EMI foam on top of ICs

[subliti]

Hi

I saw this teardown video from Dave (https://youtu.be/sKcH4JxnxbQ?t=992) and some of the chips had some kind of emi foam on top of it. I never saw this before and i find it interesting. Does this only work for low freq and does something similar exist for high freq ? And what is high or low freq in this context ?

I was wondering....could one reduce the overall noise floor of a rf radio chip that is in the same enclosure with a bunch of other chips lika a mcu etc if i put this foam on top of the mcu etc, could this improve something ? Even if the rf section is already shielded by a metal case, could this improve something ?

[Kleinstein]

A closed metal can is a RF resonator. For the really high frequency stuff (> 1 GHz) sometimes addition absorbers are added to dampen the resonances. The higher the frequency the more important it gets.

Having this in a low frequency meter is odd. I am a bit with Daves guess  - maybe a desperate late addition to meet EMI requirements.   

[coppercone2]

those digital chips can make high frequency emissions (MCU).

If the converter has a pass transistor built into it then maybe? It could maybe have a high impedance some where that is being modulated by digital signals to effect a power rail (acting as a RF amplifier mainlining noise into the power rail at low impedance).