Multilayer Substrate Notch Design for Bending Stress Relief
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Solution Overview
Problem
Multilayer boards with interlayer connection conductors face flexibility issues and stress concentration when bent, leading to potential peeling and structural challenges, especially in small-sized designs.
Innovation Solution
A multilayer board design featuring a flexible base material with laminated insulator layers, an interlayer connection conductor, and strategically positioned notches that disperse bending stresses, allowing the conductor to be placed within a region defined by the notches and their connecting lines, with a curvature radius greater than outside regions, reducing stress concentration and enabling space-saving flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If via conductors are staggered across multiple layers along the bending direction, then bending stress concentration is relieved, but the required length dimension increases making it difficult to use in small-sized boards
Solution Approach 1:
The via conductor structure is segmented into multiple via holes arranged in a matrix pattern across different layers, rather than using a single continuous via. This segmentation allows stress distribution while maintaining compact dimensions, as each via hole can independently handle localized stress without requiring extended length along the bending direction.
Solution Approach 2:
The via conductor arrangement transitions from a one-dimensional staggered linear pattern to a two-dimensional matrix distribution across multiple layers. By distributing via holes in both lateral and vertical dimensions, the structure achieves effective stress relief without increasing the length dimension along the bending direction, enabling compact board design.
2Reliability
If an interlayer connection conductor is provided in a flexible multilayer board, then electrical connectivity is achieved, but peeling may occur at and around the conductor due to lack of flexibility
Solution Approach 1:
The interlayer connection conductor is segmented into multiple discrete via holes rather than a continuous structure. This segmentation allows the conductor to flex with the board during bending without creating stress concentration points that would cause peeling, while still maintaining electrical connectivity through the stacked via holes.
Solution Approach 2:
The via conductor structure provides localized reinforcement at critical interlayer connection points while maintaining overall flexibility. The matrix arrangement of via holes creates zones of enhanced structural integrity where needed, while the spaces between vias allow for flexibility and stress distribution across the board.
Data Source
AI summary
A multilayer board includes a flexible base material including laminated insulator layers and curved along an X-axis direction on a plane orthogonal or substantially orthogonal to a lamination direction, an interlayer connection conductor on the flexible base material, and a notch pair on the flexible base material at positions symmetrical or substantially symmetrical in the X-axis direction with respect to a position of the interlayer connection conductor, the notch pair extending in a Y-axis direction orthogonal or substantially orthogonal to the X-axis direction on the plane. The interlayer connection conductor is within a region defined by the notch pair and lines respectively joining ends of the notch pair in the Y-axis direction. A radius of curvature of a region of the flexible base material between the notch pair in the X-axis direction being greater than curvature radii of regions outside of the notch pair.