Stepped Terminal Electrode for ACF Adhesion in Display Devices
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Solution Overview
Problem
The existing display devices with terminal parts connected via anisotropic conductive films (ACF) face reliability issues due to weak adhesion, leading to peeling of the flexible printed circuit (FPC) substrate, despite conductive particles being captured on the terminal electrodes, because of inadequate contact area and adhesion strength between the terminal electrodes and the ACF.
Innovation Solution
The terminal electrodes in the display device are designed with a convex-concave surface structure, featuring an underlying structure layer with inclined and flat surfaces, which increases the contact area with the ACF, enhancing adhesion and reducing contact resistance, thereby preventing peeling of the FPC substrate or driver IC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If irregularities are provided to the surface of a terminal electrode to capture conductive particles, then electrical connection is improved, but adhesion strength with ACF deteriorates
Solution Approach 1:
The invention transitions from two-dimensional surface irregularities to three-dimensional stepped surfaces. The terminal electrode is structured with multiple levels (first, second, and third stepped surfaces at different heights) that extend vertically, creating a multi-level contact interface with the ACF. This dimensional change allows for both particle capture and enhanced adhesion area simultaneously.
Solution Approach 2:
The terminal electrode surface is segmented into multiple distinct stepped surfaces at different heights. Each stepped surface can independently interact with the ACF - higher surfaces capture conductive particles while lower surfaces provide stable adhesion. This segmentation allows different regions of the electrode to fulfill different functions without interfering with each other.
2Ease of manufacture
If a flat surface is used for the terminal electrode, then manufacturing is simple, but contact area with ACF is insufficient
Solution Approach 1:
Instead of creating complex lateral patterns on a single plane, the invention adds vertical dimensionality through stepped surfaces. This achieves increased contact area without significantly complicating the manufacturing process, as the stepped structure can be formed through sequential deposition or etching processes that are extensions of standard thin-film fabrication techniques.
3Reliability
If adhesion of ACF is weak, then FPC substrate peels away, but increasing adhesion may require complex structure
Solution Approach 1:
The stepped surfaces create localized regions with different properties - upper surfaces optimized for particle capture and lower surfaces optimized for adhesion. This local differentiation allows the same terminal electrode structure to simultaneously address both particle retention and adhesion strength without requiring entirely separate structures for each function.
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 design significantly improves the adhesive strength between the terminal electrodes and the ACF, ensuring reliable electrical connections and preventing peeling, even with various types of resin layers, thus enhancing the versatility of ACF materials and the overall reliability of the display device.
Implementation Method 1
When adhesion of the ACF is weak at this time, the FPC substrate peels away from the display device
Implementation Method 2
a structure is disclosed in Japanese Laid Open Patent Publication No. 2003-202583 in which irregularities are provided to the surface of a terminal electrode so that conductive particles included in an ACF are securely captured
Implementation Method 3
The terminal part is connected with a flexible wiring substrate (also called a FPC 'flexible printed circuit' substrate herein) using an anisotropic conductive film
Implementation Method 4
A terminal part and FPC of a display device are electrically and physically connected by thermo-compression sandwiching an ACF
Data Source
AI summary
A display device in an embodiment according to the present invention includes a substrate, a pixel part including a circuit element over the substrate, and a terminal part including a terminal electrode and located over the substrate, the terminal electrode electrically connected with the circuit element. The terminal electrode located over an underlying structure layer having a surface formed from at least one inclined surface, the underlying structure layer arranged between the terminal electrode and the substrate and a flat surface, and the terminal electrode including a stepped surface along a surface formed from the inclined surface and the flat surface of the underlying structure layer in a surface of the terminal electrode.