Flexible Printed Circuit Board Cover Portion Stress Distribution
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Solution Overview
Problem
Conventional liquid crystal display devices experience disconnection of flexible printed circuit boards due to mechanical stress when bent, particularly because the Ni layer is brittle and prone to fatigue under repeated bending and tensile stress.
Innovation Solution
The flexible printed circuit board is designed with a cover portion that overlaps with the first substrate, featuring a Ni layer with a thickness of 10 μm or more, and is fixed using a resin or adhesive, distributing stress and preventing disconnection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the Ni layer thickness is reduced to lower manufacturing costs, then manufacturing precision requirements are relaxed, but the reliability of the flexible printed circuit board decreases due to increased brittleness and fatigue under bending stress
Solution Approach 1:
The patent changes the thickness parameter of the Ni layer from a thin layer (prone to fatigue) to a thick layer of 10 μm or more. This parameter change fundamentally alters the mechanical properties of the Ni layer, making it resistant to fatigue and disconnection under repeated bending stress, while still allowing manufacturing without precise thickness control
Solution Approach 2:
The patent creates a composite structure where the thick Ni layer (10 μm or more) is combined with the FPC substrate and adhesive layers. This composite structure leverages the high strength and fatigue resistance of the thick Ni layer to prevent disconnection, while the adhesive layers provide bonding functionality, achieving both reliability and ease of manufacture
2Adaptability or versatility
If the FPC is bent to fit the compact mobile phone design, then the adaptability to device form factor is improved, but mechanical stress causes disconnection of the FPC from the first substrate
Solution Approach 1:
The patent applies beforehand cushioning by using a thick Ni layer (10 μm or more) that is formed in advance on the FPC connecting portion. This thick Ni layer serves as a pre-built protective element that cushions against the mechanical stress of bending, preventing fatigue and disconnection before they can occur during device operation
Solution Approach 2:
The patent changes the thickness parameter of the Ni layer to 10 μm or more, which fundamentally alters the mechanical behavior of the FPC connecting portion. This parameter change enables the FPC to withstand repeated bending cycles without disconnection, allowing compact device integration while maintaining connection reliability
Data Source
AI summary
A display device includes: a first substrate which constitutes a display panel; and a flexible printed circuit board which is connected to the first substrate. The flexible printed circuit board is electrically and mechanically connected with terminals formed on the first substrate. The flexible printed circuit board includes a board portion, a wiring layer which is mounted on the board portion, and a cover portion which covers the wiring layer. The wiring layer includes a connecting portion which is electrically and mechanically connected to a terminal portion formed on the first substrate. The cover portion is removed at the connecting portion, and the cover portion in the vicinity of the connecting portion overlaps with the first substrate. The cover portion in the vicinity of the connecting portion is fixed to the first substrate.