving power planes and ground planes?  I've done some googling and
haven't found anything really relevant to potential things you may not want
to do.

For example, is it considered OK to place a power fill plane on the same
layer as some of your digital I/O?  (None of this is high speed).

I'm hoping maybe someone has a list of things I should watch out for.

I know there are some guys on here with *years* of layout experience, so I
figure I would poke the grey matter a bit before sending off this board.

--


Shawn Wilton (b9 Systems)
http://black9.com

2006\01\30@100541 by alan smith

picon face
sure...I have done it all the time.  Its the sandwiched ground plane layers you really don't want to cut up, if its multi-layer.  

Shawn Wilton <spam_OUTblack9TakeThisOuTspamgmail.com> wrote:  For example, is it considered OK to place a power fill plane on the same
layer as some of your digital I/O? (None of this is high speed).

I'm hoping maybe someone has a list of things I should watch out for.

I know there are some guys on here with *years* of layout experience, so I
figure I would poke the grey matter a bit before sending off this board.

--


Shawn Wilton (b9 Systems)
http://black9.com

2006\01\30@103312 by Bob Axtell

face picon face
Remember the movie "Michael", where the Angel Gabriel explains that
you can never eat too much sugar? Well, you can NEVER have too much
ground.

I normally expand a ground plane  onto every layer  that I have space.

--Bob

alan smith wrote:

{Quote hidden}

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2006\01\30@123935 by Bob Axtell

face picon face
>
>
>Remember the movie "Michael", where the Angel Gabriel explains that
>you can never eat too much sugar? Well, you can NEVER have too much
>ground.
>
>I normally expand a ground plane  onto every layer  that I have space.
>
>  
>
Actually, besides improved performance because you have a good ground
system,
you will discover that your PCB manufacturing costs will fall as well,
because in
high quantities, the vendor considers  the cost of the  etchant
(chemical that removes
the copper) and the amount of dross created (copper in solution that has
to be recycled,
a pain in the a_ _).  Since you have filled in all the empty spaces with
ground pour,
his costs just dropped quite a bit.

See? its a win win situation all around!

--Bob

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2006\01\30@125705 by David VanHorn

picon face
>
> Actually, besides improved performance because you have a good ground
> system,


Until you start working with RF systems, and those stubs start acting like
resonators on the 3rd and 5th harmonics of the frequencies in use..

Or, you blow something simple, like tying the micro's crystal caps to a long
fat ground track that the micro also ties to somewhere else.  You just made
a nasty shunt fed antenna.. I've seen this one thing severely flunk a system
for part 15, and after only modifying this, the same system passed easily.

2006\01\30@164851 by alan smith

picon face
Often a board house will do whats called "copper thieving" bunches of little squares of copper inside the large open areas, to reduce the refuse from the etch process, among other things.

               
---------------------------------

What are the most popular cars? Find out at Yahoo! Autos

2006\01\30@171758 by David VanHorn

picon face
On 1/30/06, alan smith <EraseMEmicro_eng2spam_OUTspamTakeThisOuTyahoo.com> wrote:
>
> Often a board house will do whats called "copper thieving" bunches of
> little squares of copper inside the large open areas, to reduce the refuse
> from the etch process, among other things.


It's really entertaining when you get something like an interdigital
microwave filter back, where the board shop has plopped their logo in and
hosed it all up..

2006\01\30@175828 by alan smith

picon face
it was open space.......fair game for them to put the artist touch?
 
 I got back an analog board..same thing....copper thieving all around the finely crafted analog layout.  Turned out ok....just...wasnt what I expected

David VanHorn <dvanhornspamspam_OUTmicrobrix.com> wrote:
 On 1/30/06, alan smith wrote:
>
> Often a board house will do whats called "copper thieving" bunches of
> little squares of copper inside the large open areas, to reduce the refuse
> from the etch process, among other things.


It's really entertaining when you get something like an interdigital
microwave filter back, where the board shop has plopped their logo in and
hosed it all up..

2006\01\30@194544 by William Chops Westfield

face picon face
On Jan 30, 2006, at 2:58 PM, alan smith wrote:

> copper thieving all around the finely crafted analog layout.

Is there a common way to designate areas of a board that must
NOT have this sort of thing done?

BillW

2006\01\30@194615 by David VanHorn

picon face
On 1/30/06, alan smith <@spam@micro_eng2KILLspamspamyahoo.com> wrote:
>
> it was open space.......fair game for them to put the artist touch?
>
> I got back an analog board..same thing....copper thieving all around the
> finely crafted analog layout.  Turned out ok....just...wasnt what I expected


I splain it to them very clearly. NO CHANGES TO THE GERBERS.

2006\01\30@195612 by David VanHorn

picon face
On 1/30/06, William Chops Westfield <KILLspamwestfwKILLspamspammac.com> wrote:
>
> On Jan 30, 2006, at 2:58 PM, alan smith wrote:
>
> > copper thieving all around the finely crafted analog layout.
>
> Is there a common way to designate areas of a board that must
> NOT have this sort of thing done?


