**Layout** refers to the process of placing components on the PCB in a manner that optimally balances signal quality, electromagnetic compatibility (EMC), thermal management, design for manufacturability (DFM), design for testing (DFT), structural integrity, safety regulations, and other factors. In high-speed PCB design, an effective layout is the crucial first step toward a successful design. Now, Banermei and team will share insights into the key principles and best practices for PCB layout—valuable knowledge you won’t want to miss.

**PCB Design Layout Concepts and Principles**

**Layout Concepts**

When designing the PCB layout, the first factor to consider is the overall size of the PCB. Next, account for components and areas that require structural positioning, such as constraints on height, width, or the need for cutouts and slots. Following this, pre-layout each circuit module based on the direction of signal and power flow. Finally, proceed with the placement of all components, guided by the design principles of each circuit module.

**Basic Layout Principles**

1. **Collaborate with stakeholders** to ensure that structural, signal integrity (SI), DFM, DFT, and EMC requirements are met.

2. Using the structural element diagram, place key components—such as connectors, mounting holes, and indicator lights—that have specific positioning requirements. Assign these components fixed attributes and determine their dimensions.

3. Refer to the structural diagrams and special requirements of certain components to designate no-route or no-layout zones.

4. Carefully balance PCB performance with manufacturing efficiency when selecting the process flow. Choose from options like single-sided SMT, single-sided SMT with through-hole components, double-sided SMT, or double-sided SMT with through-hole components. Ensure the layout aligns with the selected processing method.

5. Follow the pre-layout plan when placing components, adhering to the principle of “large components first, then small, with difficult placements before easier ones.”



6. The layout should meet the following requirements wherever possible: minimize the total length of wiring, with key signal lines kept as short as possible; completely separate high-voltage and high-current signals from low-voltage and low-current signals; isolate analog signals from digital signals; separate high-frequency signals from low-frequency signals; and ensure sufficient distance between high-frequency components. Local adjustments should be made while still satisfying simulation and timing analysis requirements.

7. Wherever possible, adopt a symmetrical, modular layout for the same circuit section.

8. The recommended grid size for layout is 50 mil, with a 25 mil grid suggested for IC device placement. In areas with high layout density, a grid size no smaller than 5 mil should be used for small surface-mount devices.

**Layout Principles for Special Components**

1. Minimize the wiring length between FM components. Components prone to interference should not be placed too close together; efforts should be made to reduce their parasitic parameters and mutual electromagnetic interference.

2. For devices and traces with potentially large voltage differences, increase the spacing between them to avoid accidental short circuits. High-power devices should be placed in areas that are less accessible to humans.

3. Components heavier than 15g should be secured with brackets before soldering. Large, heavy components that generate significant heat should not be placed directly on the PCB. Heat dissipation should be considered when these components are mounted in the machine enclosure, and heat-sensitive components should be positioned away from heat-generating components.

4. The layout of adjustable components, such as potentiometers, variable inductors, variable capacitors, and micro switches, should take into account the overall mechanical design requirements, such as height limits, hole sizes, and center coordinates.

5. Reserve space for the PCB positioning holes and mounting brackets.

**Post-Layout Check**

In PCB design, a reasonable layout is crucial for the success of the final product. Once the layout is complete, engineers must carefully check the following:

1. PCB size markings, alignment of the component layout with the structural drawing, and compliance with PCB manufacturing process requirements, such as minimum hole size and minimum trace width.

2. Verify that components do not interfere with each other in either 2D or 3D space, and that there is no interference with the structural enclosure.

3. Ensure that all required components have been placed.

4. Check that components requiring frequent plugging or replacement are accessible for easy servicing.

5. Confirm there is adequate spacing between heat-sensitive components and heat-generating elements.

6. Ensure that adjustable components and buttons are easy to access for adjustments or operation.

7. Verify that the location for mounting the heatsink or radiator is unobstructed.

8. Ensure smooth signal flow and minimize interconnection lengths.

9. Consider potential issues with signal interference.

10. Check for compatibility between connectors (plugs and sockets) and the mechanical design.

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