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Author Topic: Make a custom MXM graphics card heatsink  (Read 156 times)

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Make a custom MXM graphics card heatsink
« on: February 22, 2018, 08:17:33 AM »
The process below relates to making a simple custom heatsink with limited tool access for an ATI/AMD 6700M MXM graphics card (AMD 5950M recognised by the system as an 6700M) to fit inside a HP Elitedesk 800 G1 USDT (Ultra-Small/Slim Desk Top) computer. Notwithstanding the heat-sink itself, to actually run an MXM card an 180W external power adapter is needed (Part No. #613766-001 or alternatively #613766-002).

Parts used/needed;
- AMD/nVidia Type III MXM card[1].
- Copper or aluminium plate or sheet[2].
- 40 x 40 x 30mm aluminium heatsink[3].
- 3M double-sided thermal adhesive pad/tape[4].
- CPU/GPU thermal pad/s (silicone)[5].

- Machine screws/bolts; M2 (2mm x 8mm) and M1.6 (1.6mm x 5mm)[6].

Tools used for the job
- junior hacksaw with metal blade.
- standard bastard file for metal.
- needle files (round).
- 2mm drill bit for metal.
- pin-vice.
- wet-n-dry fine grit.
- craft knife.
- scissors.

Making the heat-sink
To keep the process as simple as possible, the plan is to mount the aluminium heatsink square on a section of plate that’s cut to size and drilled so it can be mounted to the posts for the MXM card on the motherboard. To avoid waste and keep the amount of work to a minimum, the baseplate will first be draw to size on a sheet of paper or thin card. This will then be cut out, placed on the metal sheet, which will be marked and cut based on this, mounting holes included.

The basic MXM heatsink with aluminium block and copper baseplate

First mark the mounting holes to determine base-plate actual size.
The simplest way to do this is use the MXM cards mounting bracket (if the MXM board has no mounting bracket use the holes the bracket will attach to). Hold a piece of paper over the bracket (board underside) and poke holes through where the mounts are. Double-check position and alignment (cf. #1 below).

Holes puched in paper to double-check measurements for baseplate

With holes punched, the distance between them should be;

 - 46mm centre-to-centre

Using at minimum a 2mm drill-bit to match the M2 mounting bolts/screws, this makes the inside edge-to-edge measurement 45mm, with an outside edge-to-edge of 47mm[7] (cf. below).

Basic measurements for the copper baseplate - 46mm centre-to-centre, 56x56mm

Knowing mounting hole size and placement the heatsink plate can be drawn relative to the MXM card’s overall size and the GPU’s position on the board[8].
Using 2mm thick copper or aluminium plate[9] and the centre-to-centre mount hole distance of 46mm, add another 5mm hole-centre to outside edge, making the plate 56mm x 56mm[10] overall (5mm from hole-centre to outside plate edge). This forms the template and should look similar to the image below;

Paper and card templates used to draw/scribe copper baseplate

Once drawn the MXM heatsink template can be cut out and transferred.
Double-checks measurements after initial layout then cut paper or card template using a craft knife and straightedge or steel ruler. Place on copper or aluminium plate and mark or scribe the baseplates outline and centre-punch the mounting holes [11].

The basic heatsink baseplate marked on 2mm thick copper plate

Cut to shape and drill mounting holes.
Using a metal cutting saw cut as close to the outside edge of the heatsink as possible (the outer border)[12] to minimise the amount of excess material that need to be removed. Once cut, confirm the mounting hole centres are clearly punched and drill using a 2mm or 3mm drill-bit for metal[13]. Finish up using a metal file to finalise the shape, and remove any heavily scribed lines or marks on the upper surface with wet-n-dry sanding paper or other abrasive.

Cooper (2mm) baseplate scribed, drilled and sized

Clean, de-oxidise and de-grease surfaces.
To make sure the heat-resistant double-sided tape sticks the aluminium heat-sink block and baseplate firmly together clean and de-grease using surface cleaners and/or alcohol[14] – this is critical for lasting adhesion. Apply the tape to the underside of the heatsink block – cut to shape/size and/or trim excess where needed. Centre the block over the plate and press down firmly[15]. The MX heatsink unit is now ready to install.

