PCB Circuit Board Heat Treatment

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1. High heat generating device with heat sink and heat conducting plate

When there are a few devices on the PCB that generate a large amount of heat (less than 3), a heat sink or a heat pipe can be added to the heat generating device. If the temperature cannot be lowered, a heat sink with a fan can be used to enhance heat dissipation. When the number of heat generating devices is large (more than 3), a large heat sink (board) can be used. It is a dedicated heat sink customized according to the position and height of the heat generating device on the PCB board or a large flat plate radiator. The heat shield is integrally fastened to the component surface and is in contact with each component to dissipate heat. However, due to the poor consistency of the components during welding, the heat dissipation effect is not good. A soft thermal phase change thermal pad is usually added to the component surface to improve heat dissipation.

2. Cooling through the PCB board itself

Currently, widely used PCB sheets are copper-clad/epoxy glass cloth substrates or phenolic resin glass cloth substrates, and a small amount of paper-based copper-clad sheets are used. Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation properties. As a heat dissipation path for high-heat-generating components, it is hardly expected to conduct heat from the resin of the PCB itself, but to dissipate heat from the surface of the component to the surrounding air. However, as electronic products have entered the era of miniaturization, high-density mounting, and high-heating assembly, it is not enough to dissipate heat from the surface of a component with a very small surface area. At the same time, due to the large number of surface mount components such as QFP and BGA, the heat generated by the components is transferred to the PCB in a large amount. Therefore, the best way to solve the heat dissipation is to improve the heat dissipation capability of the PCB itself in direct contact with the heat generating components. Conducted out or emitted.

3. Use reasonable wiring design to achieve heat dissipation

Since the resin in the sheet has poor thermal conductivity, and the copper foil line and the hole are good conductors of heat, increasing the copper foil residual ratio and increasing the heat conducting hole are the main means of heat dissipation.

To evaluate the heat dissipation capability of the PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of the composite material composed of various materials having different thermal conductivity.

4. For devices that use free convection air cooling.

It is preferable to arrange the integrated circuits (or other devices) in a vertically long manner or a horizontally long manner.

5. The devices on the same printed board should be arranged according to their heat generation and dissipation as far as possible.

Devices with low heat generation or poor heat resistance (such as small signal transistors, small scale integrated circuits, electrolytic capacitors, etc.) should be placed at the uppermost flow (inlet) of the cooling airflow, devices with large heat or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the most downstream of the cooling airflow.
 

PCB Circuit Board Heat Treatment

6. In the horizontal direction, place high-power devices as close to the edges of the printed board as possible to shorten the heat transfer path.

In the vertical direction, place high-power devices as close to the top of the printed board as possible to reduce the effect of temperature on other devices.

7. Place temperature-sensitive devices in the lowest temperature area, such as the bottom of the device. Avoid placing them directly above heating devices, and stagger multiple devices horizontally if possible.

8. The airflow path should be considered during the design, as the heat dissipation of the printed circuit board depends mainly on the airflow. When air flows, it tends to flow in areas with low resistance. Therefore, avoid leaving large air spaces in certain areas when configuring devices on the printed circuit board. The same applies when configuring multiple printed circuit boards in the whole machine.

9. Avoid hot spots on the PCB by distributing power evenly across the board. Keep the temperature performance of the PCB surface uniform and consistent. If necessary, perform a thermal performance analysis of printed circuits. Thermal performance index analysis software modules, added in some professional PCB design software, can help optimize circuit design.

10. Place devices with the highest power consumption and maximum heat generation near the best position for heat dissipation. Avoid placing higher heat generating components on the corners and peripheral edges of the printed board unless a heat sink is placed near it.

11. High heat dissipation devices should minimize the thermal resistance between them when connected to the substrate. Use thermal conductive materials, such as a layer of thermal silica gel, on the bottom surface of the chip to maintain a contact area for the device to dissipate heat.

12. When connecting devices to the substrate:

(1) Minimize the length of the device leads;

(2) Consider the thermal conductivity of the lead material when selecting a high-power device. If possible, choose the maximum cross-section of the lead;

(3) Select a device with a large number of pins.

13. When selecting a device package:

(1) Consider the package description of the device and its thermal conductivity;

(2) Provide a good thermal conduction path between the substrate and the device package;

(3) Avoid air partitions on the heat conduction path. Use a thermally conductive material for filling if necessary.

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