Offset Ground Via BGA Substrates for High-Speed Signal Integrity
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Solution Overview
Problem
High-speed interconnects in semiconductor packaging face challenges due to higher-order electromagnetic modes that propagate within Ball Grid Array (BGA) packages, leading to signal degradation and integrity issues, especially at frequencies exceeding 224 Gbps, as the pitch dimensions limit the maximum usable frequency range and bandwidth.
Innovation Solution
A substrate structure with laterally offset ground vias and metal balls, where the ground vias are arranged to surround signal vias and have a tighter pitch than the metal balls, reducing the equivalent waveguide width and increasing the cut-off frequency threshold to mitigate higher-order mode excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the pitch of BGA balls is increased to accommodate larger package sizes, then the package area is improved, but the cut-off frequency decreases leading to higher-order mode propagation and signal degradation
Solution Approach 1:
The ground via structure is segmented into multiple vias arranged in a specific pattern around each signal via. This segmentation creates multiple smaller electromagnetic confinement regions rather than one large region, effectively increasing the cut-off frequency while maintaining large package area. The segmented ground via arrangement prevents higher-order mode propagation by creating electrical length constraints in multiple directions.
Solution Approach 2:
The patent transitions from considering only the horizontal pitch dimensions to incorporating the vertical dimension by implementing ground vias at different depths and positions. The ground via structure extends in the vertical dimension with varying depths and lateral offsets, creating a three-dimensional electromagnetic confinement system that increases cut-off frequency without limiting the horizontal package area.
2Ease of manufacture
If the pitch of BGA balls is increased, then the ease of manufacture is improved, but the maximum usable frequency range decreases due to lower cut-off frequency
Solution Approach 1:
The ground via structure implements local quality variations by positioning ground vias at specific lateral offsets from signal vias and assigning different via depths to different locations. This non-uniform local arrangement creates electromagnetic confinement in critical regions while maintaining overall manufacturability through standardized via fabrication processes. The local quality enhancement at via locations compensates for the increased overall pitch.
3Device complexity
If ground vias are aligned directly with metal balls, then the device complexity is reduced, but higher-order electromagnetic modes are excited leading to signal degradation
Solution Approach 1:
The patent introduces asymmetry by laterally offsetting ground vias from direct alignment with metal balls. The ground via pattern is asymmetrically arranged around signal vias with specific lateral offsets, creating an asymmetric electromagnetic field distribution that prevents higher-order mode excitation. This asymmetric arrangement maintains manageable device complexity while significantly improving signal integrity at high frequencies.
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
The proposed structure enhances signal integrity by increasing the cut-off frequency, thereby improving high-frequency performance and reducing signal degradation in semiconductor packaging systems.
Implementation Method 1
at least one of the plurality of first ground vias may be laterally offset from at least one corresponding first metal ball along a direction orthogonal to the substrate... reducing the equivalent waveguide width and increasing the cut-off frequency threshold to mitigate higher-order mode excitation
Data Source
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AI summary
Devices including a substrate structure with laterally offset ground vias and metal balls are provided. A device may include a substrate, a plurality of first ground vias, and a plurality of first metal balls. The plurality of first ground vias may be formed within the substrate and surrounding a plurality of signal vias. The plurality of first metal balls may be disposed on the substrate and electrically coupled to the plurality of first ground vias. One first metal ball may be electrically coupled to one first ground via. A part of the plurality of first ground vias may be laterally offset from a corresponding part of the plurality of first metal balls along a direction orthogonal to the substrate.