Re: [SI-LIST] : Another capacitor question

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From: Mark Randol (m.randol@motorola.com)
Date: Thu Jan 27 2000 - 12:10:29 PST


Doug Brooks wrote:
>
> I am curious what effects these are and how they manifest
> themselves. i.e. are they purely EMI related (field orientation) or are
> there other effects also?

I once moved an unwanted resonance in a circuit by just rotating the
caps from the "wrong" orientation. The resonance moved from a couple
100MHz to well over 1 GHz.

The mean height of the capacitor placed correctly is higher, so it
likely is not due to inductance, but the parasitic capacitance of the
plates to the PCB. Double check ATC's app notes, but I think this
agrees with their analysis.

As to other surface mount caps not being suited to marking, most of the
0402's through 0805's I use are very nearly square at the terminals, so
rotation would not be a problem. Most capacitor manufacturers I have
spoken with aren't interested in marking for orientation even in these
cases.

-- 
Mark Randol, RF Measurements Engineer
Motorola SPS, Inc.
M/S EL381
2100 E. Elliot Road
Tempe, AZ 85284
(480)413-8052 Voice
(480)413-3455 FAX
M.Randol@motorola.com

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