I have been known to draw a box and put text "Your Logo Here".
In one case, they put their logo somewhere else, and left the text alone.

..sigh..

2006\01\30@201617 by Tomas Larsson

flavicon
face
As far as I know venting and thieving are used to balance the copper on the
board.
Say that you have a board, one part with very dense pattern i.e. a
address-bus and a data-bus
0.2 mm tracks and 0.2 mm clearance and planes.
On the other side you have a power supply with mains voltage, 2 mm tracks
and up to 5 mm clearance and no planes.
In order to balance the copper, so it etches evenly over the board, with no
over- or under-etching, they have to apply some venting and thieving areas,
normally outside the board.

With best regards

Tomas Larsson
Sweden

Verus Amicus Est Tamquam Alter Idem

> {Original Message removed}

2006\01\30@202851 by Jinx

face picon face
> I have been known to draw a box and put text "Your Logo
> Here". In one case, they put their logo somewhere else, and
> left the text alone.
>
> ..sigh..

Haha, godluv'em. The sort of person who writes "OK" in
the "Do not write in this" box on forms

2006\01\30@210547 by David VanHorn

picon face
>
>
> Haha, godluv'em. The sort of person who writes "OK" in
> the "Do not write in this" box on forms


I was at mcdonalds for lunch one day, and noticed a box of cleaning
supplies.
The large gallon jug of purple window cleaning fluid was labeled in big
block letters:
"DO NOT DRINK"

The scary thought is that there's someone out there that needs that label.

2006\01\30@211456 by Shawn Wilton

picon face
Normally you can designate keep-out layers/areas.  Hard to say if they'll
pay attention though.


On 1/30/06, William Chops Westfield <RemoveMEwestfwTakeThisOuTspammac.com> wrote:
>
> On Jan 30, 2006, at 2:58 PM, alan smith wrote:
>
> > copper thieving all around the finely crafted analog layout.
>
> Is there a common way to designate areas of a board that must
> NOT have this sort of thing done?
>
> BillW
> -

2006\01\30@212411 by Peter Todd

picon face
On Mon, Jan 30, 2006 at 09:05:47PM -0500, David VanHorn wrote:
> I was at mcdonalds for lunch one day, and noticed a box of cleaning
> supplies.
> The large gallon jug of purple window cleaning fluid was labeled in big
> block letters:
> "DO NOT DRINK"
>
> The scary thought is that there's someone out there that needs that label.

Nah, the scary thought is did the manufacture save stocking costs by
using the same connector for the cleaning fluids as for the drink
machines?

--
spamBeGonepetespamBeGonespampetertodd.ca http://www.petertodd.ca

2006\01\31@050034 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu [RemoveMEpiclist-bouncesspamTakeThisOuTmit.edu]
>Sent: 31 January 2006 01:16
>To: 'Microcontroller discussion list - Public.'
>Subject: RE: [EE] PCB Layout - Dos and Do nots
>
>
>As far as I know venting and thieving are used to balance the
>copper on the board. Say that you have a board, one part with
>very dense pattern i.e. a address-bus and a data-bus 0.2 mm
>tracks and 0.2 mm clearance and planes. On the other side you
>have a power supply with mains voltage, 2 mm tracks and up to
>5 mm clearance and no planes. In order to balance the copper,
>so it etches evenly over the board, with no
>over- or under-etching, they have to apply some venting and
>thieving areas, normally outside the board.

ISTR also helps prevent the board warping when it goes through the reflow oven or wave solder machine.

Regards

Mike

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2006\01\31@093935 by alan smith

picon face
I was told after....make a note on the assembly drawing thats sent to the board house, so they know not to do this

William Chops Westfield <westfwEraseMEspam.....mac.com> wrote:  On Jan 30, 2006, at 2:58 PM, alan smith wrote:

> copper thieving all around the finely crafted analog layout.

Is there a common way to designate areas of a board that must
NOT have this sort of thing done?

BillW


'[EE] PCB Layout - Dos and Do nots'
2006\02\02@084207 by Alan B. Pearce
face picon face
>I was at mcdonalds for lunch one day, and noticed a box
>of cleaning supplies. The large gallon jug of purple window
>cleaning fluid was labeled in big block letters: "DO NOT DRINK"
>
>The scary thought is that there's someone out there
>that needs that label.

I guess some street corner wino would think it was drinkable, well it is the
right colour ...

2006\02\03@021933 by Vasile Surducan

face picon face
On 1/30/06, David VanHorn <EraseMEdvanhornspammicrobrix.com> wrote:
> >
> > Actually, besides improved performance because you have a good ground
> > system,
>
>
> Until you start working with RF systems, and those stubs start acting like
> resonators on the 3rd and 5th harmonics of the frequencies in use..

