PCB layout is the "skeleton" of hardware design, directly determining circuit performance, manufacturability, and stability. Beginners often fall into the trap of "laying and modifying as they go" due to a lack of systematic methods. However, by mastering the logic of "prioritizing planning, prioritizing core areas, and implementing details," you can quickly get started. Based on practical experience, the following 7 reusable steps will help you avoid 90% of common pitfalls.

I. Understand the "Underlying Logic": 3 Core Principles to Avoid Mistakes

Understanding the underlying logic before layout is more efficient than blindly memorizing rules. These 3 principles are the foundation of all skills; remembering them will save you 80% of the trouble:

• Signal Flow Prioritization

Place components in the natural order of "input → processing → output." For example, power supplies should be placed from "interface → filter → power chip → load IC," and signals from "sensor → amplifier → MCU → output interface." Avoid cross-placement of components, which can cause circuit bends. For example, place the network interface (input) near the PHY chip, and the PHY near the MCU (processing) to reduce signal backlash.

• Functional Zoning for Isolation

To prevent circuits with different "tempers" from interfering with each other, the PCB is divided into four main functional areas, using physical space to isolate interference. The specific zoning logic is as follows:
High Voltage/High-Power Area (Power Modules, Motor Drivers): Located away from the board edge, with dedicated heat dissipation space;
Digital Area (MCU, Memory, Logic Chips): Centrally located near the center;
Analog Area (Sensors, Op-Amplifiers, ADCs): Located away from clock/high-speed signals, surrounded by ground lines;
Interface Area (USB, Ethernet, Buttons): Placed close to the board edge for easy plugging/unplugging and wiring.

• "Key Components" Take Center Stage

First, determine the core components, then prioritize the supporting components. Secure three categories of components first, and the subsequent layout will revolve around them:
* Core Chips (MCU, FPGA, Power IC): Place in the center of the PCB or near signal convergence points;
* Large/Heavy Components (Transformers, Heatsinks): Keep away from board edges and stress points (such as screw holes) to prevent vibration from causing them to fall off;
* Interface Connectors (Power Ports, Data Ports): Attach to the board edge according to structural requirements, ensuring pin 1 is correctly positioned (reverse connection will directly cause circuit failure).

II. Four-Step Layout: A Practical Process from Planning to Implementation

Step 1: Structural Constraints First, Avoiding Rework

First, address the "unchangeable" structural requirements. This is the "foundation" of the layout; mistakes will lead to a complete design overhaul:

Confirm Height Limits and Mounting Holes
Mark the height-limited areas on the board (e.g., H=1.8mm, H=2.0mm). Components with height, such as capacitors and inductors, must not be placed there. Leave a 5mm no-layout zone around screw holes to prevent damage to components or wiring during installation.

Fix Interfaces and Structural Components
According to the imported 3D structural file, place components requiring matching structures, such as USB ports, network ports, and housing clips, paying particular attention to the connector pin 1 position. This must be consistent with the schematic and structure (e.g., network port pin 1 corresponds to TX+; incorrect pins will cause communication failure).

Step 2: Functional Zoning Layout to Reduce Interference

Following the previously defined four zones—"High Voltage / Digital / Analog / Interface"—use "blank areas" or "ground lines" for isolation. Specific instructions are as follows:

Analog Zone: Place operational amplifiers and sensors in the upper left corner, with a complete analog ground plane below them, leaving at least 2mm of clearance between them and the digital zone.

Power Supply Zone: Position power supply chips close to the input interfaces, with the outputs facing the digital/analog zones, minimizing current paths (e.g., a 5V power supply chip should be no more than 10mm from the USB interface).

Clock Zone: Place crystal oscillators and clock distributors close to the MCU's clock pins, ≤10mm away, surrounded by ground lines ("grounding"), and away from power chips and heatsinks.

Step 3: Detail Optimization, Balancing Performance and Manufacturing

This step determines the quality of the layout, focusing on three easily overlooked details:

Heat Dissipation Design
Distribute heat-generating components (power MOS, LDO, LED driver) evenly, avoiding clustering; keep heat-sensitive components (crystal oscillators, electrolytic capacitors) away from heat sources (at least 3mm away), for example, place the LED driver chip at the board edge, away from high-precision ADCs.

Component Orientation
Ensure similar components are oriented in the same direction (e.g., resistor silkscreens all face right, electrolytic capacitor positive terminals all face upwards). Place SMT components on the same side as much as possible to reduce the number of times they need to be flipped during factory soldering, lowering the probability of cold solder joints; arrange wave soldering components (e.g., through-hole resistors) in the same direction to avoid solder buildup.

Spacing Control: Sufficient spacing should be maintained according to manufacturing specifications to avoid solder bridging or safety issues. Core spacing references: ≥0.2mm between surface-mount components (≥0.15mm for 0402 packages); creepage distance ≥2.5mm in high-voltage areas (e.g., 220V input) (adjusted according to safety standards); leave 1mm clearance around test points and debugging devices to facilitate probe contact.

Step 4: Pre-inspection to avoid routing pitfalls

After layout, don't rush into routing. Perform three key checks to avoid later board modifications:

• Rotation channels: Check for straight paths for high-speed signals (such as DDR, USB). For example, check for components obstructing the data lines from the MCU to the memory. Leave at least two trace widths of space.
• Power paths: Check for bottlenecks in main power supply traces (such as 12V input). Ensure the trace width is sufficient (calculated by current: 1A corresponds to 1mm trace width, 2A corresponds to 2mm).
• 3D inspection: Use the 3D function of EDA software to check for interference between components and the casing (e.g., capacitors too high touching the casing). Ensure connectors are aligned with structural holes.

