hi,

my reply is embedded.

...I would like to know the best height for spacing 20 pin LCCCs off the
board...

can't give you the answer without a lot more data.  actually, i couldn't give you the answer even if i had the data.  you need a mechanical engineer to help you out. however, some of the information this m.e. will need is:  a) what is the cte of the substrate you are mounting the lcc to, b)what is the environment to which it will be exposed, and c)what is the expected life?

...and the best means of achieving this height...

we use 4 mil, minimum posts implemented with dry film solder mask.  i think i'd prefer using solder columns similar to those that a company like 6 sigma could apply, because its tough piling on enough solder paste to get an acceptable solder fillet when you take the dryfilm post approach.

...My concern is that there be some compliance to allow CTE mismatch between the part and the board during themal cycling...

actually, you should be extremely concerned.

phil

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