PCB Pad Anti-Pad Layout for Stub Impedance Discontinuity
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Solution Overview
Problem
The capacitive coupling between the pad stub and the reference ground forms capacitive impedance discontinuity, leading to poor transmission quality of high-speed signals due to signal reflection and impedance fluctuations.
Innovation Solution
A printed circuit board design that includes a signal layer with a pad and a reference layer with anti-pads to reduce capacitive coupling by increasing the distance between the stub and the reference ground, optimizing impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pad is designed to be long to ensure soldering reliability, then soldering reliability is improved, but capacitive coupling between the pad stub and reference ground increases, leading to impedance discontinuity and poor signal transmission quality
Solution Approach 1:
The reference layer is segmented into multiple sub-reference layers positioned at different vertical heights. The first sub-reference layer is located closer to the pad stub while the second sub-reference layer is positioned farther away. This vertical segmentation allows the design to maintain adequate distance from the harmful second reference ground while preserving the beneficial first reference ground for impedance control, thereby resolving the contradiction between soldering reliability and capacitive coupling reduction.
Solution Approach 2:
The patent transitions from a single-layer reference ground structure to a multi-layer reference ground structure with different vertical positions. By utilizing the vertical dimension, the design can simultaneously achieve both close coupling for impedance control (first sub-reference layer) and distance for reducing capacitive coupling (second sub-reference layer), thus resolving the technical contradiction.
2Reliability
If the pad is designed to be long to ensure soldering reliability, then soldering reliability is improved, but signal transmission quality deteriorates due to impedance discontinuity
Solution Approach 1:
The reference layer is divided into multiple sub-reference layers with different vertical positions. The first sub-reference layer provides close coupling for impedance control near the pad stub, while the second sub-reference layer provides distant coupling to reduce capacitive effects. This segmentation enables simultaneous optimization of both soldering reliability and signal transmission quality.
Solution Approach 2:
The patent changes the vertical position parameter of the reference ground by introducing multiple sub-reference layers at different heights. This parameter change allows the design to achieve both adequate coupling for impedance control and sufficient distance to minimize capacitive coupling, thereby improving signal transmission quality while maintaining soldering reliability.
3Object-affected harmful factors
If the distance between the stub and reference ground is increased to reduce capacitive coupling, then signal transmission quality is improved, but impedance control becomes difficult
Solution Approach 1:
The reference layer is segmented into multiple sub-reference layers at different vertical positions. The first sub-reference layer is positioned closer to the stub to provide strong coupling for impedance control, while the second sub-reference layer is positioned farther away to reduce overall capacitive coupling. This segmentation resolves the contradiction by providing both close and distant reference grounds simultaneously.
Solution Approach 2:
By utilizing the vertical dimension, the patent can position different sub-reference layers at different heights relative to the stub. This dimensional approach allows the design to achieve both close coupling (first sub-reference layer) and distant coupling (second sub-reference layer), thereby maintaining impedance control while reducing capacitive coupling effects.
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
Improves signal transmission quality by reducing impedance discontinuity and signal reflection, enhancing signal integrity and channel bandwidth.
Implementation Method 1
the stub is coupled to a reference ground, which forms a capacitive impedance discontinuity
Data Source
AI summary
The present disclosure relates to a printed circuit board having a pad, and a communication device. The printed circuit board comprises: a signal layer and a reference layer, wherein the signal layer is provided with a pad, the pad comprises a stub, the reference layer is provided with a first anti-pad, the vertical projection of the stub in the reference layer is located in a coverage area of the first anti-pad, and the first anti-pad is used for reducing the impedance of the stub.