How to Select Heat sinks for Electronics and PCBs

All electronic components dissipate heat through Joule heating, which can cause them to reach high temperatures and eventually fail. Large processors, amplifiers, and other integrated circuits are common components that can generate significant heat during operation. The simplest method for keeping these components cool is to use a heat sink that mounts directly to a component. Alternatively, these can mount to one side of the PCB or an enclosure.

Among all the options available on the market, which heat sink should you use? Should a custom heat sink be used for your product? We’ll cover some of the primary points to consider when selecting heat sinks in this guide.

Important Specifications for Heat Sinks

What Material Should Be Used?

Most commercially available heat sinks are made from an aluminum alloy. Aluminum is a low cost option with reasonably high thermal conductivity compared to other heat sink materials. Other options include copper and stainless steel. Copper has higher thermal conductivity, but it carries higher cost due to difficulty in fabrication. For more rugged systems, stainless steel is an appropriate option, although it provides lower thermal conductivity than the other two metals listed here.

Ceramics are another option that can be engineered to have a specific thermal conductivity. They are commercially available and are commonly used in LED arrays. The table below shows some thermal conductivity data for heat sink materials.

Match the Heat Sink to the Package

Most heat sinks come in a square form factor, but they may not be specified for a particular package. Some specialty heat sinks will target specific packages in terms of exposed surface area and mounting style. Rather than surface attachment to a component with a thermal interface material, other components like power transistors can be attached with screws, clips, or spring-mounted graphics.

Some larger heatsinks can be used with these mounting styles to take heat from multiple components. Furthermore, the heat sinks could have a board surface attachment mechanism that allows the heat sink to be grounded to the same reference as the PCB. An example with multiple transformers in TO packages is shown below.

MOSFETs in power electronics can be ganged into a larger heatsink and attached with small screws.

Surface Area

Finally, the most important point that determines the total heat flux that can be transported from a hot component is the exposed surface area. This is one of the primary reasons heat sinks are designed with exposed fins: to increase the available surface area for cooling. The exposed surface area could also allow airflow to be pulled through the heat sink using a fan.

The limiting factor here is typically the z-axis height of the heatsink. Increasing the surface area requires increasing the height of the heat sink, and eventually it may not be able to fit into its enclosure. This is one area where the electrical and mechanical designer have to collaborate to find some balance between heat sink height and enclosure size.

Custom Heatsink Design or Off-the-Shelf?

Most heat sinks that will be used in a PCB to target a group of components, a large processor, or the enclosure will be off-the-shelf. This is especially the case for prototypes, simply because it is a lower cost option and the component can be purchased at quantity 1. A short cross section of available heat sinks from a major electronics distributor is shown in the list below.

The other option is a custom design, which requires a mechanical engineer to design and prepare for production. Custom heatsinks have to be manufactured, and the economics only work when they are produced at high volume. Therefore, one path forward is to prepare prototypes with off-the-shelf heat sinks, then make the transition to high volume with a custom heatsink. Typically this component would be fabricated with an extrusion process, stamping, or die casting.

The custom heatsink can then be evaluated with CFD simulations and measurements before mass production to verify it will beat the off-the-shelf option. Additional heat dissipation can be provided with an appropriate thermal interface material attached to the component. With iterative simulation and optimization, the design can be steadily improved in terms of form factor and equilibrium temperature.

To make the best component selection choices and evaluate the reliability of their products, designers need the complete set of system analysis tools from Cadence. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity. Cadence PCB design products also integrate with a multiphysics field solver for thermal analysis, including verification of heat sink designs.

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