Archon

[Grinder]

So, I made an error with the fujipoly extreme, thinking that it was adhesive. However I'll be able to use it in my Blood and Guts build to redo the VRM heatsink on my Crosshair V Formula Z.

It's probably just as well, since it got me thinking about how to better cool the VRMs on my GPUs. I'm planning on this setup for VRM2 and the RAM on my R9 290s, and since they don't make much heat it's no big deal to stick with the thermal tape that came on the ramsinks rather than the fujipoly extreme. Apologies for the crappy shots, these are just mockups of the GPU cooling:



For VRM1, I was planning on this but while researching the fujipoly I realized that it wouldn't provide enough surface area:



So I resolved to use some aluminum to better cool VRM1. I went to a local metals shop and bought a few off-cuts, about $10 worth:



They are 1/4" thick in order to fit on the VRMs, I have a 1/4x1/4, a 1/4x1/2, and a 1/4x1 piece. At first I was thinking of making a tee, with the thermal pad on the bottom and between the base and top of the tee, and the ramsinks adhered to the top. Here is a mockup:



But I'd have to attach the top through the base and the mounting holes in the pcb. I think this would be lighter and more elegant, while requiring one layer of fujipoly instead of two, and radiating more heat. I'll cut a notch at the ends, drill (ahhhhhhhhhh!) through for the mount, and put the ramsinks on the sides of a single 1/4x1 piece, like so:



The cuts shouldn't be difficult, and I can polish the aluminum bar a bit before I install the ramsinks. What do you guys think?


*edit* Actually, I just tried the last mockup with another ramsink sitting right on top. Fits perfectly and hides the edge of the aluminum bar.

[Grinder]

This shows a little better what I am considering here. Just a rubber band holding the heatsinks for now. The one on the right might need two or three layers of fujipoly to clear the components, and has a less finished look due to the heatsinks on the sides being cut in half. Whereas the one on the left is kinda large.

[DazMode]

I'm pretty sure that multiple layers of thermal pad is not recommended.

[gdesmo]

I think I have a much better solution for you, but you have to give me an hour or two. Have a Ducati coming over that needs a little TLC from me first. Send a couple pictures of the areas to be covered with their dimensions. You have too many contact areas there to work correctly, I like your outside the box thinking though.

[Grinder]

I'm pretty sure that multiple layers of thermal pad is not recommended.

Thanks Daz, that's why I'm leaning towards the 1/4 x 1 inch bar, despite it's size. I've read of people using more than one layer, but that doesn't make it the right thing to do...

I think I have a much better solution for you, but you have to give me an hour or two. Have a Ducati coming over that needs a little TLC from me first. Send a couple pictures of the areas to be covered with their dimensions. You have too many contact areas there to work correctly, I like your outside the box thinking though.

Thanks, I do try to channel MacGyver as much as possible! So two contact areas is too much? If I use the 1/4 x 1 inch, the extreme thermal pad will be between the VRMs and the bar, and the "mystery" tape between the bar and the ramsinks.

You are very kind gdesmo. I don't want to impose on you, considering that I need two of these for this build and one for another, but I have to admit that I'm curious what you have in mind. The base has to be 1/4" to cover the VRMs properly. As for height, the grey components closest to the VRM's are a smidge over 1/4, say 5/16th's. I have a pic of a 1/4 x 1/4 bar sitting on the VRMs:



From the left edge of the bar to the grey components is 1/16, while on the right side the distance from the edge of the bar to the caps is 5/16. The resistors beside the VRMs are perhaps 1/16 taller than the VRMs. The caps are 1/16 higher than the grey components. The mounting holes are 3 and 3/8 inches apart.

If you can improve this by advising me, please do. I can pm pics or a better description if you tell me what you need.

[gdesmo]

Hmmm, I was thinking about using something like this big heatsink I have and slicing it into 2 fins along its length. Would be 10mm by 125mm long and 38mm high, not sure if there is enough space between your other card though for the 38 mm height. You could also cut it with 3 fins and it would be 18mm wide. Here's a few pics.

