If I were doing broadside coupled pairs (tandem pairs) I would not rely
on layer core to layer core registration for signal quality issues. If
you absolutely need to do broadside coupling then I would put the
broadside coupled nets on a layer pair that is on the same core instead
of a putting them on to different cores separated by a pre-preg. By
doing this you will get better registration between the pairs. The
registration from top to bottom of the same core will be much tighter
because it has less manufacturing tolerance built into the process. As
for core to core registration issues; I have always relied on the
annular ring requirements and a good manufacturing house. If crosstalk
is a huge concern for higher speed designs then you must figure the
tolerance into your formulas for determining tandem gaps or by adjusting
the coupled length for the possible increase in accumulative noise.
Thanks
Tony Cosentino
Tekelec
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
McConnell, Karen E
Sent: Wednesday, April 09, 2008 2:00 PM
To: [log in to unmask]
Subject: Re: [DC] [TN] layer to layer registration?
Layer to layer registration concerns more than annular ring. If a layer
is misaligned, high speed signals could have cross talk problems. Plus
tandem differential signals may not work correctly.
-------------
Karen McConnell
Senior Member Engineering Staff
LM EPI Center
http://www.epic.lmco.com
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Murphy, John
Sent: Tuesday, April 08, 2008 11:35 AM
To: [log in to unmask]
Subject: Re: [DC] [TN] layer to layer registration?
Thank you Mr. Vischulius for your input, you make a good point.
Basically, I interpret layer to layer registration on a finished
bare board as the accuracy of alignment of physical features of each
layer with respect to each other.... to match the master artwork layers
exactly aligned, being the definitive baseline standard from which to
calculate a deviation. I thought that to be a common interpretation,
perhaps not. Which is why I ask the question " Is it a good idea to
specify layer to layer registration for Class II"
I think soldermask to copper pattern alignment is one answer to your
other point. What I believe makes my issue is that when multilayers are
stacked it is a mechanical process to align layer to layer which can go
wrong if not controlled for a number of reasons (one of which is
scaling). Granted the annular ring specification addresses drill to
pad concentricity but it does not address layer to layer. I guess you
could argue that if two pads on adjacent layers were misaligned and
their common plated thru hole were too pass thru both within spec. ,
then all is good.
-----Original Message-----
From: Donald Vischulis [mailto:[log in to unmask]]
Sent: Monday, April 07, 2008 7:04 PM
To: TechNet E-Mail Forum; Murphy, John
Subject: Re: [TN] layer to layer registration?
John,
How do you define layer to layer registration? While this might appear
to be a trivial question, if minimum annular ring and holding master
artwork line widths within tolerance aren't sufficient to define your
needs, what additional requirements have to be met?
Don Vischulis
-----Original Message-----
>From: "Murphy, John" <[log in to unmask]>
>Sent: Apr 7, 2008 12:13 PM
>To: [log in to unmask]
>Subject: [TN] layer to layer registration?
>
>Greetings,
>
> Is it a good idea to specify layer to layer
>registration for Class II
>
>multi-layer PCB's? My searching thus far indicates it is not directly
>contained
>
>in any IPC specification (other than annular ring requirements) but
>relegated to
>
>the Master Drawing.
>
>
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