Over-molded Keypad with Fluid Cushions for Cavity Preservation
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Solution Overview
Problem
Existing over-molding processes for keyboards often flatten the space between key switches and circuit boards, preventing proper function, and silicone-containing materials may not fully adhere to plastic frames, allowing contaminants to enter the keypad assembly.
Innovation Solution
A method involving a substrate with donut-shaped recesses filled with elastomeric cushions, a flex circuit layer, and an over-molded thermoplastic elastomer layer that forms a hermetic seal, maintaining the switch cavity space and ensuring a tight seal around keypad components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If over-molding process is used to seal gaps between key switches and frame, then sealing performance is improved, but the space between key switches and circuit board is flattened causing loss of function
Solution Approach 1:
The circuit board is pre-positioned within the frame before the over-molding process begins. This preliminary positioning ensures that the circuit board is correctly located and supported before the sealing material is applied, preventing the flattening issue while maintaining sealing effectiveness.
Solution Approach 2:
A support structure or spacer is introduced as an intermediary element between the circuit board and the over-molding material. This intermediary maintains the necessary spacing during the molding process, preventing direct compression of the key switch cavity while still allowing the sealing material to form a proper seal around the components.
2Reliability
If silicone-containing materials are used for over-molding, then sealing properties are improved, but adhesion to plastic frame is insufficient allowing contaminant ingress
Solution Approach 1:
The sealing material is formulated as a composite composition that combines silicone-based polymers with adhesion promoters or coupling agents. This composite material maintains the excellent sealing and flexibility properties of silicone while adding chemical groups that enhance bonding to plastic frame materials, thereby preventing contaminant ingress.
Solution Approach 2:
The chemical composition and physical properties of the over-molding material are optimized by adjusting parameters such as cross-linking density, polymer chain structure, and additive content. These parameter changes enable the material to achieve both high sealing performance and strong adhesion to the plastic frame simultaneously.
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 maintains the switch cavity space during over-molding, prevents contaminant ingress, and ensures a functional keypad with a tight seal, enhancing the reliability and durability of electronic devices like cell phones and medical devices.
Implementation Method 1
Each of the plurality of cushions 110 may be formed of an elastomeric polymer material
Implementation Method 2
an over-molded thermoplastic elastomer layer 116 disposed on the plurality of metal membranes 114
Data Source
AI summary
Described is a keypad and its method of manufacture. In one embodiment, a keypad is provided that includes a substrate having a plurality of donut-shaped recesses located at each site of a button for inputting user information, a plurality of cushions each filled with an incompressible fluid (e.g., water), a flex circuit layer, a plurality of metal membranes and an over-molded thermoplastic elastomer layer. During the over-molding of the thermoplastic elastomer layer, the plurality of cushions filled with an incompressible fluid prevents collapse of the space between the flex circuit layer and the plurality of metal membranes. After the layers of the keypad are assembled, the incompressible fluid is removed which leaves a space between the flex circuit layer and the plurality of metal membranes.