WHAT IS HEATSINK?
I. The Thermodynamics of Heat Dissipation
Heat transfer from the electronic component to the ambient air occurs through a three-stage process involving all three forms of heat transfer:
Conduction (Solid-to-Solid): Heat is first transferred from the component's die (junction) through its casing and into the heatsink base via direct physical contact. High thermal conductivity materials like copper (approx 385 W/mK) and aluminum (approx 235 W/mK) are essential for this stage.
Conduction (Base-to-Fin): The heat conducts through the bulk material of the heatsink base and spreads outward into the fins. The geometry of the fins is designed to maximize this distribution.
Convection and Radiation (Fin-to-Air): This is the final and most critical stage. The heat is transferred from the fin surfaces to the surrounding air:
Convection: The majority of heat transfer occurs as the air moves across the fins, carrying the thermal energy away. This is categorized as natural convection (passive, air moves due to density changes) or forced convection (active, air moved by a fan).
Radiation: A smaller portion (approx 5% to 25%) is lost as infrared radiation, particularly from heatsinks with dark or specially treated surfaces.
II. Quantifying Performance: Thermal Resistance ($\mathbf{R_{\theta}}$)
Heatsink performance is mathematically defined by its thermal resistance (R_theta), measured in degrees Celsius per watt (°C/W). This metric quantifies how efficiently the heatsink can lower the temperature for a given heat load (P).
The goal of any heatsink design is to achieve the lowest possible R_theta.
The Thermal Circuit Analogy
Thermal resistance is analogous to electrical resistance. The temperature difference (Delta T) across a thermal path is the product of the heat flow (P, in Watts) and the thermal resistance (R_theta):
The Purpose of TIM
Thermal Paste or Pads (TIMs) are essential because microscopic air gaps always exist between the component and the heatsink base. Since air has a very low thermal conductivity (approx 0.026 WmK), these gaps create a massive thermal resistance. TIMs fill these voids with a conductive material (e.g., metal oxide compounds) to reduce R_heta, interface to near-zero, ensuring maximum heat transfer into the heatsink.
III. Manufacturing Methods and Design Constraints
The fabrication method directly impacts the fin density, geometry, and ultimately, the heatsink's thermal resistance.
| Method | Description | Pros | Cons/Application |
| Extrusion | Softened aluminum is pushed through a die. | Cost-effective, most common, good for mass production. | Limited fin height and aspect ratio (fin height/spacing). |
| Skived Fin | A blade shaves fins from a solid block of copper/aluminum. | Creates extremely high fin density for superior performance. | Higher cost, primarily used for copper heatsinks. |
| Bonded Fin | Individual fins are soldered or epoxied into grooves on the base. | Allows very high fin height and the use of copper fins on an aluminum base. | Higher assembly cost, small thermal resistance penalty at the bond line. |
| Forging | Compressing metal under high pressure into a mold. | Creates complex geometries (e.g., pin fin heatsinks) ideal for omnidirectional airflow. | Limited geometric flexibility compared to machining. |