Why the grounding tabs on faceplates for motherboards?

[Stephen Tashi]

TL;DR

Are the tabs on the faceplates for motherboards useful?

Summary: Are the tabs on the faceplates for motherboards useful?

Typical motherboards come with "plates" that fit over the connectors that are exposed on the outside of the computer case. These plates have tabs that press against metal around the connectors - presumably to furnish a ground. Are these tabs actually useful? Aren't there already enough grounds without these tabs?

 

[hutchphd]

Summary: Are the tabs on the faceplates for motherboards useful?

Summary: Are the tabs on the faceplates for motherboards useful?

Typical motherboards come with "plates" that fit over the connectors that are exposed on the outside of the computer case. These plates have tabs that press against metal around the connectors - presumably to furnish a ground. Are these tabs actually useful? Aren't there already enough grounds without these tabs?

Yes indeed because if you scuff across the carpet and touch the case you want the path to ground to not include any integrated circuit

 

[Stephen Tashi]

Yes indeed because if you scuff across the carpet and touch the case you want the path to ground to not include any integrated circuit

The metal around the connectors is already grounded to the motherboard without the tabs attached. The motherboard is grounded to the case by the metal stand-offs. So how does grounding explain a need for tabs?

 

[DaveE]

I think they are primarily there to reduce RF emissions. A good shielded enclosure for electronics will minimize the size of holes and slots that can allow EMI out. So it's not really about "ground points" as it is about a continuous emi shielding.

 

[hutchphd]

I think they are primarily there to reduce RF emissions. A good shielded enclosure for electronics will minimize the size of holes and slots that can allow EMI out. So it's not really about "ground points" as it is about a continuous emi shielding.

I am unsure as to the geometry here. So are these additional plates to keep short wavelength stuff from rattling around inside the case by trapping it in the motherboard/groundplane proper?

 

[Baluncore]

The box is full of RF noise radiated by exposed internal signals. Any gap or slot longer than about one tenth of a wavelength may radiate RF energy that can interfere with the operation of nearby external communications equipment. A 3 GHz processor clock has a fundamental wavelength of 10 cm, so slots need to be kept shorter than 1 cm. The fingers are not protective “earthing” or “grounding” so much as they are “shorting” the RF currents that would otherwise circulate around the longer slot aperture, reducing it to many shorter slots with significantly lower total radiation.

 

[DaveE]

I am unsure as to the geometry here. So are these additional plates to keep short wavelength stuff from rattling around inside the case by trapping it in the motherboard/groundplane proper?

It's to keep the EM radiation inside the box so it won't mess up your neighbors radio reception.
Most people are completely unaware of how crummy our technology would work if there weren't rules to keep your phone, radio, car, TV, PC, washing machine, microwave, etc. from messing up each other.

 

[Nik_2213]

Long ago, before strict EM regulations, when many TVs still had dial tuners, my neighbour rang to say my Apple ][+ 3D Astronomy program's elusive bug was a re-used variable name on line whatever...

Yeah, my TV modulator was spamming the entire street !