The performance of a PCB board depends 70% on its layout design. The same schematic can lead to either normal operation or frequent failures with different layouts and routing, even directly impacting stability, EMC compliance, and production yield. Whether you're a novice in PCB design or a seasoned engineer seeking optimization solutions, mastering the following key points can save you 90% of the trouble in your design process.

I. Pre-Design Preparation: 3 Steps to Lay a Solid Foundation and Avoid Rework

1. Define Design Constraints: Confirm the PCB board's physical dimensions, number of layers (single/double/multilayer board selection), impedance requirements (e.g., 50Ω high-speed signal, 90Ω differential signal), power rail voltage drop limits, EMC standards (CE/FCC, etc.), and manufacturing process parameters (minimum trace width, trace spacing, via size) in advance. Write these constraints into Design Rules (DRC) to avoid violations from the outset.

2. Schematic Review and Optimization

Before layout, a second schematic review is essential: check the power, ground, and signal paths for rationality, avoiding unnecessary intersections; group functional modules (such as power modules, high-speed interfaces, and analog circuits) to provide logical basis for subsequent layout planning; label key signals (such as clock and differential pairs) for focused control during layout.

3. Component Selection and Package Confirmation
Prioritize components with standardized packages and reasonable pin pitch (avoid fine-pitch packages below 0.4mm, which increase soldering difficulty); confirm the accuracy of the package library (pin definitions, silkscreen locations, pad sizes), especially for precision components such as BGA and QFP, as incorrect packaging can directly lead to design failure.

II. Layout Design: Follow the Three Principles of "Zoning, Proximity, and Heat Dissipation"

1. Functional Zoning Layout

Divide the layout into sub-regions according to signal type and function: Analog area (ADC/DAC, sensors), Digital area (MCU, FPGA), Power area (power chips, inductors, capacitors), Interface area (USB, Ethernet, RF). Reserve isolation bands (recommended ≥3mm) between each area to prevent digital signals from interfering with analog signals.

2. Prioritize the Layout of Critical Components: Place power supply chips (LDO, DC-DC) close to the load to reduce power path length; place inductors and capacitors close to the power supply chip pins to form a complete filtering circuit (avoid "flying wire" layouts).

Place high-speed signal sources (such as crystal oscillators and clock chips) close to the receiver to shorten the transmission path and reduce interference coupling; ground the crystal oscillator casing and leave a copper-free area of ​​≥5mm around it.

Keep heat-generating components (such as power transistors and LED drivers) away from sensitive components (such as MCUs and sensors), and provide sufficient space for heat dissipation; design copper-plated heat sinks if necessary.

3. Check the Layout Rationality: Ensure component pins are not obstructed and silkscreen markings are clearly legible; ensure through-hole component spacing is ≥2.5mm and surface-mount component spacing is ≥0.5mm; place connectors and interface components close to the PCB edge for easy insertion, removal, and routing.

III. Cabling Design: "Short, Straight, and Smooth" as the Core, while considering impedance and EMC.

1. Basic Cabling Rules: Prioritize routing critical signals (clock, differential pairs, high-speed data signals), then general signals; power and ground lines take precedence over signal lines to ensure stable power supply.

Keep cabling as short and straight as possible, avoiding unnecessary bends and vias; if bends are necessary, use 45° angles or rounded edges, avoiding 90° right angles (to reduce signal reflection and EMC radiation).

Track Width Matching: Select the trace width according to the current (e.g., 1A current corresponds to 1mm trace width, 0.5A corresponds to 0.5mm, signal trace width is recommended to be 0.2-0.3mm); differential signal trace width and spacing must strictly adhere to impedance requirements (e.g., USB 3.0 differential pairs require a trace width of 0.2mm and a spacing of 0.4mm).

2. Key Points for High-Speed ​​Signal Routing
Differential signals (such as HDMI, PCIe, and Ethernet) must be of equal length, parallel, and tightly coupled, with a length difference controlled within 5mm. Avoid branching or using vias.

Clock signals should use a star or daisy-chain topology to avoid direct parallel connection of multiple loads. Use ground copper around the clock line to form shielding and reduce crosstalk.

High-speed signals should avoid crossing split areas (such as power and ground planes), otherwise it will disrupt the reference plane and cause signal integrity issues.

3. Routing Pitfalls Avoidance Guidelines
Signal lines are not allowed to cross power or ground plane splits. If crossing is unavoidable, a via should be added at the crossing point to connect to the reference plane.

