Coaxial Cable Direct PCB Pad Connection for Signal Integrity
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Solution Overview
Problem
High-speed signals on printed circuit boards (PCBs) face signal integrity issues due to 90-degree transitions, rough surfaces causing skin effect losses, impedance variations, and cross-talk problems from ground vias, leading to routing density issues and reflections.
Innovation Solution
A coaxial or micro coaxial cable is directly connected to the bottom or interior side of PCB pads with the center conductor attached to an outer or inner conductor layer and the outer shielding connected to a ground or power plane, eliminating 90-degree transitions and improving impedance control, using methods like solder, conductive epoxy, or metallic plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signals pass through 90 degree transitions from horizontal trace layers through vertical vias, then connection between layers is achieved, but signal reflections and unwanted effects are created
Solution Approach 1:
The patent extracts the harmful 90-degree transition structure from the signal path by implementing direct through-hole connections that eliminate the via transition. The coaxial cable is connected directly to the PCB pad through a via without requiring 90-degree bends in the trace, thereby removing the source of signal reflections while maintaining layer connectivity.
Solution Approach 2:
Instead of routing signals through horizontal traces that bend at 90 degrees into vertical vias, the patent inverts the approach by using direct vertical through-hole connections that pass through the PCB substrate. This inverts the traditional routing topology, eliminating the need for 90-degree transitions and their associated reflections.
2Ease of manufacture
If horizontal traces are manufactured with standard PCB processes, then manufacturing is simplified, but rough surfaces are created causing skin effect losses
Solution Approach 1:
The patent uses a coaxial cable with a smooth center conductor as a template or copy of the ideal signal transmission path. By connecting this pre-manufactured smooth conductor directly to the PCB pad through a via, the smooth surface geometry is replicated in the high-speed signal path, reducing skin effect losses while keeping the PCB manufacturing process itself unchanged.
3Object-affected harmful factors
If ground vias surround high speed vias to provide shielding, then cross talk is reduced, but routing density issues increase
Solution Approach 1:
The patent merges the signal via and ground reference into a single integrated structure. The coaxial cable's outer shielding is connected to ground, and the center conductor carries the signal, eliminating the need for separate ground vias surrounding the signal via. This consolidation reduces routing complexity while maintaining shielding effectiveness through the coaxial structure itself.
Solution Approach 2:
The coaxial cable acts as an intermediary that provides built-in shielding between the signal and surrounding PCB structures. The outer shielding of the coaxial cable, when connected to ground, serves as a mediator that blocks electromagnetic fields from adjacent traces and vias, reducing cross talk without requiring additional ground vias in the PCB routing.
4Reliability
If coaxial cable is directly connected to PCB pad, then signal integrity is improved, but additional manufacturing steps are required
Solution Approach 1:
The coaxial cable is prepared in advance with its center conductor and outer shielding ready for connection. The PCB is pre-manufactured with the via and pad structure in place. During assembly, the cable is simply inserted and connected, with the preliminary preparation of both components reducing the complexity of the final assembly process despite the specialized connection requirement.
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 approach reduces signal reflections, minimizes skin effect losses, enhances routing density, and decreases cross-talk, thereby improving signal integrity and reducing unwanted effects in high-speed PCB applications.
Implementation Method 1
the center conductor and the ground shielding of said coaxial cable can be connected to the corresponding metal of said PCB by solder, conductive epoxy, metallic plating, friction fit or any other method known in the art
Implementation Method 2
the center conductor and the ground shielding of said coaxial cable can be connected to the corresponding metal of said PCB by solder, conductive epoxy, metallic plating, friction fit or any other method known in the art
Implementation Method 3
the outer shielding of the coaxial cable being connected to one or more internal metal layers of said PCB to provide said cable with a connection to a ground or power plane or planes of the PCB
Implementation Method 4
Due to the skin effect, this rough surface of the traces creates a longer path for the current to travel and creates a greater loss with frequency
Data Source
AI summary
A method and an apparatus for connecting a coaxial (or a micro coaxial) cable to the bottom side of a printed circuit board (PCB) in order to improve signal integrity of a test circuit. A coaxial or a micro coaxial cable is directly connected to a coaxial cable to the bottom sides of pads located on an exterior later of the PCB.