[SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
- Date: Tue, 01 Dec 2009 09:05:08 -0500
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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