AC86U Heatsink Mod

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sorachan

Occasional Visitor
My AC86U warranty expires this month, after seeing this thread, I want to mod my AC86U as well.

So I bought many cheap components from China: copper blocks, thermal pads, thermal paste, sping loaded screws and some cheap aluminium heaksinks. Total about 15 bucks + shipping.

thumbnail_IMG_5035.jpg


The router is not really hard to open, note there are also two screws underneath the label. You can search youtube for detailed instruction, AC68U and AC86U both use the same casing.

thumbnail_IMG_5038.jpg


I firstly used a thin layer (0.5mm) of thermal pad as cushion. (Update: Do not use thermal pads)

thumbnail_IMG_5040.jpg


Those two wifi chips are about 1mm lower than the CPU chip, so I used 15*15*1.5mm copper block for the CPU and 13*12*2.5mm copper block for the wifi chips.

thumbnail_IMG_5042.jpg


To prevent breaking CPU die, I used spring loaded screws like the ones used for graphic cards. It's pretty much impossible to break your die if you use sping loaded screws. (Size: M2.5*10mm)

thumbnail_IMG_5044.jpg


I also added thermal paste for the front panel thermal pads just in case the pads are not high enough to touch the panel.



Finally, added some cheap heatsinks.



Before the mod, my CPU temperature is about 75 degrees (room temperature 20 degrees).

Here is the after:


Not bad...

-----------------------------------------

CPU temperature increased to 65 degrees after 6 hours, not good!

Since the pressure from spring loaded screw is fairly low, I decided to remove the thermal pads. I also changed screws for higher pressure (M2.5*7.5mm for the middle screw, and M2.5*9mm for the corner screws).


The result is very very promising.



----------------

After 10 hours, the temperature is at around 50-55 degrees. I'm quite satisfied now.
 
Last edited:

dev_null

Senior Member
I like the idea and thanks for sharing. I would note for others considering this: when I apply thermal paste (to computer CPUs) I put a tiny bead (think grain of rice, or maybe two grains) on the CPU in the center and spread it with a razor blade. The intention is not to use it as glue but to fill in the almost-molecular imperfections between the chip and the heatsink, to create that better heat-transferring connection.

So I would have used less paste, and I might have considered a bit between the copper and the heatsink itself.

In any event in comparison to a CPU there's not much heat to be transferred and you've demonstrated a significant reduction in temperature.
 

sorachan

Occasional Visitor
I like the idea and thanks for sharing. I would note for others considering this: when I apply thermal paste (to computer CPUs) I put a tiny bead (think grain of rice, or maybe two grains) on the CPU in the center and spread it with a razor blade. The intention is not to use it as glue but to fill in the almost-molecular imperfections between the chip and the heatsink, to create that better heat-transferring connection.

So I would have used less paste, and I might have considered a bit between the copper and the heatsink itself.

In any event in comparison to a CPU there's not much heat to be transferred and you've demonstrated a significant reduction in temperature.
You are right, but because the spring pressure is fairly low, I applied a lot of thermal paste just to be on the safe side...
 

John Fitzgerald

Senior Member
My AC86U warranty expires this month, after seeing this thread, I want to mod my AC86U as well.

So I bought many cheap components from China: copper blocks, thermal pads, thermal paste, sping loaded screws and some cheap aluminium heaksinks. Total about 15 bucks + shipping.

View attachment 33196

The router is not really hard to open, note there are also two screws underneath the label. You can search youtube for detailed instruction, AC68U and AC86U both use the same casing.

View attachment 33208

I firstly used a thin layer (0.5mm) of thermal pad as cushion。

View attachment 33204

Those two wifi chips are about 1mm lower than the CPU chip, so I used 15*15*1.5mm copper block for the CPU and 13*12*2.5mm copper block for the wifi chips.

View attachment 33206

To prevent breaking CPU die, I used spring loaded screws like the ones used for graphic cards. It's pretty much impossible to break your die if you use sping loaded screws. (Size: M2.5*10mm)

View attachment 33207

I also added thermal paste for the front panel thermal pads.



Finally, added some cheap heatsinks.



Before the mod, my CPU temperature is about 75-80 degrees (room temperature 20 degrees).

Here is the after:


Not bad...

