Hi Tim-

This is a derived specification. The PCB fabricators understand this as
requirements on the annular ring of a drilled and plated through hole. Look
up stuff related to "break-out". I think Class 2 requires no more than 90%
breakout, but many customers separately specify "NBO" for No BreakOut.
There's really not much of a difference between these if you're a
fabricator, as long as "teardrops" or "snowmen" are allowed on the artwork.

Anyway, the breakout spec controls the total mis-alignment between the
drilling process and final conductor formation process (be that etching or
additive plating). If the tolling holes/artwork are too mis-aligned, the
fabricator won't make the breakout spec. 

Sophisticated board designers know this inherently, so if they want a board
to have high accuracy of artwork to tooling holes, they'll have some plated
through holes with whatever minimum annular ring the PCB fabricator will
commit to.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Cables, Tim
Sent: Tuesday, April 21, 2015 9:46 AM
To: [log in to unmask]
Subject: [TN] Tooling hole to Artwork tolerance

Can anyone tell me what the IPC spec is for this and which standard it is
listed in?


Tim


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