Flexible Keymat Layer for Mobile Keypad Gap Elimination
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Solution Overview
Problem
Conventional film-in-plastic (FIP) keypads for mobile devices suffer from gaps between actuators and domes causing 'keypad floating', exposure to contaminants, abrupt tactile feedback, and reduced key travel due to hard actuators.
Innovation Solution
A keypad design featuring a keymat layer made of flexible material, such as silicon rubber, molded onto the back side with slits cut around keys to provide flexibility without exposing the domes, filling gaps between actuators and domes, and enhancing tactile feedback by allowing longer key travel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If hard actuators are injection molded into the back side of key cap pockets, then the key cap structure is formed, but gaps appear between actuators and domes causing keypad floating
Solution Approach 1:
The key cap is divided into two separate components: a rigid key cap body for structural support and a flexible actuator layer for precise dome contact. This segmentation allows each component to be optimized independently - the key cap body for manufacturing ease and the actuator layer for precision fit against the dome, eliminating the gap issue while maintaining manufacturing efficiency.
Solution Approach 2:
The keypad assembly uses composite construction combining a rigid key cap material (such as polycarbonate) with a flexible actuator material (such as silicone rubber or thermoplastic elastomer). This composite approach allows the rigid portion to provide structural integrity while the flexible portion conformably contacts the dome, eliminating gaps without compromising manufacturing ease.
2Ease of operation
If slits are cut around keys to make them flexible, then keys become easier to press, but dome sheet and main PCB are exposed to contaminants
Solution Approach 1:
A flexible actuator layer is placed over the dome sheet and main PCB, covering the areas that would otherwise be exposed through slits. This flexible film provides contaminant protection while still allowing the keys to flex and compress the domes underneath, maintaining ease of operation without exposing internal components to harmful factors.
Solution Approach 2:
The flexible actuator layer serves as an intermediary barrier between the external environment and the internal components (dome sheet and main PCB). It allows mechanical interaction (key pressure transmission) while blocking contaminant ingress, thus mediating between the need for key flexibility and the need for component protection.
3Strength
If hard actuators are used, then key cap structure is maintained, but abrupt tactile feedback and increased noise are generated
Solution Approach 1:
The actuator material parameters are changed from rigid (hard plastic) to flexible (elastomeric or rubber-like materials). This parameter change in material hardness and elasticity allows the key cap to maintain its structural shape while the flexible actuator provides gradual, smooth tactile feedback and reduces impact noise when contacting the dome.
4Ease of manufacture
If hard actuators are used, then manufacturing is simplified, but key travel is reduced degrading tactile feedback quality
Solution Approach 1:
The flexible actuator layer can be designed with sufficient thickness to allow extended key travel distance while maintaining ease of manufacture through conventional molding processes. The flexibility of the material enables greater compression distance compared to rigid actuators, improving tactile feedback quality without significantly complicating the manufacturing process.
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 flexible keymat layer prevents contaminants from entering, reduces noise, and improves tactile feedback by eliminating gaps and allowing extended key travel, thus enhancing the keypad's structural integrity and user experience.
Implementation Method 1
a keymat layer can be molded onto the back side of the keypad sheet
Implementation Method 2
The flexible keymat layer prevents contaminants from entering, reduces noise, and improves tactile feedback by eliminating gaps and allowing extended key travel
Data Source
AI summary
A keypad is described herein in which the keypad can have a keypad sheet and a keymat layer molded onto the back side of the keypad sheet. The keypad sheet can include a plurality of keys formed on a front side of the keypad sheet and a plurality of actuators formed on a back side of the keypad sheet and protruding from the back side of the keypad sheet. Slits are cut around at least some of the keys to provide the keys with flexibility. The slits do not pierce the keymat layer.