Yep the pinky bits are the core, it pretty clear which is core and which is pre-preg. Both use a single ply of glass looks like 7628 in the pre-preg and 1080 in the core. 
CAF usually occurs along the strands which have been in contact with a chemical solution, the white streaks look more like reflections. 
Is the failure always between the core/always the same cores?
What laminate is it?

________________________________

From: TechNet on behalf of Jack Olson
Sent: Wed 21/11/2007 4:57 PM
To: [log in to unmask]
Subject: [TN] Core Quality Issue?



Sorry to re-start a previous discussion, but I'm still dealing with a board
failure and I'm trying to learn fast.

I received a higher-resolution picture of a board problem we are having

http://www.frontdoor.biz/PCBportal/corequestion.jpg<http://www.frontdoor.biz/PCBportal/corequestion.jpg>

and if I look at it closely, I can see the dividing line between all ten
layers of dielectric.

By looking at which way the copper is located from each dividing line, I can
tell which are cores and which are prepreg (because the prepreg layers will
flow "around" the copper features)
For example, the thin pinkish layer is a core. Am I on the right track so
far?

So, our problem is a 120V end-of-line test frying two out of every hundred
boards right through the pinkish core material with the white streak through
it
(3.2 mils, which should handle a few kilovolts at least, right?)

So here's the question:
Should I be questioning the material quality rather than the bare-board
manufacturing process itself?

I realize you guys have already been generous with helping me on this, so I
hope I'm not pushing your patience...

onward thru the fog,
Jack (aka "the new guy")

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