[SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: "'Hirshtal Itzhak'" <ihirshtal@xxxxxxxxxx>, "'Scott McMorrow'" <scott@xxxxxxxxxxxxx>, "'Lee Ritchey'" <leeritchey@xxxxxxxxxxxxx>
- Date: Wed, 02 Dec 2009 10:23:29 -0800
Itzhak
Think about what determines Zo. It is the relationship between the signal
path and its return path(s). If the signal path and return path do not
change from rigid to flex to rigid then Zo does no change. If you add extra
metal or insulation at the boundaries that effect the fields then you will
get changes in Zo. It all depends on how you design your system.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Hirshtal Itzhak
Sent: Wednesday, December 02, 2009 1:37 AM
To: Scott McMorrow; Lee Ritchey
Cc: Gert Havermann; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
Hi Scott
As I've already told a few times in my emails, my main concern is impedance
continuity across the rigid-flex-rigid combination.
If the tolerance of the 3 sections is independent of each other, and if the
flex tolerance is +/-20%, assuming a standard +/-10% tolerance on the rigid
boards, this could create a substantial impedance discontinuity, e.g:
120-Ohm on the Flex and 90-Ohm on the Rigids.
I just wanted to know if and how it's practical, and over what flex-length,
to transfer a few GHz (up to 3.125GHz) signals from one rigid board to the
other
Thanks
Itzhak
________________________________
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Tuesday, December 01, 2009 4:05 PM
To: Lee Ritchey
Cc: Hirshtal Itzhak; Gert Havermann; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
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>
<mailto:ihirshtal@xxxxxxxxxx>
To: Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>
<mailto:Gert.Havermann@xxxxxxxxxxx> ; <si-list@xxxxxxxxxxxxx>
<mailto: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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-----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
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
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