The reason there's a difference is because of etchback. The hole is drilled
about 50um oversize and plated up for a specific barrel thickness, but the
etchback removes some of the resin/glass that's supporting the land. All
this is happening after lamination, where the internal layers are imaged and
etched.
Hence to preserve that support, you need to make sure there's enough 'meat'
on the land on inner layers to get a thin annular ring past the drill,
etchback, electroless/electroplate stages and still retain a reliable
connection.
You don't have that problem on the outer layers because there is no land
there yet - that doesn't happen until after imaging and etching of the
external layers, and that's after
drilling/etchback/electroless/electroplate.
Cheers........
Andy Kowalewski
SyChip Inc
Office phone (972) 202 8852
-----Original Message-----
From: Jack C. Olson [mailto:[log in to unmask]]
Sent: Wednesday, July 02, 2003 9:20 AM
To: [log in to unmask]
Subject: Re: [DC] Annular Ring Question
I was really hoping you would get an answer to this.
I'm surprised NO ONE has stepped up,
Gary Ferrari where are you?
Sorry, I can't help you either,
I thought I knew, because when it was explained to me at the C.I.D.
training it made perfect sense, but now that I want to explain it to
someone else I realize I don't understand it well enough. (and it
doesn't seem to be in the training materials. Glenn Wells was the
one who explained it to me, but now I don't remember.
I would think it would be related to the fact that if you break out
a pad on an inner layer that cuts a trace, then you are relying on the
plating to re-connect it. (which it might, but not reliably enough).
But now I'm just guessing.
good luck,
Jack
Mark Holmes
<[log in to unmask]
COM>
Sent by:
DesignerCouncil To:
[log in to unmask]
<DesignerCouncil@listse cc:
rv.ipc.org>
07/02/2003 02:57 AM Subject: Re: [DC]
Annular Ring Question
Please respond to
"(Designers Council
Forum)"; Please respond
to Mark Holmes
Caterpillar: Confidential Green Retain Until: 08/01/2003
Retention Category: G90 -
General
Matters/Administration
Hi All,
I have re-read my post and realised I made a typo and not made myself very
clear. The paragraph I am referring to is IPC-2221 9.1.2.
I would really like to know why the annular ring for an external land
includes the plating, but the annular ring for an internal land does not.
Best regards,
Mark
-----Original Message-----
From: Mark Holmes [mailto:[log in to unmask]]
Sent: Friday, June 27, 2003 10:42 AM
To: [log in to unmask]
Subject: [DC] Annular Ring Question
Hi All,
IPC-2221 9.2.2 Annular Ring Requirements states:
"The minimum annular ring on EXTERNAL layers is the minimum amount of
copper
(at the narrowest point) between the edge of the hole and edge of the land
AFTER PLATING of the hole"
"The minimum annular ring on INTERNAL layers is the minimum amount of
copper
(at the narrowest point) between the edge of the drilled hole AFTER
DRILLING
the hole"
I am confused as to why there are two definitions. Can anyone help?
I have a few Ideas of my own, but would appreciate an explanation.
Best Regards,
Mark
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