StellarEquilibrium
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(Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 3:11 am

Image

As you can see this is a Pi 4 8GB Model B and the case is supposed to passively cool the components (the top comes ont top of the bottom part and will enclose the pie tightly. Plus a few pillars of metal(?) will press the pads firmly + transfer heat from the chip to the top part but that's irrelevant.

I marked the power chip and a thermal pad placed on the chip, inside of the picture with a red circle in the left hand corner.

My question is, is this a fire hazard / does the flimsy thermal pad present a fire danger?
Take into consideration the pi 4 eats >3A@5.1V, thats a lot of power.
The case's manual was terrible and can't help us here.

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Imperf3kt
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 5:04 am

Thee is no fire hazard as those pads are made of silicon, sometimes with tiny particles of ceramic suspended within them.
Even if it were made of paper though, that chip won't get hot enough to cause combustion (typically well over 200°C for paper) and the hardware can only cause a spark if physically damaged.

That's not to say it's a good idea though. Does the pad contact the metal heatsink? If it doesn't, then you may instead create a thermal insulator instead of interface material, which could lead to overheating of the chip and force it to shut down if it reaches its thermal limit.
It may also impede convection, further hindering passive cooling.

If it does contact the heatsink, it might inadvertently heat the chip instead of cooling it (although this is not likely as the chip in question is one of the hottest on the Pi4b)
For an example of what I mean, think of your car exhaust, typically around 230°C - if you install a heatsink and then use that same heatsink to cool the steering wheel (hypothetical) it will instead heat the steering wheel by transferring the heat from the exhaust, into the heatsink and then into the steering wheel.
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rpdom
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 5:53 am

StellarEquilibrium wrote:
Wed May 12, 2021 3:11 am
Take into consideration the pi 4 eats >3A@5.1V, thats a lot of power.
No, it doesn't.

The Pi 4B uses up to 2.8A 1.8A@5.1V (usually quite a bit less). The remaining 1.2A is for any USB peripherals.

Also, just because a fair chunk of that 2.8A 1.8A will be going through that chip, doesn't mean it will get really hot. Only a small amount will be lost as heat. The rest is needed to run the Pi.
Last edited by rpdom on Wed May 12, 2021 8:52 am, edited 3 times in total.
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drgeoff
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 7:37 am

rpdom wrote:
Wed May 12, 2021 5:53 am
StellarEquilibrium wrote:
Wed May 12, 2021 3:11 am
Take into consideration the pi 4 eats >3A@5.1V, thats a lot of power.
No, it doesn't.

The Pi 4B uses up to 2.8A@5.1V (usually quite a bit less). The remaining 1.2A is for any USB peripherals.

Also, just because a fair chunk of that 2.8A will be going through that chip, doesn't mean it will get really hot. Only a small amount will be lost as heat. The rest is needed to run the Pi.
Something wonky with your calculator. It is getting the wrong answer for 3 minus 1.2. :)
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rpdom
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 8:51 am

drgeoff wrote:
Wed May 12, 2021 7:37 am
Something wonky with your calculator. It is getting the wrong answer for 3 minus 1.2.
Doh! Yes. Head not awake yet. I moved the wrong bead on my abacus.
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LTolledo
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 9:36 am

@OP...
one only needs to put that on the SoC and only when attaching a heatsink on the SoC.

the rest.... give it a rest!

if you expect those part's (you covered with the thermal pad) temperature to go beyond 180C then..... then your board is toast!
the thermal pads might still survive.....
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StellarEquilibrium
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 1:16 pm

rpdom wrote:
Wed May 12, 2021 8:51 am
drgeoff wrote:
Wed May 12, 2021 7:37 am
Something wonky with your calculator. It is getting the wrong answer for 3 minus 1.2.
Doh! Yes. Head not awake yet. I moved the wrong bead on my abacus.
Why did you have to choose that profile picture, my stomach is about to exhale not air but vomit and my hair starts to tingle. :-(

StellarEquilibrium
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 1:25 pm

Imperf3kt wrote:
Wed May 12, 2021 5:04 am
Thee is no fire hazard as those pads are made of silicon, sometimes with tiny particles of ceramic suspended within them.
Even if it were made of paper though, that chip won't get hot enough to cause combustion (typically well over 200°C for paper) and the hardware can only cause a spark if physically damaged.

