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Regole di cablaggio della scheda PCB ad alta frequenza
Blog PCB
Regole di cablaggio della scheda PCB ad alta frequenza

Regole di cablaggio della scheda PCB ad alta frequenza

2022-01-13
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Author:pcb

1. Component arrangement rules
1) Under normal conditions, all components should be arranged on the same side of the circuiti stampati. Only when the top components are too dense, some devices with limited height and low heat generation, such as chip resistors and chip capacitors, può essere posizionato. , paste IC, ecc. on the bottom layer.
2) On the premise of ensuring the electrical performance, i componenti devono essere posizionati sulla griglia e disposti parallelamente o perpendicolarmente l'uno all'altro, so as to be neat and beautiful. Generalmente, overlapping of components is not allowed; the arrangement of components should be compact, and the input and output components should be kept as far away as possible.
3) There may be a high potential difference between certain components or wires, and the distance between them should be increased to avoid accidental short circuit due to discharge and breakdown.
4) Components with high voltage should be arranged in places that are not easily accessible by hand during debugging.
5) Components located at the edge of the board, at least 2 board thicknesses away from the edge of the board
6) The components should be evenly distributed and uniform in density on the entire board surface.

PCB board

2. The principle of layout according to the direction of the signal
1) Usually, the positions of each functional circuit unit are arranged one by one according to the signal flow, and the components of each functional circuit are taken as the center, and the layout is carried out around it.
2) The layout of the components should facilitate the flow of signals and keep the signals in the same direction as possible. Nella maggior parte dei casi, the signal flow is arranged from left to right or from top to bottom, and the components directly connected to the input and output terminals should be placed close to the input and output connectors or connectors.

3. Prevent electromagnetic interference
1) For components with strong radiated electromagnetic fields and components sensitive to electromagnetic induction, the distance between them should be increased or shielded, and the direction of component placement should cross the adjacent printed wires.
2) Try to avoid high and low voltage devices being mixed with each other, and devices with strong and weak signals being staggered together.
3) For components that generate magnetic fields, such as transformers, speakers, induttori, ecc., attention should be paid to reducing the cutting of magnetic lines of force to printed wires during layout, e le direzioni del campo magnetico dei componenti adiacenti dovrebbero essere perpendicolari l'una all'altra per ridurre l'accoppiamento tra loro.
4) Shield the interference source, and the shield should be well grounded.
5) For circuits operating at high frequencies, the influence of i parametri di distribuzione tra i componenti devono essere considerati.

4. Suppress thermal interference
1) For the heating element, it should be arranged in a position that is conducive to heat dissipation. If necessary, a radiator or a small fan can be set up separately to reduce the temperature and reduce the impact on adjacent elements.
2) Some integrated blocks, Tubi di grande o media potenza, resistors and other components with high power consumption should be arranged in places where heat is easy to dissipate, and should be separated from other components.
3) The thermal element should be close to the measured element and away from the high temperature area, in modo da non essere influenzati da altri elementi equivalenti di potenza termica e causare malfunzionamenti.
4) When placing components on both sides, lo strato inferiore generalmente non posiziona componenti riscaldanti.

5. The layout of adjustable components
For the layout of adjustable components such as potentiometers, variable capacitors, adjustable inductance coils or micro switches, the structural requirements of the whole machine should be considered. If it is adjusted in the machine, it should be placed in the place where the printed circuit board is adjusted.

Progettazione di circuiti stampati
SMT circuit board is one of the indispensable components in surface mount design. SMT circuit board is the support of circuit components and devices in electronic products, which realizes the electrical connection between circuit components and devices. Con lo sviluppo della tecnologia elettronica, the volume of the PCB board is getting smaller and smaller, the density is getting higher and higher, and the PCB board layer is continuously increasing. Therefore, la scheda PCB deve essere nel layout complessivo, anti-interference ability, technology and manufacturability. Increasingly demanding.

The main steps of printed circuit board design
1) Draw a schematic diagram.
2) Creation of component library.
3) Establish the network connection relationship between the schematic diagram and the components on the printed board.
4) Wiring and layout.
5) Create printed board production usage data and placement production usage data.