Applying thermal paste to any thermal pad(s) is a mistake. The paste will cause the pad to disintegrate (melt, collapse, tear)
Only use one or the other.
Putting a copper shim on the pad is OK so long as the flip side paste will not spill over. (pad -> shim ->paste -> heatsink)
 

sorachan

Occasional Visitor
Applying thermal paste to any thermal pad(s) is a mistake. The paste will cause the pad to disintegrate (melt, collapse, tear)
Only use one or the other.
Putting a copper shim on the pad is OK so long as the flip side paste will not spill over. (pad -> shim ->paste -> heatsink)
I don't really understand. Since the thermal pad is silicone, the thermal paste is also silicone, how can the paste cause the pad to disintegrate? Both paste and pad I bought are sold as pure non-conductive silicone product. The thermal conductivity of the pad is 6.0W/m-k, the paste is 9.5W/m-k.

Here is a graphic card thermal pad instruction:
 
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John Fitzgerald

Senior Member
I don't really understand. Since the thermal pad is silicone, the thermal paste is also silicone, how can the paste cause the pad to disintegrate? Both paste and pad I bought are sold as pure non-conductive silicone product. The thermal conductivity of the pad is 6.0W/m-k, the paste is 9.5W/m-k.

Here is a graphic card thermal pad instruction:

Take it apart in a year and post the pictures.
 

sorachan

Occasional Visitor
Take it apart in a year and post the pictures.
If you claim silicone thermal pad + silicone thermal paste = bad thermal conductivity, I kind of understand though I don't know if it's ture.

However, silicone thermal pad + silicone thermal paste = disintegration makes no scentific sense, how can the same element react to each other? If you use graphite thermal pad with silicone paste, or silicone pad with liquid metal, they probably can chemically react at higher temperature, but silicone + silicone definitely will not react unless you heat them up to 400 degrees, they will melt at 1414 degrees.
 

John Fitzgerald

Senior Member
If you claim silicone thermal pad + silicone thermal paste = bad thermal conductivity, I kind of understand though I don't know if it's ture.

However, silicone thermal pad + silicone thermal paste = disintegration makes no scentific sense, how can the same element react to each other? If you use graphite thermal pad with silicone paste, or silicone pad with liquid metal, they probably can chemically react at higher temperature, but silicone + silicone definitely will not react unless you heat them up to 400 degrees, they will melt at 1414 degrees.

So the "thermal pad" is made of solid silicone and the "paste" has no other binders?
 

sorachan

Occasional Visitor
So the "thermal pad" is made of solid silicone and the "paste" has no other binders?
No, but it makes no sense. Silicone and polymer compounds are all very stable chemically, even mixing them together is really really hard. I would prefer concrete evidences rather than speculations.

If no concrete evidence, I may report back after a year if I still can remember this issue.

I also opened a topic at LTT to ask the same question: https://linustechtips.com/topic/1327316-silicone-thermal-pad-silicone-thermal-paste-disintegration/
 

sorachan

Occasional Visitor
So the "thermal pad" is made of solid silicone and the "paste" has no other binders?
I'm looking at Dow material brochure for silicone thermally conductive materials. I'm reasonably confident it won't react with thermal pad. These products should be very chemically stable, noncorrosive, some even have UL94 rating (flame retardant)...
 
Last edited:

Tech9

Very Senior Member
Paste on top of pad doesn't improve thermal transfer. Waste of material and unnecessary mess. Here is a similar mod with low noise fan behind the router:

Untitled_M.jpg
 

sorachan

Occasional Visitor
Paste on top of pad doesn't improve thermal transfer. Waste of material and unnecessary mess. Here is a similar mod with low noise fan behind the router:

View attachment 33220
The purpose is not to improve thermal transfer, but rather just in case the factory pads are not high enough to touch the front panel.

Fan definitely works very well, except it sucks too much dust into the router. I used to use fans but wanted to have a change as warranty expires this month.
 

Darkje

Occasional Visitor
@sorachan i just wanna say awesome you try this....

so i did same today, only copper mod on the cpu. The basic results are also cpu at 60 and the rest is same. Soooo best option would be to do the copper mod on the wifi but that is really fragile
 

sorachan

Occasional Visitor
@sorachan i just wanna say awesome you try this....

so i did same today, only copper mod on the cpu. The basic results are also cpu at 60 and the rest is same. Soooo best option would be to do the copper mod on the wifi but that is really fragile
It's pretty much impossible to break the chips if you are using spring loaded screws. If not, then you would have to be very very careful. The temperature decrease is not significant for wifi chips anyway so you can leave them alone.
 
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Darkje

Occasional Visitor
Iam not using spring load screws...
I just replaced the therma pad for copper. It's running now for a few hours. And it has settled on 65 degrees. So that's a major plus. Coming from 80~90 degrees. I use 2 cable connections and a vpn. Including 2 old 68u's as mesh.
 

Kendo

Regular Contributor
Nice project. Congrats.
 

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