[SI-LIST] Re: Losses - 2.5Gbps on FR4

Just as a point of reference, we see a consistent loss tangent of .0215 
for FR-4 from one of our fabricators using Polyclad materials.  But it 
is something that should be measured for your particular fab process and 
stackup (it will change with different glass/resin ratios and process 
impurities).  Be sure to have a good launch into your board in order to 
make this measurement.  A bad launch will distort the loss measurement.  
And perform some comparision measurements across a few traces or 
structures of different sizes to be sure that all measurement artifacts 
have been removed.

best regards,

scott

-- 
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com


Raymond W. Waugh wrote:

>A loss tangent of 0.030 may sound lossy when compared to more expensive PCB
>materials (such as the Teflon-based materials used at X-Band and higher by
>we microwave geeks), but it is pretty typical for FR4.  I have measured
>several six inch test lines over a wide range of frequencies, and have found
>that FR4 comes in at 0.030 almost every time, and over a range of frequency
>from 1 to 6 GHz.
>
>I also agree with Jeff - ten hours of simulation to obtain losses is
>excessive.  You can fabricate and test a microstrip line in less time...
>
>Ray Waugh
>Volcano Microwave
>
>----- Original Message -----
>From: <jeff_latourrette@xxxxxxxxxxx>
>To: <dorin.oprea@xxxxxxxxxxx>
>Cc: <si-list@xxxxxxxxxxxxx>
>Sent: Tuesday, July 29, 2003 9:01 AM
>Subject: [SI-LIST] Re: Losses - 2.5Gbps on FR4
>
>
>Dorin:
>Sounds real to me, tand = 0.03 is pretty lossy material.
>
>Based on information provided, I also ran your scenario (in msec) on
>Linecalc, part of Agilent's ADS, and got 5.5 dB power loss (for just the 30"
>line) at 1.25 GHz ("fundamental" of switching frequency).  Loss was 9.9 dB
>at 2nd harmonic and 18.4 dB at 4th, which sounds very high, but seems to
>compare well with Geoff's results.
>
>You shouldn't have to run 10 hours of simulation just to get losses,
>although I'm sure there are other things you are after.  You could simulate
>(& measure to compare) an inch or two of FR-4 to get dB/inch.
>
>Experimental boards allowing different connector types and run lengths are
>invaluable for this type of work.
>
>Some colleagues of mine at Agilent wrote a great paper on this at ONIDS 2002
>.....
>
>The Path to 10 Gb/s:Connector and Backplane Capabilities for High-Speed
>Applications
>
>http://literature.agilent.com/litweb/pdf/5988-7053EN.pdf
>
>
>Enjoy,
>
>Jeff LaT.
>
>
>-----Original Message-----
>From: Dorin [mailto:dorin.oprea@xxxxxxxxxxx]
>Sent: Tuesday, July 29, 2003 7:47 AM
>To: si-list
>Subject: [SI-LIST] Losses - 2.5Gbps on FR4
>
>
>Hi,
>The simulation I did shows 5dB voltage loss on 30" long interconnect on
>FR4 (tan loss 0.03) which includes 0.005" traces 0.5 oz. copper, one
>NexLev and two Metral connectors. Two pulses P/N, 2V with 50 ohm series
>were applied to the circuit and one 100 ohm resistor as a termination.
>Is this loss real? If not, can you tell what is the approximate
>deviation, just to get a feeling?
>I was told that hspice simulated losses are too optimistic and
>therefore, long traces should be chopped; if so, what would be the
>optimum segment length recommended for the loss simulation so that the
>simulation time is not excessively long (now I need over 10 hours on
>Linux LSF server).
>
>Thanks,
>Dorin
>
>
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