Christer,
	I couldn't find the CRES303 in any of my references.  However, the 303 
number is from the Stainless Steel group.  It shows 18% CR, 9% Ni, and a CTE 
of 18.7 ppm/C.  I think you are right about the CTEs where the two materials 
are acting like a bimaterial strip.  Ceramic has a CTE of about 7 ppm/C (if 
Alumina).  As they cool from the solder temp they won't shrink the same 
amount, stresses will build up, and something may give. 
	We recently had a similar situation.  We were using a conductive epoxy 
to attach the heatsink to a ceramic sub.  We didn't have separation, but we 
did have bow across the substrate that was unacceptable.  To get around this, 
there are several things you could try.  1)  Increase thickness of heatsink  
2)  Change adhesive to low temp solder or epoxy/silicone adhesive  3)  Change 
heatsink material to Kovar (CTE of 5.9).
	Good luck.

Glenn Pelkey
Maxtek Components Corp.
Quality/Reliability Engineer

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