Flexible Circuit Board Stress Distribution via Segmented Conductors

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Solution Overview

Problem

Conventional circuit boards are prone to detachment from printed wiring boards due to stress on solder connections caused by bending, either because they are rigid and do not bend with the wiring board or because flexible boards cannot handle the stress of attached semiconductor components.

Innovation Solution

A circuit board with a laminated body of flexible insulating-material layers, where internal conductors are overlaid on external electrodes but not connected through via hole conductors, allowing for flexibility and stress distribution to prevent detachment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a rigid circuit board is used, then the board maintains structural stability, but the solder connection is prone to breakage when the printed wiring board bends

Engineering Contradiction:

Improvestructural stabilityVSAvoidsolder connection reliability

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The circuit board transitions from a rigid structure to a flexible structure that can dynamically adapt to bending of the printed wiring board. The flexible insulating layers allow the board to bend without breaking solder connections, while the internal conductors maintain electrical connectivity through the flexible substrate.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circuit board uses flexible insulating layers (thin films) as the base structure instead of rigid ceramic layers. This flexible substrate allows the board to bend with the printed wiring board, preventing solder breakage while maintaining structural integrity through the layered construction.

Inventive Principle:

Principle #30Flexible shells and thin films

2Reliability

If a flexible circuit board is used, then the board can bend with the printed wiring board, but the electronic component may detach due to stress on external electrodes

Engineering Contradiction:

Improveboard attachment reliabilityVSAvoidelectronic component attachment strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The conductive structure is segmented into internal conductors within the flexible board and external electrodes on the surface. The internal conductors are disconnected in the region overlaying the external electrodes, creating separate stress zones. This segmentation allows the flexible board to bend without transmitting stress to the external electrodes and mounted components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The internal conductors act as intermediaries that carry electrical signals without being directly connected to the external electrodes in the stress-prone region. This intermediary structure allows the flexible substrate to move independently from the rigid electronic components, preventing stress transmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If internal conductors are connected through via hole conductors in the overlay region, then electrical continuity is maintained, but stress is transmitted to external electrodes causing detachment

Engineering Contradiction:

Improveelectrical continuityVSAvoidcomponent attachment strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The via hole conductors that would normally connect internal conductors across the external electrode region are extracted or removed in that specific area. This creates a discontinuity in the internal conductor path where it would otherwise overlay the external electrodes, preventing stress transmission while allowing electrical connection through alternative routing in non-overlay regions.

Inventive Principle:

Principle #2Taking out (Extraction)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The circuit board effectively prevents electronic components from detaching by distributing stress and allowing the board to bend with the printed wiring board, reducing the risk of solder breakage and maintaining connectivity.

Implementation Method 1

a laminated body including a laminate of a plurality of insulating-material layers (16a to 16h) made of a flexible material

Methodology Applied

Scientific EffectFlexibility: Elasticity

Implementation Method 2

effectively prevents an electronic component (50) from being detached from the circuit board (10)... distributing stress

Methodology Applied

Scientific EffectStress distribution: Stress Relaxation

Data Source

PatentUS9986641B2Circuit board

Publication Date: 2018.05.29 MURATA MFG CO LTD

AI summary

A circuit board includes a laminated body including a laminate of a plurality of insulating-material layers made of a flexible material. External electrodes are provided on the top surface of the laminated body. An electronic component is mounted on the external electrodes. A plurality of internal conductors, when viewed in plan in the z-axis direction, are overlaid on the external electrodes and are not connected to one another in regions in which the internal conductors are overlaid on the external electrodes.