Vertical Via Interconnect Layout for Reduced High-Frequency Capacitance
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Solution Overview
Problem
Conventional vertical interconnections in multi-layer substrates exhibit strong capacitive behavior due to dielectric loading, leading to mismatch issues at high frequencies and increased insertion loss, which are challenging to address effectively in high-frequency or millimeter-wave applications.
Innovation Solution
A vertical interconnection structure is designed with non-circular ground planes and pullback regions surrounding via pads, along with ground vias and signal vias, to electrically isolate the signal paths from the ground planes, improving electrical isolation and reducing capacitive effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional vertical interconnections are used in multi-layer substrates, then the structure is simple and easy to manufacture, but strong capacitive behavior occurs due to dielectric loading, causing mismatch issues at high frequencies and increased insertion loss
Solution Approach 1:
The ground plane is segmented into two distinct regions: a first ground plane region adjacent to the via pad and a second ground plane region separated by a ground pullback region. This segmentation reduces the capacitive coupling between the signal via and the ground plane, thereby reducing strong capacitive behavior and improving high-frequency performance without requiring completely new structures
Solution Approach 2:
A ground pullback region is introduced as an intermediary element between the via pad and the ground plane. This pullback region acts as a buffer that electrically isolates the via pad from the ground plane, reducing the direct capacitive coupling and dielectric loading effects while maintaining the overall structural simplicity
2Reliability
If ground planes are placed close to via pads for electrical connection, then the connection is strong and reliable, but capacitive effects increase due to dielectric loading, causing mismatch at high frequencies
Solution Approach 1:
The ground plane is extracted or pulled back from its conventional position adjacent to the via pad, creating a ground pullback region. This extraction reduces the capacitive coupling between the signal path and ground while maintaining reliable electrical connection through the via structure itself, thereby reducing mismatch at high frequencies
Solution Approach 2:
The ground pullback region is designed to maintain equipotential conditions while being separated from the via pad. By keeping the ground plane at a consistent potential but at a controlled distance, the design reduces capacitive effects while maintaining reliable grounding and electrical connection
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 frequency operation and achieves better voltage standing wave ratio (VSWR) performance, allowing for a 10-30 dB bandwidth improvement within a frequency span of 15-50 GHz without requiring additional matching components, making it suitable for high-frequency applications like 5G radio frequency devices.
Implementation Method 1
Conventional vertical connections in a multi-layer substrate exhibit strong capacitive behavior resulting from dielectric loading due to the presence of the substrate and dielectrics
Data Source
AI summary
A vertical interconnection structure of a multi-layer substrate includes a first via pad disposed in a first layer of metal interconnect of the multi-layer substrate; a second via pad disposed in a second layer of metal interconnect of the multi-layer substrate; a signal via electrically connecting the first via pad to the second via pad; a non-circular first ground plane disposed in the first layer of metal interconnect of the multi-layer substrate and surrounding the first via pad; and a non-circular first ground pullback region between the first via pad and the non-circular first ground plane for electrically isolating the first via pad from the non-circular first ground plane.