design with flexible PCB

What is wrong with using shielded ribbon cable and conventional IDC connectors? The flexy may be cheaper in volume, and probably thinner, but your connector is probably going to wipe out most of these potential advantages.

Things to watch with multilayer fexible circuits are keeping the build- up balanced, and not bending them around excessively tightly radiused bends. Hewlett-Packard used flexies in their linear-motor based X-Y recorder back in the 1970's, and wrote up the development at length in the Hewlett-Packard Journal at the time. They paid a lot of attention to the risk that the flexible circuits involved would become brittle with time and break, and did quite a lot of testing to make sure that this didn't happen.

In principle, the contents of the H-P Journals are accessible on-line, but I can't get anything out of their search engine.

-- Bill Sloman, Nijmegen

Flex cable takes less volume. I also hope to find smaller connector (at least on one side). Cost is not that much of an issue. There are ways to attach robust connector to flex cable (U have seen TH electrolytic caps on flex board).... I have to talk to our board house... Thank you. Michael

Few manufacturers can actually do flex [or more likely rigiflex] properly. Cost may not be that much of an issue, but a typical flex will cost at least 6x [and probably more] the equivalent rigid + interconnect. Many manufacturers say they can do it, but you'll be plagued by poor yield unless you go to a much more expensive outfit (who are expensive because they _can_ do it).

Unless you have a compelling reason for flex, I would advise against it. I have used rigiflex boards where I needed to, incidentally, and they can work great, but they have their drawbacks.

Cheers

PeteS