Fans are most often seen as the best defense against hot components in a PCB assembly, and yet fans inside an enclosure are meaningless without the ability to move heat away from the enclosure. The enclosure itself can provide heat sinking or it can aid airflow into an electronic device, which will help keep temperatures low in the enclosure. These three simple enclosure design techniques can help keep your electronics cool.
Enclosure Features for Electronics Cooling
Slats and Grates
If forced airflow or convection is used to carry heat away from components, then the enclosure will need to have openings on its surfaces. Typically slats and grates are used to provide an intake and exhaust for forced air, as well as a location to mount a fan. The fan can then pull cold air into the enclosure and provide the required cooling.
Circular grate for airflow in a power supply.
MCAD software users who will be implementing slats or grates as intake and exhaust for airflow will typically place these at the long ends of an enclosure, basically making the enclosure into a wind tunnel. A more sophisticated method could be to pull air through an exhaust on top of the enclosure through a small vent, thereby taking advantage of the Venturi effect and pulling a lot of air from a large enclosure.
Direct Bonding to Enclosures
Another option for working cooling into an enclosure is to use the enclosure itself as the heat sink. Large metal enclosures are not only used as durable options or shielded options for housing electronics, a large enclosure can provide an efficient means of moving heat away from components.
Implementing this design choice requires mounting the board directly to an enclosure with some large thermal pad or thermal interface material. If a thermal interface material is used, the best option is a large thermal pad that bonds one surface of the PCB to its enclosure. Advanced thermal pads can provide a high thermal conductivity path to a specific surface in the enclosure.
Obviously, one surface of the enclosure will get quite hot especially if the enclosure is made from sheet metal. However, that hot surface can be bonded or fastened to a larger body that can absorb all of the heat from the system.
Another heat dissipation option that can be incorporated into an enclosure is encapsulation. This is where a potting compound is used to fully encase a printed circuit board, its cabling, and connectors inside the packaging. This is also very useful when there is no mounting hardware in the enclosure, or insertion of tooling/fasteners into the enclosure is very difficult during final assembly. Potting compounds used for encapsulation have a range of material properties, including thermal conductivity.
The right potting compound can provide heat dissipation away from components in a PCB assembly.
Encapsulation is normally performed with a silicone, epoxy, or polyurethane potting compound, which will fill all the open areas inside the enclosure. This means that the only mechanism for moving heat to the outside of the enclosure is thermal conduction. Depending on the enclosure, this could be a superior option for ensuring heat dissipation compared to forced airflow or bonding to the enclosure. There will be more assembly costs involved in using potting compounds due to the additional process steps and material costs.
Next, in instances where an enclosure is used to dissipate heat, but the enclosure is not connected to any other body to remove heat, an enclosure with fins would be preferable. These finned heat sinks are typically made from extruded aluminum and are very durable, and the fins on the enclosure provide greater surface area for heat dissipation into air. Essentially, the enclosure functions like a large heat sink; it will work best when the enclosure is connected directly to the board, such as with a thermal interface material.
Extruded aluminum finned enclosure.
Evaluate Cooling With Simulations
Thermal-aware design of enclosures for electronics will require simulation and measurement to determine the temperature distribution in your system as it operates. For systems with airflow, CFD simulations are the standard tool for examining airflow and the temperature distribution in the system. It’s possible to determine steady-state temperature, identify hotspots, and experiment with multiple fan/inlet/exhaust positions in the enclosure. For thermal materials and encapsulation, thermal simulations can be used to determine enclosure temperature.
Your enclosure can be the unsung hero in thermal management, but only if you use the best set of system analysis tools from Cadence to design and simulate thermal behavior in your enclosure. 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 thermally sensitive chip and package designs.