[SI-LIST] Re: Capacitors arrays. worth it or not?
- From: "Hill, John" <jhill@xxxxxxxxxx>
- To: <Mark.Randol@xxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 22 May 2006 11:11:07 -0400
Hello Mark,
When the capacitor plates are horizontal there is a parallel resonance
that can show up. I believe it is the cavity resonance between the
bottom plate of the capacitor and the underling ground.
Vertical plates avoid this resonance, but there are others resonances at
higher frequencies. See the attached application note from American
Technical Ceramics.
AVX has a new BGA capacitor array with vertical plates. I am about to
check it out. The attached PDF shows the lead inductance is 25 pH.
Best regards,
John
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Mark Randol
Sent: Monday, May 22, 2006 10:33 AM
To: si-list
Subject: [SI-LIST] Re: Capacitors arrays. worth it or not?
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx=20
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Jerry Martinson
>=20
> I've always wondered how discrete cap performance is affected=20
> if the caps plates are parallel with the underlying plane or=20
> if they are perpendicular. I'd think that having them rolled=20
> 90 degrees
> (perpendicular) might make them perform better in some=20
> regions. I wonder how this would extend to arrays and=20
> whether arrays are configured rolled or not. Does anyone=20
> know? =20
American Technical Ceramics (ATC) used to recommend 'vertical' placement
of their porcelain caps for just this reason. I've seen it make several
100MHz's of difference in the measured resonance frequency. That was on
a relatively thick 2 layer PCB, so on a board with a thinner component
to ground layer spacing this could be more significant <guess>. I
didn't find it on their web site, but here is their link.
http://www.atceramics.com/
Now how much of this was due to plate coupling to the substrate, or
reduced effective capacitance and inductance because of current crowding
towards the new 'bottom' of all the plates, beats me. It seems to me in
the horizontal orientation, the upper plates would have slightly more
inductance due to the greater loop area. Which effect dominates,
capacitance or inductance? =20
The problem at the time was fixed, so we didn't investigate further.
--
Mark Randol, RF Evaluation & Application Engineer
Not speaking for my company, etc
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