PCB Блог - техника проектирования теплоотвода панелей PCB

1. The importance of PCB board thermal design
The electrical energy consumed by electronic equipment during operation, усилитель мощности радиочастоты, FPGA chips, электроэнергетическая продукция, in addition to useful work, большая часть теплоотвода. The heat generated by the electronic equipment causes the internal temperature to rise rapidly. Если тепло не растает вовремя, the equipment will continue to heat up, оборудование устаревает из - за перегрева, and the reliability of the electronic equipment will decrease. SMT повышает плотность установки электронного оборудования, уменьшение площади эффективного теплоотвода, and the temperature rise of the equipment seriously affects the reliability. поэтому, the research on thermal design is very important. удаление тепла на панели PCB является очень важным звеном, so what is the heat dissipation technique of the PCB board circuit board, Давайте обсудим это вместе. For electronic equipment, во время эксплуатации будет произведено определенное количество тепла, so that the internal temperature of the equipment rises rapidly. Если тепло не растает вовремя, the equipment will continue to heat up, оборудование может утратить силу из - за перегрева. The reliability of the electronic equipment Performance will decrease. поэтому, важное значение имеет хорошая термообработка платы.

2. Analysis of PCB board temperature rise factors
The direct cause of the temperature rise of the printed board is due to the existence of circuit power consumption devices. мощность электронного оборудования различной степени, интенсивность нагрева изменяется в зависимости от размера потребляемой энергии.
Two phenomena of temperature rise in printed boards:
(1) Local temperature rise or large area temperature rise;
(2) Short-term temperature rise or long-term temperature rise. затраты времени на анализ тепловой работы панели PCB, it is generally analyzed from the following aspects.
2.1 Electrical power consumption
(1) Analyze the power consumption per unit area;
(2) Analyze the distribution of power consumption on the PCB.
2.2 The structure of the printed board
(1) The size of the printed board;
(2) The material of the printed board.
2.3 How to install the printed board
(1) Installation method (such as vertical installation, horizontal installation);
(2) The sealing condition and the distance from the casing.
2.4 Thermal radiation
(1) The emissivity of the printed board surface;
(2) The temperature difference between the printed board and the adjacent surface and their temperature
2.5 Heat conduction
(1) Install the radiator;
(2) Conduction of other installation structures.
2.6 Thermal convection
(1) Natural convection;
(2) Forced cooling convection.
The analysis of the above-mentioned factors from the PCB board is an effective way to solve the temperature rise of the printed board. в продуктах и системах эти факторы часто взаимосвязаны и зависят друг от друга. Most of the factors should be analyzed according to the actual situation. Конкретные фактические обстоятельства могут быть более точно определены или оценены в таких параметрах, как повышение температуры и расход энергии.

3. Some methods of PCB board thermal design
1. Heat dissipation through the PCB board itself
At present, the widely used PCB boards are copper-clad/эпоксидный стеклопластик или бакелитовый материал, and a small amount of paper-based copper-clad boards are used. Хотя эти плиты обладают отличными электрическими свойствами и обрабатываемыми свойствами, их дисперсия. As a heat dissipation method for высокий-heating components, Вряд ли можно ожидать теплопередачи от самих смол PCB, but to dissipate heat from the surface of the component to the surrounding air. Однако, as electronic products have entered the era of miniaturization of components, монтаж высокой плотности, высокотемпературная сборка, it is not enough to rely on the surface of a component with a very small surface area to dissipate heat. одновременно, due to the large use of surface mount components such as QFP and BGA, количество тепла, получаемого от сборки, переносится на панель PCB. поэтому, the solution to heat dissipation is to improve the heat dissipation capacity of the PCB board directly in contact with the heating element, и перетащите его через PCB - панель. Go out or send out.
