Coaxial Via Ground Shielding for PCB Signal Integrity
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Solution Overview
Problem
Existing coaxial via structures in printed circuit boards do not provide ground shielding for the entire length of the signal via, leading to a non-impedance controlled environment and compromised signal integrity during trace routing.
Innovation Solution
A method and structure where coaxial vias extend the entire length of the signal via, incorporating either a ground vias cage or a ground trench for comprehensive ground shielding, ensuring continuous impedance control and signal integrity by using copper plating and conductive epoxy to maintain the ground reference across multiple layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ground shielding is not provided for the entire length of the signal via, then the structure is simpler and easier to manufacture, but signal integrity deteriorates due to non-impedance controlled environment
Solution Approach 1:
The ground shielding is segmented into two distinct configurations: a ground vias cage for traces entering from built-up layers, and a ground trench for traces accessing from other orientations. This segmentation allows each shielding type to be optimized for its specific use case while maintaining overall signal integrity throughout the via length.
Solution Approach 2:
The ground vias cage and ground trench act as intermediary structures between the signal via and the reference planes. These intermediaries provide the necessary ground reference and shielding without requiring direct connection to both reference planes, thus maintaining impedance control while simplifying the overall structure.
2Reliability
If the coaxial via structure is extended to provide ground shielding for the entire length, then signal integrity is improved, but manufacturing complexity increases
Solution Approach 1:
The manufacturing process is segmented into distinct stages: drilling and plating the signal via, forming the ground vias cage or ground trench, and selective plating of the shielding structures. This segmentation allows each component to be manufactured using standard PCB processes, avoiding the need for complex single-step fabrication.
Solution Approach 2:
The ground vias cage and ground trench are formed preliminarily before the final signal via plating. This preliminary action ensures that the shielding structures are in place to maintain impedance control during subsequent manufacturing steps, while allowing the use of standard plating processes rather than requiring complex simultaneous formation.
3Reliability
If ground vias cage or ground trench is implemented, then continuous ground shielding is achieved, but device complexity and manufacturing steps increase
Solution Approach 1:
Different ground shielding configurations are applied locally based on the specific routing requirements: ground vias cage is used when traces enter from built-up layers, while ground trench is used for other trace access orientations. This local quality approach ensures optimal shielding for each scenario without requiring a complex universal solution.
Solution Approach 2:
Instead of providing continuous solid ground shielding around the entire via length, the patent inverts the approach by using discrete ground vias arranged in a cage configuration or a ground trench that provides equivalent shielding functionality. This inverted approach achieves the same impedance control goal with reduced material and structural complexity.
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
The solution effectively maintains signal integrity by providing continuous ground shielding, reducing return loss and reflections, and ensuring impedance control throughout the signal via length.
Implementation Method 1
using copper plating and conductive epoxy to maintain impedance and signal integrity
Implementation Method 2
The vias are plated with metallic plating 12 (unlike the via's in U.S. Pat. No. 5,421,083) and are preferably plated with copper (Cu) plating. The next step of the method for forming the structure 5 of the present disclosure is shown in FIG. 2B in which a non conductive paste 14 such as an epoxy is used to fill the void of the ground vias.
Data Source
AI summary
A method and a structure for a coaxial via that extend along the entire length of a signal via in a printed circuit board. Signal integrity is improved by providing ground shield for the entire length of the coaxial via. The ground shielding can be implemented by either providing ground cage vias around a signal via and routing a trace to the signal via on a built up layer or by providing a semi circle ground trench through a build up layer to permit a trace access to the signal via.