A heat sink is used in electronic devices to dissipate heat and prevent overheating. It is typically made of a metal such as aluminum or copper. It absorbs and transfers heat from the device’s central processing unit (CPU) or other heat-generating components. Heat sinks work by increasing the surface area available for heat transfer and using fins or other structures to increase the flow of air or other cooling medium over the surface of the heat sink. This helps to keep the device operating at a safe temperature and prevent damage from overheating.
In many applications, the device is an electronic component (e.g. CPU, GPU, ASIC, FET ，IGBT etc.) and the surrounding fluid is air. The device transfers heat to the heatsink by conduction. The primary mechanism of heat transfer from the heatsink is convection, although radiation also has a minor influence. There are two distinct types of convection:
Natural convection – where the movement of the fluid particles is caused by the local changes in density due to transfer of heat from the surface of a solid to the fluid particles in close proximity.
Forced convection – where the movement of the fluid particles is caused by an additional device such as a fan or blower.
Heatsinks are designed to significantly increase the contact surface area between solid and fluid, thereby increasing the opportunity for heat transfer. A typical ASIC may have a surface area in contact with air of only 1600mm2. The surface area of a typical heatsink used to cool that device may be 10 or 20 times that value.
The thermal performance of a heatsink is primarily governed by the following key factors:
Within a given installation envelope, increasing the effective surface area enhances the contact area between the heatsink and the surrounding air, thereby improving heat dissipation.
Modern heatsink designs often achieve this by reducing fin thickness, increasing fin density, and maximizing the number of fins. Advanced manufacturing methods such as skiving, bonded fins, and high-density fin structures are widely adopted to increase surface area within limited space.
The heat transfer coefficient is strongly influenced by airflow velocity, flow characteristics, and heatsink geometry.
Under passive cooling conditions, performance can be improved by optimizing airflow paths, reducing flow resistance, and enhancing natural convection.
For active cooling systems, increasing airflow velocity, improving fan performance, and optimizing the interaction between the fan and the heatsink can significantly enhance convective heat transfer.
Radiative heat transfer depends on the emissivity of the heatsink surface. Common methods to enhance emissivity include surface coating, sandblasting to increase roughness, anodizing, and black oxidation treatments.
It should be noted that radiative heat transfer has a noticeable impact under natural convection conditions, especially in low or zero airflow environments. However, under forced convection, heat dissipation is dominated by convective heat transfer, and the contribution of radiation is relatively small and can typically be neglected.
Therefore, in most forced-air cooling simulations, radiative heat transfer is generally not considered a dominant factor.
When electronic components operate, they generate heat due to the flow of electricity through them. This heat must be dissipated to prevent the parts from overheating and failing. A heat sink works by absorbing this heat and spreading it out over a larger surface area, allowing it to dissipate more efficiently.
The heat sink is typically attached to the electronic component using a thermal interface material, such as a thermal paste or pad. This material helps to transfer the heat from the component to the heat sink.
Once the heat is transferred to the heatsink, it dissipates into the surrounding air through convection. The larger the surface area of the heat sink, the more efficient it is at dissipating heat.
Adequate cooling is essential for electronic devices, and heatsinks are an important component of any cooling solution
There are many designs for heatsinks, but they typically comprise a base and a number of protrusions attached to this base. The base is the feature that interfaces with the device to be cooled. Heat is conducted through the base into the protrusions. The protrusions can take several forms, including:
Heatsinks are usually constructed from copper or aluminum. Copper has a very high thermal conductivity, which means the rate of heat transfer through copper heatsinks is also very high. Whilst lower than that of copper, aluminum’s thermal conductivity is still high and it has the added benefits of lower cost and lower density, making it useful for applications where weight is a major concern.
The performance of heatsinks are a consequence of many parameters, including:
The last item is very important. Whilst electronic components and heatsink bases are manufactured to be very flat and smooth, at a microscopic level their surfaces are rough. This results in very few points of contact and many tiny air gaps between the component and its heat sink. Air has a low thermal conductivity, resulting in poor conduction of heat from the device to the heatsink. To combat this, a thermal interface material (TIM) can be applied to the base of the heatsink to fill these gaps and provide more conduction paths between device and heatsink.
Heatsink performance is characterized by its thermal resistance. This parameter can be thought of as the difference in temperature between the air around the heatsink and the device surface in contact with the heat sink per unit of input power. Thermal resistance is denoted by the symbol θ and has the unit °C/W.
The junction temperature (TJ) is the temperature of the hottest part of the device. This is the critical temperature for its correct operation. The case temperature (TC) is the temperature of the surface of the device which is in contact with the heatsink assembly. TC is lower than TJ due to the junction-to-case thermal resistance (θJC). The performance of the heatsink assembly is defined by the case-to-ambient thermal resistance (θCA). This is the difference in temperature between the device surface (TC) and the surrounding air (TA) for a unit of input power.
The increase in TJ over TA for each Watt of thermal power the device generates is the sum of θJC and θCA.
Heatsinks can be manufactured in a variety of ways depending on the required performance, cost and volume. These include:
For more complex thermal issues, heatpipes and vapor chambers may be employed within the heatsink assembly. These devices are sealed objects containing a fluid (typically water) and utilize the release of heat during fluid phase changes to vastly increase their conductivity when compared to a solid metallic object of the same geometry.