Heat is one of the worst enemies of electronics, especially semiconductor electronics. So, engineers find different ways to transfer the heat away from the integrated circuits such as CPUs, GPUs, Memory Chips, Storage, MOSFETS, etc. One of the simplest ways to transfer this heat is to use a metal (usually copper but sometime aluminum) in the form of heat sink. But in order to make clean contact between the surface of the IC and the heat sink, we use special Thermal Interface Materials. The two popular and common materials are Thermal Paste and Thermal Pad. In this guide, we will compare Thermal Paste vs Thermal Pad.
First, we will take a look the basics of these two thermal interface materials. We will also see their advantages and disadvantages. After that, we will compare Thermal Paste vs Thermal Pad. Finally, we will figure out which is a better solution to transfer heat.
A Brief Note on Thermal Interface Materials (TIM)
We use heat sinks and cooling fans to keep the electronic devices cool. But Thermal Interface Materials play an important part in the heat transfer process.
If we take a heat sink and place it on top of a power device (MOSFET), and IC, or any “hot” electronic component, there will be tiny air gap between these two surfaces.
Even though they appear to be in contact, there is still some game will air filled in that gap. We know that air is a very bad conductor of heat. So, the air gap between the surface of the component and the heat sink will act as an insulator and restricts the transfer of heat.
This is where different Thermal Interface Materials come into picture. What they do is fill the air gap with a thermally conductive material. This will not only eliminate the air gap but also acts as a thermal bridge between the surface of the component and the heat sink.
Here are some of the common Thermal Interface Materials:
- Thermal Paste
- Heat Spreader
- Thermal Pad
- Gap Pad
- Thermal Grease
- Dielectric Pad
- Thermal Compound
- Thermal Gel
What is Thermal Paste?
Thermal Paste is one of the most popular and widely used Thermal Interface Materials. Some other names for Thermal Paste are Thermal Grease, Thermal Compound.
As the name suggests, thermal paste or compound is in the form of, well, a paste (a semi-solid liquid). You have to apply this thermal paste between the IC (CPU, GPU, etc.) and the heat sink.
There are several discussions on the amount of thermal paste you need to apply and also the different procedures on how to apply. But the important thing is the Thermal Paste acts as an excellent filler of the gap between the chip and the heat sink.
Most CPU and GPU manufacturers recommend thermal pastes as the main thermal interface material between the surface of the chip and the surface of the heat sink. Additionally, you can use a cooling fan to further dissipate the heat from the heat sink.
Advantages
- Thermal Paste is very efficient at transferring the heat away from the surface of an IC even with minimum quantity.
- As it is essentially a liquid, you can use it on all types of surfaces and the surface doesn’t have to be flat.
- Very easy to apply. Usually, thermal paste or compound come in a syringe (or similar dispenser). Just apply it on the surface of the IC (in the form of a dot or x-shape).
- Thermal Paste is very inexpensive. You can get very good quality thermal compound from reputable manufacturer for very little price.
Disadvantages
- Can get messy, especially if you are applying for the first time.
- You have to apply the Thermal Paste very carefully and make sure that you leave no air gap.
- There are some less expensive thermal pastes or compounds that do not fulfil all the qualities of a decent thermal paste. One important one being electrical conductivity.
What is Thermal Pad?
As the name suggests, a Thermal Pad is a soft pad that acts as a Thermal Interface Material. They are solid material that sits on top of relatively flat surfaces.
Applying thermal pad is very simple. Just place the pad on the surface of an electronic component (an IC or MOSFET) and attach a heat on top of the pad.
While thermal pads are very good at transferring heat from the surface of the IC to the heat sink, their solid nature means they cannot spread to fill all the air gaps as thermal paste would do.
As a result, we do not see thermal pads on critically hot components such as CPUs, GPUs, or Power MOSFETS. We use thermal pads on relatively “not so hot” ICs such as memory chips (RAM or NVMe), small integrated circuits, etc.
Advantages
- They are very easy to apply.
- There is no mess while applying thermal pads.
- You can shape the pad precisely to the shape of the surface as they are essentially soft pads.
- Suitable for small to medium heat producing devices.
Disadvantages
- Thermal Pads are relatively expensive when we compare to thermal paste.
- After applying thermal pad and using it for some time, it gets quite difficult to remove the pad from the surface of the IC or the Heat Sink.
- There is no reusability with thermal pad. Once you remove them, you have to apply a new thermal pad.
Thermal Paste vs Thermal Pad: Which Provides Better Heat Transfer?
Now coming to the important question: Thermal Paste vs Thermal Pad, which is better?
Both these products are excellent thermal interface materials. Both of them have their fair share of advantages and disadvantages.
When you apply thermal paste properly, it can fill all the air gaps between the surface of an IC and the surface of the heat sink. As a result, most CPU and GPU Manufacturers recommend good quality thermal compound to transfer heat away from the chips.
Coming to thermal pad, they are equally good materials to transfer heat. But you have to apply very carefully and make sure that there is no gap between the surface of the chip and the heat sink.
If you are beginner and are not sure about the quantity of thermal paste you need for your CPU or GPU or doesn’t know the procedure to apply it, then you can choose a good quality thermal pad as a suitable replacement without any doubt.
But if you have enough experience with thermal pastes or compounds, then we recommend a good quality thermal paste with your CPU or GPU.
If you are dealing with slightly low power devices such as NAND Flashes, or Integrated Circuits (other than CPU, GPU and Power MOSFETS), then a Thermal Pad is a much better option as all the surfaces are relatively flat.
If the surface isn’t flat, then thermal paste can easily spread into all the gaps and provide better thermal conductivity.
Conclusion
Electronics run hot and we need to transfer this heat away from them so that they continue to run without failure or thermal throttling.
As a result, we use heat sinks and cooling fans with our CPUs, GPUs, Power MOSFETS, and other electronic components.
But the problem with direct application of heat sink on top of an IC is that there will be small gaps between the two surfaces and this gap is filled with air. We know air is an insulator of heat and hence, the heat from the IC will not transfer to the heat sink very efficiently.
Thermal Interface Materials or TIMs are responsible to increase the thermal conductivity between two surfaces, in this case, between the CPU or GPU and its heat sink.
The two most common thermal interface materials are Thermal Paste and Thermal Pad.
In this guide, we saw the basics of these two materials. We also saw their advantages and disadvantages.
If we have a Thermal Paste vs Thermal Pad showdown, then the answer depends on the type of application, ease of use and good thermal conductivity.
One Response
There are two main issues not covered. The perfect point of contact with a surface silicon to copper from that tiny point the heat transfer is far higher than any available paste or pad. The problem is getting a pair of surfaces so flat and smooth the air gap doesn’t exist. That is where these materials come in at to fill microscopic valleys because smooth and flat is expensive and hard ideally you would want the thinnest layer between as possible to give the highest rate of transfer the thicker the pad the more material that is going to need to pass watts the rating for each material is the speed that it moves at most pads are around 6-8w/k the highest silicon type I have found is around 16 w/k carbon nanotubes/graphine offer pads in the 60 to 70w/k which is close to liquid metal. Most pastes operate in similar levels with the highest end pastes (silver/aluminum/diamond/carbon) being 15w/k and liquid metal being 60+w/k