[PCB_FORUM] Re: Copper balancing "thieving dots"

Alan:

In most cases I would agree with you, but in our case, we have had some
problems with thieving being added on the outer surface over critical analog
traces on inner layers.  This caused a major problem with signal fidelity in
high gigahertz inputs.  It is much easier to define a thieving keepout and
do it our selves.  As you can imagine, people don't want to pay $20K or more
for a scope that won't display their signals correctly :)

Mitch:

We have increasingly been using boards where 10-14 layers are processed and
plated up, then 2-3 layers are laminated to the whole stack using low Dk
prepregs and the whole board run thru plating again.  What this means is
that the thieving has to be added to the original "core" board outer layers
to minimize warpage, and the real outer layers then need it as well.

You may not have noticed the results of not adding thieving because your
boards are smaller, or because the manufacturer was scrapping boards for
flatness issues before they were delivered.

-- 
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272         Fax: 503-627-5587
http://www.tektronix.com    http://www.pcb-designer.com

It's my opinion, not Tektronix' 



-----Original Message-----
From: Ritter, Alan [mailto:Alan.Ritter@xxxxxxxxxx] 
Sent: Wednesday, September 22, 2004 10:52
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Copper balancing "thieving dots"


In general, we leave the addition of thieving up to the board fab house.
They know their process and what their requirements are to keep the trace
widths consistent.  Because we design medical equipment, we have some boards
where electrical safety concerns prohibit copper in certain areas, and these
are called out on the fab drawings.

On a lot of our boards, the only thieving required is on the tooling
bars...none on the active area of the board itself.

When it's a board fab process issue, I prefer letting the fab house dictate
what to do (within certain limits) rather than trying to second-guess them.
We EEs (yes, I'm an EE in addition to resident layout guru) generally don't
have a clue as to what is required, unless we have taken the time to visit
and/or talk extensively with the fab house.  Basically, we have a solid
enough relationship with the fab house that I know I can trust them to
follow instructions and make the "engineered" artwork files match both their
process requirements and our electrical requirements.

/s/jar (alan.ritter@xxxxxxxxxx)
        http://www.mtritter.org






Bausch & Lomb
150 Years of Perfecting Vision, Enhancing Life (TM)






EMAIL DISCLAIMER 

Please Note: The information contained in this message may be privileged and
confidential, protected from disclosure, and/or intended only for the use of
the individual or entity named above. If the reader of this message is not
the intended recipient, or an employee or agent responsible for delivering
this message to the intended recipient, you are hereby notified that any
disclosure, distribution, copying or other dissemination of this
communication is strictly prohibited. If you received this communication in
error, please immediately reply to the sender, delete the message and
destroy all copies of it.

Thank You

-----------------------------------------------------------
To subscribe/unsubscribe: 
        Send a message to icu-pcb-forum-request@xxxxxxxxxxxxx
        with a subject of subscribe or unsubscribe

To view the archives of this list please login at
http://www.freelists.org. Our list name is icu-pcb-forum
or go to http://www.freelists.org/archives/icu-pcb-forum/

Problems or Questions:
        Send an email to icu-pcb-forum-admins@xxxxxxxxxxxxx

Want to post a job listing ?  DON'T DO IT HERE!  
Better yet, join our jobs listing forum.

SUBSCRIBE:  icu-jobs-forum-subscribe@xxxxxxxxxx
POST:       icu-jobs-forum@xxxxxxxxxx
-----------------------------------------------------------
-----------------------------------------------------------
To subscribe/unsubscribe: 
        Send a message to icu-pcb-forum-request@xxxxxxxxxxxxx
        with a subject of subscribe or unsubscribe

To view the archives of this list please login at
http://www.freelists.org. Our list name is icu-pcb-forum
or go to http://www.freelists.org/archives/icu-pcb-forum/

Problems or Questions:
        Send an email to icu-pcb-forum-admins@xxxxxxxxxxxxx

Want to post a job listing ?  DON'T DO IT HERE!  
Better yet, join our jobs listing forum.

SUBSCRIBE:  icu-jobs-forum-subscribe@xxxxxxxxxx
POST:       icu-jobs-forum@xxxxxxxxxx
-----------------------------------------------------------

Other related posts: