Flexible Circuit Board Via Stack Design for Layer Density
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Solution Overview
Problem
Conventional flexible circuit boards require multiple electroplating processes for through holes, blind holes, and buried holes, which increases complexity and size, limiting the number of stacked layers and flexibility.
Innovation Solution
A via structure stack using liquid crystal polymer (LCP) layers and metal layers, where via structures with conductive material are aligned to provide electrical connections between metal layers, reducing the need for electroplating and allowing for a smaller, more flexible multi-layer structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional electroplating processes are used for through holes, blind holes, and buried holes in multiple layers, then electrical connection between circuit layers is achieved, but the number of electroplating processes increases, the size of via structures increases, and the number of stacked layers is limited
Solution Approach 1:
The patent divides the via structure into multiple segments stacked vertically, where each segment is formed in a separate LCP layer. These segmented via structures are aligned and stacked to form continuous electrical pathways through the multi-layer circuit board, replacing the conventional single-step electroplating process with multiple layers.
Solution Approach 2:
The patent uses Liquid Crystal Polymer (LCP) material for the via structures instead of conventional electroplated materials. LCP provides both mechanical support and electrical conductivity, creating a composite structure that eliminates the need for separate electroplating processes while maintaining reliable electrical connections between layers.
2Volume of moving object
If via structures are formed using conventional electroplating, then electrical connectivity is achieved, but the via size is large, limiting the number of stacked layers and increasing overall board size
Solution Approach 1:
The patent changes the material parameter from conventional electroplated copper to Liquid Crystal Polymer (LCP), which has different physical and electrical properties. This parameter change enables smaller via structures with reduced diameter while maintaining electrical conductivity, allowing for increased layer stacking density.
Solution Approach 2:
The patent transitions from planar via structures to three-dimensional stacked via structures. By aligning and stacking via structures vertically across multiple LCP layers, the patent creates continuous electrical pathways in the vertical dimension, enabling higher layer counts within a compact footprint.
Data Source
AI summary
A flexible circuit board includes liquid crystal polymer (LCP) layers and metal layers including circuit routes. Each of the LCP layers includes via structures. The metal layers and the LCP layers are alternatively stacked to form a multi-layer structure. Adjacent metal layers are electrically connected through the via structures. Some via structures of different LCP layers are substantially aligned with one another to form a stack of via structures. Each of the via structures includes openings filled with conductive material. The size of the opening fulfils the following equation: Vb≥cos(Bh/Vh)*Vt/k*2, where Vb is a diameter of a smaller aperture, Vt is a diameter of a bigger aperture, Vh is a combined thickness of a LCP layer and a metal layer, Bh is a thickness of a LCP layer and k is a tensile modulus.