Three-Layer Flex Circuit for Dense High-Speed Signal Routing
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Solution Overview
Problem
Existing flex circuits degrade in signal integrity as length increases, and twin axial cables are too fat to fit on standard die package substrates without causing warping, limiting the ability to route at least 1024 high-speed differential signal pairs from one major surface.
Innovation Solution
A three-layer flex circuit design with alternating ground and signal conductors and optimized dielectric layers, using liquid crystal polymer for improved dielectric properties, maintains signal integrity and allows for high-density connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If twin axial cables are used to route high-speed differential signal pairs, then signal transmission capability is improved, but substrate warping occurs due to excessive cable thickness
Solution Approach 1:
The patent replaces traditional thick twin axial cables with thin flexible printed circuit board (FPC) cables that have a total thickness of less than 0.2mm. These thin-film flexible circuits maintain the necessary electrical connectivity while eliminating the mechanical burden that causes substrate warping, thus resolving the contradiction between signal transmission capability and substrate shape stability.
Solution Approach 2:
The patent changes the physical parameters of the interconnection medium by transitioning from thick twin axial cables to thin FPC cables with controlled thickness less than 0.2mm. This parameter change enables high-speed differential signal transmission while preventing substrate warping, as the reduced thickness eliminates the excessive mechanical load on the substrate.
2Adaptability or versatility
If flex circuit length increases to accommodate routing requirements, then routing flexibility is improved, but signal integrity degrades
Solution Approach 1:
The patent employs FPC cables constructed with composite material structures, specifically using low-loss dielectric materials with optimized tangent delta values less than 0.005. This composite construction enables the flex circuit to maintain excellent signal integrity over extended lengths while preserving routing flexibility, as the specialized material composition compensates for the increased path length.
Solution Approach 2:
The patent optimizes the electrical parameters of the flex circuit by controlling the dielectric tangent delta to be less than 0.005 and adjusting the characteristic impedance to 100 ohms differential. These parameter optimizations enable the flex circuit to transmit high-speed differential signals effectively over longer distances without significant signal integrity degradation, thus resolving the contradiction between routing flexibility and signal integrity.
3Ease of manufacture
If standard flex circuit design is used, then manufacturing simplicity is maintained, but density is insufficient to route at least 1024 differential signal pairs
Solution Approach 1:
The patent transitions from planar two-dimensional circuit board routing to three-dimensional flexible circuit cable routing. This dimensional change enables the system to accommodate at least 1024 differential signal pairs by utilizing the vertical and lateral flexibility of FPC cables, achieving high-density interconnection while maintaining manufacturing simplicity through standardized FPC fabrication processes.
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 flex circuit design supports high-speed data transmission up to 120 Gbps with improved signal integrity and density, enabling routing of at least 1024 differential signal pairs without substrate warping.
Implementation Method 1
using liquid crystal polymer for improved dielectric properties
Data Source
AI summary
Flex circuit embodiments are provided having high signal conductor density and high signal integrity. Electrical communication systems are described that are configured to be placed in electrical communication with the flex circuits. Electrical communication systems are described that include an electrical connector that is selectively intermatable with an electrical connector that is mounted to a flex circuit, and an electrical connector that is mounted to a substrate such as a printed circuit board (PCB).