Here are some reasons rigid-flex is preferable over connectors:

- On designs with a large number of connections between boards,
  you have a way to get rid of two (and sometimes four) expensive
  connectors, and remove a large number of potential failures due
  to soldering, handling, mating, etc

- For designs that are expected to survive a lot of shock and vibration,
  usually the connectors fail first. Thus, a design without connectors
  is more robust.

- For high-volume production, you remove the BOM cost and any
  associated problems related to purchasing, lead time, component
  obsolescence. Its like getting a bare-board where the connectors
  have already been assembled and tested.

- For signal integrity, you have to adjust impedance calcs for the
  different materials, but this is still better than the mismatches
  through double connectors (and cable) in many cases, unless you
  buy expensive connectors. Pay attention to that reference plane!

Your "10 times higher" quote must have been prototype quantity
and likely a U.S. manufacturer?
You will get a much different ratio quoting 10,000 a month from
China, guaranteed. I'm only guessing but I think our bare-boards
are maybe 15-25% higher, and that's not counting the savings on
connectors, assembly and test.

For a low volume product, you should stay with the ribbon cable,
unless there are other factors that justify the cost and hassle.
(the primary "hassle" is that tooling costs are high so you don't
want to keep revising, you have a limited number of vendors,
and lead times are way longer).
A stable design with high volumes is perfect for rigid-flex,
but not what you described.

that's my opinion, anyway

good luck,
Jack



On 11/1/06, Brooks,Bill <[log in to unmask]> wrote:
>
> I'm curious as to how folks can justify going to Flex circuits with the
> enormous costs involved in making them... (suffering from sticker shock)
>
> The costs going from rigid to rigid-flex seem to be about 10:1.
>
> Is that typical?
>
> Any comments on making the transition to flex that someone with the
> 'scars'
> can share?
>
> P.S. - Please call me if you have some idea of how to keep flex costs down
> and make this technology a viable option in a commercial low volume
> product.
> Otherwise I think a ribbon cable and connector are much cheaper
> alternatives
> to building the cable into a rigid-flex board.
>
> Best regards,
>
>
> Bill Brooks
> PCB Design Engineer, C.I.D.+
> Tel: (760)597-1500 Fax: (760)597-1510
> Datron World Communications, Inc.
> Vista, California
>
>
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