We use .015 nominal clearance to avoid this type of problem; and also because most non plated through holes have fasteners in them with knife-edge threads.  The threads can chew up some board under vibration.  If that hits the copper, FOD can result.  Even if you are using the ring to conduct ground, you still have a positive connection between the ring and the washer/bolt head.

Mike Green
Electronic Packaging Design
LMCO-Sunnyvale
408-743-1635
One Corporation, One Team
“If it were easy, they wouldn't call it rocket science.”  M. Green, 2009


-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Wendi Boger
Sent: Friday, March 12, 2010 8:11 AM
To: [log in to unmask]
Subject: [IPC-600-6012] Edges and Crazing/Haloing

Everyone,



   I seem to remember a discussion about Haloing of edges and non plated
holes at one of our recent meetings.   The requirement for the haloing
to be less than 50% the distance to nearest conductor works assuming the
design has a reasonable space from conductor to edge.  I looked in
IPC2221 but did not find a guideline for suggested minimum distance.  We
are seeing non-plated tolling holes with surface ground rings at <10mils
hole edge to copper.  Depending on the material and hole size it's
difficult to meet the 50% rule.



   Is there a section in 2221 I can send the designers to so we can
avoid this type of issue?



Thanks,

Wendi Boger





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