Heat Sink Guide: Aluminium, Copper, and Passive Cooling

A heat sink is a passive thermal management component that absorbs heat from an electronic device and dissipates it into the surrounding air. From tiny SOT-23 voltage regulators to large IGBT modules, almost every power component benefits from a properly sized heat sink. This guide covers materials, designs, and selection criteria to help Indian makers choose the right heat sink for any project.

Why Heat Sinks Are Essential

Every electronic component has a maximum junction temperature (Tj max). Exceed it, and you get degraded performance, parameter drift, or permanent failure. A heat sink increases the surface area available for heat dissipation, lowering the thermal resistance between the component junction and ambient air.

Consider a TO-220 voltage regulator like the LM7805 dissipating 2W. Without a heat sink, the junction-to-ambient thermal resistance is around 65°C/W, meaning the junction temperature rises 130°C above ambient. At 40°C ambient (typical Indian summer), that is 170°C — well above the 150°C maximum. A simple aluminium heat sink drops this to safe levels for just ₹10-20.

Aluminium vs Copper Heat Sinks

Aluminium (Al 6063 alloy) is the most popular heat sink material. It is lightweight, inexpensive, easy to machine, and has a thermal conductivity of about 200 W/m·K. Over 90% of commercial heat sinks are aluminium.

Copper (C110) has nearly double the thermal conductivity at 385 W/m·K, making it superior for high heat flux applications. However, copper is heavier, more expensive, and harder to extrude into complex fin shapes. Copper heat sinks are common on CPU coolers, high-power LEDs, and premium electronics.

Heat Sink Design: Fins, Pins, and Profiles

Fin-type heat sinks have parallel fins extruded from a base plate. They work best with directed airflow from a fan. Common in power supplies and amplifiers.

Pin-type heat sinks have cylindrical or square pins protruding from the base. They perform well with airflow from any direction, making them ideal for natural convection and environments where airflow direction is unpredictable.

Stamped heat sinks are made from sheet metal bent into fins. They are cheap but have limited thermal performance. Suitable for low-power applications under 1W.

Black anodised heat sinks radiate heat about 20% more efficiently than bare aluminium, thanks to higher emissivity. Always prefer black-anodised models for passive cooling setups.

Thermal Resistance and How to Calculate It

Thermal resistance (Rth) is measured in °C/W and tells you how many degrees the temperature rises per watt of heat dissipated. The total thermal resistance chain is:

Tj = Ta + P × (Rjc + Rcs + Rsa)

Where: Tj = junction temperature, Ta = ambient temperature, P = power dissipated, Rjc = junction-to-case, Rcs = case-to-sink (thermal paste/pad), Rsa = sink-to-ambient.

Example: A MOSFET dissipating 5W, Rjc = 1°C/W, Rcs = 0.5°C/W (with thermal paste), required Rsa to keep Tj under 100°C at 45°C ambient: Rsa = (100 – 45)/5 – 1 – 0.5 = 9.5°C/W. A small aluminium heat sink with 8-10°C/W rating would work.

Mounting Methods: Clips, Screws, and Thermal Tape

Spring clips and push pins: Common on CPU coolers and TO-220 packages. Provide good mechanical contact and easy removal.

Screws and standoffs: Most secure method. Drill and tap the heat sink, use thermal paste between surfaces. Essential for vibration-prone environments.

Thermal adhesive tape: Pre-applied on many small heat sinks (like Raspberry Pi models). Convenient but permanent — you cannot easily reposition. Thermal conductivity is lower than paste (typically 1-3 W/m·K vs 4-8 W/m·K for paste).

Passive vs Active Cooling: When to Add a Fan

Passive cooling (heat sink only, no fan) works when:

• Power dissipation is low (under 3-5W for a medium heat sink)
• Ambient temperature is moderate
• There is adequate natural convection (vertical mounting helps)
• Noise must be zero (audio equipment, bedroom projects)

Add a fan (active cooling) when:

• Power dissipation exceeds the passive heat sink’s capability
• Ambient temperatures are high (Indian summers)
• The enclosure restricts natural airflow
• Space constraints prevent using a larger heat sink

Best Heat Sinks for Common Components

• Raspberry Pi: 3-in-1 or 4-in-1 aluminium sets cover CPU, RAM, and USB controller. Add the copper set for overclocked Pi 4.
• Stepper motor drivers (A4988/DRV8825): Small 9×9×5mm aluminium heat sinks, typically sold in packs of 5.
• 3D printer hotend: MK7/MK8 aluminium heat sink blocks. These are structural — they separate the hot zone from the cold zone.
• Voltage regulators (TO-220): Aluminium finned heat sinks, 20×15mm minimum.
• Power MOSFETs and IGBTs: Large finned aluminium heat sinks with fan, 40×40mm or larger.

Buying Heat Sinks in India

Zbotic stocks a wide range of aluminium and copper heat sinks for every common use case — from tiny Raspberry Pi sets at ₹13 to large GPU-grade sinks at ₹211. All come with thermal adhesive tape pre-applied or included. Shipping is fast across India, and bulk orders get additional discounts.

When ordering, always buy thermal paste separately if your application involves more than 2-3W dissipation. The pre-applied thermal tape is sufficient for low-power use but paste gives better thermal performance for serious projects.