What Are the Heat Dissipation Techniques for PCB Circuit Boards

For electronic equipment, a certain amount of heat will be generated during operation, which causes the internal temperature of the equipment to rise rapidly. If the heat is not dissipated in a timely manner, the equipment will continue to heat up, components will fail due to overheating, and the reliability of the electronic equipment will decrease. Therefore, effective heat dissipation treatment of the circuit board is extremely critical. Heat dissipation of the PCB circuit board is a key link in electronic design, so what are the heat dissipation techniques for PCB circuit boards? Let's discuss them in detail below.

#01 Heat Dissipation Through the PCB Board Itself At present, the most widely used PCB substrates are copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, with a small amount of paper-based copper-clad substrates also in use. Although these substrates have excellent electrical properties and processability, they have poor heat dissipation. As a heat dissipation path for high-heat-generating components, it is almost impossible to rely on the resin of the PCB itself to conduct heat; instead, heat is dissipated from the surface of the component to the surrounding air. However, as electronic products have entered the era of component miniaturization, high-density mounting, and high-heat-generation assembly, it is far from sufficient to rely only on the component surface with a very small surface area for heat dissipation. At the same time, due to the extensive use of surface mount components such as QFP and BGA, a large amount of heat generated by the components is transferred to the PCB board. Therefore, the best solution for heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heat-generating components, and conduct or dissipate the heat through the PCB board.

#02 Adding Heat Sinks and Thermal Conductive Plates to High Heat-Generating Devices When a small number of devices (less than 3) on the PCB generate a large amount of heat, a heat sink or heat pipe can be added to the heat-generating devices. If the temperature still cannot be reduced, a heat sink with a fan can be used to enhance the heat dissipation effect. When there are a large number of heat-generating devices (more than 3), a large heat shield (plate) can be used. It is a customized dedicated heat sink designed according to the position and height of the heat-generating devices on the PCB board, or a large flat heat sink with different component height positions milled out. The heat shield is integrally buckled on the component surface, contacting each component for heat dissipation. However, due to the poor consistency of component height during mounting and soldering, the heat dissipation effect is often unsatisfactory. Usually, a soft phase change thermal conductive pad is added on the component surface to improve the heat dissipation effect.

#03 For Equipment Adopting Free Convection Air Cooling, It Is Optimal to Arrange Integrated Circuits (or Other Devices) in a Longitudinal or Transverse Elongated Manner.

#04 Achieve Heat Dissipation Through Reasonable Routing Design Since the resin in the substrate has poor thermal conductivity, while the copper foil traces and vias are good thermal conductors, increasing the residual rate of copper foil and adding thermal vias are the main means of heat dissipation. To evaluate the heat dissipation capacity of a PCB, it is necessary to calculate the equivalent thermal conductivity (λeq) of the insulating substrate for PCB, which is a composite material composed of various materials with different thermal conductivity coefficients.

#05 Devices on the Same Printed Board Should Be Arranged in Zones According to Their Heat Generation and Heat Dissipation Capacity as Much as Possible. Devices with low heat generation or poor heat resistance (such as small-signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) shall be placed at the most upstream (inlet) of the cooling air flow, while devices with large heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) shall be placed at the most downstream of the cooling air flow.

#06 In the Horizontal Direction, high-power devices shall be arranged as close to the edge of the printed board as possible to shorten the heat transfer path; in the vertical direction, high-power devices shall be arranged as close to the top of the printed board as possible to reduce the impact of their operation on the temperature of other devices.

#07 The heat dissipation of the printed board in the equipment mainly relies on air flow, so the air flow path shall be studied during design, and devices or printed circuit boards shall be configured reasonably. Air flow always tends to flow in places with low resistance, so when configuring devices on the printed circuit board, avoid leaving a large empty area in a certain region. The same attention shall be paid to the configuration of multiple printed circuit boards in the whole machine.

#08 Temperature-sensitive devices should preferably be placed in the area with the lowest temperature (such as the bottom of the equipment), and must never be placed directly above heat-generating devices. Multiple devices are preferably arranged in a staggered layout on the horizontal plane.

#09 Arrange the Devices with the Highest Power Consumption and Maximum Heat Generation Near the Position with the Optimal Heat Dissipation Effect. Do not place devices with high heat generation at the corners and peripheral edges of the printed board, unless a heat dissipation device is arranged near it. When designing power resistors, select devices with a larger size as much as possible, and ensure sufficient heat dissipation space when adjusting the layout of the printed board.

#10 Avoid the Concentration of Hot Spots on the PCB, Distribute the Power on the PCB Board as Evenly as Possible, and Maintain the Uniformity and Consistency of the Temperature Performance on the PCB Surface. It is often difficult to achieve strict uniform distribution in the design process, but it is necessary to avoid areas with too high power density, so as to prevent hot spots from affecting the normal operation of the whole circuit. If conditions permit, it is necessary to perform thermal performance analysis of the printed circuit. For example, the thermal performance index analysis software module added in some professional PCB design software can help designers optimize the circuit design.

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