Serious capacitance values requires embedded high-K dielectric like
Faradflex. The recommended Google search brings that up as the first item.
And you're right, Lee. "FR-4" is a concept, not a spec per se.
Orin
On Wed, Jul 20, 2016 at 3:16 PM, Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
wrote:
The dielectric constants of the materials commonly called "FR-4" with a
resin content that works for these purposes is rarely over 4. Usually more
like 3.8. As a side note, FR-4 does not specify a material. It
specifies
a UL flame retardant class.
Wonder when we will cease using only the term FR-4 to call out a material.
IF that is all that is on the fab drawing it is possible to get more than
30
different PCBs, all of which satisfy this spec.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Joseph.Schachner@xxxxxxxxxxxxxxxxxx
Sent: Wednesday, July 20, 2016 12:37 PM
To: james.f.peterson@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: embedded capacitance for decoupling
Capacitance of parallel plates with dielectric is C = k E0 A / d where E0
is
the permittivity of space (close enough to air) which is 8.854e-12, k is
dielectric constant (of FR4: about 4.5), A is Area of the plates and d is
separation between the plates.
So, how much area on two adjacent layers are you willing to devote to this?
I'll pick a really large guess: how about a square 30cm on each side, so
the
Area is 900 cm^2
I'll also be generous and say there are only 0.2mm between those planes.
So:
C = 4.5 * 8.845e-12 * 0.9m^2 / 2e-4 = 0.1793uF
thirty 0.22uF capacitors total 6.6uF.
SO, you need about 37 times more capacitance than a 30cm * 30cm square with
0.2mm separation gives. You almost certainly don't have enough layers or
enough area to get there.
In short: no, the capacitance realized by embedding capacitance in the PCB
stackup can not (reasonably) replace thirty 0.22uF caps.
--- Joe S.
From: "Peterson, James F (Chief Engineers)"
<james.f.peterson@xxxxxxxxxxxxx>
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Date: 07/20/2016 02:51 PM
Subject: [SI-LIST] embedded capacitance for decoupling
Sent by: si-list-bounce@xxxxxxxxxxxxx
Can the capacitance realized by embedding capacitance in the PCB stackup
replace discrete decoupling capacitors?
Let's say the discrete decoupling solution for a processor's Vcore rail has
thirty 0.22 uf Hi-F caps. Is there a practical way to use an embedded
passives approach in the PCB stackup to achieve the needed decoupling
capacitance and thus remove these thirty discrete capacitors?
If so, are there any papers published around this? (I've searched and can't
find anything substantial on replacing discrete ceramic capacitors with
embedded PCB capacitance.)
Thanks,
Jim Peterson
Honeywell Aero
------------------------------------------------------------------
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 forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
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 forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
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 forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