That's not to say it's a good idea though. Does the pad contact the metal heatsink? If it doesn't, then you may instead create a thermal insulator instead of interface material, which could lead to overheating of the chip and force it to shut down if it reaches its thermal limit.
It may also impede convection, further hindering passive cooling.

If it does contact the heatsink, it might inadvertently heat the chip instead of cooling it (although this is not likely as the chip in question is one of the hottest on the Pi4b)
For an example of what I mean, think of your car exhaust, typically around 230°C - if you install a heatsink and then use that same heatsink to cool the steering wheel (hypothetical) it will instead heat the steering wheel by transferring the heat from the exhaust, into the heatsink and then into the steering wheel.
It does I believe since it has a pillar. Look in the attachment area. I dont trust the manual because it has some other issues as well for example "remove the plastic from the thermal pad back. The pads have plastic film on both sides, so I removed both of them.
The second picture also has no thermal pad on the power chip, though the power chip has its own pillar/column. Also near the gigabit port the chip has a thermal pad but no column. So I dont entirely trust the manual.

In closing, yes I believe the power-chip thermal pad is in contact with the power chip metal column/pillar of the top.
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rpdom
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 2:31 pm

StellarEquilibrium wrote:
Wed May 12, 2021 1:16 pm
Why did you have to choose that profile picture, my stomach is about to exhale not air but vomit and my hair starts to tingle. :-(
It is a picture of my wife holding one of her favourite pets. I could change it to a picture of one of the others. I've had maybe three comments on it since 2012.
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ejolson
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 4:24 pm

rpdom wrote:
Wed May 12, 2021 8:51 am
drgeoff wrote:
Wed May 12, 2021 7:37 am
Something wonky with your calculator. It is getting the wrong answer for 3 minus 1.2.
Doh! Yes. Head not awake yet. I moved the wrong bead on my abacus.
The greatest power draw I've seen (so far) on a Pi 4B running 32-bit Raspberry Pi OS is about 1.27A.

viewtopic.php?p=1852335#p1852335

Has anyone found a combination of CPU (and maybe GPU) tasks which consume closer to 1.8A? Having a firm number for maximum current draw can be important for many types of projects.

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davidcoton
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 5:34 pm

ejolson wrote:
Wed May 12, 2021 4:24 pm
Having a firm number for maximum current draw can be important for many types of projects.
The maximum value given here is 1A25. Using a figure of 1A4 would seem to be a conservative design guideline.
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LTolledo
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Wed May 12, 2021 8:04 pm

on this SSD native boot dual monitor RPi4B-4GB desktop, with USB powered speaker attached, am using this heatsink-fan combo
ArmorTopCover.jpg
ArmorTopCover.jpg (39.93 KiB) Viewed 358 times

it only has pillars for the SOC and the memory, none for the power regulator
no fire hazard detected as of this time....
and probably same on others who placed heatsink on the SoC only.

the famous FLIRC case for the RPI4B has pillar on the SoC only as well....
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Thu May 13, 2021 3:55 am

rpdom wrote:
Wed May 12, 2021 5:53 am
Also, just because a fair chunk of that 2.8A 1.8A will be going through that chip, doesn't mean it will get really hot. Only a small amount will be lost as heat. The rest is needed to run the Pi.
Being picky .... any energy that doesn't go to connected peripherals, RF power, sound or light will become heat, energy isn't consumed when the cpu is producing work, its converted into heat.

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rpdom
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Re: (Beginner question) Installed a passive case for Pi 4b. Is thermal pad on Power Chip a fire hazard danger?

Thu May 13, 2021 5:46 am

pidd wrote:
Thu May 13, 2021 3:55 am
rpdom wrote:
Wed May 12, 2021 5:53 am
Also, just because a fair chunk of that 2.8A 1.8A will be going through that chip, doesn't mean it will get really hot. Only a small amount will be lost as heat. The rest is needed to run the Pi.
Being picky .... any energy that doesn't go to connected peripherals, RF power, sound or light will become heat, energy isn't consumed when the cpu is producing work, its converted into heat.
Yes. That will be heat from the CPU and other chips. It won't be output as heat from the power controller chip.
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