Hi Thomas,

I agree with all of those who have indicated that it is desirable to
balance the copper density on both sides of the board.  In cases such as
you mention, the board manufacturer still has some options available.
Remember that the board manufacturer will take your data and step and
repeat it onto a panel.  In addition to your data, this panel also
includes venting or thieving patterns surrounding your data.  The
density of these patterns can be modified to compensate for an
unbalanced condition in your "raw" data.  In a case such as you mention,
the manufacturer could put a very dense venting pattern on the side of
the board having the widely spaced traces and a very sparse venting
pattern on the side containing the ground plane.  Additionally, if the
board is small enough (so that there are a lot of boards on the panel),
then some of them can be turned "ground plane up" and some can be turned
"ground plane down", again helping to balance the copper.

Best regards,

Max P. Henzi
CEO, PentaLogix LLC
Tel.   (925) 952-3890
Fax.  (925) 934-6978
Email [EMAIL PROTECTED]
Web.  www.pentalogix.com
 
 

-----Original Message-----
From: Thomas [mailto:[EMAIL PROTECTED]] 
Sent: Tuesday, October 08, 2002 4:20 PM
To: 'Protel EDA Forum'
Subject: Re: [PEDA] OT - Complex boards and time to Layout?

Sometimes that's just not possible though.
I've recently finished a double sided PCB with allot of controlled
impedance
tracks on one side widely spaced to prevent xtalk and to prevent arcing
(its
a surge protection device) with a solid ground plane on the other side.

My board house has not complained (yet).

Tom.

> -----Original Message-----
> From: Brad Velander [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, 9 October 2002 04:18
> To: 'Protel EDA Forum'
> Subject: Re: [PEDA] OT - Complex boards and time to Layout?
> 
> 
> Aj or others,
>       same issue with plating. Differences in copper density 
> (over area)
> effect the plating rate of Cu to the circuit pattern. 
> Balanced copper side
> to side, area to area, is the fabricators best friend (yours 
> also in the
> end).
> 
> Sincerely,
> Brad Velander.
> 
> Lead PCB Designer
> Norsat International Inc.
> Microwave Products
> Tel   (604) 292-9089 (direct line)
> Fax  (604) 292-9010
> email: [EMAIL PROTECTED]
> http://www.norsat.com
> Norsat's Microwave Products Division has now achieved ISO 9001:2000
> certification 
> 
> 
> 
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, October 08, 2002 9:51 AM
> > To: Protel EDA Forum
> > Subject: Re: [PEDA] OT - Complex boards and time to Layout?
> > 
> > 
> > Interesting, I thought that the copper "balancing act" was only for
> > containing possible warpage. Makes sense, though. Thanks for tip.
> > 
> > aj
> > 
> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] 
> > >...
> > > I did this type of pour and had the board house 
> > > slap my wrists ...The explanation was that if 
> > > you have a big pour with lots of copper on one 
> > > side you need about the same copper on the other
> > > side to balance it. Otherwise the acid on one side 
> > > gets weak while the other side remains strong, 
> > > resulting in overetching on one side or 
> > > under-etching on the other
> 


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