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Quick question about motherboard mounting

S

shadowwyvern

Gawd
Joined
Sep 22, 2005
Messages
604
This is so simple, I almost feel silly for asking it, but how many of you use the <carboard, metal, plastic> washers that come with cases for use on the motherboard screws? I personally have never used them, but as a result the screws tear up their solder pad and leave metal flakes everywhere... but some part of me thinks that those solder pads are there because the board uses them as grounds. What is the best policy for these things?

Thanks :)
 
It won't hurt to use them, but I too have found their purpose lacking.
Its to keep the stud from touching any part of the board that may, at some point, have a higher voltage than 0.
The screw-head side of the board normally has a metal ring around the hole, and that is grounded. If the back side of the board also has this ring, than it really doesn't matter
however, if your board doesn't have this protective metal ring, use the washers

-Steven
 
rub it on the carpet a bit for good luck. Nono I figure if the mobo company supplies something usually good to use it
 
I am sure that would result in a comical RMA :)

So, the general consensus is to use these washers (metal or otherwise) on the back (riser) side of the board, but if there are metal pads on both sides then don't use them?

My current thinking is to use them (in my case paper/plastic non-conducting washers )on the front side of the board to protect the pad from getting ground up by a rotating screw head, but if there is no metal pad on the back, then you lose a ground, and that just does not seem right. Is the best practice just to damn the metal pads and screw into them anyway?

And if there is no metal pad, this is all academic, I would use the washers to protect the PCB.
 
doghucat said:
http://www.hardwaresecrets.com/article/145/2
I think this article hits the problem right on the head or the reason for the washers
Click to expand...

LOL whomever wrote that article .... well let me just inform, That "unmetalized hole" is the target for registration of the artwork that creates the board and then is drilled out to be used in manufacturing to hold the board to any fixtures etc. It has nothing to do with mounting the board in a computer case. Well as I read on, the review does get it right but it is a confusing explanation. Bottom line, you dont need the washers.

S. Wong has it correct.

Back in the bad ole days there where sometimes traces next to the mounting holes a screw head could work through the soldermask (the top protective coating) and short a trace so the washers where a good idea. I have not seen a board in 10 years like that. Due to the cost of returns and just good quality practices all screw holes now have ground pads around them and there are no traces where the screw head can touch (keep out area).

An argument can be made that the washers now would interfere with good grounding of the board to reduce EMI etc etc. but I agree it is not critical one way or the other, I have a coffee cup 1/2 full of the damn things thinking some day I will have a use for 10,000 little red paper washers. If a ticker tape parade comes along I am all set. hmmm New Years confetti ?

Actually it would be good for the metal head of the screw to dig into the solder pad a bit, but the underside of the screw is so smooth (typically, I have see a few with serations to grab the surface. ) but you would have to overtighten them. Smartly snug is all you need or you will crush the PCB material. Really I build a lot of systems, just toss the washers, snug the screws down and forget about it.

But watch the metal "fingers" on those damn I/O plates, the ones for the "stacks" of usb/ethernet connections like to get inside the connector instead of resting on the top of the "stack" on the outer metal cover.
 
Thanks for that article, it pretty much answered my question.

Those fingers can be really pesky, i have ended up bending them out of the way more than once because when you combine those with the standoffs, getting a board to actually seat well enough to screw it down can be a bit of a chore.
 
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