Having received a clear answer to my earlier question (below) on fracturing
of Polyimide in the plated thru hole, I am posting a summary of the
responces.  Thanks to all who responded.

The condition is best described as Radial Cracking.  There are acceptance
criteria defined for this condition only for Copper-Invar-Copper (CIC)
boards.  In the case of CIC boards, the condition is evaluated in the
horizontal direction in the plane of the CIC foil.

In polyimide multilayers, (not with CIC cores) there were no defined
acceptance criteria identified for Radial Cracking.  All those who responded
indicated that they used or would use the criteria for wicking as the
acceptance criteria.


George Franck
Raytheon Systems
Falls Church Virginia
"My Opinions are just that."

----------
From: George Franck <[log in to unmask]>
To: [log in to unmask]
Subject: [Fab] Fracturing
Date: Tue, 18 Aug 1998 17:31:50 -0400

Good Afternoon all,

I have received Class 3 PWB's built of Polyimide material.   We reviewed the
cross section sent in with the order.  In the supplier provided cross
sections we found the resin material fracturing all around the plated holes.
 Into these cracks, copper has plated.  It appears that the feed rates were
a bit excessive during the drill operation, and some "punching" perhaps
occured.

The copper plating in the cracks indicate that solution at one time founds
it's way into these cracks.  The copper plated cracks extend 2 to 5 mils
from the hole into the laminate.  Sometimes these plated cracks extend
beyond the pads, into the "B" evaluation zone for Laminate Voids.  This
raises concerns with possible shorting, and/or spacing violations.

I see two evaluation options.  Evaluate the plated cracks as wicking, or
evaluate the plated cracks as laminate voids.  Or other ideas?
How would you evaluate the copper plating in these fractures?  When is it
"too much"?  Again, these are Class 3, Hi-rel PWB's.

Thanks for your thoughts.

George Franck
Raytheon Systems
Falls Church Virginia
"My Opinions are just that."

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