Heat dissipation through the PCB board itself
The widely used PCB boards are copper-clad / epoxy glass cloth substrates or phenolic resin glass cloth substrates, and a small number of paper-based copper-clad boards are used. Although these substrates have excellent electrical properties and processing performance, but poor heat dissipation, as a high heat-generating components of the heat dissipation path, almost can not be expected to conduct heat from the PCB itself resin, but from the surface of the component to the surrounding air heat dissipation. However, as electronic products have entered the era of miniaturization of components, high density mounting, and high heat generation assembly, it is not enough to rely only on the surface area of very small components to dissipate heat. At the same time, due to the large number of QFP, BGA and other surface-mounted components, the heat generated by the components is transmitted to the PCB board in large quantities, so the best way to solve the heat dissipation is to improve the direct contact with the heat-generating components of the PCB’s own heat dissipation capacity, through the PCB board to conduct out or emit out.
High heat-generating devices plus heat sink, thermal conductivity plate
When there are a few devices in the PCB when the heat generation is large (less than 3), you can add heat sink or heat pipe on the heat-generating devices, when the temperature can not be lowered, you can use a heat sink with a fan to enhance the heat dissipation effect. When the amount of heat-generating devices is more (more than 3), a large heat sink cover (board) can be used, which is customized by the location and height of the heat-generating devices on the PCB board and a special heat sink or a large flat heat sink keyed to different component height positions. The heat sink is snapped onto the component surface as a whole, and each component is in contact with the heat sink. However, the heat sink is not effective due to the poor consistency of the height of the components when they are mounted and soldered. Usually a soft thermal phase change pad is added to the component surface to improve heat dissipation.
Pay attention to air convection cooling
For devices with free convection air cooling, it is best to arrange the integrated circuits (or other devices) in a longitudinal manner or in a long horizontal manner. Pay attention to make forced ventilation and natural ventilation in the same direction; the heat dissipation of the printed circuit board in the device mainly relies on air flow, so the air flow path should be studied during the design and the device or printed circuit board should be reasonably configured. Air flow always tends to flow to the place with less resistance, so when configuring devices on the printed circuit board, avoid leaving a large empty space in a certain area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same issues.
Heat dissipation by using a reasonable alignment design
Since the resin in the board has poor thermal conductivity, and copper foil lines and holes are good conductors of heat, increasing the residual rate of copper foil and increasing the number of heat-conducting holes are the main means of heat dissipation. Placing as many metalized vias as possible, with as large an aperture and plate surface as possible, relying on the vias to help dissipate heat; planning the minimum channel width according to the current density of the device; paying special attention to the channel wiring at the joints; surfaceizing the high-current lines as much as possible; considering the use of sinks if the requirements cannot be met;
Reasonable layout
The devices on the same printed board should be arranged as much as possible according to their heat generation size and heat dissipation degree partition, the devices with small heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) are placed in the uppermost stream of the cooling airflow (entrance), and the devices with large heat generation or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed in the most downstream of the cooling airflow. Can also consider the high heat generation, radiation components specifically designed to be installed on a printed board;
In the horizontal direction, high-power devices are arranged as close as possible to the edge of the printed board in order to shorten the heat transfer path; in the vertical direction, high-power devices are arranged as close as possible to the top of the printed board in order to reduce the impact of these devices on the temperature of other devices when working. The devices with the highest power consumption and the highest heat generation are arranged near the best location for heat dissipation. Do not place the higher heat-generating devices in the corners and around the edges of the printed board, unless there are heat sinks arranged near it. When designing power resistors, choose larger devices as much as possible, and adjust the layout of the board so that it has enough space for heat dissipation.
Temperature-sensitive devices are best placed in the lowest temperature areas (such as the bottom of the device), never place it directly above the heat-generating devices, multiple devices are best staggered layout on the horizontal plane.
Process method
For some double-sided equipped with devices in the area prone to local high temperature, in order to improve the heat dissipation conditions, you can mix a small amount of fine copper material in the solder paste, and then after the flow of solder in the device below the solder joint on a certain height. So that the gap between the device and the printed board increases, increasing the convection heat dissipation.
Pay attention to the selection of materials
As the components installed on the printed board also emits part of the heat, affecting the operating temperature, the choice of materials and printed board design should take these factors into account, the hot spot temperature should not exceed 125 ℃; choose a thicker copper-clad foil as much as possible; special circumstances can choose aluminum-based, ceramic-based and other small thermal resistance of the plate; the use of multilayer board structure helps PCB thermal design; RF amplifier or LED PCB using metal Base substrate.
Avoid hot spot concentration
Avoid the concentration of hot spots on the PCB, as far as possible, the power is evenly distributed on the PCB board to maintain uniform and consistent temperature performance of the PCB surface. Often the design process to achieve a strict uniform distribution is more difficult, but be sure to avoid areas of too high a power density to avoid excessive hot spots affect the normal operation of the entire circuit.
