Coplanar Waveguide Layout with Vertical Ground Planes for Low Cross-Talk
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Solution Overview
Problem
Existing coplanar waveguide architectures require substantial packaging real estate, leading to low interconnect densities and significant cross-talk between signal traces due to large ground traces and non-proximity of the ground or signal return path.
Innovation Solution
Incorporation of vertical ground planes within the core of package substrates using laser-assisted etching processes to form vias that extend through or partially through the substrate, blocking electromagnetic fields and reducing the need for wide ground traces, thereby increasing capacitance and reducing cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coplanar ground traces are used on the same plane as signal traces, then the ground return path is provided, but substantial packaging real estate is consumed and interconnect density is limited
Solution Approach 1:
The patent moves the ground return path from the coplanar (2D) configuration to a vertical (3D) configuration using via holes that extend through the substrate thickness. This dimensional transition allows the ground plane to be positioned in a different layer, reducing the horizontal area occupied by ground traces while maintaining effective ground coupling with the signal traces.
2Reliability
If large coplanar ground traces are used, then ground return path is established, but cross-talk between signal traces increases
Solution Approach 1:
By positioning the ground plane vertically below the signal traces through via holes, the patent creates spatial separation between adjacent signal traces' ground paths. This vertical stacking reduces electromagnetic coupling between neighboring traces, thereby reducing cross-talk while maintaining adequate ground return paths for each signal line.
Solution Approach 2:
The ground system is segmented into discrete via holes positioned at specific intervals along the signal traces, rather than using continuous coplanar ground traces. This segmentation allows for localized ground coupling while reducing the continuous electromagnetic field that causes cross-talk between adjacent signal lines.
3Strength
If thick substrates are used for package cores, then structural integrity is improved, but creating compact transmission lines becomes more difficult due to non-proximity of ground or signal return path
Solution Approach 1:
The patent utilizes the vertical dimension of the thick substrate by creating via holes that extend through the substrate thickness to establish ground connections. This approach transforms the thickness disadvantage into an advantage, using the vertical space to create compact transmission lines with proper ground coupling without requiring large horizontal dimensions.
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 allows for compact transmission lines with high interconnect densities and reduced cross-talk, enabling efficient use of packaging space and supporting high-speed signaling.
Implementation Method 1
laser-assisted etching processes to form vias that extend through or partially through the substrate
Data Source
AI summary
Embodiments disclosed herein include coplanar waveguides and methods of forming coplanar waveguides. In an embodiment, a coplanar waveguide comprises a core, and a signal trace on the core. In an embodiment, the signal trace has a first edge and a second edge. In an embodiment, a first ground trace is over the core, and the first ground trace is adjacent to the first edge of the signal trace. In an embodiment, a first ground via plane is below the first ground trace. The coplanar waveguide may further comprise a second ground trace over the core, and the second ground trace is adjacent to the second edge of the signal trace. In an embodiment, a second ground via plane below the second ground trace.