Common PCB layout constraint principles
The following aspects are often considered in PCB component layout:
(1) Does the PCB shape match the whole machine?
(2) Is the spacing between elements reasonable? Are there any horizontal or high level conflicts?
(3) Does PCB need to be assembled? Are process edges reserved? Are mounting holes reserved? How to arrange locating holes?
(4) How to place and cool the power module?
(5) Are the components that need to be replaced frequently placed at a convenient location? Is the adjustable element easy to adjust?
(6) Is the distance between the thermal element and the heating element considered?
(7) How about the EMC performance of the whole board? How can the layout effectively enhance the anti-interference capability?
As for the spacing between components, based on the different distance requirements of different packages and Altium Designer’s own characteristics, if rules are set to constrain, the setting is too complex and difficult to implement. Generally, draw lines on the mechanical layer to mark the peripheral dimensions of the components, as shown in Figure 1. In this way, when other components are close to each other, their spacing can be roughly known. This is very practical for beginners, and can also enable beginners to develop good PCB design habits.
Element arrangement principle
(1) Under normal conditions, all components should be arranged on the same side of the PCB. Only when the top level components are too dense can some components with limited height and low heat generation (such as chip resistance, chip capacitance, chip IC, etc.) be placed on the bottom layer.
(2) On the premise of ensuring the electrical performance, the elements shall be placed on the grid and arranged in parallel or vertical to each other, so as to be neat and beautiful. In general, overlapping of components is not allowed. The components shall be arranged compactly. The input components and output components shall be separated as far as possible without crossing.
(3) There may be high voltage between some components or wires, so their distance shall be increased to avoid accidental short circuit caused by discharge and breakdown. Pay attention to the layout space of these signals as much as possible during layout.
(4) Components with high voltage shall be arranged at places where it is not easy to reach during commissioning.
(5) The element located at the edge of the plate shall be two plate thicknesses away from the edge of the plate as far as possible.
(6) The components shall be evenly distributed on the whole board surface, and one area shall not be dense and the other area shall not be loose, so as to improve the reliability of the product.
According to the layout principle of signal trend
(1) After placing the fixed components, arrange the position of each functional circuit unit one by one according to the flow direction of the signal, and take the core component of each functional circuit as the center, and carry out local layout around it.
(2) The layout of elements shall be convenient for signal flow, so as to keep the signal as consistent as possible. In most cases, the flow direction of the signal is arranged from left to right or from top to bottom. The components directly connected to the input and output terminals should be placed near the input and output connectors or connectors.
Prevent electromagnetic interference
(1) For components with strong radiation electromagnetic field and components sensitive to electromagnetic induction, the distance between them shall be increased, or shielding cover shall be considered for shielding.
(2) Try to avoid high and low voltage components mixing with each other and components with strong and weak signals interlacing.
(3) For components that will generate magnetic fields, such as transformers, loudspeakers, inductors, etc., attention should be paid to reducing the cutting of magnetic force lines on printed wires during layout. The magnetic field directions of adjacent components should be perpendicular to each other to reduce the coupling between them. Figure 2 shows the arrangement of inductors 90 ° vertically.
(4) The interference source or easily interfered module shall be shielded, and the shielding cover shall be well grounded. The planning of the shield is shown in Figure 3.
Thermal interference suppression
(1) For heating elements, priority should be given to the position conducive to heat dissipation. If necessary, a radiator or small fan can be set separately to reduce the temperature and the impact on adjacent elements, as shown in Figure 4.
(2) Some high power consumption integrated blocks, high-power tubes, resistors, etc., should be placed in places where heat dissipation is easy, and should be separated from other components at a certain distance. As the leading online authorized agent of electronic components in China, Weiyang Mall is selling more than a variety of models of resistors, mos tubes, etc., to meet your demand for genuine spot purchase of components.
(3) The thermal element shall be close to the element under test and away from the high temperature area, so as to avoid the influence of other thermal power equivalent elements, which may cause misoperation.
(4) When the element is placed on both sides, the heating element is generally not placed on the bottom layer.
Layout principle of adjustable components
For the layout of adjustable components such as potentiometers, variable capacitors, adjustable inductance coils, microswitches, etc., the structural requirements of the whole machine should be considered: if it is adjusted outside the machine, its position should adapt to the position of the adjustment knob on the chassis panel; If it is adjusted in the machine, it should be placed on the PCB where it is easy to adjust.