Heatsink
Thermal Management
Finned metal that gives watts of waste heat a path from a small hot chip to the ambient air. The difference between a regulator that lasts years and one that cooks itself is usually a few rupees of aluminium.
What it looks like
Heatsink
A typical thermal management — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Thermal resistance
°C/WThe one spec that matters: temperature rise per watt dissipated. A 10 °C/W sink dissipating 5 W runs 50 °C above ambient.
Size / fin area
mmMore surface area = lower °C/W. Orientation matters: fins vertical for natural convection.
Mounting
—TO-220/TO-3 hole patterns, clip-on, push-pin, or adhesive. Poor mounting pressure ruins a good sink.
With/without airflow rating
°C/WForced air can cut °C/W to a third — datasheets list both.
Markings
Rarely marked; identified by profile and size. Vendor listings give °C/W — for unknown salvage sinks, estimate from size or test (see below).
Standard values
TO-220 clip sinks: ~20 °C/W. 50×50×25 mm extrusion: ~5 °C/W. Large amplifier extrusions: 0.5–2 °C/W. CPU sink+fan: <0.3 °C/W effective.
How to choose
Work the thermal chain: Tjunction = Tambient + P × (θjc + θcs + θsa). 1) Find watts dissipated (e.g. a 7805 dropping 12→5 V at 0.5 A burns 3.5 W). 2) Allow junction ≤125 °C but design for ≤85 °C. 3) Solve for the required sink θsa and pick one lower. 4) Use thermal paste/pad, and an insulating kit if the tab is live (TO-220 tabs often are). 5) When in doubt, bigger.
Pinout & package
Mechanical only. TO-220/TO-247 sinks bolt through the tab hole (mica washer + shoulder bushing when isolation is needed). SMD parts sink into copper pour with thermal vias to the other side.
Example circuits
- 7805 linear regulator on a 20 °C/W clip sink for a 3 W drop
- Class-AB audio amp output pairs bolted to a shared 1 °C/W extrusion
- Peltier module hot side on a CPU sink+fan (mandatory)
- LED COB star mounted on an aluminium slug with thermal adhesive
Common failures
The sink itself doesn't fail — the interfaces do: dried-out paste, loose mounting (chip cooks despite the sink), missing insulator shorting a live tab to grounded chassis, dust blanketing the fins, and dead fans turning a forced-air design into a passive one that can't cope.
How to test
Touch test with care (>60 °C is 'can't hold finger'), or IR thermometer: measure chip tab vs sink surface — a big gap means bad interface contact. Verify insulated mountings with a continuity check tab-to-sink. Estimate an unknown sink's °C/W by dissipating a known wattage (power resistor) and measuring the rise.
Substitutes
Any sink with equal or lower °C/W and workable mounting. Salvaged CPU/amplifier sinks are excellent free stock. Short-term, a metal chassis or thick aluminium plate serves as an emergency sink.