Rigid Flex Circuit Signal Integrity at 14 Gb/s
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Solution Overview
Problem
Traditional rigid flex PCB design techniques are unsuitable for high-speed data transmission frequencies above 14 Gb/s due to signal degradation issues, such as feed-through vias, transmission line interconnects, and low impedance ground connections, making them inadequate for modern optoelectronic modules.
Innovation Solution
A rigid flex circuit is constructed using a combination of flexible and rigid sections with specific insulating layers and signal transmission lines, including a root mean square surface roughness of 20 micrometers or below, and filled signal vias passing through the rigid insulating layer, to minimize signal degradation and support higher data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional rigid flex PCB design techniques are used, then manufacturing cost and assembly effort are reduced, but signal degradation occurs at data rates above 14 Gb/s
Solution Approach 1:
The patent changes critical parameters of the PCB design including trace geometry (width, spacing, curvature), via configurations (filled vs. through-holes, positioning), and impedance control settings to optimize signal transmission at high frequencies while maintaining manufacturability
Solution Approach 2:
The patent applies different design qualities to different regions of the PCB - signal traces have specific roughness requirements, vias have specific filling requirements, and different sections of the board have different impedance requirements to optimize high-speed signal transmission locally where needed
2Volume of moving object
If flexible PCB sections are used to transition from dual-side rigid edge connector to transmitters/receivers, then space efficiency is improved, but signal transmission reliability deteriorates at high frequencies
Solution Approach 1:
The patent divides the PCB into distinct flexible and rigid sections, with the flexible section containing controlled impedance traces and minimized via structures to maintain signal integrity while achieving the required spatial transition
Solution Approach 2:
The patent uses the flexible PCB section to create three-dimensional routing paths that transition signals from the planar rigid connector region to the vertically oriented transmitter/receiver region, utilizing flexibility as an additional degree of freedom for signal routing
3Productivity
If data signal frequency is increased to increase communication rate, then data transmission speed is improved, but signal degradation worsens
Solution Approach 1:
The patent optimizes trace geometry parameters (width, spacing, curvature radius) and via parameters (diameter, filling material, positioning) to minimize signal loss and maintain impedance control at higher frequencies, enabling increased data rates without proportional signal degradation
Solution Approach 2:
The patent replaces traditional mechanical connector designs with optimized rigid flex PCB trace structures and filled via configurations that provide more stable electrical characteristics at high frequencies, substituting physical connection optimizations with controlled electromagnetic field structures
Data Source
AI summary
High-speed pluggable rigid-end flex circuit. A circuit includes a flexible section, rigid section, connector disposed on the rigid section, and electrically conductive signal transmission line electrically coupled to the connector. The flexible section includes a first portion of a flexible insulating layer. The rigid section includes a second portion of the flexible insulating layer and a rigid insulating layer disposed on the second portion of the flexible insulating layer. The connector is configured to form a pluggable conductive connection. The electrically conductive signal transmission line includes a first signal trace having a root mean square surface roughness below 20 micrometers and a filled signal via configured to pass through at least a portion of the rigid insulating layer. The flexible and rigid insulating layers have a dissipation factor equal to or below a ratio of 0.004 and a dielectric constant equal to or below a ratio of 3.7.