Introduction to PCB Design and Layout

PCB design and layout form the foundation of every electronic circuit's functionality and reliability. At FanyPCB, we combine industry expertise with advanced design tools to help engineers transform schematics into manufacturable circuit boards. This guide of how to design a pcb circuit board covers essential PCB design principles, from basic layout concepts to advanced high-speed techniques.

PCB Layout Tools We Use

• Altium Designer

• Cadence Allegro

• Pads

• KiCad 

Schematic Design Best Practices

A well-structured schematic serves as the blueprint for successful PCB layout. Start by organizing components logically, grouping related circuits together for intuitive understanding. Implement consistent naming conventions for nets and components to prevent confusion during layout. Power and ground nets should be clearly identified using distinctive symbols or labels. Always include proper decoupling capacitors near IC power pins, with values clearly specified. Before proceeding to layout, perform thorough electrical rule checks (ERC) to catch any connectivity errors or missing connections.

Component Placement Strategies

Strategic component placement significantly impacts board performance and manufacturability. Begin by positioning connectors and mechanical components according to enclosure requirements. Place critical components like processors, FPGAs, or RF modules first, ensuring optimal signal paths to associated peripherals. Group related components together based on circuit functionality, minimizing trace lengths between connected parts. Consider thermal management during placement, spacing heat-generating components appropriately and providing adequate copper areas for heat dissipation. Always verify component footprints match physical parts before finalizing placement.

PCB Stackup Design Considerations

The layer stackup configuration fundamentally determines a board's electrical characteristics and manufacturability. For simple designs, a 2-layer board may suffice, but most modern applications require 4 or more layers:

• 4-layer boards for moderate complexity

• 6+ layers for high-speed designs

• Mixed signal separation

• Impedance control requirements

Routing and Signal Integrity Guidelines

Effective routing requires balancing electrical requirements with physical constraints. Start critical signals first, particularly high-speed traces and sensitive analog lines. Maintain consistent trace widths appropriate for the current carrying requirements - general signals can use 0.15mm to 0.2mm traces, while power traces may need to be much wider. For controlled impedance signals, calculate required trace widths based on your stackup's dielectric properties. Route differential pairs together with consistent spacing, maintaining length matching where necessary. Avoid sharp 90° angles in traces, opting instead for 45° angles or curved traces to prevent impedance discontinuities. Always provide adequate clearance between traces of different voltages or signal types.

Power Distribution Network Design

A robust power delivery network (PDN) is essential for stable circuit operation. Use solid power planes where possible, with multiple vias connecting to components to reduce inductance. Implement proper decoupling with a mix of capacitor values - place smaller value capacitors (0.1μF) closest to IC power pins, with larger bulk capacitors (10μF) distributed across the board. For boards with multiple voltage rails, consider split planes or separate layers for different voltages. Calculate expected current draws to ensure power traces and planes can handle the load without excessive voltage drop. Include test points at key power nodes to facilitate debugging and verification.

Grounding Techniques and EMI Reduction

Proper grounding is critical for both signal integrity and EMI performance. Use a solid ground plane whenever possible, avoiding splits that can create return path discontinuities. For mixed-signal designs, implement careful partitioning of analog and digital grounds, connecting them at a single point near power inputs. Provide adequate grounding for shielding cans and connectors to prevent antenna effects. Maintain consistent clearance between ground pours and other nets to prevent accidental shorts while ensuring good high-frequency connectivity. Consider the use of stitching vias around board edges and between ground areas to reduce ground loop areas.

Design for Manufacturing (DFM) Considerations

To ensure smooth transition from design to production, incorporate DFM principles throughout the layout process. Adhere to your manufacturer's minimum trace/space requirements, typically 0.1mm/0.1mm for standard boards. Include proper solder mask expansion (usually 0.05mm-0.1mm) around pads to prevent bridging. Implement teardrops at pad-to-trace connections to strengthen these junctions. Balance copper distribution across layers to prevent warping during manufacturing. Add fiducial markers and tooling holes if required for assembly. Always perform a final design rule check (DRC) using your manufacturer's specific rules before releasing files.

Documentation and Output Files

Complete documentation ensures accurate manufacturing and assembly. Generate comprehensive fabrication drawings including layer stackup details, special material requirements, and finish specifications. Provide assembly drawings with component locations and orientations clearly marked. Export Gerber files using RS-274X format with accompanying drill files. Include a bill of materials (BOM) with complete part numbers, values, and manufacturer references. For assembled boards, supply centroid (pick-and-place) files with precise component coordinates. Always package all files together with a readme document explaining any special requirements.

Verification and Testing Strategies

Before finalizing the design, implement verification measures to catch potential issues. Perform signal integrity simulations for critical high-speed nets if possible. Check power plane resonance and impedance profiles for the PDN. Review the layout for common errors like unconnected nets or insufficient clearances. Create a testing plan that verifies all critical functions, including provisions for test points or probe access. Consider designing in any necessary test fixtures or programming interfaces. For complex designs, prototype testing with breakout boards for critical sections can save time and rework.

These PCB design and layout guidelines provide a foundation for creating reliable, high-performance circuit boards. However, complex designs often benefit from professional expertise. FanyPCB offers complete PCB design services, from schematic capture to final layout, backed by decades of combined experience across industries. Our engineers can optimize your design for manufacturability, signal integrity, and cost-effectiveness while meeting your specific performance requirements.