Reference Plane Surface Profile Modification for Crosstalk Reduction
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Solution Overview
Problem
Current techniques to reduce fringing magnetic fields between transmission lines on circuit boards, such as adding space or shield traces, compromise routing density and increase costs, while existing methods to control mutual capacitance are limited by manufacturing challenges and impedance control requirements.
Innovation Solution
Modifying the surface profile of the reference plane layer by forming trenches or protrusions to reduce the resistance of the return current path and adjusting the effective dielectric constant of the insulating layer to control magnetic field distribution and mutual capacitance between transmission lines without affecting routing density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If space is added between transmission lines or shield traces are added, then fringing magnetic field interference is reduced, but routing density decreases and circuit board body size increases
Solution Approach 1:
The reference plane layer is modified to have non-uniform thickness with localized protrusions positioned adjacent to transmission lines. These localized structural changes create regions of different electrical properties that control magnetic field distribution without requiring uniform spacing between all transmission lines, thereby maintaining high routing density while reducing fringing magnetic field interference in critical areas.
2Object-affected harmful factors
If reference plane is moved closer to signal traces, then mutual capacitance is reduced, but manufacturing challenges and impedance control difficulties increase
Solution Approach 1:
Instead of uniformly moving the reference plane closer to all signal traces, the invention introduces localized protrusions in the reference plane layer only in regions where mutual capacitance control is critical. This selective approach reduces mutual capacitance where needed while maintaining manufacturable spacing elsewhere, avoiding the manufacturing and impedance control challenges associated with uniform close spacing.
Solution Approach 2:
The invention controls mutual capacitance by modifying the reference plane layer in the vertical dimension (creating protrusions of different thicknesses) rather than relying solely on horizontal spacing. This dimensional change allows for precise control of electrical characteristics while maintaining practical manufacturing dimensions and impedance control.
3Ease of manufacture
If uniform reference plane thickness is used, then manufacturing is simplified, but magnetic field distribution and mutual capacitance cannot be controlled
Solution Approach 1:
The reference plane layer transitions from uniform thickness to non-uniform thickness with localized protrusions positioned strategically adjacent to transmission lines. These localized variations create controlled regions with different electrical properties that enable magnetic field distribution control and mutual capacitance management while maintaining relative manufacturing simplicity through targeted rather than universal modifications.
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 approach effectively reduces fringing magnetic fields and mutual capacitance, allowing for increased routing density without increasing board size, thereby improving crosstalk performance and maintaining signal integrity while reducing costs.
Implementation Method 1
The distribution of a magnetic field within and around a transmission line determines the amount of self-inductance of the transmission line and the mutual-inductance of the transmission line to adjacent signal lines
Implementation Method 2
A surface profile of the reference plane layer is modified to decrease a resistance of a return current signal path through the reference plane layer
Implementation Method 3
The mutual capacitance between two adjacent transmission lines on a common circuit board is a major factor in determining important characteristics such as crosstalk and differential impedance
Implementation Method 4
The mutual capacitance is directly proportional to the relative permittivity (effective dielectric constant) of the dielectric medium that separates the two transmission lines
Data Source
AI summary
Magnetic field distribution and mutual capacitance control for transmission lines are provided. A first circuit board is fabricated by attaching a reference plane layer to a dielectric material layer, and attaching a first trace to the second surface of the dielectric material. A surface profile of the reference plane layer is modified to decrease a resistance of a return current signal path through the reference plane layer, to reduce a magnetic field coupling between the first trace and a second trace. A second circuit board is fabricated by attaching a reference plane layer to a dielectric material layer, attaching a trace to the dielectric material, and forming a solder mask layer on the dielectric material layer over the trace. An effective dielectric constant of the solder mask layer is modified to reduce or increase a mutual capacitance between the first trace and a second trace on the dielectric material.