DEC750 NVMe thermal pad?

[foxxx0]

Hey folks,

I recently received my DEC750 and noticed the NVMe temperature is a bit high for my taste.

Depending on the room/ambient temperature and the I/O load, the NVMe sits around 63-67°C in idle and easily goes up to 75°C+ under load.

The CPU on the other hand stays comparatively cool, sitting around 48-52°C at idle, with an enclosure surface temperature of ~39°C.

I wasn't able to find teardown pictures of the DEC750, only the DEC850 on reddit, which is based on a completely different PCB and enclosure. However, there it looked like the NVMe had no "direct" thermal contact with the enclosure. Apparently there is a recess milled into the enclosure top to make space for the NVMe but I didn't see any thermal pads there.

Comparing the NVMe temperature and the enclosure surface temperature leads me to believe that there is no direct thermal transfer between the two, only passive thermal radiation.

So before I open the DEC750 myself, I thought I'd just post this question here.
I'm kinda hoping I could just purchase a thermal pad of the necessary thickness (guessing somewhere between 0.5-3mm) to improve the NVMe temperature.


Thanks in advance!


Cheers,
foxxx0

[pfry]

[...]I'm kinda hoping I could just purchase a thermal pad of the necessary thickness (guessing somewhere between 0.5-3mm) to improve the NVMe temperature.[...]

Some things to consider:

• Thermal pad will be better than air;
• ...But contact/pressure is important, and M.2 boards are worthless/weak and generally unsupported;
• The controller is the major power consumer, so your focus should be on it;
• Be aware of component height - I have M.2 SSDs where the controller is .25mm lower than surrounding components, a critical but hard-to-see issue.

You'll want a dead soft pad. I'd recommend getting a few and seeing what you can work with. Ideally you can trial the thing (such that you can directly view contact) or take an impression (via, say, very soft clay) to try to see how applying pressure to the controller will flex the board. Some motherboards use medium foam supports under the board, but sourcing something like that might be tough. On one of my tiny ARMs I had to trial several pads and thicknesses to find one that didn't simply flex the board such that the controller surface was no longer parallel to the opposite surface, resulting in limited contact. Foam pads are garbage from a thermal standpoint, but may be better from a physical standpoint.

Good luck.

[patient0]

the NVMe sits around 63-67°C in idle

Are you using a RJ45 module in one of the 10G SFP+? The NVME sits behind the SFP+ ports and got warm/hot when I did test RJ45 modules. But it was only for testing in my case so I didn't install any pads and can't help with that. I think the gap between the NVMe and the enclosure is quite substantial but maybe that changed with later models. There was a cutout for the RAM stick and like a pedestal (whatever the correct english word would be) for the CPU, nothing else.

Motherboard on the shop website:
https://shop.opnsense.com/dec700-series-opnsense-desktop-security-appliance/
https://shop.opnsense.com/wp-content/uploads/2021/11/NetBoard-A10_Gen.3_P1.0-CN_2021-Nov-08_03-52-59PM-000_CustomizedView15531474162.png

I'll upload a few of the pictures I took (some time ago) and update this post.

Update: four photos under https://kupper.org/OPNsense-DEC740/ . Open the images in a separate tab/window for the bigger size. And I'm very much not a web guy, so sorry about that.

[foxxx0]

Are you using a RJ45 module in one of the 10G SFP+? The NVME sits behind the SFP+ ports and got warm/hot when I did test RJ45 modules.

Nope, just a passive DAC SFP+ cable, so pretty much as low-power as you can go.
I've managed to completely stay away from those SFP+ RJ45 modules, precisely because of that.

I think the gap between the NVMe and the enclosure is quite substantial but maybe that changed with later models. There was a cutout for the RAM stick and like a pedestal (whatever the correct english word would be) for the CPU, nothing else.

Motherboard on the shop website:
https://shop.opnsense.com/dec700-series-opnsense-desktop-security-appliance/
https://shop.opnsense.com/wp-content/uploads/2021/11/NetBoard-A10_Gen.3_P1.0-CN_2021-Nov-08_03-52-59PM-000_CustomizedView15531474162.png

Update: four photos under https://kupper.org/OPNsense-DEC740/ . Open the images in a separate tab/window for the bigger size. And I'm very much not a web guy, so sorry about that.

Thank you so much for the detailed high-res photos. That finally gives some insight.

Based on these I might try to fit a thin m.2 heatsink onto the NVMe, I've got a couple different ones lying around somewhere^tm. The gap does indeed look way to big for just a thermal pad.

At least I have something to go off of and if I do indeed find a different case-heatsink-design in my DEC750 I'll just have to adapt.

[...]I'm kinda hoping I could just purchase a thermal pad of the necessary thickness (guessing somewhere between 0.5-3mm) to improve the NVMe temperature.[...]

Some things to consider:

• Thermal pad will be better than air;
• ...But contact/pressure is important, and M.2 boards are worthless/weak and generally unsupported;
• The controller is the major power consumer, so your focus should be on it;
• Be aware of component height - I have M.2 SSDs where the controller is .25mm lower than surrounding components, a critical but hard-to-see issue.

You'll want a dead soft pad. I'd recommend getting a few and seeing what you can work with. Ideally you can trial the thing (such that you can directly view contact) or take an impression (via, say, very soft clay) to try to see how applying pressure to the controller will flex the board. Some motherboards use medium foam supports under the board, but sourcing something like that might be tough. On one of my tiny ARMs I had to trial several pads and thicknesses to find one that didn't simply flex the board such that the controller surface was no longer parallel to the opposite surface, resulting in limited contact. Foam pads are garbage from a thermal standpoint, but may be better from a physical standpoint.

Good hints, thanks for that. If necessary I'll try to fit some (foam) padding underneath the NVMe to prevent its PCB from bending (i.e. between the NVMe and the mainboard).
Given the pictures above, I might have to just go for a low-profile off the shelf m.2 heatsink instead though.

[OPNenthu]

These videos show a DEC740 taken apart (same channel):

https://www.youtube.com/watch?v=v86V-E70RKA
https://www.youtube.com/watch?v=jl23_mrM7cQ

Not sure if it's the same dimensions exactly as the 750 but at least some more angles you can look at.

[patient0]

Not sure if it's the same dimensions exactly as the 750 but at least some more angles you can look at.

The DEC750 is identical but with 8GB RAM instead of 4 and 256GB NVME instead of 128GB. At some point the DEC750 had 3 2.5GbE ports while the DEC740 still got 3 1GbE ports (but wasn't available in the store). But now they both got 3 2.5GbE ports.