2. High heat-generating components plus radiator and heat conduction plate
When a small number of components in the PCB board generate a large amount of heat (less than 3), можно добавить радиатор или тепловую трубу на элемент нагрева. When the temperature cannot be lowered, радиатор с вентилятором можно использовать для увеличения теплового излучения. When the number of heating devices is large (more than 3), a large heat dissipation cover (board) can be used, which is a special heat sink customized according to the position and height of the heating device on the PCB or a large flat heat sink Cut out different component height positions. полная петля крышки теплоотвода на поверхности элемента, and it is in contact with each element to dissipate heat. Однако, the heat dissipation effect is not good due to the poor consistency of height during assembly and welding of components. обычно, для повышения теплоотдачи на поверхности элемента добавлена тепловая подушка мягкой фазы.
3. оборудование для охлаждения воздуха с свободной конвекцией, the integrated circuits (or other devices) are arranged vertically or horizontally.
4. Use reasonable wiring design to achieve heat dissipation
Because the resin in the plate has poor thermal conductivity, медная фольга провода и отверстия являются хорошим проводником тепла, увеличение остаточности медной фольги и увеличение теплопроводных отверстий являются главными средствами теплоотвода. оценка теплоотдачи панелей PCB, it is necessary to calculate the equivalent thermal conductivity of a composite material composed of various materials with different thermal conductivity-an insulating substrate for a PCB board.
5. The devices on the same printed board should be arranged as far as possible according to their calorific value and degree of heat dissipation. Devices with low calorific value or poor heat resistance (such as small signal transistors, малая интегральная схема, electrolytic capacitors, сорт.) should be placed On the upstream (inlet) of the cooling airflow, devices with large heat or heat resistance (such as power transistors, large-scale integrated circuits, сорт.) are placed downstream of the cooling airflow.
6. In the horizontal direction, оборудование большой мощности как можно ближе к краю печатной пластины, чтобы сократить путь теплопередачи; в вертикальном направлении, high-power devices are placed as close as possible to the top of the printed board to reduce the temperature of other devices when these devices work. влияние.
7. теплоотдача от щитка оборудования в основном зависит от потока воздуха, so the air flow path should be studied during the design, устройство или печатная плата должны быть разумно настроены. When air flows, Он всегда склоняется к низкому сопротивлению, so when configuring devices on a printed circuit board, не покидать район. Следует также обратить внимание на одну и ту же проблему при размещении нескольких печатных плат во всей машине.
8. The temperature-sensitive device is placed in a temperature area (such as the bottom of the device). Never place it directly above the heating device. расположение нескольких устройств на перекрещивающихся горизонталях.
9. размещение тепловыделяющих и тепловыделяющих элементов вблизи места. Do not place high-heating devices on the corners and peripheral edges of the printed board, если только рядом нет радиатора. When designing the power resistor, выбрать максимальное устройство, and make it have enough space for heat dissipation when adjusting the layout of the printed board.
10. The RF power amplifier or LED PCB board adopts a metal base substrate.
11. Avoid the concentration of hot spots on the PCB board, по возможности равномерно распределять питание на панелях PCB, and keep the surface temperature performance of the PCB board uniform and consistent. в процессе проектирования обычно трудно обеспечить строгое равномерное распределение, but areas with too high power density must be avoided to prevent hot spots from affecting the normal operation of the entire circuit. если возможно, it is necessary to analyze the thermal performance of printed circuits. например, the thermal performance index analysis software module added in some PCB board design software can help designers optimize the circuit design.

4. Summary
4.1 Material selection
(1) The temperature rise of the wires of the PCB board due to the passing current plus the specified ambient temperature should not exceed 125 degree Celsius (commonly used typical value. It may be different depending on the selected board). Since the components installed on the printed board also emit some heat, это влияет на рабочую температуру, Эти факторы следует принимать во внимание при выборе материалов и дизайна печатных плат, and the hot spot temperature should not exceed 125 degree Celsius. по возможности выбрать бронзовый лист.
(2) In special cases, алюминиевая группа, ceramic-based, можно также выбрать другие пластины с низким тепловом сопротивлением.
(3) Adopting multilayer board structure is helpful for PCB board thermal design.
4.2 Ensure that the heat dissipation channel is unblocked
(1) Make full use of the components arrangement, медная оболочка, открыть окно и отверстие для отвода тепла, создать разумный и эффективный канал для снижения теплового сопротивления, чтобы обеспечить плавный вывод тепла из панелей PCB.
