To do a good job of a PCB circuit board, in addition to the main circuit performance, electrical characteristics such as EMI, EMC, ESD (electrostatic discharge), signal integrity, etc. must also be considered, and the heat dissipation of the mechanical structure and high power consumption chips must also be considered. Then consider the aesthetics of the circuit board on the basis of it, just like doing artistic sculptures, and consider every detail of it

1. Common PCB layout design principles

There are often the following considerations in the layout of PCB components.

(1) Does the PCB shape match the whole machine?

(2) Is the spacing between components reasonable? Is there any level or height conflict?

(3) Does the PCB require imposition? Whether to reserve a craft edge? Are mounting holes reserved? How to arrange the positioning holes?

(4) How to place and dissipate the power module?

(5) Is it convenient to replace components that need to be replaced frequently? Are the adjustable elements 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 to layout can effectively enhance the anti-interference ability?

2. 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 a shielding cover should be added for shielding.

(2) Try to avoid mixing of high and low voltage components and interleaving of components with strong and weak signals.

(3) For components that generate magnetic fields, such as transformers, speakers, inductors, etc., attention should be paid to reducing the cutting of the printed wires by the magnetic lines of force during the layout. The magnetic field directions of adjacent components should be perpendicular to each other to reduce the coupling between each other. The figure shows the layout of the inductor and the inductor perpendicular to 90°.

(4) Shield the interference source or modules that are susceptible to interference, and the shielding cover should have a good grounding. The plan of the shield is shown in the figure.

Vertical 90° layout between inductor and inductor

3. Suppress thermal interference

(1) For heating elements, they should be arranged in a position that is conducive to heat dissipation. If necessary, a radiator or small fan can be installed separately to reduce the temperature and reduce the impact on neighboring elements, as shown in the figure.

(2) Some large power-consumption integrated blocks, high-power tubes, resistors, etc., should be placed in places where heat is easy to dissipate, and separated from other components by a certain distance.

Shield planning

Thermal considerations for layout

4. The principle of adjustable component layout

For the layout of adjustable components such as potentiometers, variable capacitors, adjustable inductance coils, micro switches, etc., the structural requirements of the whole machine should be considered: if it is adjusted outside the machine, its position should be adapted to the position of the adjustment knob on the chassis panel ; If it is adjusted inside the machine, it should be placed on the PCB where it is easy to adjust.

5. Component arrangement principle

(1) Under normal conditions, all components should be arranged on the same side of the PCB. Only when the top components are too dense, can some components with limited height and low heat generation (such as chip resistors, chip capacitors, Chip IC, etc.) are placed on the bottom layer.

(2) On the premise of ensuring the electrical performance, the components should be placed on the grid and arranged in parallel or perpendicular to each other in order to be neat and beautiful. Under normal circumstances, the components are not allowed to overlap. The arrangement of components should be compact, and the input components and output components should be separated as far as possible, so as not to cross.

(3) Some components or wires may have higher voltages. The distance between them should be increased to avoid accidental short circuits due to discharge and breakdown. Pay attention to the layout space of these signals as much as possible during layout.

(4) Components with high voltage should be arranged as far as possible in places that are not easily reachable by hands during debugging.

(5) The components located at the edge of the board should be as far away as possible from the edge of the board by two board thicknesses.

(6) The components should be evenly distributed on the entire board. Don't be dense in this area and loose in the other area to improve the reliability of the product.

6. Follow the principle of signal layout

(1) After placing the fixed components, arrange the positions of each functional circuit unit one by one according to the flow of the signal, with the core component of each functional circuit as the center, and carry out partial layout around it.

(2) The layout of the components should facilitate the signal flow, so that the signal keeps the same direction as possible. In most cases, the signal flow is arranged from left to right or 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.