Jeff Maybe from a skew standpoint the flex could be better and yes there are skew issues with ribbonized coax's that have to be considered. From what I am hearing about at conferences there are miniature coax's, single and ribbonized out there now that run up to 10-12 gb/s with <10% eye closure. One way around the flex stiffness problem is simply to fabricate with 1/4 or 1/8 oz copper. Disc drive mfg's have been doing this for years. According to my cable loss calculator one can be off +/- 5% with impedance and still have a good >20db return loss. Richard > From: jeff.loyer@xxxxxxxxx > To: ihirshtal@xxxxxxxxxx; si-list@xxxxxxxxxxxxx > Date: Wed, 2 Dec 2009 12:48:25 -0800 > Subject: [SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility > > In my experience, both flex and coax have their pros/cons > Perhaps some flex can change its dimensions and hence impedance when bent > tightly, but I haven't experienced this (maybe because I keep the designs > very thin?). And most applications can (and should) limit this or form the > bend permanently. > > RigidFlex (or flex) does take a lot of care to keep from introducing > inadvertent problems. Some that I've fought through include: > * too rigid - couldn't bend the thing without a hammer and vise. Stripline > that isn't hatched will do this, as will "book binding", in my experience (it > was supposed to make it more flexible, but failed miserably in my experience > - simple physics, as it turned out. You'd have to have the 2 parts of the > book-binding VERY close to each other, otherwise you've introduced a very > thick beam) > * be sure to not pass over severe bends at a right angle. Haven't experienced > failures when not doing this (always did it), but heard from experts that > it's something to avoid. > * impedance control over a hatched ground plane. Good luck modeling that one. > It's tough, and the design will probably have to be tweaked based on > empirical data. And, you'll have to be conscious of increased cross-talk, if > routing density is high. > * low loss dielectric covered with high-loss coverlay, ending up with more > loss than expected. > * you have to adjust trace width between the flex and rigid portions to keep > Z0 constant. Check this carefully, beforehand and afterwards. I've had > vendors apply the same aperture to my entire trace, undoing my careful > modeling. > > In general, I'd say expect a spin or two to get it right. Plan on building > some test boards in your schedule. > > But coax isn't without challenges, either. > * You must be sure your manufacturer really knows how to control skew between > signals, especially diff. pairs. You might want to plan on a verification > build to ensure this is done, or paying handsomely. > * At some point, you've got to attach that beautiful clean coax to your > board, and that attachment point deserves careful design, both for Signal > Integrity and strain relief reasons. > > Again, I'd plan on a spin to verify your design if this is your first foray. > > Regarding the original question (if I read it correctly), I think most > vendors will give you +/-10% for your design w/o too much cost adder. But > you're right, you'll have to treat the transition from flex to rigid-flex the > same way as a layer transition in your simulations - assume no correlation > between impedance of the two. But, at least there isn't a via. So, if the > design guide allows 2 or more layer transitions, you're golden. Else, you'll > be in the gray area. > > My 2 cents - good luck, > Jeff Loyer > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On > Behalf Of Richard Jungert > Sent: Wednesday, December 02, 2009 12:01 PM > To: tom dogastino; hirsh itzack; Scott McMorrow; lee ritchey; > gert.havermann@xxxxxxxxxxx; si list freelist > Subject: [SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility > > Guys. > > > > If you bend the flex cable the Zo changes too. BTW. Bend it some more while > observing the eye pattern on the scope and watch the eye pattern open and > close at higher speeds. > > > > One can fabricate a flex with 1/4 oz copper. We did a 100 ohm differential, > 12 inches long a couple of years ago with 1oz. copper and we could not bend > it without great force. Not good and the performance was not acceptable > either. Flex's are generally made for low speed apps like signals running > inside disc drives between motors. > > > > I would recommend to anyone not to do a flex but to use minature coax's or > ribbonized coax's for high speed apps and signaling between rigid boards. > > > > Richard Jungert > > > > > > > > > > > > > > > > > From: tom@xxxxxxxxxxxxx > > To: ihirshtal@xxxxxxxxxx; scott@xxxxxxxxxxxxx; leeritchey@xxxxxxxxxxxxx > > CC: Gert.Havermann@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx > > Subject: [SI-LIST] Re: AW: Multi-Giga-Hertz Rigid-Flex Feasibility > > Date: Wed, 2 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 > > > > > > > > -------------------------------------------------------------------------- > > Absender ist HARTING Electronics GmbH & Co. KG; Sitz der > > Gesellschaft: > > > > > > Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596; > > persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH; > > Sitz der Komplementär-GmbH: Espelkamp; Registergericht der > > Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH: HRB > > 8808; Geschäftsführer: Torsten Ratzmann > > > > > > -----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 > > > > > > > > > > > > The information contained in this communication is proprietary to > > Israel > > > > > > Aerospace Industries Ltd., ELTA Systems Ltd. > > > > > > and/or third parties, may contain classified or privileged > > information, > > > > > > and is intended only for the use of the intended addressee thereof. 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