[Grinder]

Thanks for the help gdesmo.

Sorry for not using metric, the bar was 1/4 inch so I ran with that. The 38mm is doable, but would extend above the "two slot" width of the card. The length is a bit much, would have to be trimmed to ~97mm.

But the stopper may be the other dimension. I think the max without using more than one layer of .5mm thermal pad (to clear the resistors beside the VRMs) would be 6 or 7 mm, as opposed to 10 or 18.

Can you suggest a means of physically securing the ramsinks to the 1/4 x 1 inch bar? Say one screw per ramsink, six per side x 2, plus another six if I did the top. Is there a small self tapping screw or adhesive I could use? If so, that would let me use the 11w/mK rated fujipoly on the ramsinks (instead of the adhesive tape), as well as between the bar and the VRMs. I can also measure the 1/2 inch bar once I've applied a layer of pad to see if 1/2 sinks attached to the side would clear the grey components.

*edit* screws would likely be too large for the ramsinks.

[gdesmo]

Let me look tomorrow for some other ones that are not so wide, I gotta hit the sack. Burned out from actually working hard.

[Hooded]

I have an old heatsink from the vrm's of an old 6970 that you can have. It's 108mm x 22mm x 12mm (l x w x h) You could cut it to 1/4 wide strip and trim length to suite your needs.
Wouldn't cost more than a couple bucks to mail it to you if you would like it.

[Grinder]

Let me look tomorrow for some other ones that are not so wide, I gotta hit the sack. Burned out from actually working hard.

Thanks gdesmo.

I have an old heatsink from the vrm's of an old 6970 that you can have. It's 108mm x 22mm x 12mm (l x w x h) You could cut it to 1/4 wide strip and trim length to suite your needs.
Wouldn't cost more than a couple bucks to mail it to you if you would like it.

Thanks Hooded, but I need three of these. It would be difficult for me to cut such a small strip off of yours and I might have found a solution.

You guys inspired me to dig around a little more in my own tickle trunk, and I found an antique that might do the job. It's a passive black aluminum heatsink from a pentium I (probably a deskpro 2000 or similar), 104mm long x 22 high x 66 wide. If I cut off just two rows of pins, I could get a strip 8mm wide, which might just fit. It's big enough that it would be easier to secure as I cut it. Here is a link:

http://www.codemicro.com/store/produ...efurbished.php

I'll call this plan B, since I'd have to cut three strips, paint the aluminum, and it has a completely different look than the ramsinks. I'm still mulling over ways to make the bar + ramsinks work.

[Grinder]

Hmmm. Arctic Silver Thermal Adhesive has a listed thermal conductivity of approx 7.5w/mK, as opposed to the alumina at .9 or so. I'm not sure which 3M tape is on my ramsinks, but it's likely < the alumina.

[Grinder]

I see the thermal conductivity of aluminum is closer to 200 - No wonder you guys were trying to steer me away from more than one thermal interface! I was going to try out my antique heatsink, but it looks like even 8mm (two rows of it) would be too wide, and possibly short against the resistors adjacent to the VRMs.

I guess I'll try out one of the aluminum bar configs, just with thermal tape, to see roughly what the real world numbers would be. Meanwhile, I'll keep looking. Hooded, gdesmo, thanks again for your help.

*edit* I used a hacksaw to cut a strip off the old pentium heatsink, and then beveled the edge a bit with a dremel, but it still looks too wide.

[Grinder]

I realized that I was wrong when I said I didn't have any easy way to cut aluminum. I bought a 10" blade for that purpose when I installed an aluminum railing system on my deck a few years ago.



I mounted the blade on my table saw, and went at the 1/4 x 1 inch aluminum bar. I haven't smoothed the rough edges yet, but I think this will work as long as it has enough surface area:

[gdesmo]

Looks good to me ! Lots of surface area, if you can get some airflow around it you will be good to go.

[nass]

didn't read the whole thread but have u thought of just getting a full cover block? I c your trying to save some cash, me bad...