Touch Panel Copper Wiring Asymmetry for Viewing Angle Dependency
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Solution Overview
Problem
Transparent conductive films used in touch panels suffer from visibility issues due to viewing angle dependency caused by the metallic luster of copper wirings, which is exacerbated by the reversely tapered cross-sectional shape of the copper wirings, making it difficult to form blackened layers on the side surfaces effectively.
Innovation Solution
A transparent conductive film with first and second thin metal wires on opposite surfaces of a transparent insulating substrate, where the line widths satisfy specific relationships to minimize viewing angle dependency, and a method involving adhesion reinforcement and wet etching to form these wires with reversely and forward tapered cross-sectional shapes, respectively, with blackened layers on the viewing side to reduce specular reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If copper wirings are thinned to 1-5 μm width to reduce visibility and moire, then the metallic luster and viewing angle dependency are reduced, but the manufacturing precision and adhesion requirements increase significantly
Solution Approach 1:
The patent applies asymmetry by forming copper wirings with different cross-sectional shapes: first copper wirings have a substantially rectangular cross-section while second copper wirings have a substantially triangular cross-section. This asymmetric design allows both wiring types to be formed with comparable line widths (1-5 μm) while achieving different optical characteristics - the rectangular wirings minimize metallic luster visibility and the triangular wirings provide good adhesion, resolving the contradiction between reducing metallic luster and maintaining manufacturing precision
Solution Approach 2:
The patent applies local quality by assigning different cross-sectional shapes to copper wirings based on their specific location and function within the touch panel. First copper wirings (transparent electrode patterns) use rectangular cross-sections optimized for visibility reduction, while second copper wirings (signal lines) use triangular cross-sections optimized for adhesion. This localized differentiation allows each wiring type to be optimized for its specific requirements without compromising overall manufacturing precision
2Strength
If reversely tapered cross-sectional shape is formed to improve adhesion, then adhesion strength increases, but viewing angle dependency increases due to visible side surfaces
Solution Approach 1:
The patent resolves this contradiction by applying asymmetry through different cross-sectional shapes for different wiring types. First copper wirings use a substantially rectangular cross-section that minimizes viewing angle dependency by presenting a flat surface to oblique light, while second copper wirings use a substantially triangular cross-section with a tapered side surface that provides enhanced adhesion. This asymmetric approach allows each wiring type to be optimized for its primary function without suffering from the drawbacks of the other shape
3Illumination intensity
If blackened layer is formed on copper wiring to reduce specular reflection, then contrast is improved, but it is difficult to form on side surfaces of tapered wirings
Solution Approach 1:
The patent applies asymmetry by forming blackened layers selectively on different surfaces of different wiring types. First copper wirings with rectangular cross-sections have blackened layers formed on their front surfaces (viewing side), which are easily accessible and provide effective contrast improvement. Second copper wirings with triangular cross-sections have blackened layers formed on their tapered side surfaces, which provide both adhesion enhancement and contrast improvement. This asymmetric blackened layer formation strategy resolves the contradiction by matching the blackening process to the specific geometry of each wiring type
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
The solution ensures excellent visibility with low viewing angle dependency by adjusting the line widths and shapes of the metal wires, reducing the visibility of the mesh pattern and minimizing reflected light influence, thereby improving the visibility and contrast of the touch panel.
Implementation Method 1
In the touch panel, specular reflection is reduced and contrast is improved by forming a blackened layer formed of a black copper oxide coating film at the end portion of the copper wiring
Implementation Method 2
it is necessary to perform wet etching by causing the resist to adhere to the copper foil with high adhesion to perform patterning of a line width of about 1 to 5 μm with high accuracy
Data Source
AI summary
A touch panel includes a first electrode formed of first thin metal wires arranged in the transmissive region and a second electrode insulated from the first electrode and formed of second thin metal wires arranged to intersect the first thin metal wire in the transmissive region, in which the second thin metal wires is arranged on the side opposite to the viewing side than the first thin metal wires.