September of 2020 brought about some of the most active forest fires on the West coast in recorded history, especially in Oregon. Fires burned all over the state rendering the skies an eerie reddish color for weeks, with some fires dangerously close to large population areas. One entire county was under different levels of evacuation warnings, and sadly some smaller towns were entirely lost to the flames. Thankfully when the weather changed, the evacuation notices quickly receded, and the cooling provided by lower temperatures and more humid conditions brought relief across the state.
This tragic scenario of fire spreading out of control is (while greatly differing in magnitude) similar to what can happen on a circuit board when the thermal activity is not considered during design. Boards with thermal problems can encounter many issues, ranging from manufacturing difficulties to outright failure of the board. There is still some debate on how to best prepare for and prevent fire disasters in the Pacific Northwest, but when it comes to PCBs the methods are tried-and-true. Here are some tips on PCB heat dissipation techniques that can help reduce the chance of thermal problems getting out of control on your next design.
Circuit Board Thermal Problems to be Aware Of
No matter what, there will always be some level of heat associated with the operation of a circuit board. While this will not be a problem with many boards, those that are running at higher current levels with high-powered components may produce enough heat to warrant concern. These thermal problems can manifest themselves in the breakdown of the dielectric materials used in electronic components, leading to their eventual failure. Excessive heat can also cause metal traces and other circuit board connectivity to burn through.
Thermal problems are not just confined to the operation of the board however, they can also be caused by the manufacturing processes used in their creation. During the fabrication of a circuit board, there’s a tremendous amount of heat and pressure used that can cause failures if the board is not designed correctly for it. In the same way, the temperatures used during assembly for soldering components to the board can create problems if the board isn’t designed specifically to evenly distribute the heat.
Fortunately, there are design techniques that can mitigate these problems, which we will look at next.
PCB Heat Dissipation Techniques that Can Help
The goal of thermal management for PCB design is to dissipate the heat that will be created due to the conditions discussed above. Here are some preventative tips:
- Materials: There are materials other than epoxy resins that are better suited to dissipate disproportionate levels of heat such as polyimides or metal cores. If these materials are used, the decision has to be made upfront as these materials will have very different electrical characteristics, completely changing the structure of the design.
- Layer stackup: How the board layer stackup is configured can also help with the dissipation of heat. One common thermal control method is to run thermal vias from under hot components to an internal plane. At the same time, the layer stackup needs to be balanced to help keep the board from warping during manufacturing.
- Parts: How the parts are placed will help control thermal problems with the board. Hot components that are placed on the edge of the board will tend to localize their heat, while the same parts placed towards the center of the design will diffuse the heat throughout the board. It’s important to provide separation between different power supply circuits to give them room to dissipate their heat.
- Routing: The more metal that is on the board, the more the heat can dissipate through it. At the same time, power components require short routes to keep their inductance low. To satisfy both needs, use wider traces and/or more copper weight. For ground nets, it is best to use solid metal planes whenever possible as long as you can maintain the short and direct routing requirements.
- Thermal reliefs: These are connections to metal planes composed of spokes instead of a solid connection. For thru-hole parts connecting to a metal plane, a thermal relief is necessary to focus the heat of soldering onto the pin instead of having it dissipate through the plane. For surface mount parts a thermal relief connection to a solid plane is important to keep the part thermally balanced during reflow solder, preventing the part from standing up on end in an effect known as “tombstoning”.
- Heat sinks: One final way to dissipate heat on your circuit board is the use of heat sinks which attach to components or areas of the board that are running hot. Heat sinks are regularly used in conjunction with cooling fans and thermal paste as well.
These are the general methods that you can utilize to manage an excessive amount of heat on your PCB design. For additional ideas, it is best to consult with CMs that have a practiced understanding of the thermal issues that circuit boards have to contend with.
Further Information on Heat Dissipation Techniques
Your local PCB contract manufacturer has years of experience building boards designed to operate with high current in applications where there will be a lot of heat. They will review your design for known problems such as areas of dense component placement, trace routing that isn’t suitable for the levels of current they are carrying, and restricted airflow for cooling hot parts. They will also review the components that you are using and can make recommendations for parts or circuitry that would operate at lower temperatures.
At VSE our engineers work with PCB designers and project teams regularly to fine-tune our customer’s circuit boards for their best performance and manufacturability. Our goal is your success and we have a long track record of doing just that with all of the electronics innovators that we have worked with.
