Specialist heat sink providers are the best resource for determining optimal cooling solutions.
All electronic devices generate excess heat. Devices that feature microprocessors typically require some form of thermal management to remove their excess heat. Without it, a device may not perform reliably, and can fail totally, well short of its expected working lifetime.
Many methods are available for applying thermal management. One of the oldest, but still the most common, is to attach a heat sink directly to a hot electronic device. This provides a destination for excess heat to travel into and away from the hot integrated circuit. Today, heat sinks are abundantly used in electronic devices with IC components, including AI processors, CPUs, GPUs, FPGAs, and power semiconductors.
Heat sink function
A heat sink is typically made from metals such as copper or aluminum. It has a flat surface that mounts directly to the top of the heat dissipating device. Usually, a thermally conductive material (TIM) is placed in the mounting interface to optimize heat transfer. Heat from the component transfers into the sink via conduction.
A heat sink then typically transfers this heat to the surrounding air, either on its own (passively) or assisted
by a fan mounted on the heat sink (actively) or by active system airflow. As such, they are designed with fins in different shapes to expose more heated surfaces to the airflow. This is heat transfer via convection.
While conduction and convection are the primary modes of heat transfer from the heat sink, radiation heat transfer plays a notable role in transporting the heat from the device to the ambient air. The amount of thermal energy transferred from a component to a heat sink, or from a heat sink to the air, is expressed as the heat flux, typically using the die size or device topside area as a reference denominator (W/cm2). Heat transfer requires a temperature difference, and heat flows through a medium from the hot to the cold side.
By attaching properly designed heat sinks, many hot components can be kept within their safe operating specs. Heat sinks are rated by their thermal resistance as a function of air velocity when tested in a wind tunnel. This resistance, °C/W, measures how well they can dissipate heat. A lower thermal resistance indicates a more efficient heat sink and better heat transfer ability. Larger heat sinks with more fins will have a lower thermal resistance than smaller versions.
Design and selection
Heat sink selection should factor in the power dissipation of the hot component. The sink should have a low enough thermal resistance that its performance maintains the component’s desired operating temperature. With components becoming more and more powerful, and devices getting smaller, finding an ideal heat sink can be challenging.
Many thousands of heat sink designs have been developed over the years, and are available from different sources. Materials and manufacturing processes can differ, however, so similar heat sinks should be compared for relative performance, ideally with actual testing.
Today’s electronics industry churns out an amazing rate of new products. Their specialty uses, production budgets, and other parameters impact all parts of a device, including the heat sinks cooling their hot components. Very often, a custom- designed heat sink is needed to meet all the application requirements.
Designing a heat sink starts with determining the boundary conditions of the application. These include basics like how much airflow is available and its temperature, how much power is being dissipated, and how much space is available for the attached heat sink. Also, what are the options for including an off-the-shelf fan?
Heat sink designers can calculate how much airflow is needed or what kind of heat sink thermal resistance is required. If there are several components in a row along a PCB, they can calculate the air temperature rise along that row of parts. There are online tools that can do the calculation and recommend a suitable heat sink (one such tool can be found at bit.ly/3ZhHyrD).
Higher performance
While increasingly powerful components and systems must be liquid cooled, there are a growing number of higher performance heat sinks on the market that can provide liquid-like cooling without its cost or concerns.
Most of these high-performance heat sinks feature integral blowers. They draw high volumes of air through their fins to convey away more heat. Some higher performing but passive heat sinks are designed with dense fin fields and special mounting systems to provide enhanced cooling levels.
Testing, production, and application of new heat sinks Computational fluid dynamics (CFD) simulations of functioning heat sinks are versatile and informative. Ideally, an OEM can provide the computer model of an application, including the board and enclosure. These can be plugged into the CFD simulations. From here, an initial heat sink design can be placed into the simulations, providing more understanding of the heat dissipation challenges.
The performance of a simple heat sink in a basic airflow situation is well understood and modelled. But these simple conditions are unusual. Some chassis are so complex they can’t be properly simulated.
The next step of the process is to produce low volume prototypes. Some heat sink providers have metalworking machines (CNC, milling, lathes, etc.) to produce prototypes for lab testing or for their customers to test in their actual systems.
Prototype development and testing is an investment, but it’s the best method for optimizing the choice of a custom heat sink design. It avoids creating too small or inefficient heat sinks, or too large, needlessly expensive heat sinks. Prototypes help resolve most considerations for when these heat sinks are scaled up into mass production. These include: What materials and processes will be used? What design is the lowest cost, but will provide the needed cooling performance? If necessary, what kind of fan can be integrated? Another factor is how a heat sink will be attached to a component. Smaller sinks may attach with thermal adhesive tape. Most, however require a hardware system that mounts the sink to the component surface with continuous pressure. These systems may be directly attached to a PCB, e.g., with push pins. Other attachment systems employ a tight frame fit around the component itself, onto which the heat sink is directly attached.
What’s next?
Air cooling remains a viable option for most electronics cooling needs. Over their decades of use, heat sinks continue to be improved to take on evolving thermal management needs. Individual heat sinks are now available with liquid cooling. In place of passive or active air cooling a circulating coolant carries heat away from the sink in a liquid loop. Specialist heat sink providers, like Advanced Thermal Solutions (ATS), are the best resource for determining optimal cooling solutions.