Via Transmission Line for Multilayer PCBs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Transitions between signal layers in multilayer printed circuit boards (PCBs) experience high return and leakage losses due to the design of via structures, which degrade the electrical performance of interconnect circuits.
Innovation Solution
A via transmission line is formed with a signal via or vias as the inner conductive boundary, surrounded by ground vias and ground plates as the outer conductive boundary, and a clearance hole that isolates the inner and outer boundaries, with specific dimensions and shapes to minimize corrugations and ensure full-value connections, mimicking the properties of a coaxial waveguide to achieve broadband operation and shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional via structures are used for transitions between signal layers, then the structure is simple and easy to manufacture, but return losses and leakage losses are high which degrades electrical performance
Solution Approach 1:
The via structure is segmented into multiple functional components: signal vias for signal transmission, ground vias for shielding and reference potential, and insulating segments (clearance holes) for electrical isolation. This segmentation allows each component to perform its specific function optimally, reducing return and leakage losses while maintaining manageable manufacturing complexity through standardized fabrication processes.
Solution Approach 2:
The via transmission line structure embeds multiple layers of conductive and insulating elements within each other. Signal vias are nested within the PCB substrate, surrounded by ground vias and insulating clearance holes, which are in turn embedded within outer ground structures. This nested configuration creates a shielded transmission path that reduces electromagnetic interference and improves electrical performance without requiring excessive external space.
2Loss of energy
If via structures with simple geometry are used, then manufacturing is easier, but frequency-dependent return losses increase
Solution Approach 1:
The clearance hole dimensions are precisely controlled with specific parameter ranges (e.g., diameter, length, positioning) to optimize the via transmission line's electrical characteristics. By adjusting these geometric parameters, the structure achieves broadband impedance matching and minimizes frequency-dependent return losses. The manufacturing process incorporates precision control methods to maintain these critical dimensions within tight tolerances, balancing performance requirements with manufacturability.
3Object-affected harmful factors
If ground plates are made larger to improve shielding, then shielding properties improve, but the dimensions of ground plates responsible for frequency-dependent return loss increase
Solution Approach 1:
The ground structure implements local quality optimization by placing ground vias and ground plates at specific locations around the signal via, rather than using uniformly large ground plates. The ground elements are strategically positioned to provide shielding where most needed (near the signal via) while maintaining appropriate spacing to avoid creating large continuous conductive areas that would increase return losses. This localized approach achieves effective electromagnetic shielding with minimized return losses.
Solution Approach 2:
Insulating clearance holes serve as intermediary elements between the signal via and ground structures. These clearance holes electrically isolate the signal path from the ground plates while allowing the ground plates to provide shielding. The clearance holes mediate the interaction between signal and ground, preventing direct capacitive coupling that would cause return losses while still allowing the ground structure to function as an electromagnetic shield.
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 configuration reduces frequency-dependent return losses, enabling low return and leakage losses across a wide frequency band, thereby enhancing the electrical performance of interconnect circuits by maintaining constant characteristic impedance and minimizing electromagnetic leakage.
Implementation Method 1
A wave guiding channel of the via transmission line is disposed between the inner and the outer conductive boundaries of the via transmission line
Implementation Method 2
Ground vias jointly with ground plates forming the outer conductive boundary provide high-shielding characteristics of the via transmission line
Implementation Method 3
The characteristic impedance control is carried out by a determination of appropriate dimensions of inner and outer conductive boundaries of the via transmission line proceeding from a formula for corresponding coaxial waveguide with homogeneous continuous inner and outer conductive boundaries
Data Source
AI summary
A via transmission line for a multilayer printed circuit board (PCB) in which a wave guiding channel is formed by a signal via or a number of signal vias, an assembly of ground vias surrounding the signal via or corresponding number of coupled signal vias, a set of ground plates from conductor layers of the multilayer PCB, and a clearance hole. In this via transmission line, the signal via, or the number of signal vias forms an inner conductive boundary, ground vias and ground plates from conductor layers of the multilayer PCB form an outer conductive boundary, and the clearance hole provides both isolation of the inner conductive boundary from the outer conductive boundary and high-performance broadband operation of the via transmission line by means of the predetermined clearance hole cross-sectional shape and dimensions where the cross-sectional shape of the clearance hole is defined by the arrangement of ground vias in the outer conductive boundary and dimensions of the clearance hole are determined according to a method to minimize frequency-dependent return losses caused by specific corrugations of the outer conductive boundary formed by ground plates in the wave guiding channel of the via transmission line.