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Date: Thu, 17 Jul 2014 02:24:12 +0200
From: Bernd Walter <ticso AT cicely7 DOT cicely DOT de>
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] opper ring flag for vias and pins
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On Thu, Jul 17, 2014 at 02:11:32AM +0200, Bernd Walter wrote:
> On Wed, Jul 16, 2014 at 02:22:50PM -0400, DJ Delorie wrote:
> > 
> > > You need to be able to remove inner layer pad annuli completely for 
> > > signal integrity reasons on some high-speed lines.
> > 
> > Aren't there manufacturability issues if you do that?  I.e. voids
> > where the copper should be, causing breaks in the barrel?
> 
> Why should there be any?
> I can't tell for sure, but when the holes are drilled and plated after
> stacking then such a plated hole without inside annular rings should
> be just the same as they would be with a standard 2-layer board.
> But I just investigated some very high densisty CPU boards I had
> within reach and all of them used microvias, but had at least rings
> on the outside layers of all vias.
> I probably should ask a board manufacturer about their opinions.

Just a random manufacturer found by websearch:
http://www.eurocircuits.com/index.php/component/content/article/28-glossary/237-ipi-inner-layer-pad-insulation
They defines spacing requirements for such a non ringed hole independend
if plated or not.
So it should be Ok to have non ringed holes in inner layers at least.

-- 
B.Walter <bernd AT bwct DOT de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.