UK How a heat sink works
A heat sink is a passive heat exchanger: a piece of metal fixed to a hot component that carries heat away from it and hands it to the surrounding air. Almost every processor, graphics chip, voltage regulator and power transistor in a computer relies on one, because a modern chip produces far more heat than its own small package can shed.
Heat moves in three steps. First it conducts from the chip into the heat sink’s base, through a thin layer of thermal interface material that fills the microscopic gaps between the two surfaces. Next it spreads through the base and up into the fins. Finally the fins pass it to the air by convection, with a little lost by radiation. Warm air rises away from the fins and cooler air takes its place, which is why fin spacing and orientation matter as much as the amount of metal.
Engineers rate a heat sink by its thermal resistance, in degrees Celsius per watt (°C/W). A heat sink rated at 0.5 °C/W, for example, lets the chip run about 5 °C above the air for every 10 W it dissipates. The lower the figure, the better the heat sink, and the figure always depends on the airflow it was measured with.
Types of heat sink
Heat sinks are grouped by how air moves over them and by how they are made. The first split decides whether a computer needs a fan at all.
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Passive heat sinks. No moving parts. They rely on natural convection, so they need generous fins with wide spacing and a clear path for air to rise. Silent and very reliable, they are the basis of fanless computers.
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Active heat sinks. A fan blows air through denser fins, which removes several times more heat from the same volume. The fan adds noise, draws in dust and is the part most likely to fail.
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Hybrid heat sinks. Large enough to cope passively at light load, with a fan that starts only when the temperature rises. Some designs keep running at reduced performance if the fan stops.
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Heat sinks with heat pipes or vapour chambers. Sealed copper pipes or plates move heat from a small chip to fins further away with very little temperature drop, so a compact processor can use a large fin area.
Heat sink materials and how they are made
Aluminium is the usual choice because it is light, easy to shape and conducts heat well, at around 200 W/m·K for common alloys. Copper conducts roughly twice as well, at about 400 W/m·K, but is around three times heavier, so it is used where heat has to spread quickly from a small hot spot, often as a copper base or heat pipes under aluminium fins.
The manufacturing method sets how thin and tall the fins can be, and so how much surface area fits in a given space.
| Method | How it is made | Strengths | Typical use |
|---|---|---|---|
| Extruded | Aluminium pushed through a shaped die | Low tooling cost, long lengths | Fanless enclosures, general electronics |
| Die-cast | Molten metal poured into a mould | Complex 3D shapes, fins and chassis in one part | Sealed enclosures and housings |
| Bonded or folded fin | Thin fins fixed into a machined base | High fin density, mixed metals | Servers, high-power processors |
| Skived | Fins sliced and lifted from one solid block | Very thin fins with no joint in the heat path | Compact high-power designs |
| Forged or pin fin | Metal pressed into round or elliptical pins | Works with airflow from any direction | Fan-cooled modules, LED lighting |
Most fanless computers combine methods: a machined or die-cast chassis that doubles as the heat sink, with heat pipes or a copper spreader under the processor.
Thermal paste, pads and heat spreaders
Two flat metal surfaces only touch at high points, and the air trapped between them insulates. A thermal interface material fills those gaps. Thermal paste gives the thinnest layer and the best transfer where the heat sink sits directly on a chip. Thermal pads are thicker and more forgiving, so they bridge the larger gaps to memory chips, voltage regulators and SSDs, which is common inside fanless enclosures.
A heat spreader is a flat plate, often copper, that evens out heat from a small die before it reaches the heat sink. Many processors have one built in as a metal lid. Neither paste nor spreader removes heat on its own: they only help it reach the heat sink. Paste dries out over years, so it is worth checking during a long-life refresh.
Heat sinks in fanless and industrial computers
In a fanless computer the enclosure is the heat sink. Heat travels from the processor through pads, a spreader or heat pipes that carry heat to the chassis, and the finned outer case sheds it to the room. Our explainer on how a fanless PC works follows that path in detail.
That design sets a few rules for installation. Fins work best running vertically, so warm air can rise between them, and they need clear space around them. The quoted temperature range assumes that mounting. Many systems also derate: some rugged computers run their full processor power only up to a lower ambient temperature and reduce it above that. When the heat sink can no longer keep up, the processor slows itself down, which our guide to why computers slow down when they get hot explains.
You can see the approach across our fanless PCs. The Premio RCO-1000-ASL rugged compact PCs run fanless from −40 to 70 °C, and the Premio ACO-6000-RPL uses an extruded aluminium heatsink chassis for railway and in-vehicle work.
Quick answers on heat sinks
Heat sinks: common questions
What does a heat sink do in a computer?
It keeps the processor and other chips below their temperature limit. Without one, a modern CPU would reach its limit within seconds and slow down sharply or shut itself off to prevent damage.
Is a heatsink the same as a heat sink?
Yes. Both spellings are used for the same part. “Heat sink” is the more common form in standards and textbooks, and “heatsink” is common in product names.
Does a heat sink need a fan?
Not always. A passive heat sink cools by natural convection alone if it has enough fin area for the heat load. A fan lets a smaller heat sink handle more power.
What is a heat sink on an SSD?
A metal cover or finned plate fitted over an M.2 SSD. Fast NVMe drives can slow down when their controller gets hot, so the heat sink, often with a thermal pad, keeps sustained transfer speeds up.
Heat sink vs heat spreader: what is the difference?
A heat spreader evens out heat; a heat sink gets rid of it. The spreader moves heat sideways from a small hot spot, and the heat sink then releases it to the air.
We match the processor, power and cooling to the installation as standard, fit the storage and memory with the right thermal pads, and check that the system stays within its rated temperature range for the site before it ships.