Tom
Your operating temperature is not difficult.
The problem will occur at cool down from solder.
You don't give any details about the board (ie thichness)
Must you use FR4? There are reinforcements other than glass which will give
you a better CTE match (Thermount for example)
There are also non-rigid interconnect substates which will not stress the
solder joint.
You might try Joe Fjelstad at Tessera 408 894 0700
Good Luck
Jerry Sallo
760 346 6717
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