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December 2009

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From:
Chris Mahanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Chris Mahanna <[log in to unmask]>
Date:
Thu, 10 Dec 2009 11:05:41 -0500
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Hi Jack,
Sorry that I missed the call yesterday.  My two cents:
As we move forward (e.g. RoHS, miniaturization...) the design activity and fabricator front-end will need to be more diligent.  Duh.
That said, the conformance status for "reasonable" designs may be very uncertain because Haloing and its measurement may have hit their limits.
I would suggest a two pronged attack
1) have 2221 put in a conformance warning, and reaffirm 600
2) determine the consensus as to what the risk is and how we might mitigate it.
The up-side is that there are probably several options.  The down-side is that you know the risk will be linked to the electrical design.  We've (IPC) got a couple problems floating around right now based upon minimum dielectric (particularly in the Z axis).
* trace routing above/below drill keep-outs
* (eyebrow) cracks vs. thermal zone
* edge issues like haloing

Chris




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Wednesday, December 09, 2009 5:23 PM
To: [log in to unmask]
Subject: [TN] FAB: Acceptability of Haloing

Fabricators,

This is an opportunity to influence the acceptability of your product!

The IPC Standards Development Committee is working on the next revision to IPC-A-600 (Acceptability of Printed Boards) which is a visual reference companion to IPC-6012.

One of the items we are currently discussing is the acceptability of haloing along the board edge. Here is a link to where we stand now:

http://frontdoor.biz/PCBportal/IPC-A-600H213.jpg

The problem is, if the designer violates the recommendation in the current IPC-2221 design guideline and puts traces or planes too close to the board outline, with the current wording of "whichever is less"
your boards can be considered rejectable with even a very small amount of haloing. Even intentional features like edge fingers can make your boards rejectable.

We aren't sure if we should reword this (and if so, how?)

So the ball is in your court (because unless there is a logical consensus we probably won't change it).
I'll compile and submit any responses to the next committee meeting.

Jack (aka "the new guy")

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