The basic MXM cooling unit with aluminium heatsink block and copper baseplate

Installing the custom MXM heat-sink.
The final step is to install the MXM heat-sink unit. Apply thermal grease to the GPU, alternatively use a silicone thermal pad. Position the heat-sink and fasten using standard M2 bolt/screws – although pressure ensures a tight fit between GPU chip and heat-sink be aware of gaps that may form when fastening pressure is unevenly applied[16].

The custom made MXM heatsink installed in a HP 800 G1 USDT
Hardware properties of AMD Catalyst in Windows 10

[1] although "Type III" MXM graphics cards may physically fit the available MXM motherboard slot, they may not be system or Operating system compatible, a condition that might not be discovered until booting up.

[2] metal plate or sheet material for baseplate should be a minimum thickness of 1.2mm to limit distortion and flexing – thicker material can be used but will typically affect ease of production.

[3] heatsink dimensions are largely determined by the height from GPU to underside of the case lid, and reduced width/depth as allowed for access to mounting holes – larger prefabbed heatsinks can be used but will need altering to allow for mounting point access.

[4] thermal tape is often used to ‘stick’ heatsinks to chips mitigating mounting pins and brackets. Success depends explicitly on clean surfaces. Thermal adhesives are not the same as silicon heatsink pads that aid heat transfer between surfaces.

[5] thermal pads made from silicone should be preferred to thermal past as the spongy resistance is used to ‘tension’ the heatsink once mounted instead of springs as might normally be used.

[6] to mount the heatsink itself to the MXM bracket the same type of M2 screws/bolts used in laptops can be used. To mount the MXM card itself to the motherboard MXM mounts M1.6 screws/bolts are needed. These requirements may vary depending on motherboard and card mounting brackets or posts.

[7] as the holes related to M2 threaded bolts/screws they will need to be slightly larger to ensure the mounting bolts have wiggle room if needed to fit the mounting plate. Drilled with a 3mm bit, or a 2mm then expanded using a needle file, either/or subject to availability, this makes the inside edge-to-edge measurement between 44mm (maximum) to 45mm (minimum) – ideally 44.5mm, and/or an outside edge-to-edge of 47mm (minimum) to 48mm (maximum) – ideally 47.5mm.

[8] ] GPU chip placement is not always centred within the space defined by the brocket and holes, or perpendicular to the MXM board edges.

[9] baseplate should be a minimum of 1.2mm thick to minimise flexing when fastened to the MXM mounting bracket.

[10] the size described here is based on defining an area that allows enough room to fully support the mounting holes without undue bending or twisting of the plate (depending on plate thickness and tempering) – the heatsink baseplate could be made large or smaller depending on the space available and/or whether partially or fully covered other onboard chips and modules is possible (they don’t obstruct the baseplate).

[11] it will be easier to mark or scribe around a card version of the template using an indelible pen, fine-line marker, or pointed object. If scribing, initial markings should be light so corrections can be made with relative ease.

[12] depending on the metal used for the base plate, use a powered, ‘junior’ or full-sized hacksaw with metal-cutting blade (teeth close together). To be absolutely sure of mounting hole placement, positioned the MXM card on top of the plate and marked down through the holes double-checking their position relative to those marked. Do this before cutting out the raw baseplate.

[13] drill one hole and double-check the diagonal (e.g. bottom-left to top-right) for placement and accuracy before drilling the opposite corner. To allow some wiggle room, use of a 3mm bit is recommended else holes may be too tight (alternatively a needle file can used to clean up or widen the holes). Countersink holes to de-burr.

[14] for copper plate in particular use Brasso or similar branded or off-brand, mild abrasive, surface cleaner/metal polish before clearing any residue with (isopropyl) alcohol or nail-polish remover.

[15] use a table and once positioned, apply full weight to the unit for a moment to ensure absolutely fast adhesion. Test by checking for any play or wiggle – if tape comes unstuck the surfaces would not properly cleaned and prepared.

[16] ideally fasteners should be spring loaded in that a long bolt is fastened to the mounting bracket under the MXM board which is then tensioned by the presence of compression springs. Unfortunately, these types of fittings are not readily available for MXM cards so the use of silicon thermal pads is recommended to provide adequate thermal transfer and compressive resistance to the downward pressure of the fixings that are used.


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