Heat sinks are essential parts of most electronic assemblies, power electronic devices, and optoelectronic components. These passive heat exchangers dissipate heat generated by electronic devices to ensure that they are operating within the limits specified by manufacturers. Some of the key factors that should be considered in heat sink design include thermal resistance, material, fin configuration, fin size and shape, fin efficiency, heat sink attachment method, and thermal interface material.
Geometries and parameters that provide maximum heat dissipation are obtained by analyzing different heat sink models. Download this free case study to learn how QRC Technologies used thermal simulation with the SimScale cloud-based CAE platform to optimize their design, improve heat sink efficiency, and prevent thermal damage to electronics. All you need to do is fill out this short form and it will play automatically. Set up your own cloud-based simulation via the web in minutes by creating an account on the SimScale platform.
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Carolina Giavedoni November 30, Read Time 7 Minutes. Cookie Policy SimScale uses cookies to improve your user experience. Accept Data Privacy. Each has its own advantages. Aluminum Heat Sinks Aluminum is the most common material for heat sinks. In particular, extruded aluminum heat sinks fit the needs of most projects. The metal is lightweight and has relatively good thermal conductivity. Copper has even better thermal conductivity than aluminum.
The metal is sometimes used where the importance of thermal conductivity outweighs weight savings. Copper Heat Sink Fins. Each heat sink manufacturing process has its own advantages and drawbacks.
There are a number of different ways to make heat sinks. The majority of heat sinks are made from extruded aluminum. The process is useful for most applications. Extruded heat sinks come at a low cost and custom specifications can be easily manufactured. The performance of extruded heat sinks can range from low to high.
Their main downside, though, is that dimensions are limited by the maximum width of extrusion. Learn more. These are normally used for applications that require large-sized heat sinks. One benefit of these is that the base material and fin material can be different. Also, a combination of aluminum and copper fins can be used instead of just one fin material.
This allows you to improve thermal performance while adding a minimal amount of weight. Bonded-fin heat sinks generally offer moderate performance and come at a high cost. Heat sinks produced through this method are normally made from copper. They are produced from a solid block of metal.
These heat sinks offer high design flexibility and you can achieve high fin-density. The heat transfer efficiencies have been measured for a wide range of heat sink configurations, and their ranges are listed in Table 4.
The improved thermal performance is generally associated with additional costs in either material or manufacturing, or both.
One can use the performance graphs to identify the heat sink and, for forced convection applications, to determine the minimum flow velocity that satisfy the thermal requirements. For natural convection applications, the required thermal resistance R sa can be multiplied by Q to yield the maximum allowable T sa. The temperature rise of a chosen heat sink must be equal to or less than the maximum allowable T sa at the same Q. The readers are reminded that the natural convection curves assume an optional orientation of the heat sink with respect to the gravity.
Also, the flow velocity in the forced convection graph represent the approach flow velocity without accounting for the effect of flow bypass. There have been a limited number of investigations 2,3 on the subject of flow bypass. For further consultation on this subject, readers are referred to the cited references.
When a device is substantially smaller than the base plate of a heat sink,there is an additional thermal resistance, called the spreading resistance, that needs to be considered I the selection process. Performance graphs generally assume that the heat is evenly distributed over the entire base area of the heat sink, and therefore, do not account for the additional temperature rise caused by a smaller heat source. Another design criterion that needs to be considered in the selection of a heat sink, is the altitude effect.
While the air temperature of an indoor environment is normally controlled and is not affected by the altitude change,the indoor air pressure does change with the altitude. Since many electronic systems are installed at an elevated altitude, it is necessary to derate the heat sink performance mainly due to the lower air density caused by the lower air pressure at higher altitude. Table 5 shows the performance derating factors for typical heat sinks at high altitudes. For example, in order to determine the actual thermal performance of a heat sink at altitudes other than the seal level, the thermal resistance values read off from the performance graphs should be divided by the derating factor before the values are compared with the required thermal resistance.
Thermal Circuit Before discussing the heat sink selection process, it is necessary to define common terms and establish the concept of a thermal circuit. Notations and definitions of the terms are as follows: Q : total power or rate of heat dissipation in W, represent the rate of heat dissipated by the electronic component during operation. Figure 1: Thermal resistance circuit Consider a simple case where a heat sink is mounted on a device package as shown in Fig 1.
Heat-Sink Selection In selecting an appropriate heat sink that meets the required thermal criteria, one needs to examine various parameters that affect not only the heat sink performance itself, but also the overall performance of the system.
Heat Sink Types Heat sinks can be classified in terms of manufacturing methods and their final form shapes.
The most common types of air-cooled heat sinks include: Stampings : Copper or aluminum sheet metals are stamped into desired shapes.
They are suitable for high volume production, because advanced tooling with high speed stamping would lower costs. Additional labor-saving options, such as taps, clips, and interface materials, can be factory applied to help to reduce the board assembly costs. Extrusion : These allow the formation of elaborate two-dimensional shapes capable of dissipating large heat loads.
They may be cut, machined, and options added. Extrusion limits, such as the fin height-to-gap fin thickness,usually dictate the flexibility in design options. Typical fin height-to-gap aspect ratio of up to 6 and a minimum fin thickness of 1.
A 10 to 1 aspect ratio and a fin thickness of 0. However, as the aspect ratio increases, the extrusion tolerance is compromised. These high performance heat sinks utilize thermally conductive aluminum-filled epoxy to bond planar fins onto a grooved extrusion base plate. This process allows for a much greater fin height-to-gap aspect ratio of 20 to40, greatly increasing the cooling capacity without increasing volume requirements.
Folded Fins : Corrugated sheet metal in either aluminum or copper increases surface area and, hence, the volumetric performance. The heat sink is then attached to either a base plate or directly to the heating surface via epoxying or brazing. It is not suitable for high profile heat sinks on account of the availability and fin efficiency. Hence, it allows high performance heat sinks to be fabricated for applications. Figure 2: Cost versus required thermal resistance The performance of different heat sink types varies dramatically with the air flow through the heat sink.
To quantify the effectiveness of different types of heat sinks, the volumetric heat transfer efficiency can be defined as where, m is the mass flow rate through the heat sink, c is the heat capacity of the fluid, and T sa is the average temperature difference between the heat sink and the ambient air. Thermal Performance Graph Performance graph typical of those published by heat sink vendors are shown in Fig. The graphs are a composite of two separate curves which have been combined into a single figure.
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