III. Special Scenarios and Techniques: Overcoming the Three Major Challenges of High Frequency, Power Supply, and EMC

Ordinary layouts rely on processes, while complex scenarios rely on techniques. For beginners facing three major pain points—high frequency signals, power supply design, and EMC protection—we have compiled reusable solutions:

1. High-Frequency/High-Speed ​​Signal Layout (e.g., DDR, USB 3.0):

• Equal Length Reservation:Place components requiring equal length (e.g., DDR chips) symmetrically around the MCU, leaving space for routing. For example, arrange four DDR chips in a square around the MCU, ensuring the distance difference between each chip and the MCU is ≤5mm, reducing the difficulty of later equal-length routing.
• Impedance Matching:Lay a complete reference ground under high-frequency lines (e.g., RF lines) to avoid reference layer breaks. Place high-frequency components close to interfaces during layout to reduce trace length (e.g., RF modules near antenna interfaces, trace length ≤20mm).
• Clock Protection:Keep crystal oscillators and clock chips away from high-power devices and high-speed signal lines. Connect a 22Ω matching resistor in series at the output (placed close to the crystal oscillator). Ground unused clock pins through a 1kΩ resistor to prevent signal reflection.

2. Power Supply and Capacitor Layout The power supply is the "heart" of the circuit, and capacitor layout directly affects power supply stability:

• Decoupling Capacitors: Place small 0.1μF capacitors close to the IC power pins (≤2mm distance), and large 10μF capacitors near the IC (≤5mm distance). For example, place a 0.1μF capacitor next to each power pin of the MCU, with the capacitor's ground via directly next to the pad to reduce grounding impedance.
• Power Supply Module: Keep switching power supplies away from analog areas and clock devices (at least 5mm away). Separate input and output layouts to avoid crossing. For example, place the input on the left and the output on the right, isolated by a ground wire to reduce electromagnetic radiation.
• Power Tree: Arrange power supply chips in the order of "Vin→Buck→LDO→Load," for example, 12V input → Buck chip (to 5V) → LDO (to 3.3V) → MCU. This minimizes the current path and reduces losses.

3. EMC Protection Layout

• ESD Protection: TVS diodes and varistors near interfaces should be placed close to the interface pins (distance ≤3mm). For example, the TVS diode for a USB interface should be placed between the interface and the MCU, close to the interface end, ensuring that electrostatic discharge (ESD) passes through the protection device first.
• Filtering Components: EMI filters and common-mode inductors should be placed close to the power input port. For example, an EMI filter for a 220V input should be placed next to the power interface, allowing the input line to pass through the filter before reaching the rectifier bridge.
• Ground Plane Treatment: Analog and digital grounds should be connected at a single point (using a 0Ω resistor or ferrite bead) to avoid ground loops. For example, a 0Ω resistor can be used to connect analog and digital grounds below the ADC. The ground plane in other areas should remain intact, without unnecessary slots.

IV. Tool Assistance: Improving Efficiency with Software Functions (Taking PADS/Altium as an Example)

Beginners often experience low efficiency due to manually placing components. Utilizing three EDA tool functions can increase layout speed by 50%:

• * **Alignment Tool:** Use the "Align" function to quickly align components (e.g., select multiple resistors, align left with one click, and distribute them evenly). In PADS, access this through "Edit→Align," and in Altium, use the shortcut "Ctrl+A."
• * **Grid Settings:** Set the grid according to package size (0.05mm grid for 0402 packages, 0.1mm for 0603) to ensure component alignment. In PADS, use "Setup→Grids" and enable "Snap to Grid" to avoid misalignment.
• * **Group Layout:** Set functional modules (e.g., chips, capacitors, inductors in a power module) as "Groups" and move them as a whole to avoid scattering. In PADS, select the component and right-click "Group→Create," and in Altium, use "Ctrl+G" to group.

V. Beginner to Advanced: 3 Habits from "Knowing How to Layout" to "Layout Well"

Skills can help you get started, but habits will help you advance. Develop these 3 habits, and you can go from "beginner" to "proficient" within a month:

1. **PCB Copying and Learning:** Find high-quality PCB examples (such as open-source projects and development boards from major manufacturers), analyze their layout logic, such as how STM32 development boards partition and arrange capacitors, imitate and summarize the patterns;
2. **Review and Summarize:** After each project, record the problems encountered in the layout (such as "forgetting to leave heat dissipation space leading to chip overheating" or "clock lines being too long causing signal interference"), and compile them into your own "avoidance list";
3. **Practical Tooling:** Use free EDA software (such as LCSC EDA) to practice small projects, starting with simple circuits (such as LED driver boards and serial port modules), gradually challenging complex designs (such as MCU boards with WiFi), and consolidating your skills through practical experience.

Summary: The Core Logic for Quick Start

There is no "perfect" PCB layout solution, but beginners can quickly get started by remembering the 12-word logic: "Plan first, then partition, focus on key elements, and check frequently."

• Planning Phase: Clearly define signal flow and structural constraints; avoid blindly placing components.
• Partitioning Phase: Isolate interference according to function, and tackle challenges such as high frequencies and power supplies.
• Detail Phase: Pay attention to heat dissipation, orientation, and spacing, balancing performance and manufacturing.
• Checking Phase: Use 3D modeling and pre-routing to check and proactively avoid problems.

Start with simple projects to practice. After 1-2 projects, you'll develop your own layout rhythm. Further refine your work based on specific needs, gradually improving your design skills.