PCB design requires careful consideration at different stages, with varying grid points used at each stage. For the layout phase, larger grid points are suitable for placing devices.
For large components, such as ICs and non-positioning connectors, a grid point accuracy of 50 to 100 mils is typically sufficient. However, for smaller passive components like resistors, capacitors, and inductors, a finer grid of 25 mils is recommended. Using larger grid points helps align components effectively and enhances the overall aesthetics of the layout.
**Key considerations when routing PCB traces**
**PCB layout guidelines:**
1. Generally, all components should be placed on the same side of the PCB. Only when the top-layer components become too dense should certain low-profile and low-heat-generating devices, such as chip resistors, chip capacitors, or chip ICs, be placed on the opposite side of the board.
2. To ensure optimal electrical performance, components should be placed on a grid and arranged either parallel or perpendicular to each other for a neat and organized layout. In general, components should not overlap; the arrangement should be compact, with components distributed uniformly and densely across the entire board.
3. The minimum distance between adjacent pads of different components on the PCB should be no less than 1mm.
4. The distance from the edge of the PCB should typically not be less than 2mm. The ideal shape for a PCB is rectangular, with an aspect ratio of 3:2 or 4:3. If the PCB size exceeds 200mm by 150mm, consider the mechanical strength the board needs to withstand.
**PCB Layout Techniques:**
In PCB layout design, the board’s functional units should be carefully analyzed, with the layout based on the specific functions required. When placing all the components, the following principles should be followed:
1. Position each functional circuit unit according to the signal flow to facilitate signal circulation. As much as possible, signals should be routed in the same direction.
2. Place the core components of each functional unit at the center and arrange surrounding components accordingly. These components should be laid out uniformly, integrally, and compactly on the PCB to minimize and shorten the connections between them.
3. For high-frequency circuits, the distribution parameters between components must be carefully considered. In general, components should be arranged in parallel, which not only enhances aesthetics but also simplifies installation and supports efficient mass production.
**Special Components and Layout Design:**
Special components in PCB design refer to key components in high-frequency sections, critical circuit components, those susceptible to interference, high-voltage components, components that generate significant heat, and certain components with opposing characteristics. The placement of these special components requires careful analysis to ensure the layout satisfies both functional and production requirements. Improper placement can cause circuit compatibility issues, signal integrity problems, and potential PCB design failure.
When placing special components on the PCB, the board’s size must be considered first. A larger PCB increases the length of the traces, raising impedance, reducing anti-interference performance, and increasing cost. Conversely, a smaller PCB may not allow for proper heat dissipation and could lead to interference between adjacent traces. Once the PCB size is determined, the position of special components should be decided, and the remaining components should be laid out according to their respective functional units.
