PCB Via Hole Clearance Area Design for Impedance Control
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Solution Overview
Problem
High-frequency signal transmission in multi-layer printed circuit boards faces issues with impedance discontinuity, radiation loss, and signal interaction coupling due to the design constraints and requirements for via holes, which affect the yield rate and electrical characteristics of finished products.
Innovation Solution
The design includes varying sizes and shapes of annular clearance areas and the addition of radial slots and isolation slots around ground via holes to adjust impedance characteristics, concentrating ground via holes near the center via hole and reducing radiation leakage, while maintaining flexible transmission line outlet directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If via holes are used to connect metals of different layers for signal transmission, then signal transmission between layers is achieved, but impedance discontinuity and radiation loss occur at high frequencies
Solution Approach 1:
The patent segments the ground connection structure into multiple components: ground via holes surrounding the center via hole, annular clearance areas on different layers, and ground planes. This segmentation creates a distributed ground system that maintains impedance control and reduces radiation loss by providing multiple localized ground return paths instead of relying on a single via hole connection.
Solution Approach 2:
The patent introduces annular clearance areas as intermediary structures between the center via hole and the ground via holes. These annular clearance areas act as impedance control elements that mediate the transition between different impedance zones, ensuring smooth signal transmission and reducing reflections at the via hole structure.
2Manufacturing precision
If multiple ground via holes are arranged intensively to form a C-shaped ground ring, then impedance control is improved, but the transmission line outlet direction is limited and area is occupied
Solution Approach 1:
The patent employs asymmetric arrangements of ground via holes and annular clearance areas that are optimized for impedance control while leaving specific regions open for flexible transmission line routing. The ground via holes are strategically positioned around the center via hole rather than in a symmetric pattern, allowing transmission lines to exit in multiple directions without being constrained by a fixed C-shaped ground ring configuration.
3Loss of energy
If the clearance area size is increased to reduce signal coupling, then radiation loss is reduced, but the area occupied by the via hole structure increases
Solution Approach 1:
The patent applies local quality by creating annular clearance areas with specific dimensional characteristics localized around the center via hole. The clearance area has an optimized inner diameter and width that provides sufficient isolation to reduce signal coupling and radiation loss while maintaining a compact overall structure. This localized optimization allows the via hole structure to achieve low radiation loss without occupying excessive board area.
Data Source
AI summary
A high frequency signal cross-layer transmission structure in a multi-layer printed circuit board includes a bottom metal layer, a middle metal layer and a top metal layer. The bottom metal layer includes a bottom ground plane and a bottom conductive area. The middle metal layer includes a middle ground plane. The top metal layer includes a top ground plane and a top conductive area. The bottom ground plane defines and surrounds a bottom annular clearance area. The middle ground plane defines and surrounds a middle clearance area. The top ground plane defines and surrounds a top annular clearance area. The bottom annular clearance area surrounds at least one part of the bottom conductive area. The top annular clearance area surrounds at least one part of the top conductive area. A size-shape of the top annular clearance area is different from a size-shape of the middle clearance area.