Outside of what Wayne discussed (and a good posting it was!), for other feature's tolerance, I don't think there is any hard and fast requirement in the standards. The rest of the tolerances are controlled by the fabrication drawing for the PWB and can vary according to the design. This would include dimensional tolerances for locations of drilled holes with respect to X, Y datum reference points (as specified in the drill table on the PWB fab drawing), fiducials, artwork, etc. For a Class 1 PWB the tolerances might be much more than those for a Class 3, but even then not necessarily so. It all boils down to what the designer and the customer require for full functionality and whatever level of reliability limitations they can live with (or not).
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Cables, Tim
Sent: Tuesday, April 21, 2015 9:16 AM
To: [log in to unmask]
Subject: Re: [TN] Tooling hole to Artwork tolerance
Thanks, Wayne,
If anyone has any other thoughts on this please comment.
Regards
Tim Cables
PCB Design
Aclara
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Tuesday, April 21, 2015 10:05 AM
To: [log in to unmask]
Subject: Re: [TN] Tooling hole to Artwork tolerance
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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