In your message dated Monday 18, November 1996 you wrote :
> 
> 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.

Is the separation in the electroless copper layer or are these direct plated 
boards?

If the evidence suggests cracking of the electroless layer then it could be due 
to too fast a plating rate causing coarse grains and brittle deposits which 
crack under thermal cycling. Electroless copper must be a fine grain system and 
the plating rate tightly controlled (typically <2.5 microns in 30 minutes).

The stress of z-axis thermal expansion is greater at the surface layers than in 
the centre due to the laminate expanding more than the copper which is why 
failures will tend to occur on the outermost inner layers.

Good luck,
Paul Gould
EMail [log in to unmask]

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