(2) The setting of heat dissipation through holes Design some heat dissipation through holes and blind holes, эффективное увеличение площади теплоотвода, уменьшение теплового сопротивления, and increase the power density of the circuit board. например, set up via holes on the pads of LCCC devices. в процессе производства схемы заполнения припоя, чтобы повысить теплопроводность. теплоотдача от работы схемы может быть быстро перемещена через отверстие или слепое отверстие на металлический теплоноситель или медную подушку на обратной стороне.. в определенных случаях, специально спроектированная и используемая плата с теплоотводящим слоем. The heat dissipation material is generally copper/молибден и другие материалы, such as printed boards used on some module power supplies.
(3) The use of thermally conductive materials In order to reduce the thermal resistance in the thermal conduction process, использование теплопроводных материалов в соприкосновении между приборами с высоким энергопотреблением и основной пластиной для повышения теплопроводности.
(4) The process method is likely to cause local high temperature in some areas where the device is mounted on both sides. для улучшения условий теплоотвода, a small amount of small copper can be mixed into the solder paste, после непрерывной сварки под оборудованием будет определенное количество сварных точек. high. увеличение зазора между оборудованием и печатными платами, and the convection heat dissipation is increased.
4.3 Arrangement requirements of components
(1) Perform software thermal analysis on the PCB board, and design and control the internal temperature rise;
(2) It can be considered to specially design and install components with high heat generation and large radiation on a printed circuit board;
(3) The heat capacity of the board is evenly distributed. обратите внимание на то, что не следует концентрировать сборки большой мощности. If it is unavoidable, place short components upstream of the airflow and ensure that sufficient cooling air flows through the heat-consumption concentrated area;
(4) Make the heat transfer path as short as possible;
(5) Make the heat transfer cross section as large as possible;
(6) The layout of components should take into account the influence of heat radiation on surrounding parts. Heat sensitive parts and components (including semiconductor devices) should be kept away from heat sources or isolated;
(7) (Liquid medium) Keep the capacitor away from the heat source;
(8) Pay attention to the direction of forced ventilation and natural ventilation;
(9) The additional sub-boards and device air ducts are in the same direction as the ventilation;
(10) As far as possible, make the intake and exhaust have a sufficient distance;
(11) The heating device should be placed above the product as much as possible, and should be placed in the air flow channel when conditions permit;
(12) Components with high heat or high current should not be placed on the corners and peripheral edges of the printed board. Они должны быть установлены на радиаторе как можно дольше, and kept away from other components, and ensure that the heat dissipation channel is unobstructed;
(13) (Small signal amplifier peripheral devices) Try to use devices with small temperature drift;
(14) Use metal chassis or chassis to dissipate heat as much as possible.4.4 Requirements for wiring
(1) Board selection (reasonable design of printed board structure);
(2) Wiring rules;
(3) Plan the channel width according to the current density of the device; pay special attention to the channel wiring at the junction;
(4) The high-current lines should be as surface as possible; if the requirements cannot be met, the use of bus bars can be considered;
(5) To minimize the thermal resistance of the contact surface. поэтому, the heat conduction area should be enlarged; the contact surface should be flat and smooth, and thermally conductive silicone grease can be coated if necessary;
(6) Consider stress balance measures for thermal stress points and thicken the lines;
(7) The heat-dissipating copper skin needs to adopt the window method of heat dissipation stress, and use the heat-dissipating solder mask to open the window properly;
(8) If possible, use large-area copper foil on the surface;
(9) Use larger pads for the ground mounting holes on the printed board to make full use of the mounting bolts and the copper foil on the surface of the printed board for heat dissipation;
(10) Place as many metalized vias as possible, диафрагма и поверхность диска должны быть максимально крупными, relying on vias to help heat dissipation;
(11) Supplementary means for device heat dissipation;
(12) In the case that the large-area copper foil on the surface can be guaranteed, the method of adding a heat sink may not be used for economic considerations;
(13) Calculate the appropriate heat dissipation copper area of the PCB board surface according to the power consumption of the device, the ambient temperature and the allowable junction temperature (guarantee principle tj≤(0.15815½ * 0.8)tjmax).