Durante la progettazione di circuiti stampati:
1) It is necessary to ensure that the component graphics of the circuit schematic diagram are consistent with the real object and that the network connection in the circuit schematic diagram is correct.
2) The design of the printed circuit board not only considers the network connection relationship of the schematic diagram, but also considers some requirements of circuit engineering. The requirements of circuit engineering are mainly the width of power lines, ground wires and other wires, the connection of lines, High-frequency characteristics of some components, impedance of components, anti-interference, etc.
3) The installation requirements of the whole system of the printed circuit board mainly consider that the installation holes, tappi, positioning holes, punti di riferimento, etc. devono soddisfare i requisiti, and the placement positions of various components must be accurately installed in the specified positions, e allo stesso tempo, it is necessary to facilitate Installation, debug del sistema, and ventilation and heat dissipation.
4) The manufacturability of the printed circuit board and its technological requirements, it is necessary to be familiar with the design specifications and meet the production process requirements, so that the designed printed circuit board can be produced smoothly.
5) Considering that the components are easy to install, debug, and repair in production, and at the same time, the graphics, pastiglie, vias, etc. on the printed circuit board must be standardized to ensure that there will be no collision between components and easy installation.
6) The purpose of designing a printed circuit board is mainly for application, so we have to consider its practicability and affidabilità, and at the same time reduce the layer and area of the printed circuit board, riducendo così i costi, and appropriately larger pads, Through holes, wiring, etc. are conducive to the improvement of reliability, reducing the number of vias, optimizing the wiring, making it uniform in density and consistency, and making the overall layout of the board more beautiful. To make the designed circuit board achieve the expected purpose, Il layout complessivo del circuito stampato e il posizionamento dei componenti svolgono un ruolo chiave, which directly affects the installation, reliability, ventilation and heat dissipation of the entire printed circuit board, and the straight-through of wiring. Tasso.

The outer size of the printed circuit board is given priority. When the size of the PCB board is too large, the printed lines will be long, the impedance will increase, the anti-noise ability will decrease, and the cost will also increase. If it is too small, the heat dissipation will be poor, and the adjacent lines will be easily interfered. , Prima di tutto, give a reasonable positioning for the size and shape of the PCB board. Then determine the location of special components and unit circuits, etc., according to the circuit process, dividere l'intero circuito in più circuiti o moduli di unità, and center the components of each unit circuit (such as integrated circuits), e altri componenti devono essere L'ordine dei componenti è uniformemente, neatly and compactly arranged on the PCB board, ma non avvicinarti troppo a questi grandi componenti, there must be a certain distance, especially some relatively large and relatively high components to maintain a certain distance around, which is helpful for welding and Rework. For integrated circuits with high power, the color heat sink should be considered, e abbastanza spazio dovrebbe essere riservato per esso, and it should be placed in a place where the ventilation and heat dissipation of the printed board are good. Allo stesso tempo, non essere troppo concentrato. Several large components are on the same board, and there must be a certain distance, and they should be in the direction of 45 degrees. Smaller integrated circuits such as (SOP) should be arranged in the axial direction. I componenti sono allineati verticalmente e assialmente, all of which are relative to the direction of conveyance in the production process of the PCB board. In this way, i componenti sono disposti regolarmente, thereby reducing defects in welding. Light-emitting diodes used for display, etc., should be considered to be placed at the edge of the printed board because they are used for observation during the application process. Some switches, elementi di taglio, etc. should be placed where they are easily accessible. In the same frequency circuit, the distribution parameters between components should be considered. Generalmente, the distribution parameters between components should be considered in high-frequency circuits. In generale, the components should be arranged in parallel as much as possible, which is not only beautiful, ma anche facile da installare e saldare. Easy to mass-produce, components located on the edge of the circuit board must be 3-5 cm away from the edge. Quando si considera la posizione dei componenti, the thermal expansion coefficient, thermal conductivity, heat resistance and bending strength of the PCB board should be fully considered to avoid adverse effects on the components or the PCB board during production.After the position and shape of the components on the PCB are determined, the wiring of the PCB is considered.

