[SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
- From: alex@xxxxxxxx
- To: "Hirshtal Itzhak" <ihirshtal@xxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Sun, 29 Nov 2009 14:16:09 +0100 (CET)
Hi Itzhak,
I spent the last hour writing a nice email for the SI-List, but following
a browser problem, I lost it... :(
Anyway, here is a few links to help you:
http://www.flexiblecircuittechnology.com/formflex.htm
Sorry, but you'll need to register.
Flex Rigid article:
http://pcdandf.com/cms/magazine/41/4466
Flex material datasheet. The thickness available is 1,2,3 and 5 mil ONLY.
http://www2.dupont.com/Kapton/en_US/assets/downloads/pdf/HN_datasheet.pdf
Minco Flex circuit design guide
http://www.minco.com/uploadedFiles/Products/Flex_Circuits/Technical_Specifications/FC302.pdf
I'm pretty sure that Gert made an error when writing 0.8mm. I think it
should be 0.08mm (~3mil) which gives ~50ohm single ended impedance with a
base material of 3mil thick.
It's common for flex to use 1-2mil wide traces for high volume (LCD
panels). But depending on what you're doing, you might end up with an
almost non-manufacturable flex (been there, done that...). Since then,
I'm sticking with 4mil track and space.
The stripline configuration is hard to obtain with the base materials
available. A quick field solver result:
Copper
Polyimide, 5mil, Er=4
Tracks
Polyimide, 5mil, Er=4
Copper
Remark that the 5mil polyimide is the THICKEST available.
You need 3mil wide track width (or even thinner) to be close to 50ohm.
4mil track --> 42.5ohm
3mil track --> 48ohm
2mil track --> 55ohm
If you use thinner base material, you'll end-up with even thinner traces...
Have a nice weekend,
Alexandre Desnoyers
Electronic Designer
Qtechnology A/S
Copenhagen, Denmark
> Hello Gert
>
> First - thank you for your contribution.
>
> I have a few questions regarding your email:
>
> 1) You refer to a trace width of 0.8mm as "small". This is a 31.5mil
> width, which I hardly call "small"! I regularly use 3-4 mil trace widths
> in my designs. Is there something different in Flex circuits, which
> enforces me to use such LARGE traces (compared to my regular traces)?
>
> 2) I see the problem you mention for the Microstrip configuration. Is it
> common to use Stripline on a flex circuit? I was told this is impractical,
> although I'm not sure what the reason is.
>
> Thanks
>
> Itzhak Hirshtal
> Elta
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Havermann, Gert
> Sent: Tuesday, November 24, 2009 4:19 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] AW: Multi-Giga-Hertz Rigid-Flex Feasibility
>
> Hello Itzhak ,
>
> All Polimide (Kapton) materials will do the job from a loss and dispersion
> prospective. The tolerance you mention seems to be unreasonable high for
> an etching tolerance. I did Flex designs with impedance control, 100Ohm
> +/-10Ohm, 0.8mm tracewidth without problems (of corse I had to pay extra
> for the small trace width).
> If you refer to an impedance tolerance due to bending and surrounding
> material, thats another story. If you design it in microstrip (as you are
> planning it), then everithing touching the flex might change your
> impedance. Designing it in stripline decreases the flexibility of the flex
> and increases cost.
>
> Look for Dupont, Grace Electron or Shengyi Flex materials for more info.
>
> BR
> Gert
>
>
> --------------------------------------------------------------------------
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> -----Ursprüngliche Nachricht-----
>
> Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
> Auftrag von Hirshtal Itzhak
> Gesendet: Dienstag, 24. November 2009 14:21
> An: si-list@xxxxxxxxxxxxx
> Betreff: [SI-LIST] Multi-Giga-Hertz Rigid-Flex Feasibility
>
> Hello All
>
>
> My project manager intends to use a rigid-flex design in our next
> high-speed board.
>
>
>
> He wants to route a few pairs of 3.125GHz from a rigid section to another
> one through a flex section.
>
>
>
> Does anyone know if this is feasible? I found out that the 2 sections,
> although spec'd to be 100-Ohm diff impedance, can still differ
> substantially - as much as 30%, because the tolerance of the flex section
> is +/-20%. Can such a design work for a substantial trace length? Should I
> restrict the trace length on the flex section to be no more than an inch
> or so, in order to reduce the impact of the supposed non-uniform
> impedance?
>
>
>
> I intend to use a 2-layer flexible laminate with the pairs on one layer
> and a Ground reference on the other one.
>
>
>
> Any advice on this matter would be helpful
>
>
>
> Thanks
>
>
>
> Itzhak hirshtal
>
>
>
>
>
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