JungleJim74 said:
I currently have an Intel Motherboard which is mounted with 6 screws and
insulating washers under the head of each screw.
I have purchased a new case and the hardware package that came with it does
not have any insulating washers. This will result in the Motherboard DG43NB
being grounded to the case every place a mounting screw is used. Is this the
correct way to install this Motherboard?
Thanks in advance for any help. JungleJim74
The motherboard designer grounded the rings on purpose. So the intention
is for the standoffs underneath the motherboard, to touch and ground
the ring on each mounting point.
__
_/ \_ Screwhead can also provide a ground path, because threads touch brass standoff
| |
--------- metal ring on motherboard (top) \
FR4 PCB +---- These are grounded internally
--------- metal ring on motherboard (bottom) /
| |
| | brass post
| |
-------------- chassis metal is grounded (PSU chassis is safety ground)
The motherboard designer has several alternatives.
1) Call up a drill, and just drill a hole in the board. With a keepout area
around the hole, there would be no metal at all. FR4 (fiberglas) is an
excellent insulator, and with no metal rings at all, the thing would
inherently be insulating. So they didn't do that.
2) Call up a plated hole. That puts metal rings on the top and bottom of
the motherboard. The walls of the hole are also plated with metal, and
the screw threads can touch that metal. But, the final touch, is
connecting something to that structure electrically. If the
engineer doesn't wire up the "hole", the metal is again floating.
So (2) would behave like (1).
3) Call up a plated hole, but run a copper track to the metal. That
provides a path somewhere. The ground path may be provided, as a
better way to control emissions, or for static discharge reasons.
Personally, I don't see either of these being an advantage, and
the "spring fingers" touching the body of the I/O connectors make
more sense for those purposes. (Note that the motherboard has four
conducting layers, two of which are inside the motherboard. So you
cannot see all the copper connections with the naked eye. Some
motherboards have more layers than that, for routing or electrical
performance reasons. The number of layers allowed, is limited to
some degree, by the defined maximum thickness of the motherboard.)
Occasionally, I read accounts, of people who absolutely needed to place
insulating washers underneath the motherboard. I don't have a good
answer for why that was necessary. (I can cook up answers, but they're
not satisfying.) These people claim the motherboard won't work
properly, unless it is partially or fully insulated. All the motherboards
I own, in self-built systems, are fully grounded, and fully work. So
I've never seen the need (or logic) behind insulating them.
You should be careful, when installing a motherboard, not to jog it
too far off center. While the engineer may have tried to leave
room for the screws, sometimes I see surface mount components that
are too close for comfort. Make sure, when installing the motherboard,
that no screw head is crushing any small ceramic caps or SMT resistors.
If the PCI slots won't align properly, either replace the motherboard
or replace the case. Don't be forced into pushing the motherboard
so far from center, that stuff gets crushed or shorted.
Another thing to watch for, is there are more places to put standoffs
on the motherboard tray, than there are plated holes on the bottom
of the motherboard. Sometimes, during an upgrade (remove old
motherboard, install new motherboard), people leave unnecessary
standoffs underneath, and they short to logic signals. If the
board won't start, or it crashes, sometimes you have to pull
it all apart, and check for one of those standoffs. Standoffs
should only mate, with plated holes provided for the purpose.
HTH,
Paul
