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

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From: cadpro2k@dacafe.com
Date: Wed Apr 12 2000 - 09:27:33 PDT


E,

Check with GE (General Electric Company), Electromaterials division.
They have the best reference material on board materials I have found.
They have alot of test data on most materials, and specialize in GETEK
material.

GL.

M

---------Included Message----------
> Date: Wed, 12 Apr 2000 02:12:36 -0700
> From: "e" <evillaf@home.com>
> Reply-To: <si-list@silab.eng.sun.com>
> To: <si-list@silab.eng.sun.com>
> Subject: Re: [SI-LIST] : 回复: [SI-LIST] : Parallel Plate
Capacitance for Bypass
>
> Lee,
>
> This is pretty useful info. Do you know where I can get other
info on FR-4 and
> other board dialectric materials compiled together in one
reference?
>
> TIA
> E
>
> Ritchey Lee wrote:
>
> > FR-4 class materials have a breakdown voltage rating in excess
of 1000 Volts
> per
> > mil of thickness. This would say that your 5 mil dielectric
will withstand
> at
> > least 5000 Volts.
> >
> > Lee
> >
> > rachild.chen wrote:
> >
> > > 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 <jjohnson@minn.teradyne.com>
> > > 收件人: si-list@silab.eng.sun.com
<si-list@silab.eng.sun.com>
> > > 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 <rmiller@Brocade.COM>
> > > >> > >To: si-list@silab.eng.sun.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
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> > > >>
> > > >> --
> > > >> 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
> > > >> rmiller@brocade.com, rbmiller@sjm.infi.net
> > > >>
> > > >>
> > > >
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> > > >
> > >
> > >
------------------------------------------------------------------------
> > >
> > > Chen Rachild <rachel.chen@huawei.com.cn>
> > > Huawei Tech. Ltd
> > > SI Depart.
> > >
> > > Chen Rachild
> > > Huawei Tech. Ltd <rachel.chen@huawei.com.cn>
> > > SI Depart.
> > > Shenzhen
> > > 518057
> > > China
> > > Additional Information:
> > > Version 2.1
> > > Last Name Chen
> > > First NameRachild
> > > Label WorkShenzhen 518057 China
> > > Revision 20000331T034345Z
> >
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