If you HAVE TO use parts like that, try a low CTE PCB material, such as Arlon 85NT.  This is nice stuff, with a listed CTE under 10ppm/C.  It goes up a bit with high copper loading.  Very stable, Tg over 200C, but sucks up moisture and is hell to board route without the edge fuzzing due to the aramid fibers.

>>> [log in to unmask] 4/28/2006 1:47:58 pm >>>
Hi Ioan,
Castellated ceramic leadless chip carriers were a bad idea when the were 
developed in the '80s, and nothing has changed*oops, I forgot about that SAC-stuff 
making things worse.
The problem is not the 'castellations' per se, but the fact that they will 
not allow the CC to swim up. Thus, the solder joint thickness is at a minimum, 
producing the worst-possible SJ reliability geometry--if you shim up the CC to 
increase SJ height, you can get about the same as what you get with BGAs with 
the same ball dimension.
Putting large ceramic components on FR-4, castellated or not, is not a good 
idea.


Werner

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