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Montala
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Location: Herefordshire (U.K.)

Thickness of thermal adhesive tape?

Fri Jul 05, 2019 5:10 pm

Hi,
Rather than add this post to the rather large, “Raspberry Pi 4 Temperature” thread, I though it easier to start a new one, relating to my specific question.

It is now generally accepted that the Raspberry Pi 4 boards can, under certain conditions, run a little ‘hot’, particularly in the new ‘official’ case, and although the promised firmware update will hopefully reduce this a bit, there are still a number of users, such as myself, who wish to attach a heat-sink to the board.

One such item is (or rather was!) available from Pimoroni, with the dimensions 40 x 30 x 5 mm meaning that it can only be fitted (just!) in one position, where it will cover, not only the CPU, but also the memory chip and radio module as well.

This is fine I suppose, except of course for the fact that as they are all different ‘heights’ it is difficult for a single piece of thermal tape to make proper contact with all three. As the small piece of 3M tape supplied does not cover the whole heat-sink anyway, my first thought was to remove this, and replace it with something which did, so I have ordered a piece of 0.5 mm thick Akasa AK-TT12-80 Thermal Adhesive Tape, which I will then cut to size.

Possibly though this is not the best option, and would something like a piece of ARCTIC - Thermal Pad 50 x 50 x 0.5 mm Thermal Compound Conductivity Gap Filler be more suitable, or as the chips are different ‘heights; possibly a 1 mm, or even 1.5 mm, thick thermal pad would be a better alternative?

I would be interested to hear what other users think about this idea anyway, and which option they would go for, if indeed they were going to fit one to their Pi 4?

Thanks!

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HawaiianPi
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Location: Aloha, Oregon USA

Re: Thickness of thermal adhesive tape?

Fri Jul 05, 2019 5:44 pm

What would be best would be whatever is the thinnest that properly fills the gap. Maybe... :?

Keep in mind that a Raspberry Pi computer is a low wattage device. It doesn't take much to cool it. The RAM chip probably doesn't need cooling, and the benefits of cooling the shield over the radio chip are unknown (does that shield even make contact with the heat producing parts).

The SoC is what you want to cool, and sharing a single heatsink with multiple components may not produce the desired results (it may transfer heat to a cooler component, raising its temperature).

Try not to get too carried away with this stuff.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?

jahboater
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Joined: Wed Feb 04, 2015 6:38 pm

Re: Thickness of thermal adhesive tape?

Fri Jul 05, 2019 6:16 pm

HawaiianPi wrote:
Fri Jul 05, 2019 5:44 pm
the benefits of cooling the shield over the radio chip are unknown (does that shield even make contact with the heat producing parts).
It did on the Pi3B+ and became very hot to the touch under heavy load.

jahboater
Posts: 4843
Joined: Wed Feb 04, 2015 6:38 pm

Re: Thickness of thermal adhesive tape?

Fri Jul 05, 2019 6:23 pm

Montala wrote:
Fri Jul 05, 2019 5:10 pm
One such item is (or rather was!) available from Pimoroni, with the dimensions 40 x 30 x 5 mm meaning that it can only be fitted (just!) in one position, where it will cover, not only the CPU, but also the memory chip and radio module as well.

This is fine I suppose, except of course for the fact that as they are all different ‘heights’ it is difficult for a single piece of thermal tape to make proper contact with all three.
I purchased the Pimoroni 40x30x5 heat sink but decided not to use it because it covered the ram and the rf shield without helping to cool them, and probably restricted airflow over them. Very thick tape might help but I don't like that idea at all!

Instead I chose the new PiHut heat sink:
https://thepihut.com/products/al-heat-s ... 30-30-10mm
It is a little narrower and so leaves some of the other two parts visible.

Importantly, it is heavier and taller.

The properly specified thermal tape should be good (3M-8810).

In UK temperatures, outside of a case, this heat sink is entirely adequate and I cannot get the temp high enough to throttle.

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Montala
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Location: Herefordshire (U.K.)

Re: Thickness of thermal adhesive tape?

Fri Jul 05, 2019 7:50 pm

Thanks guys... some very good points there, which have made me think again!

If it is really only the CPU (SoC) which requires cooling, I think I would therefore prefer to use a smaller heat sink which will just cover this 'chip', so I have been looking at ones about 1.4 cm square and 5 or 6 mm high, so that they will still fit into the new 'standard' cases.

Suitable ones are available from both the Pie Hut and Pimoroni, so I will probably go for one of these instead, I think!

jahboater
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Joined: Wed Feb 04, 2015 6:38 pm

Re: Thickness of thermal adhesive tape?

Sat Jul 06, 2019 1:02 pm

Montala wrote:
Fri Jul 05, 2019 7:50 pm
If it is really only the CPU (SoC) which requires cooling, I think I would therefore prefer to use a smaller heat sink which will just cover this 'chip', so I have been looking at ones about 1.4 cm square and 5 or 6 mm high, so that they will still fit into the new 'standard' cases.
I doubt that putting any heat sink on will help if you put the Pi4 into a tiny un-ventilated case.
The problem is simply getting the 10-15w of heat out of the box.

If you must have a case, then the Pi4 FLIRC case looks good and has been popular for previous models.

https://flirc.tv/more/raspberry-pi-4-case

This case is made of aluminum and the case itself acts as a large heat sink.

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Montala
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Joined: Mon Mar 05, 2012 11:54 pm
Location: Herefordshire (U.K.)

Re: Thickness of thermal adhesive tape?

Sat Jul 06, 2019 2:04 pm

Thanks jahboater,

A similar (but more expensive) case which 'works'in a similar fashion and which has also been very popular with a lot of users is from Argon40, who are producing one specifically for the Raspberry Pi 4.

Further details can be found at https://www.argon40.com/argon-one-pi4.html and yes, I have one of these on pre-order also! ;)

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