Multilayer Flexible PCB Layout for Low-Stress Foldable Hinges
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Solution Overview
Problem
In foldable electronic devices, the reduced radius of curvature and increased stress on flexible printed circuit boards due to repeated folding operations lead to path loss and difficulty in maintaining a designed shape, especially when all layers are bonded together.
Innovation Solution
A multilayer flexible printed circuit board design with bonding layers confined to non-flexure areas, allowing adjacent pattern layers to slide relative to each other in flexure areas, reducing stress and maintaining a determined shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If all layers of the flexible printed circuit board are bonded together, then structural strength is improved, but stress increases during folding operations and the ability to maintain designed shape deteriorates
Solution Approach 1:
The flexible printed circuit board is divided into multiple layers with selective bonding. Specifically, the first and second flexible circuits are bonded to each other, while the third flexible circuit remains unbonded to adjacent layers in the folding area. This segmentation allows bonded regions to provide strength while unbonded regions accommodate folding stress and maintain shape.
Solution Approach 2:
Different bonding characteristics are applied to different regions of the flexible printed circuit board. The folding area features unbonded layers that can flex freely, while non-folding areas maintain full bonding for structural support. This local differentiation optimizes both strength and flexibility where needed.
2Stress or pressure
If the radius of curvature of the flexible printed circuit board is increased, then stress during folding is reduced, but the space required in the folding area increases
Solution Approach 1:
The flexible circuit board structure is segmented into bonded and unbonded layers in the folding area, allowing the unbonded layers to flex with smaller radius of curvature without excessive stress accumulation. This enables compact folding space while maintaining acceptable stress levels through the layered configuration.
3Reliability
If the length of the flexible printed circuit board is increased to accommodate folding operations, then connectivity between housings is improved, but path loss increases
Solution Approach 1:
The flexible printed circuit board utilizes a multi-layer stacked configuration in the thickness dimension rather than simply extending in the length dimension. This vertical stacking reduces the horizontal path length while maintaining connectivity between housings, thereby reducing path loss while ensuring reliable electrical connection.
Data Source
AI summary
An electronic device according to an embodiment of the disclosure may include a first housing in which a first printed circuit board is disposed, a second housing in which a second printed circuit board is disposed, a hinge configured to rotatably connect the first housing and the second housing, and a multilayer flexible printed circuit board configured to connect the first printed circuit board and the second printed circuit board, wherein the multilayer flexible printed circuit board may include a plurality of pattern layers and a bonding layer configured to bond a portion between at least two pattern layers of the plurality of pattern layers, wherein, in the folding area, the multilayer flexible printed circuit board may include a flexure area and a non-flexure area between flexure areas, and in the folded area, at least one bonding layer may be formed at least in part only on the non-flexure area.