PCB Edge Fingers with Ground Plane Cutouts for Impedance Matching
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Solution Overview
Problem
Existing multi-layer printed circuit boards experience impedance mismatch between the gold finger region and socketed connectors, leading to degraded signal quality due to capacitive effects and impedance deviations from the characteristic transmission line impedance.
Innovation Solution
The multi-layer printed circuit board design incorporates edge fingers with chamfers and strategically placed cut-out portions in ground reference planes, reducing capacitance between edge fingers and aligning single-ended transmission lines to form differential pairs, which helps in minimizing impedance mismatch and signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional edge finger structure is used, then manufacturing is simple, but impedance mismatch occurs between PCB transmission lines and socketed connector
Solution Approach 1:
The patent applies local quality by making the ground reference planes non-uniform through strategically placed cut-out portions. The ground plane has different configurations at different locations: complete ground plane in some areas, cut-out portions in others, creating localized impedance control zones that match the specific capacitance requirements of the edge finger region while maintaining standard manufacturing processes
Solution Approach 2:
The patent changes the geometric parameters of the ground reference planes by introducing cut-out portions with specific dimensions and positions. This modifies the capacitance distribution in the edge finger region, adjusting the impedance characteristics to match the transmission line impedance without changing the edge finger geometry itself
2Reliability
If ground reference planes extend to trailing edges of edge fingers, then grounding is improved, but capacitive effects increase causing impedance deviation
Solution Approach 1:
The patent segments the ground reference planes by introducing cut-out portions that divide the continuous ground plane into separate regions. This segmentation reduces the capacitive coupling between the edge fingers and the ground plane at critical locations while maintaining grounding connectivity through controlled pathways, thereby controlling impedance without sacrificing grounding reliability
Solution Approach 2:
The patent extracts portions of the ground reference plane by creating cut-out portions at strategic locations. This removal of ground plane material reduces the capacitive effects in the edge finger region, allowing the ground plane to provide grounding where needed while minimizing capacitance where it would cause impedance deviation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively reduces capacitive effects, aligning the impedance of the edge finger region closer to the transmission line impedance, thereby improving signal quality and reducing reflections and distortions.
Implementation Method 1
reducing capacitance between edge fingers and aligning single-ended transmission lines
Data Source
AI summary
A multi-layer printed circuit board includes an insertion end, two edge fingers provided on the insertion end, two chamfers formed at two opposite inner corners at two trailing edges of the two edge fingers, and two single-ended transmission lines extending from the two trailing edges of the two edge fingers and converging towards each other to form a differential pair. A first ground reference plane is disposed underneath the two single-ended transmission lines and the differential pair with a leading edge terminates at the trailing edges of the two edge fingers and a first cut-out portion formed at the leading edge. Other ground reference planes are disposed underneath the first ground reference plane with leading edges terminate at the trailing edges of the edge fingers and second cut-out portions are formed at the leading edges, wherein the second cut-out portions are larger than the first cut-out portion.