Con la posizione dei componenti, it is a principle to route the wiring according to the location of the components, and the traces on the printed board are as short as possible. Le tracce sono brevi, occupa un piccolo canale e un'area, so the pass-through rate will be higher. The wires of the input end and the output end on the PCB board should avoid the adjacent parallel as far as possible, e posizionare un filo di terra tra i due fili. To avoid circuit feedback coupling. If the printed board is a multi-layer board, the routing direction of the signal lines of each layer is different from the routing direction of the adjacent board layers. Per alcune linee di segnale importanti, you should reach an agreement with the circuit designer. In particolare, differential signal lines should be routed in pairs, try to make them parallel, vicini l'uno all'altro, and have little difference in length. Tutti i componenti sulla scheda PCB minimizzano e accorciano i cavi e le connessioni tra i componenti. The width of the wires in the PCB board is mainly determined by the adhesion strength between the wires and the insulating layer substrate and the current value flowing through them. When the thickness of the copper foil is 0.05mm and the width is 1-1.5mm, the temperature will not be higher than 3 degrees through the current of 2A. Quando la larghezza del filo è 1.5mm, it can meet the requirements. For integrated circuits, especially digital circuits, 0.02-0.Viene solitamente selezionato 03mm. Of course, as long as it is allowed, we use wide wires as much as possible, in particolare i cavi di alimentazione e i cavi di terra sulla scheda PCB. The spacing of the wires is mainly determined by the insulation resistance and breakdown voltage between wires in a good condition. For some integrated circuits (ICs), the pitch can be less than 5-8mm from a process point of view. The curved part of the printed wire is generally arced, and the use of traces with a bend of less than 90 degrees is avoided. The right angle and the included angle will affect the electrical performance in high-frequency circuits. In short, the wiring of the printed board should be uniform, the density should be appropriate, and the consistency should be good. Evitare di utilizzare il più possibile fogli di rame di grande area nel circuito. Otherwise, when heat is generated during use for a long time, the copper foil will easily expand and fall off. If a large-area copper foil must be used, Possono essere utilizzati conduttori a griglia. The terminals of the wires are the pads. Il foro centrale del pad è più grande del diametro del cavo del dispositivo. If the pad is too large, è facile formare saldatura virtuale durante la saldatura. The outer diameter D of the pad is generally not less than (d+1.2) mm, where d is the aperture. For some components with relatively high density, the diameter of the pad is preferably (d+1.0) mm , Dopo che la progettazione del pad è completata, the outline frame of the device should be drawn around the pad of the printed board, and the text and characters should be marked at the same time. Generally, the height of the text or frame should be about 0.9mm, and the line width should be about 0.2mm. And the lines such as marked text and characters should not be pressed on the pads. Nel caso di una scheda a due strati, the underlying characters should be mirrored.

In order to make the designed product work better and effectively, the PCB board has to consider its anti-interference ability in the design, e ha uno stretto rapporto con il circuito specifico.
Particolarmente importante è la progettazione di linee elettriche e linee di terra nel circuito stampato. According to the magnitude of the current flowing through different circuit boards, try to increase the width of the power line to reduce the loop resistance. Allo stesso tempo, la direzione della linea elettrica e della linea di terra e i dati La direzione di trasmissione rimane la stessa. Contribute to the enhancement of the noise immunity of the circuit. There are logic circuits and linear circuits on the PCB, so that they are separated as much as possible. The low-frequency circuit can be grounded in parallel at a single point. The actual wiring can be connected in series and then grounded in parallel. Il circuito ad alta frequenza può essere collegato in serie in punti multipli. The ground wire should be short and thick. For high-frequency components, a large-area ground foil can be used. The ground wire should be as thick as possible. If the ground wire is very thin, the ground potential will change with the current, which will reduce the anti-noise performance. Therefore, the ground wire should be thickened so that it can reach three allowable currents on the circuit board. If the design allows the ground wire to have a diameter width of more than 2-3mm, nei circuiti digitali, most of the ground wires are arranged in a loop to improve the anti-noise capability. In the design of PCB board, it is generally routine to configure appropriate decoupling capacitors in key parts of the printed board. Connect a 10-100uF electrolytic capacitor across the line at the power input. Generally, a 0.01PF ceramic capacitor should be arranged near the 20-30 pin. Generally, Il perno dell'alimentazione del circuito integrato con 20-30 pin dovrebbe essere organizzato. Nearby, a 0.01PF magnetic chip capacitor should be arranged. For larger chips, there will be several power pins, and a decoupling capacitor should be added near them. For chips with more than 200 pins, add them on all four sides. At least two decoupling capacitors are installed. If the space is insufficient, Un condensatore al tantalio 1-10PF può anche essere disposto su 4-8 chip. For components with weak anti-interference ability and large changes in power off, the decoupling capacitor should be directly connected between the power line and the ground line of the component. , the lead wire connected to the capacitor is not easy to be too long. Dopo che la progettazione del componente e del circuito del circuito è completata, it is necessary to consider its process design. The purpose is to eliminate various adverse factors before the production starts, and at the same time, the manufacturability of the circuit board must be taken into account in order to produce high-quality products and batches. in production.

