Mainboard Standoffs: To Do Or Not To Do ?

Well, I have finally assembled the insides of my 'replica'; it seems to work
m/b - MSI MS-6577 v2.1 (uATX form, 9.6in [244mm] square)
chipset - G845
CPU - Pentium 3.06GHz /533/512 (Northwood)
RAM- 2 x1GB PC2700 (CT12864z335)
Graphics card - GeForce 7800GS (finally, I plan to use an HD3850)
PSU - XFX TS450

About putting in a case: should I use insulating stand offs or washers to insulate the m/b from the case ?
My m/b has carefully plated areas surrounding each mounting hole, as if to enable good contact (with screws/washers) and hence the case

Dumb_Question
25.March.2016

 

No! If you look on top and under the motherboard where the mounting holes are, you will see the hole is surrounded by a large circle of solder. You will also note the standoffs are made of highly conductive brass. And you will notice the standoffs get screwed into bare metal of the case. All of this is to ensure a solid "common" ground is established with the chassis all across the motherboard. This is essential to ensure (1) there are no differences in potentials at the various grounding points, (2) all points are properly grounded, and (3) EMI/RFI (unwanted emissions and interference) does not affect the motherboard, connected components, or surrounding devices.

Properly grounding the motherboard to the case also properly grounds the motherboard to its power supply instead of relying on wires that can come loose or be damaged.

Bottom line, insulating the motherboard from the case is BAD!

Note too, whenever you reach inside a computer case, (after unplugging from the wall) you must touch bare metal of the case interior to discharge any static build-up in your body. This puts you and the ESD (electro-static discharge) sensitive devices (like your motherboard, RAM, CPU, chipset, GPU, etc.) at the "same potential". If you insulate the board, you risk zapping and destroying these very sensitive devices. And note they can be totally destroyed by an arc (spark) so tiny, you (as a human) don't even realize a discharge occurred. It can be so small, you can not hear, see or feel it, but it can easily torch a Grand Canyon sized trench (microscopically speaking) through your CPU or RAM. Not good.

 

One more thing. A common newbie or distracted pro mistake is screwing in more standoffs than the motherboard needs. Cases are designed to support 1000s of different motherboards so they almost always have more standoff mounting holes than the motherboard. So you must triple check to ensure you only have a standoff where there is a corresponding motherboard mounting hole and that you don't install any extra standoffs or you risk shorting out live circuits running through the motherboard. While there typically is no permanent damage due to the voltages running through the board are low voltage DC, if luck is not with you, permanent (and expensive) damage can occur. Not good.

 

thanks for your unambiguous reply Digerati. I shall proceed accordingly....now to find some 5/32 screws and investigate my cases...

I understand your reasoning on this point: in fact I tend to agree with it. However, it has been argued, especially in RF circles (outside the computer realm), that multiple earth points are bad, and that circuits should be grounded with one earth/ground point to avoid things like earth loops. This earth point should be provided by the PSU.
I find this subject very confusing.

Dumb_Question
26.March.2016

 

Funny you should mention this. Please understand my roots as an electronics technician are as a radio technician for USAF air traffic control facilities for over 24 years! So your comment is right up my alley.

That said, those in that "RF circle" you refer to are correct. I am afraid you just misinterpreted it.

Note I specifically said above '"common" ground'. That is NOT the same thing as "multiple Earth points". In fact, ensuring all the motherboard grounding points, the power supply, and the case are at the same ground "potential" is what establishes a "common" ground. And (in the case of Earth bound - as opposed to airborne electronics) it is this "common" ground that connects all these grounds to a single Earth point - and yes, that is through the PSU power cord.

But note with a typical PC, you have multiple devices powered through wall outlets all connected together. These include monitors, speakers, printers, and perhaps some external drives. It is essential to avoid the possibility of EMI/RFI problems that these devices are all connected via a common ground too. For this reason, all their interconnecting data cables also have at least one ground wire to connect their cases together too.

If you isolate (insulate) various devices, they can establish their own "floating" grounds that are at slightly different "potentials". And it is these slight differences in potentials that can cause or be susceptible to interference. If the potential is high enough, you can feel a "tingle" if you touch both. Not good.

Even two wall outlets in the same room on the same circuit have slightly different ground potentials. This is because one outlet will have longer wires running to it, and may go through additional junction points. Longer wires means more resistance. This is why it is best to power everything connected to your computer from the same wall outlet. This is especially true in older facilities and homes. In extreme cases where that is not possible, technicians often run separate grounding wires to "strap" the cases (or entire equipment racks) together, thus creating a "common" ground.

One last thing, just for interest. In a radio facility, there may be multiple Earth grounds (8' rods pounded into the ground) surrounding the building. But then there will be a continuous (no breaks or splices) single, copper ground wire "bonded to" and strapping all those rods together to establish a single ground for everything inside that building.

 

Thank you for that explanation, Digerati

Dumb_Question
25.March.2015