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Hardware

What is heat sink?

A heat sink is a block of metal fins, usually aluminum or copper, that draws heat away from a CPU or other chip and releases it into the air flowing past.

What is a heat sink?

A heat sink is the passive half of most air-cooling setups. It has no moving parts of its own: a flat metal base sits on a hot chip, heat conducts from the base into dozens of thin fins, and the large surface area of those fins lets moving air carry the heat off. A typical desktop CPU cooler is a heat sink with a fan clipped to it. The fan moves the air; the heat sink does the heat transfer.

Besides CPUs, heat sinks sit on graphics processors, chipsets, the motherboard's voltage regulator (VRM) area, M.2 SSDs, and some RAM modules, where a thin version is called a heat spreader.

How a heat sink works

  1. Contact. The CPU die is covered by a metal lid called the integrated heat spreader (IHS). The heat sink base presses against the IHS.
  2. Thermal interface. Neither surface is perfectly flat, so tiny air gaps remain, and air conducts heat poorly. Thermal paste or a thermal pad fills those gaps.
  3. Conduction. Heat moves from the base into the fins. Many coolers add heat pipes: sealed copper tubes holding a small amount of fluid that evaporates at the hot end and condenses at the cool end, moving heat quickly to fins farther from the chip.
  4. Convection. Air moving across the fins carries the heat away, from a fan on the heat sink, from case fans, or both.

Materials and types

  • Aluminum is light and inexpensive and is used for most fins and for basic stock coolers.
  • Copper conducts heat better but is heavier and costs more, so it often appears in the base and the heat pipes.
  • Passive heat sinks have fins only. They are common on chipsets and low-power systems, and in rack servers that rely on strong chassis fans to push air through the fins.
  • Active heat sinks carry their own fan, powered from a motherboard header usually labeled CPU_FAN.
  • Tower vs. low-profile: tall tower coolers need case clearance; low-profile coolers fit small form factor and many ITX cases.

Liquid cooling uses the same principle. A cold plate on the CPU passes heat to coolant, and the radiator, which is itself a heat sink, releases that heat into air pushed by fans.

Installing or reseating a heat sink

  • Confirm the cooler supports the CPU socket (mounting hardware differs between Intel and AMD sockets) and can handle the CPU's heat output, listed as its TDP.
  • Remove old compound from both surfaces with isopropyl alcohol and a lint-free cloth. Whenever a heat sink comes off, apply fresh paste; reused paste leaves air pockets.
  • Use a small amount of paste. Too much adds thickness and can squeeze out onto the socket area.
  • Peel any protective plastic film off the base of a new cooler. Forgetting it is a classic cause of overheating right after a build.
  • Tighten mounting screws a few turns at a time in a diagonal pattern so pressure stays even.
  • Plug the fan into the CPU fan header. Many boards show a CPU fan error at startup if nothing is detected there.

Troubleshooting

If you see random shutdowns, slowdowns under load, or high CPU temperatures in the BIOS/UEFI hardware monitor, think cooling first:

  • Heat sink loose, tilted, or held by a broken mounting clip
  • Thermal paste missing, dried out, or applied far too thickly
  • Fins packed with dust; blow them out with compressed air while holding the fan still
  • Cooler fan stopped, failing, or unplugged

An overheating CPU first thermal throttles, lowering its clock speed to protect itself. If temperatures keep rising, the system shuts down to prevent damage.

Heat sink on the CompTIA A+ exam

Core 1 objective 3.5 lists heat sink under Cooling, alongside fans, thermal paste/pads, and liquid cooling. Know that a heat sink is passive, that it needs paste or a pad between it and the CPU, that paste is replaced whenever the cooler is removed, and that dust or poor contact causes overheating. Objective 5.1 lists overheating, random shutdown, sluggish performance, and unusual noise as symptoms; a clogged or badly seated CPU cooler can explain each of them. If a scenario says a PC shuts down a few minutes after a CPU upgrade, suspect the heat sink installation before the new processor.

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Related terms

case fan

A case fan is a fan mounted in a computer case that moves air through the chassis, pulling cool air in and pushing heated air out.

CPU

The CPU (Central Processing Unit) is the primary component of a computer that performs the fundamental computational and control functions, responsible for executing instructions and coordinating the overall operation of the system.

liquid cooling

Liquid cooling is a method of heat dissipation in computers and other electronic devices that uses a liquid coolant to absorb and transfer heat away from heat-generating components, often providing more efficient cooling than traditional air-based cooling systems.

thermal pads

Thermal pads are soft, compressible materials used to fill gaps between electronic components and heat sinks to improve heat transfer and prevent overheating.

thermal paste

Thermal paste, also known as thermal interface material (TIM), is a thermally conductive compound used to improve heat transfer between two surfaces, such as a computer processor (CPU) and its heatsink.

thermal throttling

Thermal throttling is a power management mechanism that automatically reduces a computer's processing speed to prevent overheating and damage to the hardware components.

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