Design factors that influence the thermal performance of a heat sink

    When selecting or designing a heatsink the following factors must be considered:

    • Thermal resistance
    • Material
    • Fin efficiency
    • Spreading resistance
    • Fin arrangements
    • Surface colour

    What is a heatsink?

    In electronic systems, a heatsink is a passive component that cools a device by dissipating heat into the surrounding air. Heatsinks are used to cool electronic components such as high-power semiconductor devices, and optoelectronic devices such as higher-power lasers and light-emitting diodes (LEDs). Heatsinks are heat exchangers such as those used in refrigeration and air conditioning systems, or the radiator in an automobile.

    How does a heatsink work?

    A heatsink is designed to increase the surface area in contact with the cooling fluid surrounding it, such as the air. Approach air velocity, choice of material, fin (or other protrusion) design and surface treatment are some of the factors which affect the thermal performance of a heatsink.

    Where are heatsinks used and how are they attached?

    Heatsinks are used to cool computer central processing units (CPUs) or graphics processors. Heatsink attachment methods and thermal interface materials also affect the eventual die temperature of the integrated circuit. Thermal adhesive or thermal grease fills the air gap between the heatsink and device to improve its thermal performance. Theoretical, experimental and numerical methods can be used to determine a heatsink's thermal performance.

    Surface Colour

    The heat transfer from the heatsink occurs by convection of the surrounding air, conduction through the air, and radiation. Heat transfer by radiation is a function of both the heat sink temperature, and the temperature of the surroundings that the heat sink is optically coupled with. When both of these temperatures are on the order of 0 °C to 100 °C, the contribution of radiation compared to convection is generally small, and this factor is often neglected. In this case, finned heat sinks operating in either natural-convection or forced-flow will not be effected significantly by surface emissivity.

    In situations where convection is low, such as a flat non-finned panel with low airflow, radiative cooling can be a significant factor. Here the surface properties may be an important design factor. Matte-black surfaces will radiate much more efficiently than shiny bare metal in the visible spectrum. A shiny metal surface has low effective emissivity due to its low surface area. While the emissivity of a material is tremendously energy (frequency) dependent, the noble metals demonstrate very low emissivity in the NIR spectrum. The emissivity in the visible spectrum is closely related to color. For most materials, the emissivity in the visible spectrum is similar to the emissivity in the infrared spectrum; however there are exceptions, notably certain metal oxides that are used as "selective surfaces".

    The vast majority of ABL Components' Heatsinks - single piece extrusion, customised extrusion, BGA and board mount - are black anodised on-site at ABL to assist performance. High powered extrusions - because of their unique manufacturing process - are not black anodised because the performance of these heatsinks has been optomised by the excellent surface area created by the high fin ratios utilised in these designs.

    Abl heatsinks blue