Mounting Edge heatsink with Edge in Captain

I’m designing a custom carrier board for the Edge, so I’ve bought a Captain to see how the experts do it! :slight_smile: I already have an Edge I’ve been playing with, fitted with the Edge heatsink. I think there’s a problem with securely attaching the heat sink on an Edge in the Captain.

The top two holes are fine: you need a longer M2 screw to go through the heatsink, the Edge board and the Captain board, but I have those in my box of random parts so that’s fine.

But the bottom two mounting holes in the heatsink collide with the alignment lugs each side of the MXM314 connector, so it isn’t possible to secure the bottom of the heatsink. This means the heatsink flaps/hinges away from the board very easily.

Am I misunderstanding how this is meant to work, or is it a mechanical bug with the heatsink design?

I flagged the same issue with the developer sample that I was sent. I was hoping it was oversight on the first production samples … but maybe it wasn’t.

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@chewitt My next question (to myself) was how I’d design the carrier board differently to work around the problem, but this isn’t obvious. Modifying the MXM314 socket itself won’t be feasible for volume manufacture.

Maybe some sort of L shaped bracket that attaches to the heatsink and extends the lug further out beyond the edge of the MXM314 before securing it to a mounting point on the lower board?

I’d use the “u” notches to capture some kind of sprung clip (plastic or metal) that holds the heatsink in place. The heatsink doesn’t have to be screwed tight to the board to work, only pressed firmly against the SoC chip. I’d also design a heatsink that puts vanes accross the full width of the heatsink surface so you don’t need fans. IMHO fans are either noisy or unreliable (or both) and they add expense.

Yes, I think if you’re allowed to redesign the heatsink, it’s easy to fix this. Even just making the ‘bottom legs’ come out further so they can secure to the carrier board would be sufficient, although that would no longer be suitable for a bare Edge board.

What I was trying to work out is: could I design a carrier board that worked with the existing Edge and unmodified Edge heatsink, but still attached everything securely. I don’t really have an elegant idea; probably easiest to make an extension bracket or fabricate a different heatsink.

Hi ChrisW:
For the early batch the MXM3 connector if JAE with the two , later batch we use the Foxconn MXM3 connector without the red-circled parts:

Can you just cut off that part with some tool by yourself, or you can also ask for a return and we will ship you a new one instead.

Sorry for the trouble!

Hi @Gouwa! I’m fine to modify the board I have, but to build the Edge + heatsink into my own system, I’ll need to track down the Foxconn part you’re now using. I found the JAE MM70 one on Digikey and Mouser, but no other manufacturers when I searched.

Looking at the Foxconn site, is it the AS0B826-S78B-7H you’re using, or something else? (7.8mm sounds a bit high compared to the JAE part, so perhaps not?)

http://www.foxconnconnector.com/sale-11592468-as0b326-s78n-7h-foxconn-memory-connector-mxm-3-0-socket-0-50mm-pitch-314pos-7-8mm-height-smt.html

Is it possible to source the Foxconn MXM3 connectors from any of the standard distributors?

The model we used on Captain is AS0B826-S43B-7H with 4.3MM height.

BTW, the mount screws used on Captain with follow specs for your reference:

We can add these two SKU to Khadas Shop if needed.

Aha, that looks a lot more sensible height, yes. Thanks!

Thank you! :slight_smile:

Ooh, yes please. I’ve just dropped a note to a couple of different companies I use for PCB prototyping and assembly to see if they’re able to source the Foxconn part, but I expect they’ll draw a blank as they just use Digikey, Mouser, E14, etc. [Update: Seeed Fusion say they can source it; guess that makes sense as Foxconn is nearby in ShenZhen. UK assembly house can’t get it.]

Being able to order them along with the Edge modules and heatsinks, ready to supply to the PCB assembly house would be great. I suspect there will be lots of makers wanting to buy these in small quantities to incorporate Edge boards into their projects too.

I’ll make the MXM3 footprint and the ‘generic’ part of the design for a carrier board available in whatever formats I can easily convert/export it to for others to use as soon as I’ve prototyped one and checked it doesn’t have any major errors in it.

I love the way you’ve connected the ceramic chip wifi antennae with the pins onto the pads on the back of the board, by the way. Neat way to minimise impedance-controlled traces and get the chip antennae as close to the module as possible, while still having them on the carrier board. :+1:

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Available here:

Have fun!

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Thanks! A parts kit is an excellent idea. :+1:

I ordered my first prototype with the same JAE connector you used originally (although higher); next prototype will use one of these.

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