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PCB Circuit Board Heat Dissipation Problems

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For electronic equipment, work will produce a certain amount of heat, so that the internal temperature of the device rises rapidly, if not timely dissemination of this heat, the device will continue to heat up, the device will fail due to overheating, and the reliability of the electronic equipment will decline. Therefore, it is very important to carry out a good heat dissipation treatment of the circuit board. the heat dissipation of the PCB circuit board is a very important part of the thermal design, the PCB is the most important source of heat bearing, the source of its heat mainly has three aspects:

A. Heat generation from electronic components.

B. Heat generated by the PCB itself.

C. Heat from other parts.

In these three sources of heat, the component's heat generation is the largest, is the main source of heat, followed by the heat generated by the PCB board, external incoming heat depends on the overall thermal design of the system. In the actual PCB design, engineers need to consider the heat dissipation issues including the choice of board, component selection, component layout and other aspects.

Heat dissipation through the PCB board itself is currently widely used PCB boards are copper/epoxy glass cloth substrate or phenolic resin glass cloth substrate, and a small number of paper-based copper-clad boards. Although these substrates have excellent electrical properties and processing performance, but poor heat dissipation, as a high heat-generating components of the heat dissipation pathway, almost can not be expected by the PCB itself resin conduction of heat, but from the surface of the components to the surrounding air heat dissipation.

However, as electronic products have entered the era of miniaturization of components, high-density installation, high heat generation assembly, if you rely only on the surface area of the component surface is very small to dissipate heat is very insufficient. At the same time, due to the large number of QFP, BGA and other surface-mounted components, components generated by a large number of heat to the PCB board, so the best way to solve the problem of heat dissipation is to improve the direct contact with the heating components of the PCB's own heat dissipation capabilities, through the PCB board to conduct or disseminate out.

A. Add heat dissipation copper foil and adopt large area power ground copper foil.

B. Thermal over-hole.

C. Expose copper on the back of the IC to reduce the thermal resistance between the copper skin and the air.

PCB -14

PCB layout design in the heat dissipation processing

Layout belongs to the whole PCB thermal design is an important part of the PCB heat dissipation has a pivotal role. As a designer, you need to consider the following aspects when PCB layout:

A. Consider the high heat, radiation components centrally designed to be installed on another PCB board, so as to carry out a separate centralized ventilation and cooling, to avoid mutual interference with the motherboard.

B. PCB board surface heat capacity evenly distributed, do not put the large power consumption devices centralized deployment, if it can not be avoided, the shorter components in the upstream of the airflow, and to ensure that sufficient cooling air flow through the heat consumption concentration area.

C. Make the heat transfer path as short as possible. Make the heat transfer cross-section as large as possible.

D. Component layout should take into account the impact of heat radiation on the surrounding parts. Heat-sensitive parts, components (including semiconductor devices) should be away from the heat source or isolate it.

E. Pay attention to forced ventilation and natural ventilation in the same direction. Additional sub-panel, device ducts and ventilation in the same direction.

F. Heat or current components should not be placed in the corners of the PCB board and around the edges, as far as possible to install heat sinks, and away from other devices, and to ensure that the heat dissipation channel is clear.

G. Temperature detection devices placed in the hottest position.

H. The same printed circuit board devices should be as far as possible according to the size of its heat and the degree of heat dissipation zoning arrangement, heat small or poor thermal devices (such as small-signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) placed in the cooling airflow of the most upstream (at the entrance), heat large or heat-resistant device (eg, power transistors, large-scale integrated circuits, etc.) placed in the most downstream of the cooling airflow.

I. In the horizontal direction, high-power devices as close as possible to the edge of the printed circuit board layout, in order to shorten the heat transfer path; in the vertical direction, high-power devices as close as possible to the printed circuit board above the layout, in order to reduce the work of these devices on the temperature of other devices.

J. Equipment within the printed circuit board heat mainly rely on air flow, so the design should study the air flow path, a reasonable configuration of the device or printed circuit board. Air flow always tends to flow in the place of low resistance, so the configuration of the device on the printed circuit board, to avoid leaving a large airspace in a region. The whole machine in the configuration of multiple printed circuit boards should also pay attention to the same problem.

K. More sensitive to the temperature of the device is best placed in the temperature of the lowest region (such as the bottom of the device), do not put it in the heat device is directly above the multiple devices is best in the horizontal plane staggered layout.

L. In the design of the power resistor as far as possible to choose a larger device, and in adjusting the layout of the printed circuit board so that there is enough space for heat dissipation.

M. Avoid the concentration of hot spots on the PCB, as far as possible, the power is evenly distributed on the PCB board, to maintain the uniformity and consistency of the PCB surface temperature performance.


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