PCB Connector Pinfield Ground Straddling for 50 Ohm Impedance
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Solution Overview
Problem
High-speed communication links in printed circuit boards (PCBs) face impedance issues due to constrained pinfield geometry, resulting in signal via impedance less than 50 ohms, which degrades performance and increases cross-talk between differential pairs.
Innovation Solution
The implementation of ground straddling differential pairs of traces on multilayer PCBs, where traces pass on either side of a centerline through rows of reference vias, allowing for enlarged anti-pads without increasing cross-talk, achieved by optimizing spacing and routing using three-dimensional computational electromagnetic tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the anti-pad diameter is increased to achieve 50 ohm impedance, then the signal via impedance improves, but the trace routing becomes constrained and cross-talk between differential pairs increases
Solution Approach 1:
The patent inverts the conventional trace routing approach by having differential pairs straddle ground vias instead of signal vias. This inversion allows traces to pass between ground vias, creating natural spacing that reduces cross-talk while enabling larger anti-pads around signal vias to achieve proper 50 ohm impedance control.
Solution Approach 2:
Ground vias serve as intermediary elements that mediate between the need for large anti-pads (for impedance control) and the need for trace spacing (to reduce cross-talk). The ground vias act as physical separators that allow traces to maintain proper spacing while anti-pads can be enlarged without increasing cross-talk.
2Manufacturing precision
If the anti-pad diameter is increased to improve signal via impedance, then the impedance control improves, but the separation between adjacent differential pairs is reduced
Solution Approach 1:
By inverting the routing strategy to straddle ground vias rather than signal vias, the patent enables larger anti-pads without forcing differential pairs closer together. The ground vias provide natural spacing boundaries that maintain separation between adjacent differential pairs even when anti-pads are enlarged.
3Adaptability or versatility
If the pinfield geometry is constrained by connector requirements, then the connector compatibility is maintained, but the signal via impedance deviates from 50 ohms
Solution Approach 1:
The patent segments the via functions by separating ground vias from signal vias in the pinfield array. This segmentation allows independent optimization: ground vias provide reference planes and spacing, while signal vias can have enlarged anti-pads for proper impedance control, all within the constrained connector pinfield geometry.
Solution Approach 2:
The patent applies local quality by creating different via types in different locations within the pinfield. Ground vias are positioned to provide reference planes, while signal vias have enlarged anti-pads for impedance control. This local differentiation allows impedance optimization in specific areas without affecting overall connector compatibility.
Data Source
AI summary
High-speed communication links are improved by having differential pairs of traces in a connector pinfield on layers of a multilayer printed circuit board (PCB) to straddle respective rows of reference (ground) pins rather than the respective rows of signal vias. Thus, a desirable increase in the size of each an anti-pad to surrounding each signal via pad can be incorporated without forcing tracing of adjacent differential pairs closer to one another, and thus increased cross talk is avoided. Thereby, 50 ohm or close to 50 ohm impedance for each signal via is achieved. Spacing and routing between traces of each differential pair are advantageously adjusted for skew compensation and impedance optimization utilizing three dimensional computational electromagnetic tools.