What conditions expose these cracking problems quickly? Is it primarily due to the low end of thermal cycles? It seems it would be greatly exasperated by thicker planes of CIC or other materials. Is this true? Is the problem still significant with only 0.006" layers?

Is the problem unique to CIC or would the problem also exist if very thick, say 0.020-0.040" planes of copper were incorporated for thermal reasons?

Are the high temperature epoxies, i.e. 170C Tg or so, a serious problem for this?

Were working in this general area so any feedback is greatly appreciated.

----------
From: 	[log in to unmask][SMTP:[log in to unmask]]
Sent: 	Wednesday, April 16, 1997 3:38 AM
To: 	[log in to unmask]
Subject: 	Re: GEN: Radial Cracks/Fishscale Cracks

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 
[log in to unmask]       

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