thermal paste vs. thermal padsJohn Moot
Thermal paste vs. thermal pad
Thermal interface materials are undoubtedly a very critical aspect of electronic component design. They can very well make the difference between a working product and a faulty product.
The purpose of thermal pads and thermal paste is to provide a preferential heat transfer path between heat-generating components such as integrated circuits (CPUs) and heat dissipaters such as a heat sink.
The surface of a CPU or heatsink is never going to be completely flat or level. There will be tiny bumps, gaps and voids that allow air to pass through the components.
Since air is not a good conductor of heat, these gaps have a very negative effect on heat transfer.
Therefore, a thermal material with high thermal conductivity is needed to fill these gaps and improve thermal conductivity between the CPU and the heatsink. In our post 8 ready-made thermal management solutions, we described various materials that can be used for heat dissipation. We supply thermal pads with thermal conductivities up to 15 W/mK and thermal pastes with thermal conductivities up to 10 W/mK.
Thermally conductive paste
Heat conductive paste or cooling paste is a sticky mass that is applied between the heat sink and the CPU as the most common thermally conductive material. High quality pastes achieve the best performance in this regard when it comes to dissipating and transferring heat.
Thermal paste adheres for a very long time and is a very good option when it comes to heat dissipation to the heatsink: one layer of thermal paste ensures complete wetting of the component surface.
Since thermal paste is a viscous liquid, it fills all micro-depressions on the component or on the underside of the heat sink. This results in much better heat dissipation to the heat sink.
Unfortunately, application is often not easy, especially for beginners, and can lead to difficulties. Also, unlike some types of thermal pads, thermal paste is not designed to bridge larger gaps.
Thermal pads are much easier to install than thermal paste. Some heatsinks already come with the pads, because they can be applied cleanly and easily and even newcomers have no difficulties here. Heat conduction pads are also preferred in industry. Unfortunately, the heat conduction is not always as good as that of the thermal paste. However, there will still be very small gaps between the processor and the heat conduction pad. These small air gaps make for slightly lower thermal conductivity, as air is less thermally conductive.
It is important to remember that thermal pads are a one-time solution. They must be completely replaced if the heatsink is to be relocated or exchanged. In this case, all adhesive residue must also be removed, otherwise new bumps and gaps will appear. But thermal paste must also be completely removed and replaced.
Thermal pads vs. thermal paste: Durability
From a durability standpoint, some designs are expected to last for decades under harsh operating conditions. Using thermal paste to dissipate heat from the heatsink will outperform any pad in this regard, and is the more robust option in terms of wear resistance. In contrast, a thermal pad will become brittle over time under repeated thermal cycling, which can interrupt the thermal path between the heat sink and the component
This is simply due to the material used in these products. Thermal paste or thermal grease adheres and solidifies after application. Thermal pads, on the other hand, are made of a sponge-like material or soft, rubbery material. Thermal paste is more durable and less expensive. This is especially true for recurring temperature cycles.
Advantages of thermally conductive pads compared to thermal paste
- No mess – Applying thermal paste can be a messy process. Using thermal pads is a simple peel and stick process.
- Fills larger gaps – Thermal pads are available up to 20mm as opposed to a thin layer of thermal paste.
- Easier Installation – Thermal pads can be die-cut to the exact specifications of the component to ensure a perfect fit – every time.
- Conformance – Thermal pads conform precisely, regardless of surface, to ensure no air is allowed to pass through. However, small pockets of air may remain.
Common mistakes and how to avoid them
Problems often occur when installing thermal paste and thermal pads. Therefore, here are some tips to avoid them:
Never use paste and pads together. Just because both are used together does not mean better thermal conduction is achieved. In fact, the opposite is true. Applying thermal paste additionally to the pads reduces the desired effect.
In addition, several pads should never be applied on top of each other. If two or more pads are placed on top of each other between the heatsink and the CPU, this can cause damage to the processor as the heat builds up.