Blind-Via Interposer Grounding for Uniform Ground Potential
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Solution Overview
Problem
Existing interposer designs face issues with non-uniform ground potential and increased complexity due to wire bonds and through-silicon vias (TSVs) for grounding, leading to cross-talk, impedance, and manufacturing challenges, especially in optical interposers with high resistivity silicon substrates.
Innovation Solution
A composite substrate with high-resistivity and low-resistivity portions, utilizing blind via-holes for direct conductive connections between grounding patterns and mounting substrates, reducing the length of electrical connections and avoiding the need for wire bonds or TSVs, while maintaining low impedance and preventing current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire bonds are used to connect grounding patterns on interposer to ground on mounting substrate, then grounding connection is achieved, but cross-talk is generated between bonding wires and impedance increases due to non-negligible wire bond impedance
Solution Approach 1:
The invention extracts and eliminates the wire bonds from the grounding connection system. Instead of using wire bonds to connect grounding patterns, the patent uses direct conductive paths through the substrate itself, thereby removing the source of cross-talk and impedance issues associated with wire bonds.
Solution Approach 2:
The invention introduces an intermediary conductive layer within the substrate that mediates the grounding connection. This conductive layer provides a low-impedance path between grounding patterns and the mounting substrate without requiring external wire bonds, thus eliminating cross-talk while maintaining reliable grounding.
2Reliability
If wire bonds are used for grounding, then grounding connection is achieved, but inductive behavior increases due to length/section ratio of wire bonds
Solution Approach 1:
The invention removes wire bonds from the grounding system and replaces them with integrated conductive paths within the substrate. This extraction eliminates the long, thin wire bond structure that creates high inductance, replacing it with a low-inductance alternative.
Solution Approach 2:
The invention transitions the grounding connection from a three-dimensional wire bond structure (extending outside the substrate) to a two-dimensional planar conductive path within the substrate. This dimensional change reduces the length/section ratio and thereby reduces inductive behavior.
3Reliability
If wire bonds are used for grounding, then grounding connection is achieved, but footprint space increases due to space needed to accommodate bonding wires
Solution Approach 1:
The invention extracts wire bonds from the grounding system and replaces them with conductive paths that are integrated within the substrate. This eliminates the need for additional external space to accommodate wire bonds, thereby reducing the overall footprint.
Solution Approach 2:
The invention merges the grounding connection function with the substrate structure itself. By integrating conductive paths within the substrate rather than using separate wire bonds, the grounding function is combined with the existing substrate footprint, eliminating additional space requirements.
4Reliability
If through-silicon vias (TSVs) are used for grounding, then grounding connection is achieved, but manufacturing complexity increases due to additional manufacturing steps required to define, form and fill TSVs
Solution Approach 1:
The invention extracts the complex TSV formation process from the manufacturing sequence and replaces it with a simpler conductive path integration method. This eliminates the need for separate steps to define, form, and fill deep vias through the substrate, thereby reducing manufacturing complexity.
Solution Approach 2:
The invention enables the substrate to provide its own grounding paths through integrated conductive layers that are formed as part of the standard substrate fabrication process. This self-service approach eliminates the need for additional specialized manufacturing steps like TSV formation and filling.
5Reliability
If through-silicon vias (TSV) are used for grounding, then grounding connection is achieved, but footprint area increases due to large cross-sectional surface area of long TSVs
Solution Approach 1:
The invention removes the long TSV structure from the grounding system and replaces it with planar conductive paths within the substrate. This extraction eliminates the need for large cross-sectional areas associated with long TSVs, thereby reducing the footprint.
Solution Approach 2:
The invention transitions the grounding connection from a vertical three-dimensional TSV structure to a two-dimensional planar conductive path. This dimensional change reduces the cross-sectional surface area required, allowing for a smaller footprint while maintaining effective grounding.
Data Source
AI summary
A current path is provided through an interposer to ground a grounding pattern associated with a transmission line, by exploiting an interposer substrate that has a high-resistivity portion at a first surface and a low-resistivity portion extending from the high-resistivity portion to a second surface of the interposer. Moreover, a set of blind via-holes comprising electrically-conductive material extend from the first surface of the interposer substrate through the high-resistivity portion and into the low-resistivity portion. Top-to-bottom connection can be made using the conductive material in the blind vias and using the low-resistivity portion of the substrate, while the high-resistivity portion of the substrate impedes current leakage from the transmission line to the second surface of the substrate. The number and dimensions of the blind via-holes control the impedance of the grounding pattern relative to the transmission line's characteristic impedance.