Jack,

This condition is most likely to occur when the board fabricator was
processing the inner layer. The resist coating used for imaging may have
had an air pocket at that location causing a lifted resist condition.
Then during the etching process the chemical etch solution undercut the
resist. From my prospective this is an anomaly and is classified as an
etch down condition. If the remainder of the sections do not exhibit the
condition, a referee cross-section of the same serial number would
acceptable. Based on the cross-section photo it appears to be a ground
or power layer, if so IPC specification allowance for this condition. 

Regards

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Thursday, February 07, 2008 8:33 AM
To: [log in to unmask]
Subject: [TN] FAB: Thin Trace Failures

Has anyone ever seen a cross-section like this?

http://www.frontdoor.biz/PCBportal/opentrace.jpg

(ignore the words on the pic, just a guess)

Can you point me in the right direction for cause?

thanks,
Jack

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