Sounds like you have interplane separation.  It is a separation of the 
plated copper on the hole wall from the edge of the inner layer.  Dr. Alan 
Poskanzer wrote an article in Plating and Surface Finishing for March 1990 
that you might want to read.  It's title is IP Separation: Its Causes and 
Cures.  The magazine is by the American Electroplaters Society.  Since we 
are on the subject, I'd like to piggyback on this and ask:  Is anyone seeing 
post separation of the Tg 170 range materials and if so do you have a root 
cause?
 ----------
From: [log in to unmask]
To: [log in to unmask]
Subject: Interconnect Failure
Date: Monday, November 18, 1996 8:17AM


RECENTLY WE FIND INNER LAYER OPEN COMPLAINT IN EIGHT LAYER BOARDS FOR ONE
PARTICULAR PART NUMBER. ON MICRO SECTIONING WE FIND NO INTER CONNECTION
BETWEEN HOLE COPPER AND INNER LAYER (SEVENTH LAYER).
  THE CONSTRUCTION 1,2,7 & 8 ARE SIGNAL LAYERS REST ARE GROUND LAYERS.
  TWO TO SEVEN ( INNER LAYERS HAVE ONE OUNCE BASE COPPER) ONE AND EIGHTTH
LAYER
HALF OUNCE BASE COPPER.
   COPPER INSIDE THE HOLES IS >25 MICRONS. WE DONT FIND ANY WEDGE VOID OR
PINK RING.

  THE CUSTOMER BAKES THE BOARD BEFORE ASSEMBLY AND ALL BOARDS PASSED
ELECTRICAL TESTING. BUT AFTER ASSEMBLY THE CUSTOMER REPORTS INNER LAYER 
OPEN.

CAN ANYONE THROW LIGHT ON THE ABOVE PROBLEM?

Thanks in advance


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