Minimum Standoff height?

[Colinreay]

Hey, I have a quick question about motherboard standoffs. I've been scheming a design for a SFF pc, but have been held up by what standoffs to use. IIRC, the minimum standoff height in the ATX spec is 6.35mm, but I'm wondering how much lower I can go and have it work, for the sake of making the height of the case is as small as possible.

I'm terribly sorry if this has been answered before, and if it has, would really appreciate being pointed in the right direction!

I of course don't want to have the solder pads on the bottom of the board connect and short something, but for the sake of conserving space, how low could I go? The motherboard tray will also be made out of acrylic, so it shouldn't conduct.

 

[Kmpkt]

I'd recommend just threading your motherboard tray for acceptance of the standard issue brass standoffs and buy several sets of 6.35mm and shorter from Digi key. As long as you can see daylight and nothing is touching, I would imagine everything is fine. I think this would likely vary somewhat from board to board.

 

[Colinreay]

I'd recommend just threading your motherboard tray for acceptance of the standard issue brass standoffs and buy several sets of 6.35mm and shorter from Digi key. As long as you can see daylight and nothing is touching, I would imagine everything is fine. I think this would likely vary somewhat from board to board.

Yeah, that seems reasonable. One thing I could forsee being a problem is if the itx board has an M.2 slot, (Key E or M) on the back. Other than that, the solder pads themselves seem a lot smaller than requiring 6.35mm of clearance.

 

[iFreilicht]

6mm are fine, even with M.2 on the back. You should be able to go down to 4mm, but I wouldn't recommend it. Take a look at this document, section 3.4.2.

 

[Colinreay]

6mm are fine, even with M.2 on the back. You should be able to go down to 4mm, but I wouldn't recommend it. Take a look at this document, section 3.4.2.

Thank you sir! Do you think I'd be okay with 3-4mm standoffs then, if I do a cutout on the mobo tray for any M.2 + Cpu cooler mount? It looks like the conductive parts of the mobo that have to be seperated are a hair under 2.5mm tall, and the parts that can touch the case are around 3mm (not that I would want them to touch of course!)

 

[iFreilicht]

Sure, that would be possible. What you could do is use 3mm standoffs and then put on very thin washers if something touches. And you could always make the tray from acrylic instead of metal to prevent shorting. Keep in mind that you will need a cutout for the mainboards I/O shield, though! Check the specification to see how low you can put it, at some point you'll have to cut the lower mounting flange off!

 

[jeshikat]

I'd stick with the standard for standoff height. You may get away with something shorter for a particular board, but if the board dies, or won't work out for some reason, and you have to get a different motherboard.

The other things is if the standoffs are too short it gets hard to find screws that are short enough to not bottom out in them.

 

[Colinreay]

I'd stick with the standard for standoff height. You may get away with something shorter for a particular board, but if the board dies, or won't work out for some reason, and you have to get a different motherboard.

The other things is if the standoffs are too short it gets hard to find screws that are short enough to not bottom out in them.

Ah, good point. Another thing I may consider is embedding the M3 nuts into the acrylic tray, similar to what was done on EVE-02, then just 3d printing hexagonal spacers that act as the spacing part of the standoff, and using extra long M3 screws that go through the mobo, spacer, and into the embedded nuts.

I just need a way to somehow anchor the 3d printed spacers into the motherboard tray as a solid, but non-permanent solution.

 

[jeshikat]

If the inside diameter of the spacer is close to the size of the screw they shouldn't be able to move around much.

 

[ZA Design]

If I were to use, lets say, 6 mm PEMS standoffs that have been pressed into a 1.27mm thick stainless steel sheet, do you think that the remaining 4.73 mm would be enough to house an M.2 SSD?

 

[jeshikat]

Measuring my ASUS Z170I Pro Gaming, the M.2 connector sticks out from the backside of the mobo by ~4.0mm.

So 4.73mm would work, but it wouldn't leave much room.

 

[Colinreay]

If I were to use, lets say, 6 mm PEMS standoffs that have been pressed into a 1.27mm thick stainless steel sheet, do you think that the remaining 4.73 mm would be enough to house an M.2 SSD?

You might be able to squeeze by, (no idea how tall the M.2 connector height is), but the spec (ctrl f + 3.4.2) calls for a max of .2 inches, or 5 mm of protrusion (like an M.2 connector) from the bottom of the mobo pcb. Add on another .5-1mm of clearance so nothing touches the mobo tray, and it's more like 6mm - but that only applies to the max. However, you could probably make a big cpu cooler cutout, with the M.2 drive able to fit through there as well. I'm probably going to try 3.5mm 3d printed spacers as my standoffs, you may want to more like 4.73 as you said, as your going to be much more likely to short on steel

 

[ZA Design]

Measuring my ASUS Z170I Pro Gaming, the M.2 connector sticks out from the backside of the mobo by ~4.0mm.

So 4.73mm would work, but it wouldn't leave much room.

Thanks for taking the time to measure it!
The connector may be protruding by only 4mm, but the SSD itself has thickness that may contribute to an even tighter fit

 

[Necere]

Keep in mind that CPU cooler backplates can be fairly thick as well. I measured the NH-C14 backplate at around 7mm thick.

 

[jeshikat]

The connector may be protruding by only 4mm, but the SSD itself has thickness that may contribute to an even tighter fit

Ah that's true. The top of the connector is 4mm and from looking at some spec sheets it looks like the topside components on a M.2 drive could stick out 1-1.5mm past the top of the connector.

 

[ZA Design]

Oh hi there Necere! I'm a big fan of your work.

Keep in mind that CPU cooler backplates can be fairly thick as well. I measured the NH-C14 backplate at around 7mm thick.

Anyway, the cooler(s) I plan on using do not use a backplate, so I'm fine in that regard.

Ah that's true. The top of the connector is 4mm and from looking at some spec sheets it looks like the topside components on a M.2 drive could stick out 1-1.5mm past the top of the connector.

Not really, the specs for the 960 PRO (as an example) say 2.38mm thick, so with pcb and components included, it should not stick out by more than 1 mm I believe... I could be completely and hopelessly wrong however. I can't include a motherboard cutout for the style of case I am doing, as the motherboard standoffs are directly pressed into the base sheet panel.

ARGH! All this is doing my head in... Maybe I will have to stick with my trusted 8 mm high standoffs.

 

[jeshikat]

http://www.te.com/commerce/Document...m=1-1773702-1NGFFQRG-EN&DocType=DS&DocLang=EN

Yup, you're right. From Page 5 and taking Dim. C (2.48mm) + the height of the 950 Pro (2.38mm) gives 4.86mm.

 

[chx]

Is it a problem if the CPU backplate touches the case?

 

[jeshikat]

It shouldn't be as long as it is not putting pressure on it.

 

[Wolf_LikeMe]

IIRC ~=>5mm is the standard for minimum air gap to prevent (electronic) creep. You can go smaller however you will require some insulation media to prevent this, alongside which, you may encounter interferences with solder pins, m.2 connectors etc.