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

[miner_tom]

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
[email protected]

 

[Joerg]

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.

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

 

[LVMarc]

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
[email protected]

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

 

[Glen Walpert]

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
[email protected]

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

<paste>
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.

http://www.flexiblecircuits.co.uk/products/reel_to_reel.asp


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

http://www.samtec.com/flex_circuitry/Flex_standard_HS.aspx?nav=3D1760


http://www.samtec.com/cable_assemblies/data_rate/std_drc.aspx?nav=3D1754


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

</paste>

 

[Tim Williams]

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