Hello Mark,
I hope that I can help here, this can be hard to visualise and explain.
In the case of the external land, you are concerned with having enough annular ring to avoid breakout, hence it's the internal edge of the hole that will cause a problem.
With the internal land, the 'breakout' of the hole barrel will occur on it's outside diameter.
As the hole is drilled oversize to allow it to plate to it's finished size, insufficient annular ring here will allow the internal land to be 'broken' out by the drill and you will not get the full circumferential connection to the internal land that you are expecting. Hence, to achieve the same minimum annular ring that you have designed for on the external layer land, you need to consider the plating thickness for the internal land.
regards,
Phil.
-----Original Message-----
From: Mark Holmes [mailto:[log in to unmask]]
Sent: Wednesday, 2 July 2003 5:28 PM
To: [log in to unmask]
Subject: Re: [DC] Annular Ring Question
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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