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

Larry Smith (ldsmith@lisboa.eng.sun.com)
Wed, 12 Aug 1998 08:55:25 -0700 (PDT)

Vigliarolo - your point is well taken. The self inductance for
tantalum capacitors is quite a bit higher than small ceramic
capacitors. This is mostly because they are bigger. They are
longer and stick up higher off the pcb than small ceramic caps.
This causes the current to flow in a bigger loop and produces
more inductance. Tantalum capacitors usually provide some amount
of bulk capacitance and go inductive in the low MHz region. At
frequencies more than 1 MHz, ceramic capcitors are necessary.

regards,
Larry Smith
Sun Microsystems

> From: Vigliarolo Roberto <Vigliarolo@asamrt.interbusiness.it>
> To: "'Larry Smith'" <ldsmith@lisboa.eng.sun.com>
> Cc: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Surface Mount Cap Lead Inductance
> Date: Wed, 12 Aug 1998 10:47:41 +0200
> X-Priority: 3
> MIME-Version: 1.0
> Content-Transfer-Encoding: quoted-printable
>=20
> =09Sorry fom my message being late but I live in Europe and as you
> now there is
> =09at least 6h time difference between here and the USA....
> =09I agree with you all but it seems to me that the original
> question from Mike Mayer=20
> =09was related to SMD tantalum caps (7343, 6032, etc.) and my
> understanding is that
> =09their ESL is higher than the ESL of ceramic cap (1 to 3 nH: see
> for an example=20
> =09page 25 of Kemet catalog F-3102B 2/97) and so it is of the same
> order of the=20
> =09layout inductance.
> =09Of course you have to consider that the resonance you obtain is
> damped by the=20
> =09relatively high ESR of tantalum caps and so it is difficult to
> have probelms with=20
> =09resonances associated with tantalum caps.
>=20
> > ----------
> > Da:=09Larry Smith[SMTP:ldsmith@lisboa.Eng.Sun.COM]
> > Risposta a: =09Larry Smith
> > Inviato:=09marted=EC 11 agosto 1998 19.07
> > A:=09Vigliarolo@asamrt.interbusiness.it; raymonda@radium.Eng.Sun.COM
> > Cc: =09si-list@silab.Eng.Sun.COM
> > Oggetto:=09Re: [SI-LIST] : Surface Mount Cap Lead Inductance
> >=20
> > Tanmoy Roy, John Prymack and myself will be presenting a paper
> > in October at the EPEP conference that goes into a little more
> > depth on the mounted inductance of decoupling capacitors. We
> > find that there are 3 major contributers capacitor inductance:
> >=20
> > =09pad and via design=09=091.00 to 4.00 nH
> > =09plane spreading inductance=090.01 to 0.50 nH
> > =09capacitor height=09=090.20 to 0.40 nH
> > =09
> > The three components sum together. Inductance is essentially a
> > measurement of the flux or B field in the environment caused by
> > current going around a loop. The bigger the loop, the more the
> > flux and the more the inducance. =20
> >=20
> > As Ray stated below, the pad and via design are the most important
> > contributers to capacitor inductance. The design of the power planes
> > (PCB stackup) is second in importance. Third in importance is the
> > capacitor height. If the capacitor manufacturer has compensated out
> > the first two contributors to inductance (given you the self
> > inductance of the capacitor) the third (and least important) part is
> > all you get. Inductance numbers quoted for surface mount devices
> > are often mis-interpreted or mis-understood.
> >=20
> > Come to the EPEP in West Point NY on October 26-28 and get the
> > rest of the story!
> >=20
> > regards,
> > Larry Smith
> > Sun Microsystems
> >=20
> >=20
> > > Date: Tue, 11 Aug 1998 09:17:13 -0700 (PDT)
> > > From: Ray Anderson <raymonda@radium.eng.sun.com>
> > > Subject: Re: [SI-LIST] : Surface Mount Cap Lead Inductance
> > > To: Vigliarolo@asamrt.interbusiness.it
> > > Cc: si-list@silab.eng.sun.com
> > > Mime-Version: 1.0
> > >=20
> > >=20
> > > =09You 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:
> > >=20
> > > =091=09Pad Geometry
> > > =09=09=09connector traces
> > > =09=09=09via location
> > > =09=09=09Number of vias
> > > =09=09=09
> > > =092=09Stackup
> > > =09=09=09distance from mounting pads to power planes
> > > =09=09=09
> > > =09All those factors that influence the loop area seen by the
> > current
> > > flowing through the capacitor influence the mounted inductance. The
> > amount=20
> > > contributed by the capacitor is a small part and is usually
> > overwhelmed by=20
> > > the other constituents unless you do a VERY good job in minimizing
> > the other=20
> > > contributions (which can be done). The ESL of the capacitor by
> > itself is a=20
> > > very strong function of the height dimension of the part.
> > >=20
> > > =09It is the mounted inductance of a bypass capacitor that mostly=20
> > determines
> > > the effectivness of the bypassing that the part provides.
> > >=20
> > >=20
> > > Ray Anderson
> > >=20
> > > Sun Microsystems Inc.=09=09
> > >=20
> > >=20
> > >=20
> > > > 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
> > > >=20
> > > > 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=3D1/(2*pi*sqrt(ESL*C))
> > > >=20
> > > >=20
> > > >=20
> > > > > ----------
> > > > > Da:=09Mike Mayer[SMTP:Mike.Mayer@heurikon.com]
> > > > > Inviato:=09luned=EC 20 luglio 1998 22.40
> > > > > A:=09si-list@silab.Eng.Sun.COM
> > > > > Oggetto:=09[SI-LIST] : Surface Mount Cap Lead Inductance
> > > > >=20
> > > > > I was looking at a note from howard Johnson about decoupling
> > ("Bypass
> > > > > Multi-Valued Arrays"):
> > > > >=20
> > > > > http://www.sigcon.com/news/1_17.htm
> > > > >=20
> > > > > 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?
> > > > >=20
> > > > > --=20
> > > > >
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > > > =3D=3D=3D=3D=3D=3D=3D
> > > > > Mike Mayer Artesyn Communication
> > > > > Products, Inc
> > > > > Madison, WI
> > > > >
> > http://www.artesyn.com/cp
> > > > >
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > > > =3D=3D=3D=3D=3D=3D=3D
> > > > >=20
> >=20