M.2 Z-height dimension

Hi all,
I’m new to the community. My company is designing an AI Accelerator card that slides into the m.2 socket. Can anyone answer 2 mechanical questions:

  1. What is the maximum Z height allowed for a m.2 2280 card?
  2. Which type of m.2 key is preferred: Type B, M or B+M?

I measured 4.17mm clearance from the mainboard base to the top of the cooler, which is the tallest component on the mainboard which must clear the underside of the top cover.

Must have M key, but can accommodate B+M.

That’s an M key, which makes sense (PCIe x4): M.2 Interface, Key and Socket explained

The signalling is PCIe, not SATA. So no B keyed devices unless they also have the M key.


Thanks for quick reply. Just to be clear, is 4.17mm the max Z height of all components and any heat shield as measured from the top of the PCB?

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4.17mm is the height from the top of the mainboard base just under the M.2 slot to the top of the cooler, which seems to be the tallest component on the mainboard. As you see in the photo, the cooler is very close to the slot area, so even if the top cover is designed with a slight bow, there would be little change to that dimension. Anything taller than this will almost certainly contact and push against the bottom of the top cover containing the keyboard and trackpad.

This measurement must accommodate the M.2 and any heatsink. In my case, the top of my M.2 was 3.39mm from the mainboard base, leaving only 0.78mm of clearance for a heatsink. I did not feel comfortable using a 0.5mm thermal pad plus a 1mm thin copper heatspreader here. Others did and report it works for them, so there’s a little more clearance than 4.17mm - but not much! I’d be surprised if there was over 5mm.

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I think I get it: from the topside of PCB to top cover is only 0.78mm. So all components and heatsink heights cannot exceed .78mm above PCBA. Many thanks!


That’s the case for my M.2 (WD SN850), yes. I would guess it’s using industry-standard surface-mount IC thicknesses and that you wouldn’t be able to get much thinner.

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