Jim 

I have seen radial cracks especially when trying to use a copper-invar-copper
planes in the board.  The cracks occurred in the resin rich area where the
resin filled the clearance opening in the metal planes.  This also occurs
with polyimide, BT and some high temperature epoxies.  With the polyimide it
is general practice to screen Howe-fill, available from Arlon, into the holes
in the plane and partially or fully cure it before lamination.  Arlon has not
tried it on cyanate ester,  but  feel the it is compatible.  If the cracks
are occurring in the reinforced laminate area, usually some  
change in drill parameters and drill types will help.  The drills with thin
webs and relieved neck will improve this condition, also a slower down feed
is desirable.

I do not know what you mean by fish scales, perhaps you could describe.

Phil Hinton 
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