Why Plated PCB Mounting Holes?

[mayd85]

Hi,

I am designing a PCB which will be housed in a metal enclosure. Is it advisable to have plated PCB mounting holes and connect them to ground plane? I have seen some PCBs where the plated mounting hole is connected to the ground plane through an RC network. What's the reason behind this connection? Is this done to help sustain ESD?

 

[udhay_cit]

Usually the metal enclosures are connected to supply earth. If any spark or high voltage wires are touches the metal part it will bypass to the earth.

 

[mayd85]

Do you have any idea how it is done in case of a battery operated system, where there is no earth? Like an automotive system?

 

[marce]

Screening.

 

[udhay_cit]

It may be used for signal shielding. It depends on the type of the instrument & area of application. Example... electric fence is a battery operated equipment but it still need earth connectivity to close the circuit path. If the battery operated instrument is having very sensitive amplifier or line frequency noise picking circuits, then it required shielding (Example ECG machine)...

 

[mayd85]

If I have multiple ground planes on my board, which ground plane should the mounting hole be connected to?

 

[marce]

Why multiple ground planes? are we talking analogue and digital grounds... without a lot more information we can only loosely guess an answer.
Then you get into the area of are these planes totally separate or do they overlap, is there capacitive coupling etc etc

 

[mayd85]

There are three ground planes. One analog ground, one digital ground and one power ground which are ultimately connected as a star connection. They do not overlap with each other.

 

[marce]

Yep, becoming more common again these days.
My view would be to connect it to the plane least likely be affected by any noise (the power plane) or connect it via caps.
henry Ott may have some advice.
http://www.hottconsultants.com/