Capacitive Keypad Semi-Conductive Adhesive Layer Design
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Solution Overview
Problem
Existing capacitive touchpads and keypads face challenges in making reliable connections due to the inability to tolerate heat for soldering and the lack of robustness of silver paste, which complicates attaching wires to semi-conductive materials, and there is a need for thinner designs in mobile devices.
Innovation Solution
A capacitive keypad and touchpad construction featuring a flexible or rigid printed circuit board with a non-conductive top surface layer and a semi-conductive adhesive layer in between, allowing the semi-conductive layer to serve both as a construction element and a sensing element, using semi-conductive glue or double-sided adhesive tape for secure attachment and capacitive sensing, and optionally incorporating haptically active elements like piezo disks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional wiring methods (soldering or silver paste) are used to connect semi-conductive material, then electrical connections can be established, but the materials cannot tolerate heat for soldering and silver paste is not robust in use
Solution Approach 1:
The patent combines the adhesive layer and the semi-conductive material into a single integrated component. The adhesive layer itself is made semi-conductive, eliminating the need for separate wiring and connection materials. This merging resolves the contradiction by providing both mechanical attachment and electrical connectivity through a single robust layer that doesn't require heat-based soldering processes.
Solution Approach 2:
The adhesive layer performs multiple functions simultaneously: it provides mechanical bonding between the top surface layer and the circuit board, while also serving as the semi-conductive material for capacitive sensing and electrical connections. This multi-functionality eliminates the need for separate wiring components, resolving the manufacturing difficulty while maintaining connection reliability.
2Reliability
If paper sheet or ITO with certain square-resistance is used for capacitive sensing, then sensing function is achieved, but making reliable connections from the paper sheet to electronics is difficult
Solution Approach 1:
The patent merges the adhesive function and the semi-conductive sensing material into a single layer. This eliminates the need for separate connection components and simplifies the overall structure, resolving the contradiction between reliable connections and device complexity.
Solution Approach 2:
The adhesive layer is designed to be self-sufficient by incorporating semi-conductive properties directly into the adhesive material. This allows the adhesive layer to automatically provide both mechanical bonding and electrical connectivity without requiring additional wiring or connection components, thereby reducing complexity while maintaining reliability.
3Strength
If traditional multi-layer construction is used for keypads, then structural integrity is maintained, but thinness of keypads is compromised
Solution Approach 1:
The patent combines multiple traditional layers (adhesive layer and semi-conductive material layer) into a single integrated semi-conductive adhesive layer. This reduction in the number of layers directly decreases keypad thickness while the adhesive properties ensure structural integrity is maintained through strong bonding between components.
Solution Approach 2:
The semi-conductive adhesive layer serves multiple structural and functional roles simultaneously: mechanical bonding, electrical connectivity, and capacitive sensing. This multi-functionality allows the keypad to maintain structural integrity with fewer layers, thereby achieving thinness without sacrificing strength.
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 solution enables a thin, flexible, and robust keypad or touchpad with secure connections, capable of interpreting sliding and pressing contacts for navigational and keystroke inputs, while maintaining a thin profile and providing haptic feedback.
Implementation Method 1
capacitive keypad and/or touchpad construction... capacitive sensor in impedance measurement configuration... semi-conductive adhesive layer... both as constructional and as sensing element
Data Source
AI summary
A capacitive keypad and/or touchpad construction includes a flexible or rigid printed circuit board and a non-conductive keypad/touchpad top surface layer. A semi-conductive adhesive layer in between said flexible or rigid printed circuit board and said non-conductive keypad/touchpad top surface layer serves both to connect the top surface layer to the printed circuit board and to act as capacitive sensing layer.