i give below some more information on the defect.

 we use permanganate desmear and direct metalisation process which requires
microetch as last step .we do fullpattern plating after imaging. for inner 
layer adhesion we use reduced blackoxide.

The construction :

______________   1/2 Oz cu

--------------   1080
--------------   1080
_______________   0.008         Required thickness  1.6 m.m + / - 0.2 m.m

---------------   1080
---------------   2116
---------------   1080

_______________   0.008

---------------    1080
---------------    2116
---------------    1080

________________    0.008

----------------    1080
----------------    1080

________________     1/2 Oz cu   

we use FR 4 nominal Tg of 140 deg c.no mix up of different prepreg and inner
core has happened.

The microsection looks like hole wall pullaway with maximum separation at
center of hole  and minimum near inner connect.The connection in the hole is
between 
2nd and 7th layer only.

thanks in advance. 


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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