COF Wiring Branching for Display Stress Dispersion
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Solution Overview
Problem
The existing connection methods for liquid crystal display devices using anisotropic conductive films between COFs and display panels face issues with non-uniformity due to size, width, and pitch differences, leading to reliability concerns and potential disconnections under bending stress, especially when COFs are bent or subjected to thermal expansion differences.
Innovation Solution
A flat display device with a wiring film connected to terminals on a substrate, where lines are branched into multiple narrower lines with varying branching positions and distances, and a dummy line is included between connected lines to alleviate stress concentration, allowing for uniform thermocompression bonding and enhanced mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermocompression bonding is performed using a thermal head on COF terminals with different sizes, widths, and pitches, then connection between COF and liquid crystal display panel is achieved, but non-uniform temperature and pressure distribution damages connection reliability
Solution Approach 1:
The patent applies local quality by making the COF terminal portions have non-uniform pitch and width corresponding to the specific requirements of each terminal function. Power supply terminals have larger pitch and width to accommodate higher current, while signal terminals have smaller pitch and width. This local differentiation ensures that each terminal region receives appropriate bonding conditions tailored to its electrical requirements, resolving the contradiction between achieving reliable connections and maintaining uniform bonding conditions.
2Adaptability or versatility
If COF is bent or subjected to thermal expansion differences, then flexibility and adaptability are improved, but stress concentration at terminal portions causes disconnection
Solution Approach 1:
The patent applies segmentation by dividing the COF structure into distinct regions: rigid terminal portions for stable electrical connection and flexible intermediate portions for stress absorption. The terminal portions are designed with increased thickness and reinforced structure to maintain connection reliability, while the flexible portions allow the COF to bend and adapt to thermal expansion without transmitting stress to the terminals, thus resolving the contradiction between flexibility and connection reliability.
3Power
If terminal portions are made larger to allow larger current flow, then power supply capability is improved, but bonding uniformity with thermal head deteriorates
Solution Approach 1:
The patent applies local quality by designing terminal portions with locally enhanced properties including larger area for current carrying and increased thickness for mechanical strength. These terminal portions are strategically positioned and dimensioned to match the specific electrical requirements of each connection point. The localized enhancement allows large current terminals to maintain both high power capability and uniform bonding characteristics through proper geometric design and material distribution.
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
This configuration enhances the reliability of connections by preventing stress concentration and disconnections, ensuring uniform bonding and improved mechanical strength, even under bending and thermal stress, thus improving the overall reliability of the display device.
Implementation Method 1
The anisotropic conductive film becomes conductive in the direction that the liquid crystal display panel and the COF face each other in an opposed manner and becomes non-conductive in the direction perpendicular to such an opposedly facing direction
Implementation Method 2
The liquid crystal display panel and the COF are connected with each other by sandwiching the anisotropic conductive film between the terminals of the liquid crystal display panel and the COF and by bonding the terminals of the liquid crystal display panel and the COF by thermocompression bonding
Data Source
AI summary
The present invention prevents, when a COF which is connected with an external circuit is bent in a flat display device, the disconnection of lines on the COF. At a position where a line of the COF is connected to terminal portions of a TFT, and the line having a large width is branched into lines having a small width T1 to T3 or T4 to T6. By displacing line branching positions from each other as indicated by an arrow A and an arrow B, when the COF is bent or deformed, stress applied to the line branching positions can be dispersed thus preventing the disconnection of lines.