Avoid long parallel routing of signal lines on different layers (to reduce inter-layer crosstalk). The spacing between parallel signal lines on the same layer should be ≥3 times the line width.

The fewer vias, the better. Critical signals should ideally have no more than 2 vias (vias introduce parasitic inductance and capacitance, affecting signal integrity).

IV. Grounding Design: Flexible Application of "Single-Point Grounding" and "Multi-Point Grounding"

4. Grounding Principles The core of grounding is to "reduce ground loop area" and avoid interference caused by ground potential differences. Analog ground and digital ground must be wired separately and ultimately connected at a single point at the power supply (e.g., through a 0Ω resistor, ferrite bead, or direct connection). Direct mixing of analog and digital grounds is prohibited.

1. Different Types of Grounding Design

Signal Ground: Use "star grounding," connecting all signal grounds to a common grounding point to reduce crosstalk between signals.

Power Ground: Use "multi-point grounding," connecting the grounding terminals of power chips and filter capacitors to the nearest power ground plane to shorten the grounding path and reduce grounding impedance.

Shielding Ground: The grounding of metal casings and shielding covers must be reliable, with a grounding resistance ≤1Ω, avoiding the formation of "floating ground" (floating ground is prone to static electricity accumulation, leading to EMC failures).

2. Ground Plane Design Techniques
Multilayer boards are recommended to use a "power plane + ground plane" stack-up structure (e.g., Top - Power - GND - Bottom). The ground plane should be fully copper-plated to form a low-impedance reference plane. Single-layer or double-layer boards should maximize the ground copper area, using a "grid ground" or "large-area ground plane," and connecting the upper and lower ground layers through vias to enhance grounding effectiveness.

V. Power Supply Design: Filtering, Decoupling, and Voltage Regulation are All Essential

1. Power Supply Filtering and Decoupling
A 0.1μF ceramic capacitor (decoupling capacitor) must be placed next to the power pin of each active device (MCU, chip), close to the pin and ground plane, to address instantaneous current supply issues. A 10μF electrolytic capacitor + 0.1μF ceramic capacitor should be placed at the power input to filter out low-frequency and high-frequency noise.

Electrolytic capacitors and ceramic capacitors should be placed at the input and output terminals of the DC-DC power supply, respectively. The inductor terminals should be kept away from sensitive signals to prevent magnetic coupling interference.

2. Power Rail Routing
High-current power rails (such as battery power and motor drives) should use wide traces or copper plating to reduce voltage drop and heat generation; isolation strips should be reserved between multiple power rails to avoid short circuits; power segmentation should adopt an "island-style" design with clear dividing lines, and signal lines should not be allowed to cross them.

VI. EMC Optimization: Reducing Electromagnetic Interference from the Layout Source

1. Shielding Design
Sensitive circuits (such as RF receivers and analog signal processing) should use metal shielding covers with good grounding; high-speed signal and power lines should maintain sufficient spacing (≥10mm) between themselves and sensitive lines, or be isolated with ground copper.

2. Filtering and Grounding Optimization
Interface circuits (USB, Ethernet, power interfaces) should use series common-mode inductors and parallel TVS diodes to suppress common-mode interference; all signal lines of external interfaces should be filtered before being led out of the PCB.

3. Reduce Radiation Sources
Avoid long parallel wiring, unterminated transmission lines, and large areas of suspended copper. Keep clock signals and high-speed signals as short as possible and surround them with ground planes to form a "microstrip line" structure, reducing electromagnetic radiation.

VII. Post-Design Inspection: 3 Key Steps to Ensure Manufacturability and No Hidden Dangers

1. DRC Rule Check
After layout completion, a DRC check must be performed, focusing on whether trace width, trace spacing, via size, component spacing, impedance matching, etc., comply with design rules to ensure no violations.

2. Signal Integrity and EMC Simulation
For high-speed PCBs (e.g., ≥100MHz signals), signal integrity simulation (SI) is recommended to check for reflections, crosstalk, timing issues, etc. Complex products require EMC simulation (e.g., radiated emissions, electrostatic discharge) to identify and resolve interference issues early.

3. Manufacturability Check (DFM)
Visage Size: Through-hole vias ≥0.8mm, surface-mount vias ≥0.3mm, avoiding excessively small vias that cause drilling difficulties.

Solder mask and silkscreen: Solder mask openings must cover the pads to avoid exposing copper; silkscreen should not obscure pads or vias, and characters should be clearly legible.

Panel design: If panelization is required, reserve V-cut slots or stamp holes, and leave a process edge of ≥3mm at the panel edges for easy SMT production.