Embedded PCB Signal Line Shielding for Impedance Control
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Solution Overview
Problem
Printed circuit boards (PCBs) face challenges in maintaining signal integrity due to signal reflections, leakage currents, uncontrolled impedance, crosstalk, and electromagnetic noise, especially in high-frequency applications, where conventional design measures like increasing thickness to reduce noise are not feasible due to space constraints.
Innovation Solution
A PCB design featuring signal lines covered by a dielectric film with a thin conductive layer, extending over the signal lines' surfaces and sides, using materials like epoxy film and carbon, silver, or copper paste, to reduce electromagnetic interference and maintain impedance while minimizing thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the distance between signal lines and ground is increased to achieve higher impedance, then impedance control is improved, but PCB thickness increases
Solution Approach 1:
The patent applies a thin dielectric film (thickness 5-20 µm) to cover the signal line, creating a controlled impedance structure without increasing overall PCB thickness. This thin film approach allows precise impedance control while maintaining compact form factor.
Solution Approach 2:
The patent changes the dielectric parameters by using a low relative permittivity material (εr = 3.0-4.0) and controlling the film thickness to achieve the desired impedance characteristics. This parameter optimization enables impedance control without requiring increased distance between signal lines and ground.
2Reliability
If spaces between signal lines are widened to reduce crosstalk and electromagnetic noise, then signal integrity is improved, but PCB thickness increases
Solution Approach 1:
The thin dielectric film acts as a shielding layer that reduces crosstalk and electromagnetic interference between adjacent signal lines. This film-based approach provides EMI protection without requiring increased spacing between lines, thereby avoiding thickness increase.
Solution Approach 2:
The dielectric film serves as an intermediary layer between signal lines, mediating the electromagnetic field interaction and reducing harmful coupling effects. This intermediary structure improves signal integrity while maintaining compact line spacing.
3Ease of manufacture
If conventional dielectric materials are used to maintain signal integrity, then manufacturing ease is improved, but signal loss in high-frequency regions increases
Solution Approach 1:
The patent specifies a dielectric film with relative permittivity εr = 3.0-4.0 and thickness 5-20 µm, optimizing these parameters to minimize dielectric loss at high frequencies. This parameter control reduces signal attenuation while maintaining compatibility with standard PCB manufacturing processes.
Solution Approach 2:
The patent uses a composite structure combining the thin dielectric film with the underlying prepreg layer, creating a multi-layer dielectric system that optimizes both low loss characteristics and manufacturability. This composite approach balances performance requirements with production feasibility.
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 design enhances signal integrity by reducing crosstalk and electromagnetic noise, achieving predefined impedance and minimizing signal loss in high-frequency regions without increasing the PCB's thickness, thereby improving overall performance.
Implementation Method 1
The at least one signal line is covered by a dielectric film, followed by a thin conductive layer
Data Source
AI summary
A printed circuit board (11) comprising conductive layers separated by insulation layers of dielectric material, at least one conductive layer (13) being patterned and having at least one signal line (14, 15) embedded in insulation material. The at least one signal line (14, 15) is covered by a dielectric film (20), followed by a thin conductive layer (21), whereby the dielectric film covers at least one surface (14s, 15s) and both sides (14a, 14b; 15a, 15b) of the at least one signal line and the thin conductive layer (21) extends, separated by the dielectric film, over the at least one surface of the signal line and at least partially over the height (h) of both sides of the signal line.