• From: "Sirisha Godavarthy" <Sirisha.Godavarthy@xxxxxxxxxxxx>
• To: "steve weir" <weirsi@xxxxxxxxxx>, <Tim.J.Nash@xxxxxxxxxxxxx>, "silist" <si-list@xxxxxxxxxxxxx>
• Date: Tue, 19 Sep 2006 11:11:20 +0530

```Hi Steve,

Tim, this link has lot of information with equations and is useful.

Thanks&Regards,
Sirisha.
=20

-----Original Message-----
From: steve weir [mailto:weirsi@xxxxxxxxxx]=20
Sent: Tuesday, September 19, 2006 9:58 AM
To: Sirisha.Godavarthy@xxxxxxxxxxxx; Tim.J.Nash@xxxxxxxxxxxxx; silist
Subject: Re: [SI-LIST] Re: Spreading Inductance

Tim, those equations come from a presentation I made to the SCVEMC=20
January 2005.  You can find the presentation in whole on both the=20
X2Y, and Teraspeed web=20
sites:  http://www.x2y.com/bypass/method/does_position_matter.pdf,=20
and http://www.teraspeed.com/publications.html  Note that they apply=20
for specific circumstances of calculating spreading inductance=20
between a power ring, and a surrounding bypass capacitor ring.  This=20
would also work for a single Vdd / Vss pair.  However for more=20
complex pin arrays, you really need to solve the plane.  Tools from=20
IBM, KAW, Ansoft, or Sigrity are all capable of that task.

Steve.
At 05:57 AM 9/18/2006, Sirisha Godavarthy wrote:
>Hi Tim,
>I got some info regarding spreading inductance.
>Hope it helps.
>
>
>- L of PLANE_CAVITY =3D3D u0 / 2=3DF0 * H * (( ln( R2/R1 ) * KPERF ) +
>ln( R3/R2 ))
>- u0 =3D3D 31.9nH/square
>- H =3D3D cavity height
>- R3 =3D3D radius from die center to bypass cap ring
>- R2 =3D3D radius from die center to via field edge
>- R1 =3D3D radius from die center to pkg power / ground attachments.
>- KPERF scaling factor for perforation in via field
>* For perforations small compared to wavelength area ratio
>
>Thanks&Regards,
>Sirisha.
>
>Thanks&Regards,
>Sirisha.
>=3D20
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] =3D
>On Behalf Of Nash, Tim J (EHCOE)
>Sent: Friday, September 15, 2006 7:56 PM
>To: silist
>
> From what I have gathered, spreading inductance of a plane is =3D
>dimensionless
>(i.e. nH/sq) and not a function of the distance between two points, =3D
>rather a
>function of aspect ratio of the plane - L x W.  So, the size of the =3D
>plane
>isn't what affects spreading inductance, but its shape does.  Are these
=3D
>true
>statements?  I want to make sure I understand this correctly.
>Best Regards,
>Tim
>
>
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>-- File: smime.p7s
>
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