As long as it is electronic equipment, it must generate heat during running and increase internal temperature. The electronic components are unable to take effect if the heating fails to be dissipated, which leads to the lower reliability of electronic devices.
The heat dissipation of PCB plays an essential role in electronic equipment. There are three primary sources of heat:
- The heat from electronic components
- The heat from the PCB itself
- The heat from other parts except for electronic components
Among the above sources, the first one generates the highest heat value, followed by the heat generated by the PCB. In addition, the heat input from outside depends on the overall thermal design. In the actual PCB design, the heat dissipation issues that engineers need to consider include the selection of boards, components, and the layout of components.
That’s the reason why heat dissipation attaches great importance to PCB. How do we appropriately deal with PCB heating dissipation? Here are some techniques you should master.
What base materials does the PCB use?
Heat dissipation through the PCB board itself is currently widely used as a copper-clad or epoxy glass cloth substrate or a phenolic resin glass cloth substrate. Besides, a small amount of paper-based copper-clad board is also used.
What is the impact of the substrate currently used in PCB?
Although these substrates have favorable electrical performance, they possess weak heat dissipation capability. Thus, it’s not an ideal way to only rely on some substrate materials for conducting heat dissipation. With the electronic equipment has witnessed smaller size and high-density installation, it’s necessary to take other measures to solve the issue of heating inside the components.
Due to the extensive use of surface mount components like QFP and BGA, heat generated by the components is greatly transmitted to the PCB. Hence, the heating dissipation capability of PCB which direct contact with heater components should be strengthened.
Seven tips for heat dissipation of PCB
The components in the same PCB ought to be arranged and aligned with the value of heat emitting and degree of heat dissipation. For those which have lower heat emitting values and weak heat resistance capabilities, such as small-signal transistors, small-scale integrated circuits, and electrolytic capacitors should be placed at the entrance of the cooling airflow. On the contrary, those with high heat emitting values and good heat resistance, like power transistors and large-scale integrated circuits need to be placed at the lower flowing of the cooling airflow.
In the horizontal direction, the high-power components are set as close to the edge of the PCB as possible to shorten the heat transfer path.
While, in the vertical direction, they should be as close as possible to the top of the PCB in order to reduce the influence on the temperature of other devices.
The heat dissipation inside the PCB mainly depends on airflow. So the airflow path should be considered and reasonably configured the position of different components during design.
In general, the air always tends to flow toward the small resistance. When mounting some components on PCB, it prevents from leaving large space in a certain area. The configuration of multiple PCBs in the whole machine is also no exception.
For equipment cooled by free convection air, it has better to arrange the integrated circuits or other devices either vertically or horizontally.
Devices that are sensitive to temperature have better leave in the lowest temperature area such as the bottom of the device. Never place it directly above the heat-generating device. Besides, it’s recommended to distribute multiple components staggered in the horizontal direction.
Place the components with high consumption and heat emitting near the location with good heat dissipation. Do not place components with high heat generation on the corners and edges of the PCB unless there are heat sinks near them.
When designing the power resistor, choose larger components as much as possible, and make sure that they have enough heat dissipation space upon adjusting the PCB layout.
- Thermally sensitive components should be placed in an air-cooler area.
- The temperature detection device should be placed in the hottest position.
Heat emitting degree
When there are a few components ( less than 3 components) in the PCB that generate higher heat degrees, we can add a radiator or a heat pipe to them. If the temperature is still unable to cool, a radiator with a fan can be adopted to further strengthen the heat dissipation effect.
A large heat dissipation cover or board is an exclusive radiator based on the position and height of the heating components on the PCB. When there are many components with higher heat generating degrees (more than 3 components), a large heat dissipation board can be employed through whole covering the board and contact with each component.
The poor consistency of the components during assembling and soldering, however, results in a poor heat dissipation effect. To solve this condition, a soft thermal pad is usually added to the component surface.
Due to the poor thermal conductivity of the resin in the PCB, increasing the remaining copper foil and heat conduction holes are the main measures for heat dissipation.
To evaluate the heat dissipation capability of the PCB, it is necessary to calculate the equivalent thermal conductivity of the insulating substrate, which is a composite material composed of various materials with different thermal conductivity.
Pay attention to avoid the concentrated distribution of higher heat-emitting components. Try to distribute the power evenly on PCB as much as possible and keep the surface temperature consistent.
It is generally known that it is difficult to achieve a strict even distribution during design. Remember to avoid making the higher power density in an area in case of impacting the normal operation of the whole PCB.
If conditions permit, it is crucial to conduct a thermal performance analysis of PCB. For example, some professional PCB design software that has thermal performance index analysis modules enables to optimize circuit design for designer.