http://www.flexiblecircuits.co.uk/Flex_rigid.asp

The above is a link to a good explaination of the technology comparison with
more traditional structures.

You can also look at US Patent 4800461 if you wish. The title and abstract
are below

Multilayer combined rigid and flex printed circuits


Abstract
Multilayer rigid flex printed circuits are fabricated by a novel process to
provide structures having rigid sections incorporating insulator materials
which, when subjected to elevated temperatures, do not expand sufficiently in the
Z direction to cause difficulties, including delamination and cracking of
plated through barrels. The flex section includes flexible insulator materials
which extend to but not a substantial distance into the rigid section.

Hope this helps.
Joe

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