Dear Jennifer, the impedance, velocity of propagation and wavelength of the travelling wave changes with the materials used: v=c/SQR(dk) wavelength=c/f*SQR(dk) Z=Z0/SQR(dk) That means, that the density of your circuit can be higher, the higher your permitivity (dk) is. You can use smaller traces and less dielectric thickness while having the same impedance, when switching to a higher dk. If you choose to reduce the layer stack and use higher dk material to kompensate for it, then you would also reduce the crosstalk between the traces on the board, because the electric field will be more dense due to shorter GND-plane distance. 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 Jennifer Maharani Gesendet: Mittwoch, 24. Juni 2009 07:55 An: si-list@xxxxxxxxxxxxx Betreff: [SI-LIST] Low permittivity vs. High permittivity Dear all, I understand that higher subtrate permittivity the more capacitive it is, which means the more capacitive coupling will be introduced. This is obviously bad particularly for structures like multi transmission line. What is then the advantage of higher permittivity substrate like silicon over lower permittivity substrate like glass? Many thanks, Jenni ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu