# [SI-LIST] Re: Basic question on power plane capacitance

*From*: "Mikhail Matusov" <matusov@xxxxxxxxxxxx>*To*: "steve weir" <weirsi@xxxxxxxxxx>*Date*: Thu, 9 Sep 2010 14:34:43 -0400

Steve, I am measuring on a non-populated board with a simple capacitance meter, i.e. at some low frequency. I might be off in thickness by 1 mil (4 instead of 5), but that won't explain doubling the capacitance. For the dielectric constant of FR-4 I used 4.3. I doubt it can get much bigger than that. /Mikhail ----- Original Message ----- From: "steve weir" <weirsi@xxxxxxxxxx> To: "Mikhail Matusov" <matusov@xxxxxxxxxxxx> Cc: <si-list@xxxxxxxxxxxxx> Sent: Thursday, September 09, 2010 2:21 PM Subject: Re: [SI-LIST] Basic question on power plane capacitance > Assuming that you are measuring while the board is unpowered and > unpopulated, the variables are the actual thickness, and composition of > the dielectric layer. If you have some IC attached to the polygon all > bets are off. > > Steve. > > Mikhail Matusov wrote: >> Hi all, >> >> I have a small polygon in a plane layer of a multi-layer PCB. There is a >> solid ground plane underneath it and the top signal layer above. I have >> calculated from the basic plane capacitance equation that the plane >> capacitance for this polygon should be in the range of 420 pF. However, I >> am measuring 890 pF with one meter and 1 nF with another. I was wondering >> what am I doing wrong? >> >> >> Thanks, >> /Mikhail >> ------------------------------------------------------------------ >> 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: >> http://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: >> http://www.freelists.org/archives/si-list >> Old (prior to June 6, 2001) list archives are viewable at: >> http://www.qsl.net/wb6tpu >> >> >> > > > -- > Steve Weir > IPBLOX, LLC 150 N. Center St. #211 > Reno, NV 89501 www.ipblox.com > > (775) 299-4236 Business > (866) 675-4630 Toll-free > (707) 780-1951 Fax > > > ------------------------------------------------------------------ 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: http://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: http://www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu

**Follow-Ups**:**[SI-LIST] Re: Basic question on power plane capacitance***From:*Howard Johnson

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**[SI-LIST] Combine single S-Parameters (S1P) to 4Port model (S4P)***From:*Hermann Ruckerbauer

**[SI-LIST] Re: Combine single S-Parameters (S1P) to 4Port model (S4P)***From:*steve weir

**[SI-LIST] Re: Combine single S-Parameters (S1P) to 4Port model (S4P)***From:*Hermann Ruckerbauer

**[SI-LIST] Basic question on power plane capacitance***From:*Mikhail Matusov

**[SI-LIST] Re: Basic question on power plane capacitance***From:*steve weir

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