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I am no expert at this, Jack, but looking up from the bottom, I note a
silver-colored strand between the copper layers. It appears as if this
could be a cathodic-anodic filament (CAF), but it is hard to tell if it
is or if it is a reflection of light on that particular strand. If you
have CAF formations inside the PWB, it could explain your inner-layer
shorting.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Wednesday, November 21, 2007 10:58 AM
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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