PCB component layout is a crucial part of PCB design, which directly affects the performance, stability and manufacturing cost of the circuit board. During the process, the general principles that designers should follow during PCB layout are as follows:
It is best to place components on a single side of the PCB. If double-sided placement is required, through-hole components placed on the bottom layer may make the PCB difficult to position and inconvenient for soldering. Therefore, it is recommended to place only surface-mount components on the bottom layer, similar to the component layout commonly seen on computer graphics card PCBs. When components are placed on one side only, a silkscreen layer is needed on just one side of the PCB, which helps reduce costs.
Arrange the positions and orientations of interface components reasonably. Generally, connectors that connect the PCB to external sources (such as power and signal lines) should be placed at the edges of the board, like serial and parallel ports. If placed in the center, it would obviously hinder wiring and might become inaccessible due to obstructions from other components. Additionally, pay attention to the direction of the interfaces so that the connecting cables can be easily routed away from the PCB. Once the interfaces are positioned, use the component's string to clearly label the type of interface; for power interfaces, indicate the voltage level to prevent damage to the PCB due to incorrect wiring.
It is best to have a wide electrical isolation zone between high-voltage and low-voltage components. In other words, components with significantly different voltage levels should not be placed close to each other. This approach not only improves electrical insulation but also benefits signal isolation and enhances noise immunity.
Components with closely related electrical connections should ideally be placed together. This reflects the modular layout approach.
Components that easily generate noise, such as clock generators and crystal oscillators, should be placed as close as possible to the CPU's clock input when positioning. High-current circuits and switching circuits also tend to produce noise; therefore, these components or modules should be positioned away from logic control circuits, memory circuits, and other high-speed signal circuits during layout.
Place decoupling capacitors and filter capacitors around power supplies and chips as much as possible. The placement of these capacitors is an important measure to improve the power quality of the PCB and enhance noise immunity. In practical applications, PCB traces, pin connections, and wiring can introduce significant parasitic inductance, resulting in high-frequency ripples and glitches in power and signal waveforms. Placing a 0.1µF decoupling capacitor between power and ground can effectively filter out these high-frequency ripples and glitches. If using surface-mount capacitors, they should be placed close to the component’s power pins. For power conversion chips or power input points, it is advisable to place a 10µF or larger capacitor to further improve power quality.
Component identifiers should be placed close to the component outlines, with consistent size and orientation, and should not overlap with components, vias, or pads. The first pin of components or connectors should clearly indicate direction, and polarity marks should be visibly indicated on the PCB without being covered. Power conversion components (such as DC/DC converters, linear regulators, and switching power supplies) should have adequate space for heat dissipation and installation, and there should be sufficient soldering space around them.
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