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Would noise from MLCCs be cancelled out if adjacent capacitors had different pol

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demute:
I have a DC voltage with a high ripple current at 10 kHz which produces an audible noise from the MLCCs on the PCB. I can't change the frequency and I need to stick to MLCC class II capacitors for different reasons.

In this article:
https://www.newark.com/wcsstore/ExtendedSitesCatalogAssetStore/cms/asset/pdf/americas/common/nic-components/MLCC-Ringing-Singing-NSPH-SMT-FilmCapacitors-May2015.pdf
they say MLCCs mounted at the same place (e.g. same xy-coordinates) but on different sides of the PCB tend to cancel each other out. Is the same also true if the polarity of adjacent MLCCs would be reversed?

More specifically, assume I have different layouts where many MLCCs are placed close to each other, all connected to + and - of the DC-voltage:

      Layout 1               Layout 2               Layout 3
[+-] [-+] [+-] [-+]    [+-] [-+] [+-] [-+]    [+-] [+-] [+-] [+-]
[-+] [+-] [-+] [+-]    [+-] [-+] [+-] [-+]    [-+] [-+] [-+] [-+]
[+-] [-+] [+-] [-+]    [+-] [-+] [+-] [-+]    [+-] [+-] [+-] [+-]
[-+] [+-] [-+] [+-]    [+-] [-+] [+-] [-+]    [-+] [-+] [-+] [-+]

Assume 1206 capacitors placed as close to each other as possible, e.g. the wavelength of the 10 kHz is large (34 mm) in comparison to the distance between MLCCs.

Layout 2 is obviously much easier to route compared to layout 1 and 3, but that's not relevant for the discussion here. I'd just like to know, if all else being equal, would any layout above produce less noise over the others due to cancellation av sound waves?

tom66:
You would have to assume the resonances and the vibration of each capacitor is very similar, which might be optimistic. 

You could consider using some kind of flexible epoxy over the capacitors to damp the noise.

Kleinstein:
The capacitors itself are rather small and don't couple very much to the air. The main thing to worry about is the coupling of sound to the PCB and only than to the air. Here is may be about getting the capacitors longer / shorter depending on the voltage and this way bending the PCB. Chances are the capacitors are random in orientaion anyway - MLCC usually don't have a defined inner / outer contact or defined orientation. So turning them around would not change anything. The polartiy could also well be set by the DC bias. So chances are the different patterns shown would not have a significant effect.  Polulation on both sides would be more promissing, at least to reduce the more bending modes.

The idea of making the PCB stiffer with additional epoxy is also good - I don't think it has to be extra flexible as even the harder epoxy is still relatively acoustic absorbing. A main part would be from just making it stiffer and thus less amplitude (in µm) from the same force.

AVGresponding:
Stiffening the board locally with epoxy would also raise the resonant frequency, which might help.

Bud:

--- Quote from: tom66 on December 01, 2022, 04:22:21 pm ---You would have to assume the resonances and the vibration of each capacitor is very similar, which might be optimistic. 

You could consider using some kind of flexible epoxy over the capacitors to damp the noise.

--- End quote ---
Conformal coating.

Edit: But that will make repairability a nightmare.

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