Flexible Printed Circuit Board Routing for Display Stress Reduction

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Solution Overview

Problem

In display devices using flexible printed circuits (FPCs), the difference in bend radius between FPCs generates tensile stress when bent, leading to shearing forces at the joining portions, which complicates the collection of interface terminals and increases the adverse influence of stress.

Innovation Solution

A display device design where a first flexible printed circuit board extends sideward and is bent below the display panel, while a second flexible printed circuit board is arranged with specific bent portions to minimize shearing forces, allowing the collection of interface terminals at one place and reducing stress influence.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If multiple FPCs are connected and bent to a back surface of a backlight to collect interface terminals at one place, then the number of connectors is decreased, but tensile stress is generated in the outside bent FPC due to difference in bend radius

Engineering Contradiction:

Improvenumber of connectorsVSAvoidtensile stress in FPC

Core Design Contradiction:

Device complexityVSStress or pressure

Solution Approach 1:

The FPC is divided into multiple segments with different bend radii. The first FPC has a first bend radius and the second FPC has a second bend radius, allowing each segment to be optimized independently to reduce stress concentration while maintaining terminal collection functionality

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the FPC structure are given different properties - the first FPC and second FPC have different bend radii tailored to their specific positions and functions, with the first FPC optimized for its joining portion and the second FPC optimized for its connection to the backlight, thereby locally optimizing stress distribution

Inventive Principle:

Principle #3Local quality

2Stress or pressure

If the outside bent FPC is made longer than the inside bent FPC to avoid tensile stress, then tensile stress is reduced, but shearing force is generated in the joining portion between the panel and the FPC

Engineering Contradiction:

Improvetensile stress in FPCVSAvoidshearing force at joining portion

Core Design Contradiction:

Stress or pressureVSForce

Solution Approach 1:

The FPC system is segmented into a first FPC and a second FPC with different length configurations. The first FPC extends longer than the second FPC, creating a staged length distribution that distributes stress and force across different segments rather than concentrating shearing force in a single joining portion

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The solution moves from a single-dimensional length adjustment to a multi-dimensional configuration involving both length differences and bend radius differences across two separate FPC segments, distributing the mechanical stresses across multiple dimensions and degrees of freedom

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Volume of moving object

If FPCs are bent in a return direction to satisfy miniaturization demands, then the display device size is reduced, but adverse influence of stress increases

Engineering Contradiction:

Improvedisplay device sizeVSAvoidstress influence

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

The bent FPC structure is divided into segmented portions with different bend radii (first bend radius for the first FPC, second bend radius for the second FPC), allowing the miniaturized return-direction bending to be achieved while distributing stress across multiple segments rather than concentrating it in a single bent portion

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The bend radius parameter is changed and optimized for different FPC segments - the first FPC uses a first bend radius and the second FPC uses a second bend radius, allowing the system to achieve miniaturization through return-direction bending while controlling stress by varying the bend radius parameter across different segments

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8780580B2Display device

Publication Date: 2014.07.15 MAGNOLIA WHITE CORP

AI summary

A display device includes a second flexible printed circuit board electrically connected to interface terminals, a display panel joined to a first flexible printed circuit board, and a sub panel joined to the second flexible printed circuit board. The second flexible printed circuit board includes an upper end portion which extending sideward from an end portion of the sub panel above the first flexible printed circuit board, an outward bent portion bent from the upper end portion in a return direction, an intermediate portion extending from the outward bent portion such that the intermediate portion passes an electrically connecting portion with the first flexible printed circuit board below the first flexible printed circuit board, an inward bent portion bent from the intermediate portion in a return direction toward the electrically connecting portion, and a lower end portion extending from the inward bent portion and reaching the electrically connecting portion.