What Is a Heat Sink?
A heat sink is a passive thermal part that takes heat from a hot component and transfers it to the air over a large surface, lowering the component's temperature.
How Does It Work?
It's usually made of aluminum and has many fins. The fins enlarge the surface area, so the heat taken from the component by conduction spreads to the air over a wider area and the temperature drops.
Thermal Resistance
How good a heat sink is is measured by its thermal resistance (°C/W). A low value means less temperature rise per watt, i.e. better cooling. More fins and airflow lower this resistance.
| Factor | Effect |
|---|---|
| Surface area | As it grows, heat dissipation grows |
| Airflow | Much better with a fan |
| Material | Aluminum/copper |
Passive and Active
A heat sink working on its own (air only) is passive. Adding a fan makes it "active cooling"; forced airflow multiplies heat dissipation. An advanced form of active cooling is the Peltier (TEC) module, which electrically drives a surface below ambient temperature.
Where Is It Used?
Processors, power transistors, regulators, solid-state relays (SSRs), LEDs and every power component that produces heat.
Mounting
The heat sink must make good contact with the component; to leave no air gap, thermal paste/pad is applied between them. Poor contact seriously reduces the heat sink's effectiveness.
Common Mistakes
- Dry mounting: without thermal paste the contact resistance stays high.
- Insufficient size: a heat sink too small for the power can't dump the heat.
- No airflow: in a closed case the heat sink saturates; a fan is needed.
Frequently Asked Questions
Why fins?+
Copper or aluminum?+
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