Hello Wee Mei,
(apologies, I'm repeating a reply that I posted in March)
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: Lum Wee Mei [mailto:[log in to unmask]]
Sent: Tuesday, September 16, 2003 4:03 PM
To: [log in to unmask]
Subject: [DC] Annular Ring defintion (UC)
Hello there,
My colleague was reading the IPC-2221 when she come across the
difference in definition between internal and external annular ring. I,
too cannot understand why? Anyone can to try, maybe Jack Crawford can
help :8)
External Annular ring : The minimum annular ring on external layers is
the minimum amount of copper (at the narrowest point) between the edge
of the hole and the edge of the land after plating of the finished hole.
Internal Annular ring : The minimum annular ring on the internal layers
is the minimum amount of copper (at the narrowest point) between the
edge of the drilled hole and the edge of the land after drilling the
hole.
Thanks and regards,
Wee Mei
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