Flexible Substrate Microstrip Impedance Control
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Solution Overview
Problem
Flexible substrates with coplanar lines often experience deviations in characteristic impedance due to variations in distance and width, leading to suboptimal performance in high-frequency signal transmission.
Innovation Solution
A flexible substrate design featuring an insulating substrate with specific configurations of conductors, ground patterns, and via wires, where the distance between the conductor pattern and the third ground pattern is smaller than the distance between the first conductor and the first ground pattern, allowing for controlled characteristic impedance and improved bond strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between signal line and ground pattern is increased to reduce capacitance, then the characteristic impedance increases, but the bond strength between conductor and ground pattern decreases
Solution Approach 1:
The invention transitions from a two-dimensional planar arrangement to a three-dimensional stacked configuration. The conductor pattern on the second surface is positioned directly below the first conductor on the first surface, with via wires connecting them vertically through the insulating substrate. This vertical stacking allows the distance between conductors to be precisely controlled in the thickness direction while maintaining strong bonding through overlapping areas and via wire connections, thereby achieving desired characteristic impedance without compromising bond strength.
2Reliability
If the width of conductor pattern is increased to reduce characteristic impedance, then the impedance matching improves, but the insertion loss increases
Solution Approach 1:
The invention applies different geometric configurations to different parts of the transmission line structure. The conductor pattern on the second surface has a width specifically optimized for impedance matching at the connection portion, while the overall layout and spacing are designed to minimize signal loss. The via wires provide localized electromagnetic coupling that enables precise impedance control without requiring excessive conductor width that would increase resistive losses.
3Ease of manufacture
If via wires are used to connect conductor patterns across insulating substrate, then electrical connection is achieved, but manufacturing complexity increases
Solution Approach 1:
The via holes are formed in the insulating substrate before the conductor patterns are deposited. This preliminary hole formation allows for precise positioning and alignment of the via wires, simplifying subsequent manufacturing steps. The via holes are created at predetermined locations where electrical connections are required, enabling efficient assembly of the multi-layer structure without complex alignment procedures during conductor deposition.
Data Source
AI summary
A flexible substrate is disclosed. The flexible substrate includes an insulating substrate having a first surface and a second surface opposite to the first surface, a first connection portion having a first conductor, a first ground pattern, and a second ground pattern on the first surface, the first ground pattern and the second ground pattern being spaced apart from the first conductor and respectively located at either side of the first conductor, a conductor pattern formed on the second surface, the conductor pattern being connected to the first conductor, and a third ground pattern formed on the second surface, the third ground pattern being connected to the first ground pattern, wherein a distance between the conductor pattern and the third ground pattern is smaller than a distance between the first conductor and the first ground pattern.