PCB Blog - Principles and importance of PCB layout board

PCB layout board refers to arranging the positions of various functional circuit units according to the circuit flow, making the layout convenient for signal flow and keeping the signal as consistent as possible in the direction. It is centered around the core components of each functional unit and laid out around them. The components should be evenly, integrally, and compactly arranged on the PCB, minimizing and shortening the leads and connections between each component as much as possible.

PCB layout board

PCB layout board principles:

1. Component arrangement rules

1.  Under normal conditions, all components should be arranged on the same side of the printed circuit. Only when the top layer components are too dense can some devices with limited height and low heat generation, such as chip resistors, chip capacitors, and chip ICs, be placed on the bottom layer.

2.  On the premise of ensuring electrical performance, components should be placed on a grid and arranged parallel or perpendicular to each other, in order to be neat and aesthetically pleasing. Generally, components are not allowed to overlap; 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 circuits caused by discharge or breakdown.

4.  Components with high voltage should be arranged as far as possible in areas that are not easily accessible by hands during debugging.

5.  The component located at the edge of the board should be at least 2 board thicknesses away from the edge of the board

6.  The components should be evenly distributed and evenly spaced throughout the entire board surface.

2. PCB Layout board principle according to signal direction

1.  Usually, the positions of each functional circuit unit are arranged one by one according to the signal flow, with the core components of each functional circuit as the center and arranged around it.

2.  The layout of the components should facilitate signal flow and ensure that the signals remain in the same direction as possible. In most cases, the flow direction of the signal is arranged from left to right or from top to bottom, and components directly connected to the input and output terminals should be placed near the input and output connectors or connectors.

3. Prevention of electromagnetic interference

1.  For components with strong radiated electromagnetic fields and components that are sensitive to electromagnetic induction, the distance between them should be increased or shielded, and the direction of component placement should intersect with adjacent printed wires.

2.  Try to avoid mixing high and low voltage devices and interleaving strong and weak signal devices.

3.  For components that generate magnetic fields, such as transformers, speakers, inductors, etc., attention should be paid to reducing the cutting of magnetic field lines on printed wires during layout. The magnetic field directions of adjacent components should be perpendicular to each other to reduce coupling between them.

4.  Shield the interference source, and the shielding cover should be well grounded.

5.  In high-frequency circuits, the influence of distributed parameters between components should be considered.

4. Suppression of thermal interference

1.  For heating elements, priority should be given to locations that are conducive to heat dissipation. If necessary, separate heat sinks or small fans can be installed to reduce temperature and reduce the impact on adjacent components.

2.  Some components with high power consumption, such as integrated blocks, high rate transistors, resistors, etc., should be arranged in areas that are easy to dissipate heat and separated from other components by a certain distance.

3.  The thermal sensor should be close to the measured element 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 placing components on both sides, the bottom layer generally does not place heating elements.

5. Layout of adjustable components

For the layout of adjustable components such as potentiometer, variable capacitor, adjustable inductance coil or microswitch, the structural requirements of the whole machine shall be considered. If it is adjusted outside the machine, its position shall adapt to the position of the adjustment knob on the chassis panel; If it is adjusted internally, it should be placed in the adjustment area of the printed circuit board.

PCB Layout board considerations

1. According to electrical performance, it is divided into digital circuit area, analog circuit area, and power drive area.

2. Circuits with the same function should be placed as close as possible and ensure that the wiring of each component is the most concise; At the same time, make the connections between various functional blocks the most concise.

3. High quality components should consider installation location and strength; Heating elements should be placed separately from temperature sensitive elements.

4. I/O driver components should be placed as close as possible to the edge of the printed board and close to the outgoing connectors.

5. The clock generator should be located as close as possible to the device using the clock.

6. Add a decoupling capacitor between the power input pin of each integrated circuit and the ground; When the circuit board space is dense, a tantalum capacitor is added around several integrated circuits.

7. Install a discharge diode at the relay coil.

8. The layout requires balance, orderly density, and should not be too heavy or too heavy.

9. When placing components, it is necessary to consider the actual size and relative position of the components, while ensuring the electrical performance of the circuit board and the feasibility and convenience of production and installation, to make it neat and beautiful.

The importance of layout board:

1. The PCB layout determines the routing rate of printed circuit board wiring, especially for single panels. Reasonable layout can achieve a 100% routing rate, thereby reducing jumpers and avoiding the introduction of distribution parameters.

2. The layout of PCB determines that the layout of power lines and ground wires should consider the minimum area of the wiring loop in the layout of the layout structure. In particular, when laying the circuit of IC devices, the decoupling capacitor should be placed on the pin close to the power supply and ground, so that the power and ground loop area of the entire IC device can be minimized during wiring, reducing radiation coupling and high-frequency noise.

3.  When laying out components, the interconnected components should be arranged in a relatively concentrated manner, which can increase the wiring density during wiring, resulting in the shortest printed copper wire, reduced impedance, and improved noise resistance of the entire printed board.

4.  In high-speed circuits, such as crystal oscillators, the layout should be as close as possible to the pins of the components, especially the layout between high-frequency components, in order to achieve the shortest wiring and reduce electromagnetic interference between the connecting wires.

5.  The component layout should be evenly distributed, so that the conductive area of the conductive layer is relatively balanced during wiring, preventing the printed board from warping due to uneven heat dissipation.

6. When there are both analog and digital circuits, it is necessary to layout the analog and digital circuit parts reasonably; For parts that generate severe noise (such as relay coils, high current, and high voltage switches), optimize and adjust their positions as much as possible to minimize signal coupling between them during wiring and reduce electromagnetic interference.

In short, PCB layout board has a significant impact on wiring. Printed boards with neat components, uniform wiring, better suppression and reduction of electronic interference, and improved anti-interference ability are determined by the reasonable layout and wiring of various components.