Package Substrate Layout for Impedance Control and Structural Strength
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Solution Overview
Problem
Impedance discontinuity in semiconductor packages due to stray capacitance between signal ball pads and adjacent ground planes, leading to signal degradation, is addressed by removing ground planes from signal ball pads, which creates structural vulnerabilities.
Innovation Solution
A package substrate design with increased vertical height of interconnection members and smaller signal connection pads, along with conductive planes positioned to minimize stray capacitance, includes multiple signal and ground vias alternately stacked with conductive layers to ensure proper isolation and minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ground planes are removed from signal ball pads to reduce stray capacitance, then impedance discontinuity is improved, but structural strength and reliability deteriorate due to cracks propagating through dielectric material
Solution Approach 1:
The build-up structure is divided into multiple functional layers: signal ball pads at the bottom, interconnection members in the middle, and signal connection pads at the top. This segmentation allows ground planes to be selectively positioned only where needed (adjacent to signal connection pads) while maintaining structural integrity through the distributed arrangement of conductive elements and dielectric material.
Solution Approach 2:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional stacked configuration. Signal ball pads, interconnection members, and signal connection pads are arranged vertically, allowing ground planes to be positioned in the vertical dimension adjacent to signal connection pads rather than directly beneath signal ball pads, thus reducing stray capacitance while maintaining structural strength.
2Reliability
If signal ball pad area is reduced to minimize stray capacitance, then impedance control is improved, but signal transmission capability deteriorates
Solution Approach 1:
The patent utilizes the vertical dimension to extend the signal path from signal ball pads through interconnection members to signal connection pads. This three-dimensional arrangement allows the signal to traverse a longer effective path without requiring a larger horizontal area, thereby maintaining impedance control while preserving signal transmission capability.
Solution Approach 2:
The patent changes the geometric parameters of the signal path by introducing vertical height components (interconnection member height, via length) in addition to horizontal dimensions. This allows optimization of impedance characteristics through controlled parameter adjustments while maintaining adequate signal transmission area.
3Reliability
If larger intervals are placed between signal ball pads and ground planes to reduce stray capacitance, then impedance stability is improved, but device complexity increases
Solution Approach 1:
The patent segments the ground plane arrangement into distinct functional zones: ground planes are positioned adjacent to signal connection pads in the upper portion, while the lower portion near signal ball pads has different structural characteristics. This segmentation achieves impedance stability in the critical connection region without requiring uniform large intervals throughout the entire structure, thereby controlling complexity.
Solution Approach 2:
The patent applies different structural qualities to different regions: the area adjacent to signal connection pads features ground planes for impedance stability, while other regions have optimized arrangements for mechanical strength and signal transmission. This local differentiation achieves impedance stability where needed without unnecessarily increasing overall device complexity.
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
Enhances signal integrity and performance of high-speed interfaces by reducing stray capacitance and maintaining impedance at target levels, avoiding structural weaknesses.
Implementation Method 1
the signal ball pad whose area is much larger than that of the signal via or the signal bump causes the generation of an undesirable large value of the stray capacitance between the signal ball pad and a ground plane that is adjacent to the signal ball pad
Data Source
AI summary
A package substrate includes: a build-up structure; and a core layer disposed on the build-up structure, wherein the build-up structure includes: a signal ball pad; an interconnection member disposed on the signal ball pad; a signal connection pad disposed on the interconnection member; and a plurality of signal vias and a plurality of signal lines alternately arranged in a vertical direction on the signal connection pad, wherein the interconnection member has a first height in the vertical direction, wherein each of the plurality of signal vias has a second height in the vertical direction, and wherein the first height is greater than the second height.