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A PCB that I am working on has a non-plated hole into which a press-fit threaded insert is installed to provide the mounting point for an M.2 SSD. As such, when the SSD is installed, the mounting screw is not electrically connected to the PCB.

A colleague mentioned that the SSD itself uses a plated half-hole on the edge, and I determined that it is in fact tied to GND on the SSD by verifying continuity between it and GND pins on the edge connector.

M.2 nVME SSD

Should the threaded insert be installed in a plated hole that is electrically grounded?

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    \$\begingroup\$ What would be the benefit of having that GND connection? It's already present in the m.2 connector. \$\endgroup\$
    – MiNiMe
    Sep 25 at 17:32
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    \$\begingroup\$ @MiNiMe Benefit would being standard compliant with a standard. If you are not compliant with a standard you can't say you support it. \$\endgroup\$
    – Justme
    Sep 25 at 18:36
  • \$\begingroup\$ Yes, I read the answer from @jonathanjo. I've seen design though where there was non conductive holder, albeit external USB cases might have different standard. or the manufacturers ignores the spec. \$\endgroup\$
    – MiNiMe
    Sep 25 at 19:02
  • \$\begingroup\$ @MiNiMe Thinking about the benefit that made them put it in the specification: the benefit is that a) grounding can work in mysterious ways and this allows the board designers to have predictable and consistent grounding, b) the thermal benefits. From our point of view though, exactly as justme says: compliance. I suspect the USB cases you've seen aren't compliant. \$\endgroup\$
    – jonathanjo
    Sep 26 at 8:41

1 Answer 1

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It appears to be part of the M.2 requirements that the mounting screw is grounded:

  • 2.5.2. Electrical Ground Path The module Stand-off and mounting screw also serve as part of the module Electrical Ground path. The Stand-off should be connected directly to the ground plane on the platform. So that when the module is mounted and the mounting screw is screwed on to hold the module in place, this will make the electrical ground connection from the module to the platform ground plane.
  • 2.5.3. Thermal Ground Path The stand-off must provide a Thermal Ground Path. The design requirements for thermal are a material with a minimum conductivity of 50 watts per meter Kelvin and surface area of 22 Sq mm.

From M.2 Specification V1.0

The standard is from PCI-SIG, and the most recent versions of the standard are at their site but only for purchase or paying members, normally organisations.

I believe these are the up-to-date specification documents:

Links copied from PCI-SIG website, unable to verify.

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    \$\begingroup\$ Thanks, jonathanjo. I presume the current version of the specification lies behind a paywall? \$\endgroup\$
    – JYelton
    Sep 25 at 19:25
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    \$\begingroup\$ @JYelton I'd be surprised if this changed, but if I was going into production I'd try to check it against the latest spec. Current versions at PCI-SIG are behind membership wall (USD 4,000/year) or pay USD 2,000/doc. I added links to the answer. There are about 1,000 members, maybe you know someone who works at one or could ask tech support at whoever you buy your M.2 sockets and posts from. Amphenol is a member. \$\endgroup\$
    – jonathanjo
    Sep 26 at 8:36
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    \$\begingroup\$ ... as an aside, I've sometimes hired students to do "micro research projects" such as "What does the current standard X say about Y" and it takes them an hour in their research library and you get a two-page report with the appropriate quotations. \$\endgroup\$
    – jonathanjo
    Sep 26 at 8:36
  • \$\begingroup\$ This board is for a very low-volume in-house manufacturing purpose, so we'll not be applying for membership, but we definitely have FAEs that can assist, and your suggestion for student research is excellent. \$\endgroup\$
    – JYelton
    Sep 26 at 17:04

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