From design drawings to actual mass production, a circuit board must overcome numerous hurdles, including processability, manufacturability, signal integrity, and EMC. This article will systematically outline the design logic around 13 common but crucial core concepts in PCB design, enhancing your PCB engineering thinking and design capabilities.

1. FR4 Board Material: The Cornerstone of the Signal World

FR-4, the most commonly used PCB substrate, is a copper-clad laminate made of glass fiber and epoxy resin. Its heat resistance is measured by Tg (glass transition temperature).

• Low Tg Board (Tg≈130℃): Used for general applications.
• Medium Tg Board (Tg>150℃): Suitable for medium-complexity circuits.
• High Tg Board (Tg≥170℃): Recommended for high-temperature soldering environments, lead-free processes, and high-reliability scenarios, such as automotive and communications.

High Tg boards not only have strong heat resistance but also significantly improved moisture and chemical resistance, ensuring the dimensional stability of multilayer boards during long-term operation.

2. Impedance Matching: The "Guardian" of High-Speed ​​Signal Routing

In high-speed digital circuits (such as DDR, USB, PCIe), signals without precise impedance matching will experience problems such as reflection and crosstalk. Common impedance control methods include:

• Differential impedance: 100Ω/90Ω
• Single-ended impedance: 50Ω

How to design matching? Accurate simulation is required, taking into account factors such as layer stack-up, trace width and spacing, reference plane, and dielectric constant.

3. Surface Treatment Processes: Determining Soldering Quality and Lifespan

Five Common Surface Treatments:

Immersion gold or immersion tin is strongly recommended for high-frequency impedance control. Pulling tin cannot be used on BGA packaged boards.

4. Core Board/Prepreg: Key Materials Determining Board Thickness, Layer Stack-up, and Electrical Performance

The core board (Core) + PP (Prepreg) determines the structure and stability of the multilayer board. Its thickness, resin flow rate, and electrical constants all need to be considered in conjunction with layer stack-up simulation.

• Core: Rigid board with double-sided copper lamination
• PP: Semi-solid resin used for interlayer bonding

Proper proportions are crucial to avoid process issues such as board warping, voids, and copper peeling during lamination.

5. Differential Lines: Symmetrical routing is essential for signal integrity

Differential signals are used for high-speed data transmission, such as LVDS, USB, and PCIe, and must meet the following requirements:

• Equal length, width, and spacing
• Consistent ground plane reference
• Avoid discontinuous reference planes

Asymmetry in differential traces directly affects clock skew and crosstalk, and must be considered comprehensively during the layout phase.

6. Signal Integrity (SI): The soul of high-speed PCB design

Five major factors affecting signal integrity:

• Reflection (impedance mismatch)
• Crosstalk (traces too close together)
• Ground bounce (ground return current interference generated by simultaneous switching of multiple chips)
• Improper filtering design
• Inadequate PCB structure design

SI problems often lead to system failure, frequent resets, and data errors.

7. Signal Reflection: Prevent Signals from "Returning Along the Same Path"

Signal reflection can cause:

• Overshoot
• Undershoot
• Ringing
• Stepped waveforms

To control reflection, in addition to impedance matching, proper termination matching (source and load ends) is necessary, and reference plane breaks should be avoided.

8. Crosstalk: "Noise Pollution" Between Signal Lines

Tightly packed high-speed lines without a ground reference will generate severe crosstalk, especially noticeable in DDR or high-speed bus parallel routing.

Capacitive coupling → Current crosstalk
Inductive coupling → Voltage crosstalk
Solutions: Add ground plane guards, maintain proper spacing between traces, and control trace direction.

9. Internal Power Layer: The Secret Weapon for Stable Power Supply and Interference Suppression

Power and ground must be designed as large-area planes with reasonable partitioning and dense via placement to avoid floating islands and broken power loops.

10. Blind/Buried Vias: A Key Technique in High-Density PCB Design

• First-order blind via: L2-TOP
• Second-order blind via: L3-TOP
• Buried via: Interconnected between L3-L6

Blind/buried vias are widely used in HDI boards, significantly improving space utilization, but they impose high cost and processing requirements.

11. Test Points: "Fuses" for Mass Production Debugging

Used for functional testing, in-circuit programming, and debugging positioning. BGA chip areas must be addressed using flying probes or boundary scanning.

12. Mark Points: Ensuring SMT Placement Accuracy

Used for SMT placement positioning. Mark point design recommendations:

• Mostly 1mm circular;
• Leave solder mask openings around the mark points;
• Three mark points on the board should be symmetrically arranged with consistent background copper foil.

13. PTH/NPTH Holes: Carriers for Connection and Fixing

• PTH (Metallized Hole): Used for electrical connections;
• NPTH (Non-metallic Hole): Used for structural positioning, screw installation, etc.

Hole attributes must be accurately marked in the engineering file during processing to avoid rework.

Conclusion: Mastering Key Details Leads to High-Quality PCB Design

PCB design is not simply "drawing," but a complex system engineering project that considers electrical performance, process feasibility, production costs, and future maintenance. Understanding the design logic and engineering significance behind each term is the starting point for becoming a professional PCB engineer.