PCB Thermal Management: Passive vs. Active Cooling

Why Your Design’s Fate Hinges on PCB thermal management

Even when a part that is rated to last 10 years at 70°C is operated at 90 °C, its life would only be 2.5 years. This thermal debt leads to:

• Performance Throttling: CPUs and GPUs reduce their performance to avoid self-destruction.
• Signal Integrity Problems: PCB traces, whose electrical characteristics change with temperature, become the source of data errors.
• Failure of Components: Capacitors dry, solder joints crack, and silicon junctions fail.

Effective PCB thermal control provides a good conduit of heat to the external world, where the heat is supposed to go after exiting the heat source, and serves as a backup to avert such failures. Experienced PCB designers are aware of the fact that the management of heat dissipation on a per-design basis positively affects the reliability of the system and its thermal performance.

Understanding Passive PCB thermal management

Passive thermal management uses no extra power to cool a device. It is solely based on the main laws of thermodynamics: conduction, convection, and radiation – all of which are the basis of heat conduction in electrical systems.

• Conduction: Direct contact heat transfer (e.g., between a component and the printed circuit board).
• Convection (Natural): Heat transfer by movement of the air. Hot air is brought up through natural processes, and the cooler air is brought in to take the place of the hot air.
• Radiation: Transfer of heat through electromagnetic radiation.

The goal of a passive strategy is to harness the maximum of these natural processes. It is durable (few moving components) and totally silent. These techniques make for good thermal design and good material choice to ensure that heat is dissipated well without wasted energy.

Key Techniques for Mastering Passive PCB thermal management

The first step before putting in a fan would be to maximize the cooling capacity of your PCB. It is the basis of all thermal design plans and one of the reasons why effective heat dissipation is the same way all the time.

Strategic Component Placement: Your First Line of Defense

Your PCB layout software is the most affordable thermal tool.

• Sources and Victims on the Map: Determine hot components (CPUs, FPGAs, power regulators) and sensitive components (capacitors, oscillators).
• Space: Do not place hot components closely together, as this forms a hot spot. The distribution of them leads to the printed circuit board being a natural heat spreader.
• Respect Airflow: position sensitive parts off the exhaust route of hot parts. Do not place a 10W regulator in the sight of a sensitive capacitor bank.
• Chassis as a Heatsink: Secure the hot parts close to the board edge so that they may be thermally connected with the metal enclosure. This coupling and the efficiency of overall heat conduction are improved by the proper choice of material, e.g., high-conductivity copper layers.

Leveraging Copper: Thermal Vias and Copper Planes

Your FR-4 substrate is a thermal insulator (~0.25 W/mK). Your copper is a thermal conductor (~400 W/mK). Your goal is to use copper to create a thermal superhighway.

• Copper Pours: Use large, solid copper planes (ground and power) as heat spreaders. A 2-oz copper layer (70µm thick) has significantly lower thermal resistance than a 1-oz (35µm) layer and dramatically improves lateral heat spreading.
• Thermal Vias: These are critical. A thermal via is an array of vias placed under a component’s thermal pad, “stitching” it to a large copper plane on another layer. This transfers heat through the insulating FR-4 to a larger surface area (like an internal ground plane) where it can be spread. For maximum effect, use via-in-pad designs and integrate them early in the PCB layout.

The Role of Heat Sinks (Heatsinks): Enhancing Natural Convection

When a component’s own surface area isn’t enough, you add a heat sink. A heat sink is a passive component that dramatically increases the surface area available for natural convection.

More surface area means more contact with the air and more heat transferred away. For natural convection, heat sinks with relatively sparse, tall fins are needed to encourage air to rise between them without trapping it. When combined with solid thermal design principles, these methods ensure steady and effective heat dissipation across the board.

The Next Level: What Defines Active PCB thermal management?

So you have optimized your layout, are using 2oz copper, and even added a heat sink, and your device is still overheating?

This is where the passive cooling is limited. Passive cooling is dependent on the natural temperature difference between the heat sink and the surrounding air. Where the component produces excessive heat or the surrounding air is already hot, natural convection is not as effective in sustaining optimal performance or constant heat transfers within the system.

Active thermal management can be characterized as the provision of energy into the system, such as fans or pumps, in order to cause the heat transfer mechanism. It substitutes feeble natural convection with much stronger forced convection, which is one of the best thermal control methods in electronic engineering today.

Key Techniques for Implementing Active PCB Thermal Management

The active measures consist of simple fans and highly sophisticated liquid cooling systems, all aimed at enhancing the heat flow and better heat dissipation in high-power or compact spaces.

