Offset Ground Via Layout for High-Speed BGA Signal Integrity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed interconnects in semiconductor packaging face challenges due to higher-order electromagnetic mode propagation, which disrupt signal integrity and degrade performance in large or high-pin-count packages, particularly at frequencies exceeding 224 Gbps, due to structural limitations in Ball Grid Array (BGA) packages.
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
1Quantity of substance
If the pitch of BGA balls is increased to accommodate larger packages or higher pin counts, then the package size and pin count are improved, but the cut-off frequency decreases and higher-order electromagnetic modes are excited, degrading signal integrity
Solution Approach 1:
The patent introduces a lateral offset between ground vias and metal balls, creating an asymmetric three-dimensional configuration. This dimensional change modifies the electromagnetic field distribution and increases the cut-off frequency, allowing larger pitch dimensions while maintaining signal integrity at high frequencies.
Solution Approach 2:
The patent employs asymmetric positioning of ground vias relative to metal balls, where at least one ground via is laterally offset from its corresponding metal ball. This asymmetry disrupts the formation of higher-order electromagnetic modes and increases the cut-off frequency, thereby improving signal integrity in large packages with high pin counts.
2Length of stationary object
If the pitch of BGA balls is increased for larger packages, then the package size is improved, but the equivalent waveguide width increases, reducing the cut-off frequency and enabling higher-order mode propagation
Solution Approach 1:
By introducing lateral offset in the vertical dimension between ground vias and metal balls, the patent effectively reduces the equivalent waveguide width despite increased horizontal pitch. This dimensional modification raises the cut-off frequency and suppresses higher-order mode propagation in larger packages.
Solution Approach 2:
The patent applies local quality by creating non-uniform electromagnetic field distribution through lateral offset of ground vias. This localized asymmetry at via-ball interfaces modifies the equivalent waveguide characteristics, increasing cut-off frequency and preventing higher-order mode propagation while maintaining overall package size.
3Ease of manufacture
If conventional aligned ground via and metal ball structures are used, then the manufacturing process is simple, but higher-order electromagnetic modes are excited at high frequencies, degrading signal integrity
Solution Approach 1:
The patent introduces controlled asymmetry by laterally offsetting ground vias from metal balls. While this increases manufacturing complexity compared to perfect alignment, it effectively suppresses higher-order electromagnetic modes and maintains signal integrity at high frequencies, particularly in large packages with pitch greater than 0.8mm or 1.0mm.
Solution Approach 2:
The patent modifies the geometric parameters of the interconnect structure by introducing lateral offset distances between ground vias and metal balls. This parameter change transforms the electromagnetic characteristics, increasing the cut-off frequency and suppressing higher-order mode propagation, thereby maintaining signal integrity at high frequencies despite increased manufacturing complexity.
Data Source
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.