Adhesive for aluminium heatsink

[bikerhifinut]

Any recommendations for a heat conductive adhesive or adhesive film to attach a pair of 200mm x 75mm extruded aluminium heatsinks to a sheet aluminium chassis? The other side of the chassis will have the aluminium heatsink brackets of the power amplifier module and I intend to do something similar here as the conventional approach of drilling a set of holes and bolting it through will be awkward and cosmetically poor. Its a finned heatsink from RS and fits the end panel of the chassis perfectly.
The amp boards could be bolted through the chassis but its thin aluminium and not sufficiently thick to be able to countersink a mounting screw.

I considered drilling the back of the heatsinks and tapping a thread in but again they aren't really suited as inevitably I'd have to go through one of the fins which wouldn't look nice.
I've seen heatsinks stuck on computer and digital amp chips but not sure how that translates into the larger scale.
All ideas appreciated.

Andy.

[Red to black]

Have you considered pop rivets ?

[barrymagrec]

I think the Arctic Silver people do a thermally conductive 2 part adhesive - it won`t be cheap though.

If the surfaces are flat enough for there to be a small/non existent gap good old slow set Araldite will do nicely. Unlike a transistor or module you have a large surface area to play with, the small additional thermal resistance of Araldite won't matter. Done hot (60C, preheat in oven) Araldite will flow like milk.

[barrymagrec]

If you drill and tap the heatsink between the fins you can fix them with black finish screws - this looks perfectly acceptable.

[bikerhifinut]

Originally Posted by merlinmaxwell

If the surfaces are flat enough for there to be a small/non existent gap good old slow set Araldite will do nicely. Unlike a transistor or module you have a large surface area to play with, the small additional thermal resistance of Araldite won't matter. Done hot (60C, preheat in oven) Araldite will flow like milk.

That's interesting Merlin, I had assumed that epoxy wouldn't conduct the heat very well, I wonder if something like the metal loaded epoxies would work well here, the issue i would think is getting a complete surface contact.
So how about using half a dozen "spots" of epoxy and filling the gaps in with heat conductive paste?

The idea of drilling a small set of holes through and tapping could work I guess and use black finish set screws? they'd have to be M3 or smaller though. I like that idea as being reversible if needed in the future.
The power amp boards on the other side can be butted hard against the chassis side with some heatsink paste as they have mounting holes on the PCB so could bolt them down on standoffs and rely on the mechanical joint.
I've yet to drill the chassis/boxes to take the socketry and switch and then its Spray can time, etch primer followed by a satin black paint finish. These things are likely to hide behind a speaker but all the same I'd like them to look presentable in case they end up on the bottom of a rack.

Thanks for the ideas guys, I am sure there's an elegant and practical solution.
It could be argued that the aluminium case itself might have enough thermal mass to cool the boards but I would rather not take the chance.

Always a sensible answer on here.

Andy

I wonder if something like the metal loaded epoxies would work well here

Yes they would work but still have appreciable thermal resistance and be hard to make very thin that's why I suggested good old Araldite. Loaded stuff is good if you have a gap, here you can have (nearly) no gap, so much the better.

[Graham G3ZVT]

When I needed to attach some anodised aluminium floor edging to the back of a big LED array to replace the useless LED light in a cooker hood I found a product called "heatsink plaster" Cost me 99p delivered from China last year.

[G6ONEDave]

Depending on how thick the actual flat area of the heatsink is, you could try drilling through the aluminium sheet and then drill blind holes into the heatsink. You could then use tapping screws, rivets or even bolts into tapped holes in the heatsink, non of which would be visible from the heatsink external finned side. I would then use normal heatsink paste between the fixed flat areas.
Dave

[ThePillenwerfer]

I've seen an an article in the March 1984 issue of Radio & Electronics World that tells you to use epoxy to fit a home-made heatsink to an LM380 so it's certainly a recognised technique.

[bikerhifinut]

Originally Posted by G6ONEDave

Depending on how thick the actual flat area of the heatsink is, you could try drilling through the aluminium sheet and then drill blind holes into the heatsink. You could then use tapping screws, rivets or even bolts into tapped holes in the heatsink, non of which would be visible from the heatsink external finned side. I would then use normal heatsink paste between the fixed flat areas.
Dave

That seems the way to go, I'd pretty much decided on it especially as i have altered the layout so that the 200mm heatsink is going on a 300mm side of the ally chassis and a pal with a milling machine is going to cut down and edge finish a pair of nice brushed and anodised Thick ally panels for the front of the project. So the absolute cosmetic appearance is not so vital now.
However I figure using a nice long drill bit between the fins and drilling through and into the chassis to ensure it all lines up will work a treat and I have a set of taps and dies so I can cut a nice thread in the heatsink holes and use a suitable length of screw to bolt it on. The other sides the biggest challenge in respect of keeping the amp boards bracket in full contact as it must be easily removable for future servicing, but I have an idea there too.
Thanks folks, there are some very good solutions you have suggested.

Andy

[G6ONEDave]

You probably already know about this but do remember to use a smaller correct diameter drill bit for the holes that need tapping, then enlarge the holes where the screw needs to pass through unhindered. It's an easy error to drill the wrong size and I dare say that we've all done it at some stage or other.
Dave