1. Every PCB electronic device generates a certain amount of heat during operation, causing the internal temperature of the device to rise rapidly. If the heat is not dissipated efficiently, the device will continue to overheat, leading to potential failure of the PCB and a decrease in reliability.

2. Therefore, effective heat dissipation is crucial for the circuit board. Heat dissipation is a critical aspect of PCB design, and in this article, we will explore the techniques used to manage heat dissipation in PCB circuit boards.

3. **Heat Dissipation through the PCB Material**

The most commonly used PCB materials are copper-clad epoxy glass cloth substrates, phenolic resin glass cloth substrates, and, to a lesser extent, paper-based copper-clad boards. While these substrates offer excellent electrical properties and ease of processing, they are not particularly efficient at dissipating heat.

4. As high-heat components are often mounted on the PCB, relying on the PCB’s resin to conduct heat is not a viable solution. Instead, heat needs to be dissipated from the component surfaces into the surrounding air.

5. As electronic products continue to evolve with smaller, more densely packed components and higher power dissipation, relying on the small surface area of components to dissipate heat is no longer sufficient.

6. With the widespread use of surface-mount devices like QFPs and BGAs, heat generated by components is transferred in significant amounts to the PCB itself. To address this, the most effective solution is to improve the heat dissipation capacity of the PCB, particularly in areas that come into direct contact with heat-generating components.

7. **Techniques for Enhanced Heat Dissipation**

– **Adding Heat-Dissipating Copper Foil**: Including additional copper foil, particularly in areas related to power supply, can significantly improve thermal performance.

– **Thermal Vias**: The use of thermal vias helps in transferring heat away from hot spots on the PCB.

– **Exposing Copper on the Back of the IC**: Exposing copper on the backside of components like ICs can lower the thermal resistance between the copper layer and the surrounding air, improving heat dissipation.

8. **PCB Layout Considerations**

a. **Place Heat-Sensitive Components in Low-Temperature Zones**: When designing the PCB, ensure that heat-sensitive components are placed in areas less affected by the overall temperature rise.

b. **Position Temperature Sensors in High-Heat Areas**: To monitor thermal performance, place temperature detection devices at locations that experience the highest temperatures on the board.

c. Devices on the same printed circuit board (PCB) should be arranged as far as possible based on their heat generation and dissipation capabilities. Components with low heat output or poor thermal resistance (e.g., small signal transistors, small-scale integrated circuits, electrolytic capacitors) should be placed in areas with the most direct airflow (near the intake). Components that generate more heat or have better heat resistance (e.g., power transistors, large-scale integrated circuits) should be positioned in areas with lower airflow, further down the cooling path.

d. In the horizontal plane, high-power devices should be positioned as close as possible to the PCB’s edge to minimize the heat transfer path. Vertically, high-power devices should be placed near the top of the board to minimize the impact on the temperature of surrounding components during operation.

e. The heat dissipation of the PCB within a system primarily relies on airflow. Therefore, airflow pathways should be carefully considered during the design phase, with proper component placement on the PCB. Since air naturally flows through areas of lower resistance, it’s important to avoid large open spaces in any particular region when arranging components. This same principle applies when designing the layout of multiple PCBs within a system.

f. Temperature-sensitive components should ideally be placed in the lowest temperature areas (such as near the bottom of the device). Never place these components directly above high-heat-producing devices. It’s also best to stagger components on the same horizontal plane to optimize thermal distribution.

g. Position high-power and high-heat-generating components in the best locations for heat dissipation. Avoid placing such components at the corners or peripheral edges of the PCB, unless a heat sink is installed nearby. When designing power resistors, select larger components where possible, and ensure adequate space is provided for heat dissipation during the PCB layout process.

h. Recommended component spacing:

– High-heat-generating components should be combined with radiators and heat-conducting plates. If only a few components on the PCB generate substantial heat (fewer than three), a heat sink or heat pipe can be added to those components. If temperature reduction is insufficient, a heat sink with a fan may be used to further improve cooling.

– For a larger number of heat-generating components (more than three), a large heat dissipation cover (or board) can be used. This is a custom heat sink designed according to the positions and heights of the heating components on the PCB or a large flat heat sink that accommodates various component heights.

– The heat dissipation cover should be firmly attached to the surface of the components and make direct contact with each one to facilitate heat dissipation. However, this method may be less effective due to height inconsistencies during component assembly and soldering. In such cases, a soft thermal phase-change material pad is often added to improve heat dissipation performance.

– For systems using free convection air cooling, it’s best to arrange integrated circuits (or other components) either vertically or horizontally.

– A well-designed routing plan can enhance heat dissipation. Since the resin in the PCB material has poor thermal conductivity, while copper foil traces and vias are efficient heat conductors, maximizing the copper foil area and increasing the number of vias are key strategies for improving thermal management.

In power resistor design, always opt for larger components when possible, ensuring enough space for heat dissipation during layout adjustments.

To avoid excessive concentration of heat in specific areas, distribute power dissipation evenly across the PCB. This will help maintain consistent surface temperature and prevent hot spots that could disrupt the performance of the entire circuit.

Achieving perfect uniformity in heat distribution can be challenging during the design phase. However, areas with excessive power density must be avoided to prevent localized overheating from affecting circuit functionality.

If feasible, thermal efficiency analysis of the PCB should be performed. Some advanced PCB design software includes thermal efficiency modules that can assist designers in optimizing their layout for better thermal management.

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