Forced Air Cooling: The Role of Fans and Blowers

This is the most widespread and least expensive active cooling. Cool air inside and hot air outside by adding a fan, hence they are able to keep the temperatures steady, even where there is no air moving, like at the side of the board, where the trapped heat may rise.

In picking a fan, you need to trade off two things:

1. Airflow (CFM – Cubic Feet per Minute): The amount of air that the fan can transfer in an empty area. Large and open chassis are best cooled with high CFM.
2. Static Pressure (mmH 2 O): The amount of force that the fan can exert against the resistance. Airflow is impeded in a thick, 1U server chassis. To move air into and maintain a good circulation in confined areas, you require a high-static-pressure fan (also referred to as a blower) to push air where it is needed.

Liquid Cooling: Cold Plates and Closed-Loop Systems

In extreme thermal loads (e.g., high-performance data centers), air is not adequate as a cooling medium. The thermal capacity of water is greater than that of air by more than 3,000 times.

A liquid cooling system involves pumping a coolant through a cold plate attached to the hot part. The heat is absorbed by the liquid, pumped into a radiator (where the fans cool the liquid), and the cool liquid is returned. This high-tech thermal control approach maintains the uniformity of heat flow across the loop and offers a stable thermal environment of high-performing systems, even in challenging systems.

Advanced Solutions: Heat Pipes and Thermoelectric Coolers (TECs)

• Heat Pipes: These are superconductors of heat. The closed copper tube holds a liquid which, as it acquires heat, boils and flows as a vapor to the so-called cold end, condenses, and gives up its heat. The liquid is recycled to the hot end. They are also very good at transporting heat to the tight areas or the side of the board to a distant heat sink that the fan can handle.
• Thermoelectric Coolers (Peltiers): They are small heat pumps that are solid-state devices. The application of a current leaves one side cold and the other hot. They are applied to spot-cool particular sensors but are typically ineffective since they introduce their own heat into the system, and yet they contribute to enhanced heat dissipation in localized areas.

Passive vs. Active Cooling Head-to-Head

A design trade-off is the passive versus active cooling decision. Here’s how they stack up.

The Tipping Point: When Passive Cooling Isn’t Enough

You have hit the bottom line. Your simulations indicate that the temperature of your component is surging to the red zone (>100°C). This often happens due to:

1. High Power Density (TDP): Your component produces excessive heat in an excessively small size.
2. High Ambient Temperature: Your device is placed in a hot place (a factory or in the car).
3. Sealed Enclosure: The design needs to be airtight against dust or water (e.g., IP67); that is, there is no airfitment.

Now it is time to proceed to an active solution. However, this brings about new issues of noise, reliability, and dust.

The Active Solution: Reliable Cooling for Compact Designs by ACDCFAN

Active solution selection is not simply a matter of dropping in any fan; it is a matter of dropping in the correct fan that will address your thermal issue and not create some new heat issue.

This is the problem that ACDFAN was constructed to address. Our fans are high-reliability models used in designs where there is a lack of space and failure is not an option.

• Solving Reliability: The Reliability fear is that, most common one is the failure of fans. We have our core technology, which utilizes the most advanced ball bearings and thus is able to reach up to an MTBF (Mean Time Between Failure) of more than 70,000 hours. That is almost 8 years of 24/7 service, which guarantees that the life of our fan will be the same as your product.
• Solving for harsh environments: In dusty, wet, or high-altitude surroundings, our IP68-rated dustproof and waterproof encapsulated fans can offer the greatest protection in the industry.
• Manufacturing Noise-Efficiency: A 100% speed fan is noisy, and it consumes power. PWM (Pulse Width Modulation) smart speed control is incorporated into our fans. With this, you can have your system request on-demand cooling, operating silently at low loads, and only increasing the load in severe thermal conditions. This, together with a superior blade design, provides the maximum cooling with the least noise.

We are offering a solution, not a component. As a fully compliant (RoHS 2.0, UL, CE, TUV, EMC) design, we can provide an interim technical solution to your design within 12 hours.

How to Decide Which PCB Cooling Strategy is Right for You?

This decision-making framework should be used to shape your first strategy.

Conclusion

PCB thermal management is about balance. It’s not choosing “passive” or “active”; it’s about starting with a robust passive foundation and knowing when to build upon it with a smart active solution.

By optimizing your layout and leveraging your PCB’s copper, PCB designers build in “free” thermal resilience. But when physics dictates that passive is not enough, a high-quality active cooling solution is not a compromise—it’s an enabler. It’s what allows you to confidently push the boundaries of performance, knowing your design is protected by effective thermal management and guided by sound heat dissipation practices.