Flexible COF Circuit Layout for Bend-Induced Crack Prevention

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Solution Overview

Problem

Flexible circuit boards used in chip on film (COF) modules are prone to cracking and damage due to repeated bending and tensile forces, which affects their reliability and functionality in electronic devices.

Innovation Solution

A flexible circuit board design featuring a substrate with a bending area and a non-bending area, with a specific configuration of wiring pattern layers and protective layers that absorb and distribute stress, preventing cracking and enhancing reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a flexible circuit board is designed to be thin and flexible for high-density chip mounting, then adaptability and integration density are improved, but the board becomes susceptible to cracking and damage from repeated bending and tensile forces

Engineering Contradiction:

ImproveflexibilityVSAvoidcrack resistance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The circuit board is divided into a bending area and a non-bending area, with the wiring pattern layer selectively positioned. The wiring pattern layer is formed only on the non-bending area, while the bending area remains free of the wiring pattern layer, allowing it to flex without causing cracks in the conductive traces.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the circuit board are assigned different functions: the non-bending area contains the wiring pattern layer for electrical connectivity, while the bending area is designed to be flexible and free of rigid wiring structures. This local differentiation allows the board to be both functional and flexible.

Inventive Principle:

Principle #3Local quality

2Reliability

If the wiring pattern layer is formed on the entire substrate including bending area, then electrical connectivity is maintained, but cracking occurs during repeated bending

Engineering Contradiction:

Improvecrack preventionVSAvoidwiring pattern configuration

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The substrate is segmented into bending and non-bending areas, and the wiring pattern layer is selectively applied only to the non-bending area. This segmentation prevents cracking by excluding the wiring pattern from the stress-prone bending region while maintaining electrical connectivity through appropriate trace routing.

Inventive Principle:

Principle #1Segmentation

3Reliability

If a protective layer is added to prevent cracking, then reliability is improved, but the board thickness increases affecting flexibility

Engineering Contradiction:

Improveprotection against crackingVSAvoidboard thickness

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

Instead of adding a thick protective layer across the entire board, the design segments the substrate into bending and non-bending areas. The wiring pattern is restricted to the non-bending area, which inherently protects it from cracking during flexing without requiring additional protective thickness that would compromise flexibility.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11800639B2Flexible circuit board, COF module and electronic device including the same

Publication Date: 2023.10.24 LG INNOTEK CO LTD

AI summary

A flexible circuit board and an electronic device including a flexible circuit board are provided. The flexible circuit board may include a substrate having a bending area and a non-bending area, a wiring pattern layer provided on the bending area and the non-bending area, a plating layer provided on the wiring pattern layer and including an open area in an area corresponding to the bending area, and a protective layer that directly contacts one surface of the wiring pattern layer exposed at the open area and a side surface of the plating layer. The protective layer may have a larger thickness than a thickness of the plating layer.