Re: [SI-LIST] : Surface Mount Cap Lead Inductance

Ray Anderson (raymonda@radium.eng.sun.com)
Tue, 11 Aug 1998 09:17:13 -0700 (PDT)

You will probably find that the ESL of the capacitor
is only a small part of the "mounted inductance" of the part
when it is placed on a PCB. A larger percentage of the total
loop inductance that your circuit sees associated with a mounted
capacitor comes from the following factors:

1 Pad Geometry
connector traces
via location
Number of vias

2 Stackup
distance from mounting pads to power planes

All those factors that influence the loop area seen by the current
flowing through the capacitor influence the mounted inductance. The amount
contributed by the capacitor is a small part and is usually overwhelmed by
the other constituents unless you do a VERY good job in minimizing the other
contributions (which can be done). The ESL of the capacitor by itself is a
very strong function of the height dimension of the part.

It is the mounted inductance of a bypass capacitor that mostly determines
the effectivness of the bypassing that the part provides.

Ray Anderson

Sun Microsystems Inc.

> From: Vigliarolo Roberto <Vigliarolo@asamrt.interbusiness.it>
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Surface Mount Cap Lead Inductance
> Date: Tue, 11 Aug 1998 17:55:15 +0200
> X-Priority: 3
> MIME-Version: 1.0
> Content-Transfer-Encoding: quoted-printable
>
> You can easily calculate the ESL of your capacitor by looking at the
> frequency of the dip in the impedance vs frequency chart usually
> provided by capacitors manufacturer. Fresonance=1/(2*pi*sqrt(ESL*C))
>
>
>
> > ----------
> > Da: Mike Mayer[SMTP:Mike.Mayer@heurikon.com]
> > Inviato: luned́ 20 luglio 1998 22.40
> > A: si-list@silab.Eng.Sun.COM
> > Oggetto: [SI-LIST] : Surface Mount Cap Lead Inductance
> >
> > I was looking at a note from howard Johnson about decoupling ("Bypass
> > Multi-Valued Arrays"):
> >
> > http://www.sigcon.com/news/1_17.htm
> >
> > I started looking into it but can't seem to find any information on
> > lead inductance for surface mount packages, especially the types used
> > by tantalum caps (7343, 6032, etc.). Has anyone seen a source for this
> > information?
> >
> > --
> > ======================================================================
> > =======
> > Mike Mayer Artesyn Communication
> > Products, Inc
> > Madison, WI
> > http://www.artesyn.com/cp
> > ======================================================================
> > =======
> >