[SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
- From: Karthik Raj Guruchandran <karthik.guruchandran@xxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Tue, 1 Dec 2009 19:21:39 +0000
Itzhtal,
I have seen problems in matching 100 ohm impedance in microstrip
configuration on a 2 layer flex.The constraint that caused the problem was
flex thickness which had a direct relation to the base material thickness.
Since the di-electric had to be thin (to maintain flex thickness), the trace
width had to be smaller or the ground layer underneath had to be
compromised.
But if you don't have such strict constraints on flex thickness, then as Lee
and Scott mentioned, it should work just fine.
Cheers,
Karthik
On Tue, Dec 1, 2009 at 2:05 PM, Scott McMorrow <scott@xxxxxxxxxxxxx> wrote:
> I agree with Lee, microstrip works just fine for flex circuits with a
> cover layer. High performance stripline is also achievable in a
> flexible assembly if you crosshatch the planes. To do this, you need to
> do a bit of engineering homework in order to achieve controlled
> impedance and low loss.
> scott
>
>
> Lee Ritchey wrote:
> > Itzhtal,
> >
> > I use both polyamide based flex material and Liquid Crystal Polymer from
> > Rogers. Both work well. LCP has lower loss.
> >
> > The reason that stripline is usually not used in flex circuits is that
> > makes a 3 layer assembly which is not very flexible. There is nothing
> > wrong with microstrip. Works fine.
> >
> > Lee Ritchey
> >
> >
> >
> >
> >
> >> [Original Message]
> >> From: Hirshtal Itzhak <ihirshtal@xxxxxxxxxx>
> >> To: Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>; <
> si-list@xxxxxxxxxxxxx>
> >> Date: 11/29/2009 4:00:51 AM
> >> Subject: [SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
> >>
> >> 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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> >>
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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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> Scott McMorrow
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