On the basis of comprehensive consideration of signal quality, EMC, thermal design, DFM, DFT, structure, safety regulations and other requirements, the components are reasonably placed on the board. ——PCB layout
Except for special requirements, all component pad routing must meet thermal design requirements. ——General principles of PCB routing
It can be seen that in PCB design, whether it is layout or routing, engineers should consider and meet the requirements of thermal design.
The importance of thermal design
In addition to useful work, most of the power consumed by electronic equipment during operation, such as RF power amplifiers, FPGA chips, and power products, is converted into heat dissipation. The heat generated by electronic equipment causes the internal temperature to rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, the device will fail due to overheating, and the reliability of the electronic equipment will decrease. SMT increases the installation density of electronic equipment, reduces the effective heat dissipation area, and the temperature rise of the equipment seriously affects the reliability. Therefore, the study of thermal design is very important.
PCB thermal design requirements
1) When arranging components, temperature sensitive devices other than temperature detection devices should be placed near the air inlet, and located upstream of the air duct of components with high power and high heat generation, as far away from components with high heat generation as possible to avoid the influence of radiation. If it is impossible to stay away, it can also be separated by a heat shielding plate (polished metal sheet, the smaller the blackness, the better).
2) Place the components that generate heat and are heat-resistant near the air outlet or on the top, but if they cannot withstand higher temperatures, they should also be placed near the air inlet, and pay attention to stagger the positions with other heating devices and thermal sensitive devices in the direction of air rise as much as possible.
3) High-power components should be arranged as dispersed as possible to avoid heat source concentration; components of different sizes should be arranged as evenly as possible to make the wind resistance evenly distributed and the air volume evenly distributed.
4) The vents should be aimed at devices with high heat dissipation requirements as much as possible.
5) High components should be placed behind low components, and the long direction should be arranged in the direction with the least wind resistance to prevent the air duct from being blocked.
6) The radiator configuration should facilitate the circulation of heat exchange air in the cabinet. When heat is transferred by natural convection, the length direction of the heat sink fins should be perpendicular to the ground. When heat is transferred by forced air, the direction should be the same as the airflow direction.
7) In the direction of air flow, it is not advisable to arrange multiple heat sinks in close vertical distance, because the upstream heat sink separates the airflow, and the surface wind speed of the downstream heat sink will be very low. They should be arranged in a staggered manner, or the heat sink fins should be spaced apart.
8) The heat sink should be at an appropriate distance from other components on the same circuit board, and it is advisable to avoid inappropriate temperature increase through thermal radiation calculation.
9) Use PCB to dissipate heat. For example, heat can be dissipated through a large area of copper (solder mask windows can be considered), or the ground connection vias can be used to guide the heat to the plane layer of the PCB board, and the entire PCB board can be used to dissipate heat.