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Capacità di progettazione di dissipazione del calore della scheda PCB
Blog PCB
Capacità di progettazione di dissipazione del calore della scheda PCB

Capacità di progettazione di dissipazione del calore della scheda PCB

2021-12-31
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Author:pcb

1. The importance of PCB board thermal design
The electrical energy consumed by electronic equipment during operation, come amplificatori di potenza a radiofrequenza, FPGA chips, e prodotti energetici, in addition to useful work, è per lo più convertito in calore per dissipazione. Il calore generato dall'apparecchiatura elettronica fa aumentare rapidamente la temperatura interna. Se il calore non viene dissipato nel tempo, l'attrezzatura continuerà a riscaldarsi, the device will fail due to overheating, e l'affidabilità delle apparecchiature elettroniche diminuirà. SMT increases the installation density of electronic equipment, riduce l'area efficace di dissipazione del calore, and the temperature rise of the equipment seriously affects the reliability. Pertanto, the research on thermal design is very important. La dissipazione del calore della scheda PCB è un collegamento molto importante, so what is the heat dissipation technique of the PCB board circuit board, Parliamone insieme.. For electronic equipment, una certa quantità di calore è generata durante il funzionamento, so that the internal temperature of the equipment rises rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, e il dispositivo si guasterà a causa del surriscaldamento. The reliability of the electronic equipment Performance will decrease. Pertanto, è molto importante condurre un buon trattamento di dissipazione del calore sul circuito stampato.

Scheda PCB

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. Electronic devices all have power consumption to varying degrees, e l'intensità di riscaldamento varia con la dimensione del consumo energetico.
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. Quando si analizza il consumo di energia termica della scheda 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.
L'analisi dei fattori sopra menzionati dalla scheda PCB è un modo efficace per risolvere l'aumento di temperatura della scheda stampata. These factors are often related and dependent on each other in a product and system. La maggior parte dei fattori dovrebbe essere analizzata in base alla situazione reale. Le condizioni effettive specifiche possono essere calcolate con maggiore precisione o stimate parametri quali aumento della temperatura e consumo energetico.

3. Some methods of PCB board thermal design
1. Heat dissipation through the PCB board itself
At present, Le schede PCB ampiamente utilizzate sono rivestite di rame/epoxy glass cloth substrates or phenolic resin glass cloth substrates, e una piccola quantità di schede rivestite di rame a base di carta vengono utilizzate. Although these substrates have excellent electrical properties and processing properties, hanno scarsa dissipazione del calore. As a heat dissipation method for alto-heating components, è quasi impossibile aspettarsi che il calore dalla resina del PCB stesso conduca il calore, but to dissipate heat from the surface of the component to the surrounding air. Tuttavia, as electronic products have entered the era of miniaturization of components, montaggio ad alta densità, and high-heating assembly, non basta affidarsi alla superficie di un componente con una superficie molto piccola per dissipare il calore. At the same time, Grazie al grande utilizzo di componenti per montaggio superficiale come QFP e BGA, the heat generated by the components is transferred to the PCB board in a large amount. Pertanto, the solution to heat dissipation is to improve the heat dissipation capacity of the PCB board directly in contact with the heating element, e condurlo attraverso la scheda PCB. 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), un radiatore o tubo termico può essere aggiunto al componente riscaldante. When the temperature cannot be lowered, un radiatore con ventilatore può essere utilizzato per aumentare la radiazione termica. 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. Il coperchio di dissipazione del calore è interamente fibbiato sulla superficie dell'elemento, and it is in contact with each element to dissipate heat. Tuttavia, the heat dissipation effect is not good due to the poor consistency of height during assembly and welding of components. Di solito, a soft thermal phase change thermal pad is added on the surface of the component to improve the heat dissipation effect.
3. Per l'attrezzatura che adotta il raffreddamento ad aria a convezione libero, 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, e le linee e i fori della lamina di rame sono buoni conduttori di calore, increasing the remaining rate of the copper foil and increasing the heat-conducting holes are the main means of heat dissipation. Per valutare la capacità di dissipazione del calore di una scheda 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, small-scale integrated circuits, condensatori elettrolitici, etc.) should be placed On the upstream (inlet) of the cooling airflow, devices with large heat or heat resistance (such as power transistors, circuiti integrati su larga scala, etc.) are placed downstream of the cooling airflow.
6. In direzione orizzontale, high-power devices are placed as close to the edge of the printed board as possible to shorten the heat transfer path; in the vertical direction, I dispositivi ad alta potenza sono posizionati il più vicino possibile alla parte superiore della scheda stampata per ridurre la temperatura di altri dispositivi quando questi dispositivi funzionano. Impact.
7. The heat dissipation of the printed board in the equipment mainly relies on air flow, quindi il percorso del flusso d'aria dovrebbe essere studiato durante la progettazione, and the device or printed circuit board should be reasonably configured. Quando scorre l'aria, it always tends to flow in places with low resistance, quindi quando si configurano dispositivi su un circuito stampato, evitare di lasciare un ampio spazio aereo in una determinata area. The configuration of multiple printed circuit boards in the whole machine should also pay attention to the same problem.
8. The temperature-sensitive device is placed in a temperature area (such as the bottom of the device). Non posizionarlo mai direttamente sopra il dispositivo di riscaldamento. Multiple devices are arranged in a staggered horizontal plane.
9. Arrange power dissipation and heat-generating components near the heat dissipation location. Non posizionare dispositivi ad alto riscaldamento sugli angoli e sui bordi periferici della scheda stampata, unless a heat sink is arranged near it. Quando si progetta la resistenza di potenza, choose a larger device as much as possible, e farlo avere abbastanza spazio per la dissipazione del calore quando si regola il layout della scheda stampata.
10. L'amplificatore di potenza RF o la scheda PCB LED adotta un substrato di base metallica.
11. Evitare la concentrazione di punti caldi sulla scheda PCB, distribute the power evenly on the PCB board as much as possible, e mantenere le prestazioni di temperatura superficiale della scheda PCB uniformi e coerenti. It is often difficult to achieve strict uniform distribution during the design process, ma le aree con densità di potenza troppo elevata devono essere evitate per evitare che i punti caldi influenzino il normale funzionamento dell'intero circuito. If possible, è necessario analizzare le prestazioni termiche dei circuiti stampati. For example, Il modulo software di analisi dell'indice di prestazione termica aggiunto in alcuni software di progettazione della scheda PCB può aiutare i progettisti a ottimizzare la progettazione del circuito.

