You've covered it pretty well. Getting "down" to very small and fine pitch device types often does
exceed flex circuit limits. I won't get into the tolerance factors as the opening and tooling
inconsistencies you have stated make for wide variations may often overcome the device size alone -
notwithstanding solder termination area requirements. Another important factor, not mentioned, is
that of material thermal charactestic variabilities adding to the mix.
One costly (always a relative term) suggestion I would make is to use rigid/flex where small, fine
pitch device types are required. This provides an obvious solution as you now have a "normal" PCB
surface where component placement is concerned and flexibility to fit or function where needed. Will
it fit or flex where you want is another story.
Earl Moon
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