**From:** rachild.chen (*[email protected]*)

**Date:** Thu Mar 30 2000 - 19:43:45 PST

**Next message:**maher musa: "[SI-LIST] : Signal Integrity Position"**Previous message:**狶绰纷: "[SI-LIST] : Return path for stripline, two ground planes or one power and one ground?"**Next in thread:**Chris Padilla: "[SI-LIST] : Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate Capacitance for Bypass"**Reply:**Chris Padilla: "[SI-LIST] : Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate Capacitance for Bypass"**Reply:**Ritchey Lee: "Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate Capacitance for Bypass"

Who can tell me how much the break voltage of 5 mils FR4 is?We have do a

test.It will be break under 1500V.

5 mils is the littlest thickness of FR4.How much is it to support a

1500V break voltage?

Regards,

Rachild

-----Original Message-----

发件人: Jerry Johnson <[email protected]>

收件人: [email protected] <[email protected]>

日期: 2000年3月30日 9:55

主题: Re: [SI-LIST] : Parallel Plate Capacitance for Bypass

*>Ron,
*

*>
*

*>Could be we're missing each other somehow.
*

*>
*

*>What I saw was Steve say that 5 mils of FR4 would yield ~200 pF/square
*

*>inch.
*

*>
*

*>Then I thought you said "So, by extension, 2.2 mil dielectric. . .
*

*>should be
*

*>about 1000pf/in sq for FR4 . . ."
*

*>
*

*>That looked to me like you had taken [(5^2)/(2.2)^2] * 200 = 1033
*

*>pF/square inch.
*

*>
*

*>I commented that capacitance wasn't an inverse square relationship with
*

*>distance
*

*>between plates. I calculated more like [5/2.2] * 200 = 455 pF/square
*

*>inch.
*

*>
*

*>Perhaps I completely misunderstood your reasoning. If so, I'm sorry.
*

*>
*

*>Jerry Johnson
*

*>
*

*>Ron Miller wrote:
*

*>>
*

*>> Jerry
*

*>>
*

*>> maybe I am missing something or maybe we are not communicating
*

*>> well. The capacitance I am talking about would be an IC or a discrete
*

*>>
*

*>> device connected to power and ground. The capacitance would be
*

*>> somewhat limited by the quarterwave distance from that pin for any
*

*>> frequency of intrest, because above that distance the delay is too
*

*>> great for the capacitance to be of any effect.
*

*>>
*

*>> So, the 1 inch concern would roughly describe a circle with a 1/2 inch
*

*>>
*

*>> radius, which for FR4(velocity 170 ps/inch) or 85 ps.
*

*>>
*

*>> The frequency which has a quarterwavelength of 85 ps is 1/340ps=~3Ghz
*

*>> At 3 Ghz and below we get 200 pf per square inch, or about .27 ohms.
*

*>>
*

*>> Scaling from 3 Ghz, down in frequency we get higher Xc, but the
*

*>> effective
*

*>> capacitive area goes up. The limits are that several devices will be
*

*>> sharing
*

*>> the same capacitance and the board has dimensional limits so we must
*

*>> add capacitances. Scaling up in frequency, the effective capacitance
*

*>> goes
*

*>> down but so does the Xc.
*

*>>
*

*>> TRACES across a plane is an entirely different matter, and PLANE
*

*>> capacitance for the entire board is again a different matter.
*

*>>
*

*>> BOTTOM LINE:
*

*>> Capacitors below 200 pf in value are of little value for bypassing
*

*>> if you have 5 mil dielectric spacing power to ground.
*

*>>
*

*>> Ron Miller
*

*>>
*

*>>
*

*>> Gerald Johnson wrote:
*

*>>
*

*>> > Ron,
*

*>> >
*

*>> > Capacitance of planes is NOT a function of inverse square of
*

*>> > distance.
*

*>> > See thread in this list about a week ago. Well covered there.
*

*>> >
*

*>> > Valid to use inverse square distance for point source, not for
*

*>> > planes.
*

*>> >
*

*>> > Result, capacitance would be about (5/2.2)*200 = 454.6 pF if the
*

*>> > 100 pF per in^2 at 5 mils is correct.
*

*>> >
*

*>> > Jerry Johnson
*

*>> > Teradyne Inc.
*

*>> >
*

*>> > >Date: Mon, 27 Mar 2000 10:39:10 -0800
*

*>> > >From: Ron Miller <[email protected]>
*

*>> > >To: [email protected]un.com
*

*>> > >Subject: Re: [SI-LIST] : Parallel Plate Capacitance for Bypass
*

*>> > >
*

*>> > >Thanks Steve, I knew it was somewhere around there.
*

*>> > >
*

*>> > >So, by extension, 2.2 mil dielectric, available at very little if
*

*>> > any
*

*>> > >extra cost should be about 1000pf/in sq for FR4
*

*>> > >and eliminatee the need for discrete capacitors below 1000 pf.
*

*>> > >
*

*>> > >ron
*

*>> > >
*

*>> > >"S. Weir" wrote:
*

*>> > >
*

*>> > >> Ron,
*

*>> > >>
*

*>> > >> 5 mils should yield about 200pF / in sq, before taking away for
*

*>> > vias.
*

*>> > >>
*

*>> > >> Regards,
*

*>> > >>
*

*>> > >>
*

*>> > >> Steve.
*

*>> > >> At 02:30 PM 3/24/2000 -0800, you wrote:
*

*>> > >>
*

*>> >
*

*>> > **** To unsubscribe from si-list or si-list-digest: send e-mail to
*

*>> > [email protected] In the BODY of message put: UNSUBSCRIBE
*

*>> > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
*

*>> > si-list archives are accessible at http://www.qsl.net/wb6tpu
*

*>> > ****
*

*>>
*

*>> --
*

*>> Ronald B. Miller _\\|//_ Signal Integrity Engineer
*

*>> (408)487-8017 (' 0-0 ') fax(408)487-8017
*

*>> ==========0000-(_)0000===========
*

*>> Brocade Communications Systems, 1901 Guadalupe Parkway, San Jose, CA
*

95131

*>> [email protected], [email protected]
*

*>>
*

*>>
*

*>
*

*>**** To unsubscribe from si-list or si-list-digest: send e-mail to
*

[email protected] In the BODY of message put: UNSUBSCRIBE si-list

or UNSUBSCRIBE si-list-digest, for more help, put HELP.

*>si-list archives are accessible at http://www.qsl.net/wb6tpu
*

*>****
*

*>
*

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**Next message:**maher musa: "[SI-LIST] : Signal Integrity Position"**Previous message:**狶绰纷: "[SI-LIST] : Return path for stripline, two ground planes or one power and one ground?"**Next in thread:**Chris Padilla: "[SI-LIST] : Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate Capacitance for Bypass"**Reply:**Chris Padilla: "[SI-LIST] : Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate Capacitance for Bypass"**Reply:**Ritchey Lee: "Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate Capacitance for Bypass"

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