Advancements in PCB Impedance Design

With the continuous progress of technology, especially in integrated circuit materials, computing speeds have significantly improved. This has led to integrated circuits becoming denser, smaller, and more compact.

Increasing Demands for High-Frequency Response

The rapid advancements in technology have raised the requirements for high-frequency response in modern printed circuit boards. High-speed digital circuits now require precise impedance control, minimal distortion, low interference, reduced crosstalk, and the elimination of electromagnetic interference (EMI).

The Significance of PCB Impedance Design

PCB impedance design has become increasingly critical in the PCB design process. It involves simulating impedance calculations and designing impedance matching structures, which are essential for meeting customers’ demands for precise impedance control.

Main Types of Impedance and Influencing Factors

Impedance (Zo) is the total resistance encountered by alternating current in a circuit at a specific frequency. For printed circuit boards, it refers to the total impedance of a circuit layer relative to its closest reference plane under high-frequency signals.

Types of Impedance:

• Characteristic Impedance: The impedance encountered by square wave signals in electronic products.
• Differential Impedance: The impedance measured between two differential lines.
• Odd-Mode Impedance: Impedance of one line with respect to the ground.
• Even-Mode Impedance: Impedance when two identical signals are input at the driving end.
• Common-Mode Impedance: Impedance of one line with respect to the ground for both lines.

Factors Affecting PCB Impedance:

• Line Width/Spacing (W): Impedance decreases with an increase in line width and increases with greater spacing.
• Insulation Thickness (H): Impedance increases with thicker insulation.
• Copper Thickness (T): Impedance decreases with thicker copper.
• Solder Mask Thickness (H1): Impedance decreases with thicker solder mask.
• Dielectric Constant (Er): Impedance decreases with a higher dielectric constant.
• Undercut (W1-W): Impedance increases with a larger undercut.