Hi Jack... (don't say that on an airliner)
:-) (okay, I know that's a old joke...)
Many of your stated reasons are the same reasons we are looking at this
rigid flex approach...
The cable type we would use is most likely something like this...
http://www.globalsources.com/gsol/I/IDC-cable/p/sm/1000618921.htm
<http://www.globalsources.com/gsol/I/IDC-cable/p/sm/1000618921.htm>
Or this http://www.axon-cable.com/pdf/axolinkFR.pdf
<http://www.axon-cable.com/pdf/axolinkFR.pdf>
There are some other types too, including some coaxial cables but the
majority of the connections can be made with this type of commercial
interconnects. not too expensive.
Critical signals can be handled differently of course.
Shock and vibe and temp issues all are there but probably not as bad as you
are dealing with. The proper application of strain relief for cables covers
much of the issues you would see with the less expensive cabling.
Best regards,
Bill Brooks
PCB Design Engineer, C.I.D.+
Tel: (760)597-1500 Fax: (760)597-1510
Datron World Communications, Inc.
Vista, California
-----Original Message-----
From: Jack Olson [mailto:[log in to unmask]]
Sent: Wednesday, November 01, 2006 11:52 AM
To: (Designers Council Forum); Brooks,Bill
Subject: Re: [DC] Flex Circuit costs... sticker shock?
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] <mailto:[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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