Scheda PCB

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(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, che influisce sulla temperatura di esercizio, questi fattori devono essere presi in considerazione nella selezione dei materiali e nella progettazione del cartone stampato, and the hot spot temperature should not exceed 125 . Scegli il più spesso rivestimento di rame il più possibile.
(2) In special cases, a base di alluminio, ceramic-based, e altre piastre con bassa resistenza termica possono essere selezionate.
(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, pelle di rame, window opening and heat dissipation holes to establish a reasonable and effective low thermal resistance channel to ensure that the heat is smoothly exported from the PCB board.
(2) The setting of heat dissipation through holes Design some heat dissipation through holes and blind holes, which can effectively increase the heat dissipation area and reduce the thermal resistance, e aumentare la densità di potenza del circuito stampato. For example, Impostazione tramite fori sui pad dei dispositivi LCCC. Solder fills it in the circuit production process to improve the thermal conductivity. Il calore generato durante il funzionamento del circuito può essere rapidamente trasferito allo strato di dissipazione del calore metallico o al pad di rame sul retro attraverso i fori passanti o fori ciechi da dissipare. In some specific cases, un circuito stampato con uno strato di dissipazione del calore è appositamente progettato e utilizzato. The heat dissipation material is generally copper/molibdeno e altri materiali, 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, thermally conductive materials are used on the contact surface between the high power consumption device and the substrate to improve the heat conduction efficiency.
(4) The process method is likely to cause local high temperature in some areas where the device is mounted on both sides. In order to improve the heat dissipation conditions, una piccola quantità di piccolo rame può essere mescolata nella pasta di saldatura, and there will be a certain amount of solder joints under the device after flow soldering. high. Il divario tra il dispositivo e la scheda stampata è aumentato, 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. Be careful not to place high-power components in a concentrated manner. Se è inevitabile, 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. They should be installed on the radiator as long as possible, e tenuto lontano da altri componenti, 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. For this reason, l'area di conduzione termica deve essere ampliata; la superficie di contatto deve essere piana e liscia, 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, e l'apertura e la superficie del disco devono essere il più grande possibile, 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 ¤(0.5ï½ 0.8)tjmax).