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Flex Printed Circuit (FPC) used as a ribbon cable? Possible at high data rates?

Hi,

I am working on an application that requres ribbon cable runs of about a meter, for differential pairs at 100 Ohms (50 Ohms odd mode) impedance. My data rate is about 1.5 Gb/s . I have had lots of experience specifying printed circuit boards over the years and I though that "flex" pcb circuits were limited to the panel sizes of a particular fab house. Recently, I have seen some data to the effect that "ribbons", manufactured like pcbs, are available now that can be run for many feet, because of "step and repeat" fabrication processes.

Yes, I am aware of the limiting factors of long cable runs on high speed signals (dispersion, crosstalk, emi, etc) but I am wondering if FPC (flexible printed circuit) technology has advanced to the point where it can compete with ribbon cable technologies. I know that in terms of signal integrity, a pcb beats a cable.

Thank You Tom tom_cip snipped-for-privacy@hotmail.com

Reply to
miner_tom
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Last time I priced it out (roughly four years ago) flex wasn't even close in cost.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Tom,

For signal fidelity you cannot beat a coaxial cable! Now for inches of signal signal path you wont have cables, connectors etc. but for "long" paths >0.5 meters and high bandwidth (signal rates) > 300 MHz.. 1 nS rise times etc.. cable would be better than printed microstrips!

That being said flexible PCB can use high quality dielectrics, like kapton, or mylar and with proper sizing and spacing you can make a good quality RF or high data rate interconnect

marc

Reply to
LVMarc

This subject just came up on the Signal Integrity list, and this was the best response IMO:

Reel-to-reel processes are also available which allow extremely long (100 meter +) flex runs to be fabricated, so the panel size limitation goes away. Here's an example.

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At Samtec, we manufacture both high speed ribbon assemblies and high speed flex assemblies.=20

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Both have their pros and cons, and it is often a tough call as to which is best suited for a particular application. =20

For short runs (< 2 feet), flex can make a lot of sense. But for longer runs, coax or twinax ribbon cables can offer lower loss. And cable is better at handling higher power levels.

Flex can definitely work in high speed applications, but a lot of folks just don't seem to think about it that way. We're actually using flex assemblies in RF and microwave applications where coax was once considered mandatory.

In making the choice between flex and cable, mechanical requirements often win out over electrical. Flex is usually lighter and smaller. And it can offer much better flex-life performance, but usually in only one axis of flexing. Cable can offer better flexibility in all 3 axes.

Julian Ferry High Speed Engineering Manager Samtec, Inc

Reply to
Glen Walpert

I've seen it used as such in, of all things, a Polaroid-style (made by Sony or something) camera I took apart. Had flex PCB (with edge connectors) running to the motor and flash and timer/counter and whatever stuff inside the thing. Oh yeah, it was the kind with the old flat style Polaroid battery -- 4.5V. I have that battery laying around in the basement...

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

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