Hybrid Rigid-Flex PCB Layout for Low-Loss RF Signal Routing
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Solution Overview
Problem
Coaxial cables used for high-frequency transmission in electronic devices are costly and require complex assembly, and the narrow internal spaces in portable devices increase defect rates due to small connectors, while existing PCBs face challenges in efficiently transmitting high-frequency signals without noise and affecting other modules.
Innovation Solution
A high-frequency transmission line is implemented using a PCB with conductive vias and integrated FPCBs and rigid PCBs, allowing signal transmission without contact with vias and reducing line loss, thus replacing coaxial cables and optimizing space usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coaxial cables are used for high-frequency transmission lines, then signal transmission quality is improved, but material cost and assembly complexity increase
Solution Approach 1:
The patent merges the transmission line function with the PCB structure by routing high-frequency signals through vias and conductive paths integrated into the PCB layers. This eliminates the need for separate coaxial cables and their connectors, reducing assembly complexity while maintaining signal transmission quality through proper via design and grounding structures.
Solution Approach 2:
The patent introduces conductive vias and ground structures as intermediary elements within the PCB to mediate high-frequency signal transmission. These vias serve as controlled impedance transmission paths, replacing the need for external coaxial cables while maintaining signal integrity through proper electromagnetic field management.
2Reliability
If coaxial cables with small connectors are used, then high-frequency signal transmission is achieved, but defect rate increases due to narrow internal spaces
Solution Approach 1:
The transmission line is merged with the PCB structure, eliminating separate connectors that require precise assembly in narrow spaces. The high-frequency signal path is formed by integrated PCB features including vias, conductive traces, and ground planes, which are manufactured as part of the PCB fabrication process rather than assembled separately.
Solution Approach 2:
The patent replaces the mechanical connector system with an integrated PCB-based transmission line. Instead of using physical connectors that require manual or automated assembly in tight spaces, the high-frequency signal path is created through PCB fabrication processes including via plating and trace routing, eliminating assembly defects related to connector installation.
3Loss of substance
If PCB is used to replace coaxial cable, then material cost is reduced, but line loss increases
Solution Approach 1:
The patent optimizes the PCB transmission line parameters including via diameter, trace width, spacing, and dielectric material properties to control impedance and minimize signal loss. By carefully adjusting these parameters, the PCB-based transmission line achieves low line loss comparable to coaxial cables while eliminating the need for expensive external components.
Solution Approach 2:
The patent introduces ground planes and shielding structures as intermediary elements within the PCB to reduce electromagnetic interference and signal loss. These ground structures act as return paths and shields, minimizing radiation and crosstalk, thereby reducing line loss despite the shorter transmission path provided by the integrated PCB design.
4Adaptability or versatility
If FPCB is used for transmission, then design flexibility is improved, but line loss increases compared to rigid PCB
Solution Approach 1:
The patent segments the transmission path into rigid PCB sections for stable, low-loss signal transmission and flexible PCB sections for design adaptability. The rigid portions maintain consistent impedance and minimal line loss, while the flexible portions provide the necessary design flexibility for complex device layouts, optimizing both performance and versatility.
Solution Approach 2:
The patent optimizes the flexible PCB parameters including substrate material, trace geometry, and via design to minimize line loss while maintaining flexibility. By carefully controlling these parameters, the FPCB transmission line achieves acceptable signal integrity despite the inherent losses associated with flexible substrates, enabling both design flexibility and reasonable performance.
Data Source
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AI summary
A portable communication device comprises first and second electronic components and a printed circuit board (PCB) electrically connected with the first and second electronic components. The PCB includes a first flexible PCB portion in contact with a first rigid PCB portion, a second rigid PCB portion in contact with the first flexible PCB portion, and a second flexible PCB portion in contact with the second rigid PCB portion. Each rigid PCB portion includes a first insulating layer of a first material forming a first exterior surface, a first conduction layer located on or above the first insulating layer, a second insulating layer having a first thickness, a second conduction layer, and a third insulating layer of the first material forming a second exterior surface. Each flexible PCB portion includes a first insulating layer of a second material different from the first material forming a first exterior surface, a first conduction layer electrically connected with the conduction layers of the rigid PCB portions, a second insulating layer having a second thickness thinner than the first thickness, a second conduction layer electrically connected with the conduction layers of the rigid PCB portions, and a third insulating layer of the second material forming a second exterior surface.