Transparent Capacitive Key Glass With Embedded Electrodes
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Solution Overview
Problem
Existing methods for manufacturing transparent or semi-transparent elements with capacitive keys for electronic instruments face challenges in achieving both sufficient resistance to external agents and hydrostatic pressure while maintaining high sensitivity of capacitive key activation, often compromised by the thickness of the glass which increases dielectric distance between electrodes and the user's finger.
Innovation Solution
The method involves molding capacitive key electrodes into the transparent or semi-transparent element, positioning them halfway through the glass's thickness after molding, and integrating conductive tracks and contact terminals to ensure effective connection to a processing circuit, utilizing techniques like In-Mould Decoration (IMD) or Film Insert Moulding (FIM) to enhance sensitivity while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the glass thickness is increased to resist shocks and hydrostatic pressure, then the mechanical strength and pressure resistance are improved, but the sensitivity of capacitive keys deteriorates due to increased dielectric distance between electrodes and user's finger
Solution Approach 1:
The patent positions electrodes not only on the inner face but also on the outer face of the glass, utilizing the third dimension (depth/thickness) to reduce the effective dielectric distance for capacitive sensing while maintaining overall glass thickness for mechanical strength. This dimensional approach allows simultaneous achievement of both strength and sensitivity requirements.
Solution Approach 2:
The patent divides the electrode structure into multiple segments: inner face electrodes and outer face electrodes. This segmentation allows each electrode layer to serve specific functions - inner electrodes for structural integration and outer electrodes for enhanced capacitive coupling with the user's finger, thereby resolving the contradiction between thickness and sensitivity.
2Stress or pressure
If the glass thickness is increased to withstand hydrostatic pressure, then the pressure resistance is improved, but the distance between electrodes and contact surface increases reducing capacitive coupling
Solution Approach 1:
By adding outer face electrodes on the third dimension (outer surface), the patent reduces the effective dielectric distance for capacitive coupling without compromising the overall glass thickness needed for hydrostatic pressure resistance. This dimensional solution maintains reliable capacitive key functioning while withstanding high pressure.
Solution Approach 2:
The patent incorporates electrodes directly into the glass structure during the molding process, positioning them at optimal locations before the glass is subjected to pressure tests or usage. This preliminary positioning ensures both pressure resistance and reliable capacitive coupling are achieved in advance.
3Ease of manufacture
If electrodes are placed on the inner face of the glass, then the manufacturing process is simplified, but the sensitivity of capacitive keys deteriorates due to thick dielectric layer
Solution Approach 1:
The patent segments the electrode structure into inner face electrodes (for manufacturing simplicity and structural integration) and outer face electrodes (for enhanced sensitivity). This segmentation allows each part to optimize its function while maintaining overall manufacturing feasibility through integrated molding processes.
Solution Approach 2:
The patent extends the electrode structure from a single plane (inner face) to multiple planes (inner and outer faces), utilizing the depth dimension to reduce dielectric distance and improve sensitivity while maintaining manufacturing simplicity through integrated molding techniques.
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 approach improves the sensitivity of capacitive keys by reducing the distance between electrodes and the contact surface while ensuring the glass remains resistant to shocks and hydrostatic pressure, addressing the drawbacks of previous methods.
Implementation Method 1
The conductive oxide layer is deposited by evaporation over a thickness generally between 25 and 75 nm
Implementation Method 2
by chemical etching of this conductive oxide layer
Implementation Method 3
This makes it possible to form a total capacitance between the finger and the electrode, as well as between the electrode and the mass formed by the metal case of the watch
Data Source
Figure 1a~1b
Figure 2~5
Figure 6
AI summary
The method makes it possible to manufacture a transparent or semi-transparent element, such as a glass (1), provided with capacitive keys for a portable electronic instrument. This method comprises the steps of placing an insulating film (3), on which are made electrodes (2) as capacitive keys, conductive tracks (4) each connected to a respective electrode and external contact terminals (6) each connected via conductive tracks to the corresponding electrodes, in a transparent plastic substance (5) or semi-transparent in liquid form inside a mould. This liquid substance is then solidified in the mold, to coat at least part of the film which includes the electrodes, the conductive tracks and at least part of the external contact terminals of said film. On leaving the mould, a glass with capacitive keys integrated in said solidified plastic substance of the glass is obtained.