Motherboard EMI Question

[Kred890]

Could anyone advise if there might be any safety/regulatory issues from selling a PC motherboard without the I/O back plate?

I gather that one of the functions of the plate is grounding of the ports, but I believe this is to protect the ports from static built up on the user, rather than to protect the user from the ports (but not 100% sure).

I have also seen it suggested that the I/O plate forms part of the electromagnetic interference barrier along with the rest of the PC case that allows the motherboard to pass EMI standards - however this seems dubious to me as motherboard manufacturers cannot know (and therefore surely cannot rely on) the type of case/environment that the motherboard will be operated in.

Apologies if this question is a bit out of left field.

 

[JimW]

It's been a while since I designed motherboards and PC systems, but nothing has changed. The rear stake back plates are definitely part of the EMI enclosure. Nothing really to do with static protection. The PC manufacturer designs the case to seal with industry standard rear back plates, and has to (should) test with a variety of boards.

Having said that, are you building a new custom designed system? Or just integrating different third party items like cases, motherboards, and cases? Is this a one time sale, or something that you expect to sell thousands of? If you are selling a single machine, I wouldn't give it a 2nd thought (although I would try to find a suitable plate). If you plan to sell many custom designed systems, then you will need to pass FCC EMI limits, and I doubt you will pass without the back plate (but there are motherboards that are so well deigned from an emissions point of view, that you may). If you are building from standard components, then there should be all the necessary EMI shields included.

Of course the other big question is Class A vs Class B. Much easier to pass if it is for the commercial world and not intended for home use.

JimW

 

[dknguyen]

It's been a while since I designed motherboards and PC systems, but nothing has changed. The rear stake back plates are definitely part of the EMI enclosure. Nothing really to do with static protection. The PC manufacturer designs the case to seal with industry standard rear back plates, and has to (should) test with a variety of boards.

Having said that, are you building a new custom designed system? Or just integrating different third party items like cases, motherboards, and cases? Is this a one time sale, or something that you expect to sell thousands of? If you are selling a single machine, I wouldn't give it a 2nd thought (although I would try to find a suitable plate). If you plan to sell many custom designed systems, then you will need to pass FCC EMI limits, and I doubt you will pass without the back plate (but there are motherboards that are so well deigned from an emissions point of view, that you may). If you are building from standard components, then there should be all the necessary EMI shields included.

Of course the other big question is Class A vs Class B. Much easier to pass if it is for the commercial world and not intended for home use.

JimW

But how do thoes cases with giant plastic windows on the side pass the EMI test if it matters that much? Or the open-air test bench cases for that matter?

 

[Kred890]

Thanks for the replies.

But how do thoes cases with giant plastic windows on the side pass the EMI test if it matters that much? Or the open-air test bench cases for that matter?

That's what I'm wondering - I was thinking the motherboards (at least the sort that are sold separately to home-builders - your Gigabytes and your Asus's etc) must have to pass EMI regulations in the open air because many cases only partially enclose the motherboard or even don't enclose it at all (e.g. Antec Skeleton type cases).

It's got me wondering if there might be any issues with a business selling used motherboards (rather than whole systems) that do not come with the I/O plate.

 

[tronitech]

If you clearly state the motherboard is sold without back plate I can't see any problem. It has been previously pointed out that PC cases come in many designs, perspex/glass windows, all plastic design or even completely open so why worry about the lack of a back plate?