Repasting Laptops With Liquid Metal? (TeCh SuPpOrT #1, detailed)
This article will have a lot of information that is not required for the average joe; check out the brief article to save your time. Also, note that while manufacturers often cheap out on cooling systems in budget laptops, it’s generally not required to repast a brand new laptop.
If you’re reading this, it’s a good chance you know how hot laptop components get and have an interest in the hardware too. Cleaning the fans is one solution, and repasting is another. They generally go hand in hand. This article will answer the question in focus in detail.
However, to understand what is more effective at reducing the temperature of the CPU, we should first understand why they get so hot in the first place. A CPU is simply an electronic circuit that performs basic arithmetic, logical and I/O operations as specified by the instructions. They are essentially a collection of billions of on/off switches using Boolean logic. These switches are very tiny, in the range of 20-40nm, depending on the transistor, and contain “merely a couple of electrons”. A single processor, made up of silicon, contains thousands of transistors and each individual switch is in the “on” state if high voltage is applied, and “off” state if low voltage is applied (Vcc and Vss respectively).
All the data in a computer is in the form of binary, 1’s and 0’s, on or off, and to process all that data, the speed of the processor comes into the picture. Clock cycle frequency, or speed, is generally measured in Gigahertz. 1 Gigahertz equals 1 billion cycles per second. The frequency, or speed, of a CPU, depends on the structure of its switches. The faster the switches can turn on or off, the more frequency the processor will be rated. Modern CPUs are capable of reaching speeds of up to 5 Gigahertz. In the quest for maximum performance, multiple methods are being used to increase the frequency at which the switches can change their state. One way is to force the switches between the two states more rapidly, but this results in instability as the processor cannot easily distinguish the on or off state as the voltage wouldn’t be able to switch fast enough to the recognized Vcc and Vss.
One solution is to increase the voltage of the processor, and when the peak voltage is raised, Vcc effectively moves down hence stabilizing the processor. This explains the increasing amount of TDP as new generations of processors arrive.
But why do we prefer lower temperatures? Using the simple current equation I = V/R, if R is increased or V is decreased, the current I decreases. Resistance R is affected by the temperature as R = kT where k is the constant of proportionality and T is the temperature. Hence if Temperature is decreased, Resistance decreases effectively decreasing the time it takes for the switches to change their state.
Adding to this is the fact that Microprocessors heat due to the Joule effect, the process of transforming electrical energy into heat. Inside the CPU there are several conductors in charge of its internal interconnections. The Joule Effect occurs due to the shock between the electrons and the conductor ion mesh, leading to an increased temperature of the CPU. This heat has to be removed quickly to prevent the internal temperature of the processor to rise leading to a decrease in efficiency, as well as reducing the life span if its internal circuits get damaged.
Now let’s first look at the difference between laptop and desktop dies. Desktops have real estate; laptops do not. Hence desktops CPU/GPU die contains IHS (integrated heat spreader) that laptops lack. IHS is a heat spreader, a metallic plate of sorts that spreads the heat of the CPU/GPU evenly so that better heat exchange may take place, and all cores remain at similar temperatures (depends on the workload too). The IHS is in direct contact with the die, and all the heat exchange takes place through it.
On laptops, however, IHS isn’t present. For them, the heat exchange takes place directly on the die with the heat pipes instead of a mediator.
Now microscopically, no surface is completely flat. The die’s (and IHS’s) can be either concave or convex, and this is where the liquids come into action. Air is a poor conductor of heat; hence the liquids take up the space between the die (or IHS) and the heat pipes (or the cooler’s base plate), thus increasing the heat exchange.
Desktop CPU/GPU’s are accompanied by IHS, that do a good job of spreading the core heat, and we need to make contact only between the IHS and the cooler (The IHS and the die are already in good contact with each other). Hence, contact is the main criteria here and not heat spread, which is why liquid metals aren’t too big of a deal for desktops. But coming back to laptops, the heat from the core needs to be spread and transferred; hence the liquid’s importance increases.
Liquid metals, in general, are less fluid than thermal pastes. So while this will be fine for desktops, it’s a big deal for laptops. Because of less spread of liquid metal, not all die parts may get covered, leading to high temp difference between 2 cores and ultimately throttling. This is point number 1. As you can see in the picture below, there’s a big difference between core #0 and core #2. The picture is of an i7 6700HQ with a slightly poor job of applying liquid metal. The CPU is being tested in Prime95, the “CPU Killer.”
And the picture below shows us the average after reapplying liquid metal correctly.
Please note that there will be some difference between the cores’ temperatures because of their separate physical location on the die and because of the laws of physics. Always run the tests multiple times and take the average before jumping to any conclusion regarding the CPU/GPU or its performance.
Coming to 2nd point, electrical conductivity. Liquid metals are electrically conductive. And to no surprise, if any of it touches any part of the motherboard, it may cause a short circuit and fry it. As desktops have more real estate, chances of liquid metal spilling out are considerably low, hence not as much of an issue. But coming back to laptops, as you can see in the picture below, there’s very little space between the CPU die and the PCB, requiring extra caution (the picture is actually a best-case, oftentimes the gap is smaller on newer CPUs). Not to mention the less flexibility of repasting inside the chassis itself, instead of taking out the CPU/GPU and repasting it in a safer environment.
And a sub-point, liquid metal contains metals like Gallium and Indium that react with metals like copper, and if it comes in contact with something like a copper or aluminum heat pipe, it can get corroded.
The 3rd and last point is cost and availability. Thermal pastes have been here for a while, tried and trusted, while liquid metal is new turf. While they generally give 2–5C lower temps than thermal paste, they often cost more for the same amount. And because of them being relatively new, they can be hard to find, depending on the location. As small as this point might sound after going through the previous 2, this is the most important. Previous ones can be rectified easily by either being experienced or going to a trusted shop directly. And depending upon workload, the 2–5C lower temps don’t matter that much, meaning thermal paste are still fine to get by (you’ll know if you require the extra temperature headroom or not).
Now moving to something similar but mostly kept in the shadows, VRM’s. They stand for Voltage Regulator Module and accompany CPU and GPUs. They are responsible for delivering the correct voltages to the respective components (hence indirectly responsible for most of the heat). Without going into the details of how they work, they can get very hot, especially for the laptops with dedicated GPUs, since they suck up most of the system power draw. Their increased workload sometimes requires the VRM’s to have a dedicated heatsink for them. And just like the case of the die, they require a mediator for the transfer of heat to take place. As you can see in the image below, they are small and leave minute area to work with. Although generally a cooling pad is used, manufacturers often leave them exposed, especially in budget gaming laptops. And just like the die’s, they require a liquid to transfer heat. Because of the reasons stated above, it’s never a good idea to use liquid metal for this scenario.
Thus, to conclude, liquid metals do give 2–5C better temps compared to thermal pastes. But in most scenarios, there won’t be any benefit. And being relatively new, they cost more and have hidden dangers. Thus it is still recommended to give it a year or two; otherwise, you’ll be an early adopter.
Also, just a side note, intermixing 2 different thermal pastes (or liquid metal), is never a good idea. So if you plan to do it yourself, make sure to clean the die properly. As you can see below, for the same i7 6700HQ, there’s a slight thermal paste at the edges of the die. Although it is harmless in this scenario, make sure the leftover residual isn’t present directly on the die.
If you find any mistake in this article, be sure to drop a comment, I’ll rectify it asap. And please clap to increase my confidence, this is the second article I’ve ever written!
Special thanks to S1B1C1#0001 on discord for letting me use their die pic.
