Multilayer Substrate Tapered Via Structure for Stable Impedance
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Solution Overview
Problem
Existing multilayer substrates face challenges in suppressing breakage and maintaining characteristic impedance stability, particularly due to dielectric loss and structural weaknesses around signal conductors.
Innovation Solution
A multilayer substrate design featuring resin layers with hollow portions and tapered through conductors, where the hollow portions do not pass through the resin layers and have tapered regions that increase in cross-sectional area towards the surface, reducing dielectric loss and enhancing structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If hollow portions are provided in the resin layer to adjust dielectric constant and characteristic impedance, then dielectric loss is reduced and signal transmission is improved, but the structural strength of the multilayer body is weakened and breakage risk increases
Solution Approach 1:
The hollow portions are designed with curved surfaces instead of sharp edges, and the through conductors have tapered shapes with curved transitions. This curvature distributes stress more evenly throughout the structure, preventing stress concentration at sharp corners that would lead to crack initiation and propagation, thereby maintaining structural integrity while preserving the dielectric adjustment function
Solution Approach 2:
The cross-sectional area of through conductors is varied along their length through tapering, creating a gradual transition in geometric parameters. This parameter change allows the structure to adapt to stress distributions, with larger cross-sections providing greater strength where needed while smaller cross-sections maintaining the dielectric constant adjustment function, thus resolving the contradiction between strength and dielectric performance
2Strength
If through conductors are made with larger cross-sectional area to improve strength, then structural integrity is enhanced, but dielectric loss increases and characteristic impedance stability deteriorates
Solution Approach 1:
The through conductors feature a dynamic geometric design with tapered cross-sectional areas that vary along their length. This dynamic structure allows the conductor to provide greater strength where structurally necessary while maintaining smaller cross-sections in regions where dielectric constant adjustment is critical, optimizing both mechanical and electrical performance simultaneously
Solution Approach 2:
Different sections of the through conductor are designed with different cross-sectional areas tailored to local requirements. Regions near the hollow portions have smaller cross-sections to maintain dielectric constant adjustment and reduce dielectric loss, while other regions have larger cross-sections to provide structural support, implementing local quality optimization throughout the conductor
3Manufacturing precision
If the hollow portions pass through the entire resin layer to maximize dielectric constant adjustment, then characteristic impedance control is improved, but the multilayer body becomes more susceptible to breakage and peeling
Solution Approach 1:
The hollow portions are designed to extend partially through the resin layer rather than completely through it. This partial action provides sufficient dielectric constant adjustment and characteristic impedance control in the critical regions where the hollow portions are present, while avoiding the creation of complete through-holes that would severely compromise structural integrity and create peeling pathways between layers
4Reliability
If tapered regions are added to through conductors and hollow portions to reduce stress concentration, then breakage resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The formation of tapered through conductors and curved hollow portions is integrated into a single manufacturing process step using laser drilling and melting technology. This merging of operations creates both the hollow portions and the tapered conductor shapes simultaneously, avoiding the need for separate machining steps and reducing overall manufacturing complexity despite the sophisticated geometries required for breakage resistance
Data Source
AI summary
A multilayer substrate includes a multilayer body including resin layers stacked in a Z-axis direction, a signal conductor layer, and one or more through conductors passing through a first resin layer in the Z-axis direction. A first main surface of the first resin layer includes one or more hollow portions not in contact with the signal conductor layer and overlapping the signal conductor layer when viewed in the Z-axis direction. Each of the one or more hollow portions and the one or more through conductors includes a tapered region in which each of a cross-sectional area of the one or more hollow portions orthogonal to the Z-axis direction and a cross-sectional area of the one or more through conductors orthogonal to the Z-axis direction increases toward the first main surface. The tapered region is in contact with the first main surface of the first resin layer.