Thanks all for the responses.

The reason for my interest, we were having numerous units returned from the 
field.  Analysis revealed cracked solder joints on the board.  It was learned 
the units were occasionaly being subjected to a 20C per minute thermal cycle out 
in the field.  The field failure was also subsequently verified by lab testing.

The units are encapsulated for vibration protection so our thoughts were to get 
as robust a solder joint as possible and make sure the CTE and modulus at the 
temperature extremes were as benign as possible.

I remember when we had real components on the board (poke through) and the 
module had to encapsulated with a hard polymer a buffer coating was applied 
(possibly silicone) before encapsulation to help reduce the forces on the 
components, is this technique still in packaging folks play book?

Dale Hart
UTC

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