Il processo del circuito stampato è già stato coinvolto nel posizionamento e cablaggio dei componenti. The process design of the circuit board is mainly to organically assemble the circuit board and components we designed through the SMT production line, in modo da ottenere una buona connessione elettrica e raggiungere il layout di posizione dei nostri prodotti progettati. Pad design, cablaggio e anti-interferenza, etc., also need to consider whether the board we designed is easy to produce, can it be assembled with modern assembly technology - SMT technology, and at the same time, it is necessary to achieve the conditions that do not allow defective products to be produced in production. Design alto. Specifically, there are the following aspects:
1) Different SMT production lines have their own different production conditions, but in terms of the size of the PCB board, the single board size of the PCB board is not less than 200*150mm. Se il lato lungo è troppo piccolo, l'imposizione può essere utilizzata. At the same time, the ratio of length to width is 3:2 or 4:3. When the size of the circuit board is larger than 200150mm, the mechanical strength of the circuit board should be considered.
2) When the size of the circuit board is too small, it is difficult for the SMT whole line production process, and it is not easy to mass-produce. At the same time, a whole board suitable for mass production is formed, and the size of the whole board should be suitable for the size of the pasteable range.
3) In order to adapt to the placement of the production line, l'impiallacciatura dovrebbe lasciare un intervallo di 3-5mm senza posizionare alcun componente, and the panel should have a process edge of 3-8mm. Ci sono tre forme di connessione tra il bordo del processo e la scheda PCB: , with a separation groove, B ha un bordo del giro e una scanalatura di separazione, and C has a lap edge and no separation groove. Equipped with blanking technology. According to the shape of the PCB board, Ci sono diversi tipi di puzzle. The process edge of the PCB board has different positioning methods according to different models. Some have positioning holes on the process edge. The diameter of the hole is 4-5 cm. In comparison, the positioning accuracy is higher than that of the edge. The positioning hole positioning model should be equipped with positioning holes when processing PCB boards, and the hole design should be standard to avoid inconvenience to production.
4) In order to better locate and achieve higher placement accuracy, it is necessary to set a reference point for the PCB board. Whether there is a reference point and whether the setting is good or bad directly affects the mass production of the SMT production line. The shape of the reference point can be square, circle, triangle, etc. And the diameter should be within the range of 1-2mm, e la circonferenza del punto di riferimento dovrebbe essere compresa tra 3 e 5 mm, senza inserire componenti e cavi. At the same time, the reference point should be smooth and flat, without any pollution. Il design del punto di riferimento non dovrebbe essere troppo vicino al bordo della scheda, but a distance of 3-5mm.
5) From the overall production process, the shape of the board is pitch-shaped, especially for wave soldering. The use of a rectangle is convenient for conveying. Se c'è uno spazio nella scheda PCB, lo spazio dovrebbe essere riempito sotto forma di un bordo di processo. For a single SMT board, è consentita una lacuna. However, la scanalatura non è facile da essere troppo grande e dovrebbe essere inferiore a 1/3 della lunghezza del lato.
In short, the generation of defective products is possible in every link, but as for the PCB board design, dovremmo considerare tutti gli aspetti, in modo che non solo possa raggiungere lo scopo di progettare il prodotto, but also be suitable for the SMT production line in production. Produzione di massa, try our best to design high-quality PCB board, e ridurre la possibilità di prodotti difettosi.