Flexible PCB Ground Pattern with Triangular Openings for Impedance Control
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Solution Overview
Problem
Conventional flexible printed circuit boards face challenges in matching input/output impedance of circuit elements with characteristic impedance of the wiring layer, particularly when the width of the wiring layer is limited, and require high registration accuracy between wiring layers and ground patterns, which restricts design flexibility and manufacturing precision.
Innovation Solution
The implementation of a printed circuit board with a conductor pattern featuring regularly formed triangular openings reduces the opposing area between wiring layers and the conductor pattern, increasing characteristic impedance while allowing for positional shifts without significant impedance variation, thereby easing registration accuracy requirements and design restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the width of the wiring layer is reduced to raise characteristic impedance, then the characteristic impedance increases, but the wiring layer width becomes too narrow to be practical
Solution Approach 1:
The ground pattern is designed with varying local properties - dense ground lines in some regions and triangular openings in others - to create spatially varying capacitance distribution. This allows the characteristic impedance to be controlled locally without changing the overall wiring layer width, resolving the contradiction between impedance matching and practical wiring dimensions.
Solution Approach 2:
The invention changes the geometric parameters of the ground pattern (introducing triangular openings with specific side lengths and spacing) to adjust the capacitance between the wiring layer and ground pattern. This enables characteristic impedance control through ground pattern modification rather than wiring layer width adjustment, maintaining practical wiring dimensions while achieving impedance matching.
2Reliability
If the thickness of the insulating layer is increased to reduce capacitance and raise characteristic impedance, then the characteristic impedance increases, but the flexibility of the flexible printed circuit board deteriorates
Solution Approach 1:
Instead of uniformly increasing insulating layer thickness, the invention introduces localized variations in the ground pattern (triangular openings) that create regions of reduced capacitance. This achieves characteristic impedance control through spatially selective capacitance reduction rather than global thickness increase, preserving board flexibility while matching impedance.
Solution Approach 2:
The invention changes the ground pattern geometry (introducing triangular openings) to adjust capacitance and characteristic impedance without modifying the insulating layer thickness. This maintains the thin insulating layer structure necessary for flexibility while achieving the required impedance characteristics through ground pattern optimization.
3Reliability
If regular openings are formed in the ground pattern to reduce capacitance and increase characteristic impedance, then the characteristic impedance can be adjusted, but the positional restriction on wiring layers and registration accuracy requirement increase
Solution Approach 1:
The ground pattern uses asymmetric triangular openings rather than symmetric square or circular openings. This asymmetric geometry creates a more robust capacitance profile that is less sensitive to positional variations of the wiring layer, reducing the impact of registration errors and easing manufacturing precision requirements while still achieving characteristic impedance control.
4Reliability
If the area of the ground pattern region opposing the wiring layer is reduced to increase characteristic impedance, then the capacitance decreases and characteristic impedance increases, but the positional restriction on wiring layers in design increases
Solution Approach 1:
The ground pattern is segmented into multiple ground lines with triangular openings between them, creating a distributed capacitance structure. This segmentation allows the capacitance to be controlled through the density and geometry of the segments rather than the overall ground pattern area, enabling characteristic impedance matching while maintaining design flexibility in wiring layer placement.
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 solution allows for adjustable characteristic impedance and reduced positional restrictions, enhancing design flexibility and manufacturing precision by maintaining consistent capacitance across various positional relationships between wiring layers and the conductor pattern.
Implementation Method 1
The capacitance C between the wiring layer and the ground pattern is adjusted, so that the characteristic impedance of the wiring layer can be adjusted
Data Source
AI summary
A ground pattern includes a plurality of integrally formed first to third ground lines. A plurality of first ground lines are arranged parallel to one another at equal intervals. A plurality of second ground lines are arranged parallel to one another at equal intervals between adjacent ones of the first ground lines. A plurality of third ground lines are arranged parallel to one another at equal intervals between adjacent ones of the first ground lines at a predetermined angle with respect to the second ground lines. The third ground lines each connect one end of one adjacent second ground line with the other end of another adjacent second ground line. The ground lines form triangular openings.