David, when you're designing stubs, you're not using coplanar lines
but microstrip. Fortunately up to 5GHz any stub may be replaced with
passive LC using smd's.

cheers,
Vasile


> Or, you blow something simple, like tying the micro's crystal caps to a long
> fat ground track that the micro also ties to somewhere else.  You just made
> a nasty shunt fed antenna.. I've seen this one thing severely flunk a system
> for part 15, and after only modifying this, the same system passed easily.
> -

2006\02\03@023435 by Vasile Surducan

face picon face
On 1/27/06, Shawn Wilton <RemoveMEblack9EraseMEspamEraseMEgmail.com> wrote:
> Does anyone have a list of potential dos and do nots for PCB layouts

There is not a distinctive rule. Any different project may have
different rules. In a mixed digital, RF and analogic design you may
have one of more digital grounds, RF grounds, analogic grounds.
For RF grounds the rule is keep them continuous as much as possible
and use golden plate + thousens of vias (except microstrip on low
epsilon PCB where there is no  room for vias). For analogic grounds
the rule is connect them to supply in the minimum impedance point
(created by low esr capacitors) and  care about supplying comparators
versus low signal OA.
For digital ground, any rule you'll use could be insufficient. However
do not use VCC power planes on analogic or RF design, use them  only
on digital designs.
Do not mix analogic with digital ground even they are on different layers.
Use enough isolation between any kind of grounds. Use a large numbers
of vias between ground planes with the same name on different layers.
Finally: when you'll desing at least 1 square meter of PCB projects
you'll know better than us what to do.

cheers,
Vasile


{Quote hidden}

> -

2006\02\03@174346 by Marcel Birthelmer

picon face
>
> Use a large numbers of vias between ground planes with the same name on
> different layers.
>

Isn't that a problem as far as ground loops are concerned?

2006\02\06@024349 by Vasile Surducan

face picon face
On 2/4/06, Marcel Birthelmer <RemoveMEmarcelb.listsspam_OUTspamKILLspamgmail.com> wrote:
> >
> > Use a large numbers of vias between ground planes with the same name on
> > different layers.
> >
>
> Isn't that a problem as far as ground loops are concerned?

No Marcel, this is a fairly common procedure on RF boards.
Every via it's an inductance. The ideea is to minimise the inductance
value between ground planes and have a massive unique ground.
There are a huge numbers of article about this, I suggest Maxim site,
application note about RF transcievers, supply filtering on high
frequency/high slew rate operational amplifiers.

best regards,
Vasile



> -

2006\02\06@031720 by Bob Axtell

face picon face
If you look carefully at the Xylinx FPGA documents, you will notice
that operation of their FPGA's is NOT guaranteed (warranteed) unless
a ground plane is employed under it.

In most commercial designs of almost any speed, a ground plane is a
necessity.

--Bob

Vasile Surducan wrote:

{Quote hidden}

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Note: To protect our network,
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2006\02\06@034225 by Chen Xiao Fan

face
flavicon
face

> From: RemoveMEpiclist-bouncesKILLspamspammit.edu
> [piclist-bouncesSTOPspamspamspam_OUTmit.edu] On Behalf Of Bob Axtell
>
> In most commercial designs of almost any speed, a ground plane is a
> necessity.
>

I am not so sure if this is true also for AC/DC and DC-DC converters
especailly when line voltage are involved. Most likely it is not
possible to have a "good ground plane" within the high voltage side.

But I will agree that ground plane is important for even not very
high speed analog circuits if I can afford to have a good ground
plane. 4-layer boards in general have much better performance for
our optic proximity sensors but 4-layer boards are much more
expensive than normal 2-layer boards.

Regards,
Xiaofan

2006\02\07@053937 by Vasile Surducan

face picon face
On 2/6/06, Chen Xiao Fan <spamBeGonexiaofanSTOPspamspamEraseMEsg.pepperl-fuchs.com> wrote:
>
> > From: KILLspampiclist-bouncesspamBeGonespammit.edu
> > [EraseMEpiclist-bouncesspamEraseMEmit.edu] On Behalf Of Bob Axtell
> >
> > In most commercial designs of almost any speed, a ground plane is a
> > necessity.
> >
>
> I am not so sure if this is true also for AC/DC and DC-DC converters
> especailly when line voltage are involved. Most likely it is not
> possible to have a "good ground plane" within the high voltage side.

All mass production (serious) chinese supply designs have a
suplementary ground foil connected with the PCB. Usually is used for
this a single layer 10 mil FR4 continous ground board. The board is
connected with the earth pole
of the mains  connector and acts like a shield.

Vasile

>
> But I will agree that ground plane is important for even not very
> high speed analog circuits if I can afford to have a good ground
> plane. 4-layer boards in general have much better performance for
> our optic proximity sensors but 4-layer boards are much more
> expensive than normal 2-layer boards.
>
> Regards,
> Xiaofan
>
> -

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