I’ve been burned in the kitchen more times than I’d care to admit; while these once were painful lessons, they now serve as a constant reminder that kitchen work requires respect and undivided attention. When I was much younger, I marveled at the induction stovetop while visiting a friend, and while I had learned many times about the danger of a gas flame, I took a “look with my hands” approach to the novel cooking equipment. Of course, current dissipates heat across resistive loads; I wouldn’t learn this formally until years later, but you could consider it my literal hands-on introduction.
More often than not, the task for board designers is to mitigate rather than promote this heat transfer process as much as possible and limit the detrimental effects of heat on board reliability. High-power devices are more liable to experience early failure if proper alleviation techniques do not make their way into the design. While the layout, production, and revision process is integral to DFM, forward-looking designs will incorporate thermal routing to optimize power and performance. Boards with thermal problems can encounter many issues, ranging from manufacturing difficulties to outright board failure; some common pointers on PCB heat dissipation techniques can help reduce the chance of thermal runaway and other issues at the design level.
Comparison of Cooling Styles
Circuit Board Thermal Problems to be Aware Of
No matter what, some heat will always be associated with operating a circuit board. While this will not be a problem with many boards, those running at higher current levels with high-powered components may produce enough heat to warrant concern. These thermal problems can manifest in the dielectric materials’ breakdown 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 extend past the board’s operation; they can also arise due to the manufacturing processes used in their creation. During the fabrication of a circuit board, a tremendous amount of heat and pressure can cause failures if the board design lacks optimization. In the same way, the temperatures used during assembly for soldering components to the board can create problems if the board’s heat dissipation measures are less than suitable. Fortunately, there are design techniques that can mitigate these problems.
PCB Heat Dissipation Techniques That Can Help
The goal of thermal management for PCB design is to dissipate the heat created due to the above mentioned conditions. Here are some preventative tips:
- Materials – Other than epoxy, resins are better suited to dissipate disproportionate heat levels such as polyimides or metal cores. For these materials, the decision has to occur early during stackup planning, as these materials will have very different electrical characteristics, completely changing the structure of the design.
- Layer stackup – The board layer stackup configuration can also help with heat dissipation. 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 – Part placement will help control thermal problems with the board. Hot components placed on the board’s edge tend to localize their heat, while the same parts placed toward the center of the design will diffuse the heat throughout the board. It’s important to separate different power supply circuits to give them room to dissipate heat.
- Routing – The more metal on the board, the greater the heat-sinking capabilities. At the same time, power components require short routes to keep their inductance low. Use wider traces and more copper weight to satisfy both needs. Using solid metal planes whenever possible for ground nets and maintaining the short and direct routing requirements is best.
- 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 dissipating 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, an effect known as “tombstoning.”
- Heat sinks: One final way to dissipate heat on a circuit board is using heat sinks, which attach to components or areas of the board that are running hot. Heat sinks are also regularly used with cooling fans and thermal paste.
These are the general methods to manage excessive heat in a PCB design. For additional ideas, it is best to consult with CMs who 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 currents and optimize PCB heat dissipation techniques. They review designs 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 you are using and can recommend parts or circuitry operating at lower temperatures.
At VSE, our engineers regularly work with PCB designers and project teams 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 we have worked with.