PCB Board Layout Principles
Posted:10:50 AM June 18, 2021
This article provides a clear explanation of PCB board layout principles for PCB engineers.
I. Component arrangement rules
- 1) Under normal conditions, all components should be arranged on the same surface of the printed circuit. Only when the top components are too dense, can some devices with limited height and low heat generation, such as chip resistors and chip capacitors, paste IC, etc. are placed on the bottom layer.
- 2) On the premise of ensuring electrical performance, the components should be placed on the grid and arranged parallel or perpendicular to each other in order to be neat and beautiful. Under normal circumstances, components are not allowed to overlap; the arrangement of components should be compact, and the input and output components should be 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 circuits due to discharge and breakdown.
- 4)Components with high voltage should be arranged as far as possible in places that are not easy to touch during debugging.
- 5) Components located at the edge of the board should be at least 2 board thickness away from the edge of the board
- 6)Components should be evenly distributed and densely distributed on the entire board.
II. Follow the principle of signal layout
- 1) The position of each functional circuit unit is usually arranged one by one according to the flow of the signal, and the core element of each functional circuit is taken as the center, and the layout is carried out 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.
III. Prevent electromagnetic interference
- 1) For components with strong radiated electromagnetic fields and components sensitive to electromagnetic induction, the interaction between them should be increased. The distance or shielding should be provided, and the component placement direction should cross the adjacent printed wires.
- 2) Try to avoid mixing high and low voltage devices with each other, and interleaving devices with strong and weak signals.
- 3) For components that generate magnetic fields, such as transformers, speakers, inductors, etc., pay attention to reducing the magnetic force during layout. For wire-to-printed wire cutting, the magnetic field directions of adjacent components should be perpendicular to each other to reduce the coupling between each other.
- 4) Shield the interference source, and the shielding cover should have a good grounding.
- 5) For circuits operating at high frequencies, the influence of the distributed parameters between the components should be considered.
IIII. Suppress thermal interference
- 1) For heating elements, it 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 adjacent elements.
- 2) Some high-power integrated blocks, large or medium power tubes, resistors, and other components should be arranged in places where heat is easy to dissipate, and separated from other components by a certain distance.
- 3) The thermal component should be close to the component under test and away from the high-temperature area, so as not to be affected by other heating power equivalent components and cause malfunction.
- 4) When components are placed on both sides, heating components are generally not placed on the bottom layer.
V. 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 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 printed circuit board where it is adjusted.