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
>
>
>
>
>
>
>
>
>
> ∗∗ ACCEPT: CRM114 PASS Markovian Matcher ∗∗
>CLASSIFY succeeds; success probability: 1.0000 pR: 75.3676
>Best match to file #0 (nonspam.css) prob: 1.0000 pR: 75.3676
>Total features in input file: 7075
>#0 (nonspam.css): features: 1444288, hits: 289711, prob: 1.00e+00, pR: 75.37
>#1 (spam.css): features: 554608, hits: 88467, prob: 4.29e-76, pR: -75.37
>
>
>-=-Extra Stuff-=-
>
> From sentto-4505361-9835-1121335815-yahoo=dcureton.com@... Thu Jul 14 20:10:50 2005
>Return-path: <sentto-4505361-9835-1121335815-yahoo=dcureton.com@...>
>Envelope-to: yahoo@...
>Delivery-date: Thu, 14 Jul 2005 20:10:50 +1000
>Received: from n10.bulk.dcn.yahoo.com ([216.155.201.63])
>by whitetail with smtp (Exim 4.34)
>id 1Dt0g5-0004wZ-6G
>for yahoo@...; Thu, 14 Jul 2005 20:10:49 +1000
>Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys
>DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=lima; d=yahoogroups.com;
>b=Lb4DZCCehu3oAy78nYfZeu+7BDSrOiZZrHZQ5hCwm4hl4xridI2icJdqPe3ctklw2D4hKWCqeQr/ezqKR2yZdMhfQ83Vb6EH43qSLCDE1Mn8ldxv4QsahkJpW9jJf9Yo;
>Received: from [216.155.201.65] by n10.bulk.dcn.yahoo.com with NNFMP; 14 Jul 2005 10:10:15 -0000
>Received: from [66.218.69.3] by mailer2.bulk.dcn.yahoo.com with NNFMP; 14 Jul 2005 10:10:15 -0000
>Received: from [66.218.66.29] by mailer3.bulk.scd.yahoo.com with NNFMP; 14 Jul 2005 10:10:15 -0000
>X-Yahoo-Newman-Property: groups-email
>X-Sender: stefan_trethan@...
>X-Apparently-To: Homebrew_PCBs@yahoogroups.com
>Received: (qmail 22942 invoked from network); 14 Jul 2005 10:10:14 -0000
>Received: from unknown (66.218.66.216)
> by m23.grp.scd.yahoo.com with QMQP; 14 Jul 2005 10:10:14 -0000
>Received: from unknown (HELO mail.gmx.net) (213.165.64.20)
> by mta1.grp.scd.yahoo.com with SMTP; 14 Jul 2005 10:10:13 -0000
>Received: (qmail invoked by alias); 14 Jul 2005 10:08:01 -0000
>Received: from v211-056.vps.tuwien.ac.at (EHLO tu-x2pj5qeyp2u4) [128.131.211.56]
> by mail.gmx.net (mp008) with SMTP; 14 Jul 2005 12:08:01 +0200
>X-Authenticated: #9664799
>To: Homebrew_PCBs@yahoogroups.com
>References: <db55po+ei0u@...>
>Message-ID: <op.stwefmsbmg0lsf@tu-x2pj5qeyp2u4>
>In-Reply-To: <db55po+ei0u@...>
>User-Agent: Opera M2/8.01 (Win32, build 7642)
>X-Y-GMX-Trusted: 0
>X-Originating-IP: 213.165.64.20
>X-eGroups-Msg-Info: 1:12:0
> From: "Stefan Trethan" <stefan_trethan@...>
>X-Yahoo-Profile: stefan_trethan
>Sender: Homebrew_PCBs@yahoogroups.com
>MIME-Version: 1.0
>Mailing-List: list Homebrew_PCBs@yahoogroups.com; contact Homebrew_PCBs-owner@yahoogroups.com
>Delivered-To: mailing list Homebrew_PCBs@yahoogroups.com
>List-Id: <Homebrew_PCBs.yahoogroups.com>
>Precedence: bulk
>List-Unsubscribe: <mailto:Homebrew_PCBs-unsubscribe@yahoogroups.com>
>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
>Content-Type: text/plain; charset=iso-8859-15
>Content-Transfer-Encoding: 7bit
>
>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-
>
>