Flexible Circuit Board Layering for Repeated-Folding Signal Integrity

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Solution Overview

Problem

Existing flexible circuit boards in foldable electronic devices suffer from damage and noise generation due to repeated bending, which affects the conductive layers and interferes with signal integrity.

Innovation Solution

A flexible circuit board design with a multi-layer structure, where the first area has a greater thickness and additional coverlay layers compared to the second area, providing enhanced rigidity and reducing repulsive forces, thereby minimizing damage and noise during repeated folding and unfolding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the flexible circuit board uses a simple single-area structure, then the device complexity is reduced, but the reliability deteriorates due to damage and noise generation from repeated bending

Engineering Contradiction:

Improvesignal integrityVSAvoidcircuit board structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The flexible circuit board is divided into a first area and a second area with different structural configurations. The first area includes multiple coverlay layers stacked on conductive layers to provide enhanced rigidity and reduce damage during bending, while the second area has a simpler structure. This segmentation allows each area to be optimized for its specific functional requirements, resolving the contradiction between reliability and complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different areas of the flexible circuit board are assigned different structural qualities. The first area, which experiences more mechanical stress during folding, is constructed with thicker coverlay layers and greater overall thickness to enhance its resistance to damage. The second area maintains a lighter structure where full protection is not required. This local differentiation of structural quality optimizes reliability where needed without unnecessarily increasing overall complexity.

Inventive Principle:

Principle #3Local quality

2Strength

If the flexible circuit board uses additional coverlay layers to reduce damage, then the strength and rigidity are improved, but the manufacturing complexity increases

Engineering Contradiction:

Improveresistance to bending damageVSAvoidmulti-layer stacking process

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The circuit board is segmented into distinct first and second areas with different layer configurations. The first area receives multiple coverlay layers (first, second, and third coverlay layers) stacked on conductive layers, while the second area has fewer layers. This segmentation allows the manufacturing process to focus complexity only where structurally necessary, rather than uniformly increasing complexity across the entire board.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The manufacturing process is optimized by applying additional coverlay layers only to the first area where enhanced strength is required for bending resistance. The second area maintains a simpler layer structure that is easier and faster to manufacture. This local quality differentiation in the manufacturing process reduces overall manufacturing complexity while still providing enhanced strength where needed.

Inventive Principle:

Principle #3Local quality

3Stability of the object's composition

If the flexible circuit board uses a thicker structure in the first area, then the rigidity is improved and repulsive forces are reduced, but the overall flexibility of the board decreases

Engineering Contradiction:

Improvestructural rigidityVSAvoidbending flexibility

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The flexible circuit board is segmented into a first area with a thicker, more rigid structure containing multiple stacked coverlay layers and conductive layers, and a second area with a thinner, more flexible structure. This segmentation allows the board to have different mechanical properties in different regions, enabling the first area to maintain structural stability during bending while the second area preserves overall bending flexibility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first area is constructed with local quality enhancements including thicker coverlay layers and greater overall thickness to provide the rigidity needed for resisting repulsive forces during repeated folding. The second area maintains a lighter, more compliant structure that does not compromise the board's ability to bend. This localized differentiation of structural quality allows the board to simultaneously achieve rigidity where needed and flexibility where required.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20250220097A1Flexible circuit board and electronic device comprising same

Publication Date: 2025.07.03 SAMSUNG ELECTRONICS CO LTD

AI summary

According to an embodiment of the disclosure, an electronic device may include a housing including a first housing and a second housing, a hinge structure configured to rotatably connect the first housing and the second housing, and a flexible circuit board at least partially disposed on the hinge structure, wherein the flexible circuit board includes a first area at least partially configured to be bendable, the first area including a first conductive layer, a (1-1)th coverlay layer stacked on the first conductive layer, and a (1-2)th coverlay layer stacked on the (1-1)th coverlay layer, and a second area configured to extend from the first area, the second area including a second conductive layer forming the same conductive layer as the first conductive layer, and a second coverlay layer forming the same coverlay layer as the (1-1)th coverlay layer. In addition, various embodiments may be possible.