Flexible PCB Protective Layer Layout for Reliable COF Bonding
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Solution Overview
Problem
Existing flexible printed circuit boards face issues with protective layer misplacement leading to increased pad size and reduced bonding reliability due to improper positioning, which affects the overall size and reliability of the COF module.
Innovation Solution
A flexible printed circuit board design featuring a substrate with defined directions and outer patterns that allow precise control of the protective layer positioning, ensuring it is placed only where necessary to avoid unnecessary enlargement of bonding regions and prevent corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the protective layer is disposed beyond a set position, then the circuit pattern is more fully protected, but the pad portion size increases unnecessarily
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different regions on the circuit board. The protective layer is selectively disposed only in non-pad regions (wiring regions) while deliberately excluding pad portions. This localized approach ensures protection where needed (circuit traces) while avoiding unnecessary enlargement of bonding areas (pads), thus resolving the contradiction between protection capability and pad size.
2Ease of manufacture
If the protective layer position is not precisely controlled, then the manufacturing process is simpler, but the bonding reliability decreases
Solution Approach 1:
The patent employs preliminary action by pre-defining the boundary between pad portions and non-pad portions before disposing the protective layer. The pattern formation step creates a visual and physical guide that indicates exactly where the protective layer should and should not be applied. This preliminary pattern definition ensures precise positioning without requiring complex real-time control during protective layer application, thus maintaining manufacturing simplicity while ensuring bonding reliability.
3Strength
If the pad portion size increases, then the bonding area is larger, but the COF module size increases unnecessarily
Solution Approach 1:
The patent applies local quality by ensuring the protective layer covers only the wiring regions and excludes pad portions. This selective coverage prevents the protective layer from adding to the pad portion size, thereby maintaining the COF module's compact size while still providing adequate bonding area through the exposed pad portions. The local differentiation resolves the contradiction between bonding strength and overall module size.
Data Source
AI summary
A flexible printed circuit board according to an embodiment includes: a substrate; a conductive pattern disposed on the substrate; and a protective layer disposed on the conductive pattern. An upper surface of the substrate includes a first edge and a second edge facing along a first direction and each extending along a second direction perpendicular to the first direction, a lower surface of the protective layer includes a fifth edge positioned adjacent to the first edge, and a sixth edge facing the fifth edge along the first direction and positioned adjacent to the second edge. The first edge and the fifth edge are spaced apart from each other along the first direction, and the conductive pattern includes a first outer pattern extending along the first direction including at least a portion disposed between the first edge and the fifth edge.