When it comes to high-power printed circuit boards (PCBs), they require more of what we have been talking about. High-power PCBs are what is in their name, meaning they require more current than standard PCBs.
More current equals more heat equals more chances of component failure, higher current requires larger traces, more spacing in the design, and even thicker PCBs. Also, high-temperature material is required to build them. So, with more space in the design, a larger via array can be added to help with the heat. Ground planes can help too.
Additionally, heat sinks can transfer heat. Some PCB designs use an aluminum plate attached to the board to handle the higher heat caused by the higher current being used. The designer must take into consideration how to transfer the component heat onto some type of surface, preferably copper to control this potential problem.
What Is Heat Dissipation?
Heat dissipation refers to the process of transferring excess heat away from electronic components to maintain safe operating temperatures. In high-power PCBs, managing heat dissipation is critical, as excessive heat can degrade electrical performance, reduce component lifespan, and even cause complete system failures.
Heat in PCBs primarily originates from electrical resistance within traces, vias, and components. As current flows through the circuit board, power losses generate heat, which must be efficiently dissipated to prevent localized hotspots and thermal stress. Without proper heat management, prolonged exposure to elevated temperatures can lead to solder joint fatigue, material degradation, and shifts in electrical properties, which may result in intermittent failures or permanent damage.
Example of a printed circuit board with thermal via arrays.
Efficient heat dissipation relies on several factors, including PCB material selection, thermal via arrays, copper plane design, and external heat sinks. The goal is to channel heat away from critical components and distribute it evenly across the PCB, ensuring that temperature-sensitive components remain within their safe operating limits. By incorporating optimized heat dissipation techniques, PCB designers can improve the reliability, efficiency, and longevity of high-power circuit board assemblies.
Why Control Heat Dissipation?
High temperatures can be an enemy to electronics. When a component overheats, it will most likely fail in its performance. Without a way to dissipate the heat, even the solder joints holding the component onto the PCB could break.
Excessive heat can cause other problems even if the component does not fail. Heat causes changes in chemical reactions. The PCBs signals can change and even experience distortion. Overheating can cause changes in electrical properties as well. A fully assembled and out-in-the-field PCB should be reliable for a good long time, so one does not want shortened life in components, incorrect functions of the system, or, worse, complete system failure.
Why Do Components Generate Heat?
Electrical components require electricity of course, but they all require some amount of resistance to that flow of power. Any resistance generates heat. The more the resistance, the more heat. Also, if more power is applied, the heat level increases. High-power components then generate even more heat and can fail that much sooner if the heat is not dissipated somehow.
Dissipating Heat from SMT Components
Drilling an array of vias, usually 0.006-0.010 in diameter in between rows of SMTs, helps to alleviate the surface component's heat. The vias would have some minor annular ring of copper that is not covered by soldermask. The underside of the component would rest upon the exposed copper rings of the via array, and the heat generated by the component would dissipate down through the copper-plated vias to the bottom of the PCB.
Alternative, Improved Methods
It has been found that the greater the copper surface available for the heated-up component to touch, the better the disbursement of its heat. Filling the via array with conductive epoxy helps to transfer the heat. Filling the vias with silver helps even more.
An even better method is to plate the vias shut with copper (see our blog post on filling vias). An even greater method in an aid to heat dissipation is also to have a copper plane layer under those SMT components and their via array. Last, a heatsink can be designed into the PCB under the component or otherwise attached to it.
Summary
The PCB design will affect what type of component heat dissipation can be used. High-density multilayers have limited surface space to work with so via arrays would have to be contained in the available space.
The smaller the via the more vias can be drilled in the area but also the amount of available copper may be reduced. Copper plane layers come into play in these cases, as well as filling the vias. If via in-pad processing is required for the PCB, this uses non-conductive via fill, so copper plating shut the via array area would be an option.
Key Takeaways
- Proper heat dissipation is essential in high-power PCBs to prevent component failure, signal distortion, and material degradation caused by excessive temperatures.
- Thermal via arrays effectively channel heat away from SMT components by providing a direct path for heat to dissipate through the PCB, reducing localized hotspots.
- Alternative methods, such as using conductive epoxy, silver-filled vias, or copper-plated vias, further enhance thermal conductivity and improve heat dissipation efficiency.
- Copper plane layers beneath SMT components and via arrays provide additional heat dissipation pathways, while heatsinks can be integrated into the PCB for more effective thermal management.
- PCB design constraints, such as limited surface space in high-density multilayer boards, influence the choice of heat dissipation techniques, requiring careful planning of via size, placement, and material selection.
