[SI-LIST] AW: Stripline Propagation Velocity
- From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- To: "ryan.satrom@xxxxxxxxxxx" <ryan.satrom@xxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 16 Aug 2012 15:04:38 +0000
The velocity of propagation is speed of light divided by the square root of dk,
and each material has a different dk, thus the speed is different.
V=c/SQR(dk)
This dk is the effective dk, thus the resin content and glass styles used have
another strong influence on the speed. Glass has a dk of approx. 6, resin
approximately 3, the mis is somewhere between 3.3 and 4.6 depending on resin
style and glass style. In some Datasheets (like ISOLA's datasheets) you will
find dk curves for several resin contents.
BR
Gert
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von ryansatrom
Gesendet: Donnerstag, 16. August 2012 16:47
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Stripline Propagation Velocity
Hello All-
I took some VNA measurements on PCB's manufactured with several different
materials.
Each PCB material had two 50 Ohm stripline traces on different layers: A trace
between two 4 mil cores, and another trace between two 8 mil cores.
I expected that the propagation velocity of two traces to be the same, but
measuring the propagation delays indicated that they were not (the PCB launch
and vias were calculated out.)
Of the six different PCB materials that I measured, five of them were faster on
the stripline trace between the 4 mil cores. The differences in speeds were
outside the range that could be attributed to measurement error or
manufacturing tolerances.
What can the differences in speeds be attributed to?
Thanks,
Ryan
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