Rigid-Flex PCB Dummy Metal Layout for Resonance Control
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Solution Overview
Problem
Existing rigid flexible printed circuit boards (RFPCBs) face challenges in maintaining a high resonant frequency without altering the flexible portion's length, particularly in wireless communication devices, due to the difficulty in arranging conductive vias in flexible portions, which can lead to low resonant frequencies and increased crack risk.
Innovation Solution
Incorporating a dummy metal layer between rigid conductive layers on the flexible portion of the RFPCB, overlapping the transmission line, to enhance resonant frequency without changing the flexible portion's length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conductive vias are arranged in the flexible portion to raise resonant frequency, then resonant frequency is improved, but manufacturing difficulty increases due to the rigid material of conductive vias
Solution Approach 1:
The patent uses a dummy metal layer as a copy or substitute for the conventional conductive vias. Instead of forming actual conductive vias through the flexible portion (which is difficult due to rigid material requirements), the invention creates a dummy metal layer pattern that replicates the electromagnetic effect of conductive vias by overlapping the transmission line, thereby raising the resonant frequency without the manufacturing complexity
Solution Approach 2:
The dummy metal layer acts as an intermediary element between the transmission line and the ground plane. It mediates the electromagnetic field distribution in the flexible portion, providing the necessary resonant frequency control without requiring direct physical connection through rigid conductive vias, thus solving the manufacturing difficulty while maintaining electrical performance
2Reliability
If the length of the flexible portion is shortened to raise resonant frequency, then resonant frequency is improved, but the risk of cracks increases and assemblability decreases
Solution Approach 1:
The patent applies local quality by introducing the dummy metal layer specifically in the flexible portion where it is needed for resonant frequency control, while leaving the rest of the flexible portion structure intact. This localized intervention raises the resonant frequency without requiring shortening of the overall flexible portion length, thereby maintaining crack resistance and assemblability
Solution Approach 2:
The invention transitions from controlling resonant frequency through one-dimensional structural changes (length modification) to using a two-dimensional patterned dummy metal layer overlay. This dimensional approach allows resonant frequency adjustment without compromising the mechanical integrity and length of the flexible portion
3Adaptability or versatility
If the length of the flexible portion is increased to maintain flexibility, then flexibility is improved, but resonant frequency decreases
Solution Approach 1:
The patent changes the electromagnetic parameters of the flexible portion by introducing the dummy metal layer with specific patterns, positions, and dimensions. This parameter modification raises the resonant frequency without altering the physical dimensions or flexibility characteristics of the flexible portion, thereby resolving the trade-off between flexibility and resonant frequency
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 dummy metal layer effectively raises the resonant frequency, preventing resonance phenomena and maintaining flexibility, thus improving RFPCB performance in designated frequency bands like 14-GHz and up to 40 GHz.
Implementation Method 1
a resonant frequency of the transmission line may be determined according to a distance between two adjacent conductive vias of the plurality of conductive vias... it is necessary to prevent the formation of a resonant frequency within the set range and to induce the resonant frequency to be formed higher than the set range
Data Source
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Figure 2B
AI summary
A rigid flexible printed circuit board (RFPCB) may include: a first base conductive layer; a first rigid conductive layer spaced apart from the first base conductive layer in a first direction; a second rigid conductive layer spaced apart from the first base conductive layer in the first direction and spaced apart from the first rigid conductive layer in a second direction intersecting the first direction; a base cover layer spaced apart from the first base conductive layer in the first direction and positioned closer to the first base conductive layer than to the first rigid conductive layer and the second rigid conductive layer; a transmission line positioned between the first base conductive layer and the base cover layer; and a dummy metal layer disposed on the base cover layer, positioned between the first rigid conductive layer and the second rigid conductive layer, and overlapping the transmission line in the first direction.