Hi Stefan,
It is my understanding that the copper islands or orphaned copper is
removed to help with EMC (or do they call it FCC in the US) approval.
You are probably right in that a fat copper island will not do any harm.
However at very high frequencies
these isolated (in a DC sense) pieces of copper may just have the right
shape to form L's and C's that become resonant
and hey - presto , you got yourself an antenna.
Although the chances of a floating piece of copper being resonant is
probably pretty slim, when designing for EMC you take all the free runs
that you can get
Also - When I say very high frequencies - the signal cycle times do not
have to be high frequencys - they just need fast transition times.
Cheers,
David
Stefan Trethan wrote:
>On Thu, 14 Jul 2005 09:55:36 +0200, Phil <phil1960us@...> wrote:
>
>
>
>>However, I wouldn't focus on using fat traces for avoiding copper
>>removal. I think that would be the hard way to do it. I much prefer
>>to create a ground polygon that encompasses the entire board and then
>>let the layout software figure out the actual shape. In eagle, I put
>>a ground poly on both the top and bottom with isolate set to 24 mil.
>>Then I route the board. The only places eagle will take copper is for
>>isolation and "orphaned" copper areas (not connected to ground).
>>Look at http://www.geocities.com/pcbs4less/boardtop.gif for an example
>>of this. Red and green are copper areas/traces. As you can see, this
>>design keeps much more copper than one using just fat traces. It
>>seems much cleaner and makes for a quieter board, noise-wise, because
>>of the extensive ground areas.
>>Besides, thin traces just look more professional to me
>>Phil
>>
>>
>
>
>I agree, reasonably thin looks better.
>I also make groud planes, but i always wondered about islands. You say you
>don't leave the copper there, which i only partially understand (though i
>do the same, i just don't know exactly why).
>
>How bad are they? I mean i can imagine they could potentially provide more
>capacitive coupling between signals which is unwanted, but is that really
>an issue?
>Have you any information about that?
>
>Sometimes those gaps don't look right, and i'm tempted to leave them.
>
>I usually use 10mil for signal traces and 20 mil for power, but i've also
>made boards with 1mm traces for customers if they want, where 10mil would
>have been plenty, and it doesn't look bad if the components are right for
>it (only throughhole, not many ICs, ..) Esp. if all traces are that wide
>and none are thinner it looks ok.
>
>ST
>
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBs
>
>If Files or Photos are running short of space, post them here:
>http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
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>Date: Thu, 14 Jul 2005 12:08:00 +0200
>Subject: Re: [Homebrew_PCBs] Re: Another rookie starts a high volume pcb project.
>Reply-To: Homebrew_PCBs@yahoogroups.com
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>On Thu, 14 Jul 2005 09:55:36 +0200, Phil <phil1960us@...> wrote:
>
>
>
>>However, I wouldn't focus on using fat traces for avoiding copper
>>removal. I think that would be the hard way to do it. I much prefer
>>to create a ground polygon that encompasses the entire board and then
>>let the layout software figure out the actual shape. In eagle, I put
>>a ground poly on both the top and bottom with isolate set to 24 mil.
>>Then I route the board. The only places eagle will take copper is for
>>isolation and "orphaned" copper areas (not connected to ground).
>>Look at http://www.geocities.com/pcbs4less/boardtop.gif for an example
>>of this. Red and green are copper areas/traces. As you can see, this
>>design keeps much more copper than one using just fat traces. It
>>seems much cleaner and makes for a quieter board, noise-wise, because
>>of the extensive ground areas.
>>Besides, thin traces just look more professional to me
>>Phil
>>
>>
>
>
>I agree, reasonably thin looks better.
>I also make groud planes, but i always wondered about islands. You say you
>don't leave the copper there, which i only partially understand (though i
>do the same, i just don't know exactly why).
>
>How bad are they? I mean i can imagine they could potentially provide more
>capacitive coupling between signals which is unwanted, but is that really
>an issue?
>Have you any information about that?
>
>Sometimes those gaps don't look right, and i'm tempted to leave them.
>
>I usually use 10mil for signal traces and 20 mil for power, but i've also
>made boards with 1mm traces for customers if they want, where 10mil would
>have been plenty, and it doesn't look bad if the components are right for
>it (only throughhole, not many ICs, ..) Esp. if all traces are that wide
>and none are thinner it looks ok.
>
>ST
>
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBs
>
>If Files or Photos are running short of space, post them here:
>http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>
>
> -0-0-0-
>
>Message
Re: [Homebrew_PCBs] Re: Another rookie starts a high volume pcb project.
2005-07-14 by David Cureton