ROG product family

When it comes to smartphones, even back in the early days, I have gotten one request from many people – “I want a phone that doesn’t heat up”. There are a lot of issues with that one sentence and it opens a can of worms.

So, let’s go through why your phone heats up and how we can mitigate this issue.

Acer Nitro 5

This is going to be a long-ish video. We’ll have to separate it into a few segments – all of them are timestamped below – but I urge you to watch this entire video from start to finish because everything is interconnected.

1. Chipset

We’ll start off by talking about the chipset of a phone. As the name suggests, the chipset is a set of chips. There is a misconception as people call a “chipset” and the “core” and “CPU”. Those names are inherited from the old days, but as technology advances – they’ve become an SoC, also known as a “system-on-a-chip”.

Why Phone Heat

Let’s take the Snapdragon 888 as an example. This is an SoC, and we can look at the block diagram to learn that within just this one chipset, there are a bunch of different parts. Integrating all of these components into a single chip is why it’s called a chipset – or SoC.

Why Phone Heat

As you can see, the CPU is only a small part of the entire chipset. That Qualcomm Kryo 680 CPU is broken down into smaller components – the individual cores themselves.

As your know, smartphones use ARM-based cores, that’s why all of the chips are ARM Cortex-whatever cores. How all of these cores are arranged, clocked, and designed is also commonly referred to as the “CPU architecture”. More on this later, because it is very important.

Up until now, what we’ve talked about is only the designing part. You see, ARM doesn’t sell physical products. They sell the core’s design only. Then, companies like Qualcomm buys this design and implement it alongside other components to create a chipset – like the Snapdragon 888.

Okay then, how do we make those physical chips to be used in phones? Now it’s time for part 2.

2. Manufacturing

That’s where the manufacturing process comes in. Fabless chip designer companies like Qualcomm, Nvidia, AMD, and Huawei’s Kirin will seek out fabrication companies like TSMC, Global Foundries, Samsung, and many more to make those designs into tiny little chips.

One common misconception is the process node – that whatever-nm technology that many companies like to use in their marketing. That whatever-nm number purely means the gate length of an FET, also known as the “field effect transistor”. That gate length is the physical length of the gate, that is situated between the source and drain channel.

Why Phone Heat

Back in the days of 2D transistors, it used to be straightforward. Just measure the distance and we’re done. But nowadays, we’re using 3D transistors (also known as FinFET) and that gate is wrapped inside, so that process node number has lost its meaning.

One excellent article by Dr Ian Cutress of AnandTech highlights this issue as he introduced us to IBM’s world-first 2nm chip. In short, different companies will measure it differently.

And having the smallest nm number doesn’t automatically mean the greatest performance or a more efficient chip. It solely means that you can cram in more transistors within an area. The performance and efficiency mostly stem from the chip architecture that we talked about in segment 1.

3. Same chip, different performance

Okay, so now the chip is made and installed on a motherboard and made into a smartphone. Here, things start to get wild. Two different phones that have the same specs and the same chipset can have very different performances in the same benchmark or game.

Why is that? There are a few reasons, really.

3.1 Thermal design a.k.a. thermodynamics design

I’m not an expert in thermodynamics. I avoid calling it “cooler design” because there are two types of coolers – active and passive. Most phones use passive cooling – as there is no fan and any sort of cooling is done through heat conduction and convection from the surrounding air.

Passive coolers are just… not enough when it comes to high-performance devices. The heat produced is faster than the heat eliminated from the device – that’s why the temperature of your phone with flagship chipsets tends to heat up so quickly and eventually overheat.

We have seen many smartphone companies try to solve this issue by implementing having some specially-designed “liquid cooling” or “vapor chamber” and all of those. I can tell you now that they’re mostly misleading. The term “liquid cooling” is only used in marketing and yes, there is liquid inside the heatpipe but that’s not what “liquid cooling” is supposed to be. Real liquid coolers have a fan, radiator, pump, and coolant.

And before I ramble on further – I just want to point out that the reason why the Nubia Red Magic 6 can outperform the ROG Phone 5 is that the Red Magic 6 has a little fan.

Why Phone Heat

Personally, I think it’s not a good idea to have a fan in the phone as it can’t be serviced easily when dust and lint get inside. Furthermore, having an opening for the fan to take in fresh and means no IP-rating, and the fan will inevitably die at some time.

Why Phone Heat
That Nubia Red Magic 6’s fan will get clogged up.

As a quick mention – the performance difference between a phone and a tablet with the same chipset is huge – and that is because a tablet has a much larger surface area to dissipate the heat as compared to a phone.

3.2 Thermal throttling

Thermal throttling is also known as the thermal limit in some cases. A chip generates more heat as its clock speed goes higher. So, to avoid the chip from overheating, a thermal limit is set.

How it works is rather simple – if the thermal sensor detects the temperature is lower than its thermal limit, that means the chip can still operate at high performance. However, once it hits the thermal limit, the performance will need to be lowered to prevent overheating. That is how thermal throttling works.

Why Phone Heat

I can think of some examples now. The Samsung Galaxy S21 Ultra has a thermal limit of about 46°C. Same goes for the recently-announced Xiaomi 11T and the 11T Pro.

But this thermal limit can change via software update. The POCO F3 for example, overheated like crazy. That is due to Xiaomi/POCO’s negligence to do proper thermal design for the phone or set a proper thermal limit. As far as I know, Xiaomi/POCO did eventually push out an update to thermal throttle at about 46°C.

I personally think that implementing thermal throttling via software update is a touchy subject – particularly with the POCO F3. You see, the main appeal of the POCO F3 is the performance of that Snapdragon 870 chipset. But since it overheats so fast and needs thermal throttling, we’re essentially paying for a chipset with performance that we cannot use.

Why Phone Heat

In the meantime, we can get ourselves phone coolers. The most effective one that I have encountered so far is the Black Shark FunCooler 2 Pro. It works with nearly every phone in the market out there and it can really bring the temperature down by a lot.

Can you actually get a phone that doesn’t heat up? Sure, certain entry-level chipsets consume so little power that it barely heats up the device at all.
That way, you’ll be limiting yourself in terms of performance and not have to deal with the heat.


So we talked about many things regarding phones and heat – but there are many things that I have to leave out – like how the material of the phone affects the thermal transfer, how weight of the phone can be a telltale sign of the phone’s thermal conductivity, and a phone case can make or break the thermal performance.

Even software and its optimization can have a heavy impact in terms of performance and temperature. We have not touched on those topics at all – and I’ll leave all those for next time.

Long-time followers of this channel also know that we’ve dropped benchmarks in our reviews a long time ago, because benchmarks do not represent real-world usage and its performance. There are even smartphone manufacturers that literally cheat in benchmarks. That is why we would rather show gaming performance instead.

However, performance monitoring on smartphones is difficult but we’ll leave that topic for another day instead.

Where to buy the Black Shark FunCooler 2 Pro? (Affiliate links)

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