Pusher-Type Vault Switch for Thin PCBs
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Solution Overview
Problem
Existing push-button type dome switches for thin printed circuits, such as those in smart cards, face challenges with insufficient tactile feedback and reliability due to dimensional constraints, where domes with diameters of 5 to 8 mm and strokes less than 0.45 mm fail to provide discernible tactile feedback and reliable contact.
Innovation Solution
The use of two substantially identical domes arranged peripherally with a spacer, where the peripheral parts of the domes are in contact with the spacer, and the spacer has a central hole allowing the domes to come into contact under force, ensuring high reliability and tactile feedback by absorbing forces without stressing the printed circuit material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single dome is used in a push-button switch for thin printed circuits, then the structure is simple, but the tactile feedback is insufficient and reliability is low
Solution Approach 1:
The single dome structure is segmented into two domes arranged in opposition. Each dome independently contacts the insulating spacer, and both domes must be pressed simultaneously to establish electrical contact between the connection members. This segmentation improves reliability by distributing mechanical stress across two domes while maintaining tactile feedback through the dual-dome compression mechanism.
2Length of stationary object
If the dome stroke is reduced to less than 0.45 mm to meet dimensional constraints, then the smart card thickness is reduced, but discernible tactile feedback is lost
Solution Approach 1:
The domes maintain their curved, cap-shaped geometry with a defined stroke direction. The curvature of the domes allows them to compress and rebound effectively within the reduced stroke distance, providing tactile feedback through the elastic deformation of the dome material even when the total stroke is less than 0.45 mm.
Solution Approach 2:
The domes are pre-loaded with elastic energy in their uncompressed state. When pressed, the domes rapidly compress and then rebound, providing tactile feedback through this pre-stored elastic energy release. This allows effective tactile response even with limited stroke distance.
3Reliability
If force is applied to a single dome, then contact is established, but significant stresses are created in the printed circuit material
Solution Approach 1:
The force application is segmented across two domes rather than concentrated on one dome. Each dome absorbs a portion of the applied force, and the insulating spacer distributes the mechanical load evenly between the two domes. This segmentation reduces the stress concentration on the printed circuit material while ensuring reliable contact establishment when both domes are compressed.
Solution Approach 2:
The two domes act as counterbalancing elements against each other. When force is applied to compress the domes together, the domes resist each other's deformation through their elastic properties, reducing the net stress transmitted to the printed circuit substrate. The insulating spacer provides a stable reference point that helps distribute and balance the forces.
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 configuration significantly enhances tactile feedback and reliability, allowing for a higher number of maneuvers while maintaining a thin profile, as the forces are absorbed by the domes rather than the printed circuit material, ensuring effective contact.
Implementation Method 1
The part of this curve in which the force decreases while the stroke increases between the strokes Tt and Tr, gives a tactile effect which the finger which exerts pressure on the dome feels. The first part of the stroke can be as progressive as desired, by applying a force which increases slowly; however, once the maximum force Ft is reached, the transition to firm contact takes place very quickly under the action of the elasticity of the dome itself.
Data Source
Figure 1~3
Figure 4~6
AI summary
The invention relates to a vault switch. It relates to a pusher-type vault switch for a thin printed circuit having a thin substrate (20) on a surface of which is provided a printed circuit having connection pads. The switch contains two vaults (12) and an insulating strut, the peripheral portions of the two vaults (12) are each in contact with one face of the strut and are thus facing each side of the spacer, each vault (12) having a connection member (18) to a connecting pad of the printed circuit (20), and the spacer includes a central hole large enough to allow the apex of the two vaults (12) to come into mutual contact when they are submitted to mutual forces which bring them together. The invention may be applied to chip cards.