Reinforced Chip-on-Flex Structure for Stable Touch Panel Bending
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Solution Overview
Problem
The bent COF for touch panels with a large width springs back and bulges under stress, leading to undesirable bending shapes during assembly, which can interfere with driver chips and affect the display device's performance.
Innovation Solution
A flexible base with a first opening and a reinforcement sheet is used, where the reinforcement sheet is positioned on the flexible base except at the first opening and bonding area, enhancing the base's strength to prevent warping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the COF width is increased to accommodate more bonding pads for self-capacitance touch screens, then the touch precision and narrow-bezel design are improved, but the COF becomes difficult to bend and springs back under stress
Solution Approach 1:
The COF structure is segmented into distinct functional areas: a bonding area with metal bonding pads for electrical connection, a spacing area that provides separation, and a bending area where the COF is folded. This segmentation allows the bonding area to maintain its large width for high precision while the bending area can be independently optimized for flexibility and stability.
Solution Approach 2:
Different areas of the COF are given different properties: the bonding area has a large width with metal bonding pads for high precision connections, the spacing area provides mechanical separation and stress relief, and the bending area is specifically designed with appropriate width and positioning to enable stable folding without springing back. Each area's dimensions and properties are locally optimized for its specific function.
2Ease of manufacture
If holes are formed in the COF to prevent interference with driver chips during assembly, then the assembly feasibility is improved, but the COF structure becomes more complex and manufacturing difficulty increases
Solution Approach 1:
The driver chip is extracted from the COF structure and positioned on the display flexible circuit board instead. The COF's first opening provides spacing and prevents interference with the separately positioned driver chip, eliminating the need for complex hole-forming operations in the COF while maintaining assembly feasibility.
Solution Approach 2:
The spacing area acts as an intermediary region between the bonding area and the first opening, providing mechanical separation and stress relief. This intermediary spacing allows the COF to be positioned and assembled without requiring holes to be formed in the COF itself, simplifying the manufacturing process while preventing interference with the driver chip.
3Reliability
If the bonding area width is increased to match the number of ITO leads, then the electrical connection reliability is improved, but the overall COF width increases making bending difficult
Solution Approach 1:
The COF is segmented into a bonding area with large width for reliable electrical connections and a bending area with reduced width for flexibility. The spacing area separates these two regions, allowing the bonding area to be wide enough to accommodate all ITO leads and metal bonding pads for high reliability while the bending area remains narrow enough to fold easily without springing back.
Solution Approach 2:
The bonding area is locally optimized with large width and multiple metal bonding pads arranged in arrays to ensure reliable electrical connections for all ITO leads. The bending area is locally optimized with appropriate width and positioning to enable stable folding. Each area's dimensions are specifically tailored to its functional requirements, allowing the COF to simultaneously achieve high connection reliability and bendability.
Data Source
AI summary
The embodiments of the present disclosure provide a chip on flex (COF), a touch assembly, and a display device. The chip on flex includes a flexible base provided with a first opening, the flexible base includes a bonding area provided with a plurality of metal bonding pads; on the flexible base, a spacing area with a preset range is provided between the first opening and the bonding area; wherein, the flexible base is provided with a reinforcement sheet thereon, the reinforcement sheet is located on a portion of the flexible base other than the first opening, the spacing area and the bonding area.